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Pesticide contamination of groundwater in western Europe
Agriculture, Ecosystems and Environment, 26 (1989) 369-389
369
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
P e s t i c i d e C o n t a m i n a t i o n of G r o u n d w a t e r in Western E u r o p e M. LEISTRA and J.J.T.I. BOESTEN
Institute for Pesticide Research, P.O. Box 650, 6700 AR Wageningen (The Netherlands) (Accepted for publication 19 May 1989)
ABSTRACT Leistra, M. and Boesten, J.J.T.I., 1989. Pesticide contamination of groundwater in western Europe. Agric. Ecosystems Environ., 26: 369-389. In recent years, many measurements have been made of residues of pesticides in shallow and deep groundwater in western Europe. Some triazine herbicides and their transformation products have been detected most frequently. The average concentration in measuring series for deep groundwater was usually below 0.1 ]~g 1-1, and the highest values were usually below 0.5 ]~g 1-1. The concentrations of mecoprop in deep groundwater ranged up to 0.6/~g l - 1 and those of bentazone to almost 1.0/~g l - 1. Some other herbicides were found at comparatively high concentrations and the highest values were found for TBA and TCA in tile-drain water. The soil fumigant 1,3-dichloropropene was mainly found in shallow groundwater, but its admixture 1,2-dichloropropane was also found in deep groundwater (range up to 10 ]~gl - 1, sometimes even higher). Residues of the nematicides aldicarb and oxamyl have been measured in shallow and intermediate groundwater, but measurements for deep groundwater are still lacking. Some carbamoyl-oximes were incubated in subsoil materials to study their transformation and their rate of transformation in anaerobic subsoils was surprisingly high. The maximum admissible concentration of 0.1 pg l - 1 in a Directive of the European Communities of 1980 is the subject of much debate, because a toxicological basis is lacking.
INTRODUCTION
The interest of registration authorities in the possible contamination of groundwater by pesticides dates from the beginning of the 1970s. In some countries, notably F.R.G. and The Netherlands, official working groups were established then to evaluate the risk of pesticide residues leaching from the root zone to the upper groundwater. In the course of years, many pesticides have been evaluated and for several of them a substantial leaching of residues was considered to be possible. A national warning system was set up in these countries to prevent the use of potentially hazardous pesticides in the protection zone of groundwater extractions. In various regions, this protection was un0167-8809/89/$03.50
© 1989 Elsevier Science Publishers B.V.
370 fortunately difficult to achieve. The interest of the public, the drinking-water companies and the public authorities was awakened by the detection, in the early 1980s, of pesticide residues in deep groundwater, pumped for public water supply. Since then, research has been extended and the efficiency of the protection of catchment areas has been improved. The most recent "black list" in The Netherlands, of 31 pesticides whose residues might leach to the upper groundwater, is given in Table 1. In addition, there is a list of 17 compounds whose residues may leach from the root zone when applied under particular conditions, such as during winter or in greenhouses (Plant Protection Service, 1987 ). A similar "black list" of pesticides in the F.R.G. contained about 70 pesticides in 1985. At the time these lists were compiled, only laboratory data were usually available, for example those on adsorption/mobility and on transformation of the pesticides in soil. Only a few pesticides had been subjected to field trials or to monitoring. The number of measurements in the field has strongly increased in recent years. As a result of improved sensitivity in analytical techniques, ever lower concentrations of pesticides can now be measured, leading to a substantial number of positive measurements. As the evaluation of the risk of leaching is intensified, such lists of pesticides presenting a risk to groundwater quality may be expected to grow. In some western European countries, the risk of leaching to groundwater plays a major part in the registration procedure. In a Directive, the Council of the European Communities (1980) established a maximum admissible concentration of 0.1/~g 1-1 for any pesticide in drinking water. Further, the upper limit for the sum of the concentrations of pesticides and related chemicals was set at 0.5/zg l - 1. The value of 0.1/lg 1-1 was chosen because it represented a detection limit in chemical analysis. The idea was that pesticide residues should not be present in drinking water (H~sselbarth, 1987). Since groundwater is seldom purified, the Directive also applies to groundwater pumped for consumption. The member countries were obliged to incorporate this Directive into their national legislation within a few years. A toxicoTABLE1 Pesticides whoseuse is not allowedin groundwaterprotectionareas in The Netherlands {Plant Protection Service, 1987) Alachlor Aldicarb Alloxydim-sodium Asulam Benazolin Benazolin-ethyl Bentazone Borates
Bromacil Fluroxypyr Chloralhydrate Glufosinate-ammonium Chlorthal-dimethyl Hexazinone Dicamba Lenacil 1,3-dichloropropene Metalaxyl Dikegulac-sodium Metazachlor E n d o t h a l - s o d i u m Methomyl Ethiofencarb Metolachlor
Propachlor Propoxur Sodiumarsenite TCA Thiofanox Triclopyr Vamidothion
371 logical basis for this limit is missing: the vast amount of toxicological research on the presently approved pesticides is completely neglected. Consequently, the enormous differences in mammalian toxicity of the various pesticides are not accounted for. Measurements of residues above the Community's limit have raised great concern among distributors and consumers. Expensive measures have sometimes been taken to keep the residue below this detection limit. This contribution surveys the results of measurements of pesticide residues in shallow and deep groundwater in western Europe. The conditions that may be relevant for residues in a particular situation are indicated. For a few pesticides, information about their transformation in the groundwater zone is discussed. Finally, a few ways of improving the evaluation of the risk of a pesticide for groundwater quality are indicated. MEASUREMENTSIN GROUNDWATER
Triazines in the upper groundwater Samples were taken from groundwater (via boreholes) in areas with arable farming in East Anglia, U.K. and they were analysed for atrazine (Croll, 1986). In some areas with sandy soils and a shallow water table, low concentrations were found (Table 2). The concentrations of simazine were, on average, about 0.25 times those of atrazine. In the period December-May, tile-drain water samples were taken from a field with alluvial clay soil in Charente Maritime, France, on which atrazine and simazine had been applied repeatedly for a maize crop (rate 1.25 kg h a - 1). Upon drying, this soil showed clear shrinkage fissures. The residues of the herbicides were analysed (Snegaroff, 1979) and the results of the measurements are given in Table 2. The concentrations of atrazine and simazine were almost the same and rather high. Atrazine was applied in spring at a rate of 1.25 kg h a - 1to 2 fields in Lorraine, France, one with a clay soil and the other with a clay loam soil, with tile-drains at a depth of about 0.9 m. In the first 9 months following application the tiledrain water was sampled and analysed for atrazine (Schiavon and Jacquin, 1973). The results are summarized in Table 2. These soils also showed clear shrinkage fissures, through which water flowed quickly after heavy rainfall. This could explain the comparatively high concentrations of atrazine in the drain water. After repeated annual applications of atrazine to 2 maize fields in BadenWiirttemberg, F.R.G., Hurle et al. (1987) collected water from tile-drains 0.81.0-m deep. They found concentrations between 0.2 and 2.3 #g 1-1 (Table 2 ). In the years after the application had stopped, the concentration of atrazine in drain water gradually decreased. Two years after the last application, the
U.K., East Anglia France, Charente Maritime France, Lorraine F.R.G., Baden-Wtirttemberg F.R.G., Schleswig-Holstein F.R.G., Schleswig-Holstein Netherlands, Noord-Brabant Netherlands, Noord-Brabant F.R.G., Baden-Wiirttemberg Netherlands, Noord-Brabant France, Charente Maritime F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg
Atrazine
Desethylterbuthylazine
Terbuthylazine
Terbuthylazine
Simazine
Simazine
Desethyl-atrazine
Desethyl-atrazine
Atrazine
Atrazine
Atrazine
Atrazine
Atrazine Atrazine
Atrazine
Country, area.
Compound
Tile-drain water
Tile-drain water
Tile-drain water
Tile-drain water
Tile-drain water
Upper groundwater
Tile-drain water
Upper groundwater
Upper groundwater
Upper groundwater
Upper groundwater
Tile-drain water Tile-drain water
Tile-drain water
Upper groundwater
Sampled
0.8-1.0
0.8-1.0
0.8-1.0
0.8-1.0
Not given
Below 3
0.8-1.0
1 -2
Below 3
0.5-5
0.5-3
0.9 0.8-1.0
Not given
Not given
Depth (m)
3
9
5
9
11
17
8
25
29
44
24
11 9
> 24 11
No. of samples
0.05
0.4
0.49
0.4
22
<0.1
0.04
0.22
0.1
0.74
16 0.6
27
Average
-46
0.2 -35
-
0.02- 0.07
<0.1 - 1.0
0.06- 1.92
<0.1 - 1.2
12
<0.1
<0.02- 0.17
<0.08- 0.58
<0.1 - 0.8
0.01-17.5
<0.05- 6.75
6 -29 0.2 - 2.3
12
< 0.2 - 0.5
Range
Concentration (P4~1-1 )
Residues of triazine herbicides measured in the upper groundwater and in tile-drain water of treated fields
TABLE 2
Hurle et al. (1987)
Meinert and H~ifner (1987)
Hurle et al. (1987)
Meinert and H~fner (1987)
Snegaroff (1979)
Janssen and Puijker (1987)
Hurle et al. (1987)
Loch (1987)
Janssen and Puijker (1987)
Stock et al. (1987a,b)
Stock et al. (1987a,b)
Schiavon and Jacquin ( 1973 ) Hurle et al. (1987)
Snegaroff (1979)
Croll (1986)
Reference
bO
373 transformation product desethyl-atrazine could still be measured in the water. Terbuthylazine, used as an alternative to atrazine, could be measured in the tile-drain water in the first few months after application, together with its transformation product desethyl-terbuthylazine (Table 2 ). In tile-drain water and in water from shallow bores in grape-growing areas in Rheinland-Pfalz, F.R.G., the concentrations of atrazine and simazine varied between 0.01 and 0.03 #g l-1 (Hurle et al., 1987). In the upper groundwater of a forest area, no residues of these triazines could be found. The upper groundwater was collected from below maize fields in SchleswigHolstein, F.R.G., that had been treated for several years with atrazine (1-1.5 kg h a - 1) (Stock et al., 1987a,b). Most fields had humic sand soils. The results of 24 analyses for 6 observation wells in the period May-March are summarized in Table 2. Observation wells (44) were installed in 33 maize fields with sandy soil, on which atrazine had been regularly used at a dose of about 1 kg ha-1. The upper groundwater in these wells was analysed for atrazine (Stock et al., 1987a,b). The results of these measurements are also given in Table 2. Samples were taken from shallow groundwater in a catchment area in NoordBrabant, The Netherlands, in which atrazine is used in maize, grown in crop rotation (Janssen and Puijker, 1987). With the detection limit at 0.1/~g l-1, atrazine could be measured in 7 out of 29 samples (Table 2). The transformation product desethyl-atrazine was found at lower concentrations (Table 2), while desisopropyl-atrazine could not be detected. Under continuous maize on humic sand soil in Noord-Brabant, The Netherlands, the upper groundwater was sampled for atrazine analysis (Loch, 1987). This herbicide had been applied almost yearly in the spring (rate 0.5-1.2 kg ha -1), In nearly all of the samples (25) a low concentration of atrazine was found (Table 2). An arable field with sandy loam soil in Baden-Wiirttemberg, F.R.G., was treated with simazine (0.5 kg ha-1) and with terbuthylazine (0.74 kg ha-1) in April. Tile-drains were situated at a depth of 0.8-1.0 m. In the year following application, samples of drain water were taken and analysed by gas chromatography (Meinert and Hiifner, 1987). The concentration of the two triazines measured 9 times are summarized in Table 2. Already in May, after heavy rainfall, the compounds were detected in the drain water and their concentrations had increased considerably by the end of June.
Triazines in deep groundwater In the period 1983-1985, many water samples were taken from 11 groundwater bores and springs in Baden-Wiirttemberg, F.R.G., and they were analysed for residues of triazine herbicides (Hurle et al., 1987 ). One series of samples was taken in limestone areas and another in sedimentary areas. The catchment areas of these bores and springs were used mainly for agriculture,
374
with a substantial use of atrazine in maize. Atrazine could be detected (Table 3) in the majority of 238 groundwater samples. In some of the samples, desethyl-atrazine was also detected. When simazine was detected, its concentration was usually distinctly lower than that of atrazine. Water from a spring in Baden-Wiirttemberg, F.R.G., was sampled and analysed for some triazines (Hurle et al., 1987). The catchment area of this spring was used mainly for agriculture. The average concentrations of atrazine and simazine were below 0.1/zg 1-1 (Table 3). The concentrations of desethylatrazine were even lower (Table 3) and desethyl-simazine was found in only 1 out of 13 samples, at 0.03/~g l - 1. A series of 40 groundwater extraction sites in Baden-Wfirttemberg, F.R.G., was selected on the basis of the vulnerability of their catchment areas: intensive use of herbicides and low-adsorptive soil in the top layers (Roth, 1987). The maximum concentrations of atrazine and simazine measured in 120 water samples in 1984 are given in Table 3. In a subsequent measuring series of 155 samples from groundwater extraction sites, carried out in 1985, atrazine exceeded the 0.1/~g 1-1 level only twice (Roth, 1987). Samples were taken from bores producing groundwater from an aquifer in the Valley of the Danube, F.R.G. This water was analysed for residues of atrazine and simazine (Werner, 1987). The catchment areas were used for agriculture with maize as one of the crops. In 4 bores, the concentrations of atrazine ranged up to 0.06 #g 1-1 but in one bore they were distinctly higher (Table 3). The concentrations of simazine (applied on a much smaller scale) were substantially lower (Table 3). When the concentration of atrazine was comparatively high, the desethyl and desisopropyl transformation products were also detected. Their concentrations were somewhat lower (desethyl) or much lower (desisopropyl) than those of atrazine. Water samples were also taken from a large spring in a limestone area. The concentrations of atrazine and simazine measured by gas chromatography (Werner, 1987) are summarized in Table 3. The concentrations of the desethyl and desisopropyl transformation products of atrazine were about 0.6 and 0.2 times those of atrazine itself. In 1985, nine springs used for drinking water in Rheinland-Pfalz, F.R.G., were sampled and analysed for triazine residues by Hurle et al. (1987). On a large fraction of the catchment area, crops were grown. Atrazine and simazine were detected in most of the samples (Table 3). The average concentration of the transformation product desethyl-atrazine was somewhat higher and that of desethyl-simazine was much lower (Table 3). Groundwater samples were taken from 24 bores used for public water supply in 3 states of F.R.G. and they were analysed for atrazine (IPS, 1987). In 14 bores (most up to 20-m deep) in the 3 states, atrazine was detected at least once and its concentration range is given in Table 3. The highest concentrations were measured for areas with intensive agriculture. In 5 out of 20 bores for public water supply in 2 federal states, simazine was detected at least once
Country, area
F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg
F.R.G., Baden-Wiirttemberg F.R.G., Rheinland-Pfalz F.R.G., three states Italy,Pavia F.R.G., Baden-Wfirttemberg F.R.G., Rheinland-Pfalz F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg
F.R.G., Baden-Wiirttemberg F.R.G., Rheinland-Pfalz F.R.G., two states F.R.G., Rheinland-Pfalz
Compound
Atrazine Atrazine Atrazine Atrazine
Atrazine Atrazine Atrazine Atrazine Desethyl-atrazine Desethyl-atrazine Simazine Simazine Simazine
Simazine Simazine Simazine Desethyl-simazine
Spring Springs Bores Springs
Springs Bores Bores Spring Springs Spring Bores Bores
Spring
Bores, Springs Spring Bores Bores
Sampled
238 13 120 52 13 18 9 93 313 13 9 13 120 52 13 18 9 36 9
No. of samples
0.06 <0.1 0.01
0.02 0.09 0.03
0.06 <0.1
0.08 0.07
Average <0.01-0.76 <0.01-0.35 up to 0.4 <0.01-0.06 0.1 -0.3 0.1 -0.3 <0.01-0.29 <0.05-0.26 <0.05-4 <0.02-0.10 <0.02-0.44 <0.01-0.15 up to 0.2 < 0.01-0.015 0.02-0.08 up to 0.1 0.01-0.15 <0.05-0.14 <0.02-0.06
Range
Concentration (pg l - 1)
Werner (1987) Hurle et al. (1987) IPS (1987) Hurle et al. (1987)
Werner (1987) Hurle et al. (1987) IPS (1987) Berri et al. {1983) Hurle et al. (1987) Hurle et al. (1987) Hurle et al. (1987) Roth (1987) Werner ( 1987 )
Hurle et al. (1987) Hurle et al. (1987) Roth (1987) Werner (1987)
Reference
Concentrations of triazine herbicides and their transformation products in water samples taken from groundwater bores and springs. Depths of the extractions were rarely indicated (see text)
TABLE 3
e~
376 (IPS, 1987). The results for these bores are summarized in Table 3. Only one sample had more than 0.1 pg 1-1. About 2000 bores for public water supply in Lombardia, Italy, were analysed for atrazine (Galassi and Leoni, 1987). Of these bores, 14% exceeded 0.1 ttg l-1 and 1.4% exceeded 1.0 ttg l-1. Water from about 1000 private bores (shallower) was also analysed and was generally found to have higher concentrations. About 300 bores used for supplying drinking water were sampled in an area in the Province of Pavia in Italy and analysed for atrazine (Berri et al., 1983). The area was intensively cropped with rice and maize. The results of the analyses are summarized in Table 3. In 67% of the bores, atrazine was detected at concentrations between 0.05 and 4 pg l - 1. The proportion of the bores in which atrazine was found decreased from 73% of those up to 20-m deep to 59% of those between 20 and 40-m deep and to 27% of those deeper than 40 m.
Herbicides (other than triazines) in shallow and deep groundwater Groundwater samples were taken from 141 bores used for public water supply in 4 states of F.R.G. (IPS, 1987). In 11 of these bores, bentazone was measured at least once. The results of the measurements for these bores are summarized in Table 4. In a catchment area in Noord-Brabant, The Netherlands, in which bentazone was applied to maize and other crops, the upper groundwater was sampled and analysed for residues of this herbicide (Janssen and Puijker, 1987). In 10 out of 26 samples, this compound could be measured (Table 4) at a detection limit of 0.1 pg 1-1. The concentrations of the transformation product anthranilic acid isopropylamide were below this detection limit. Bromacil is used on a large scale for weed control on railway tracks. Residues of this herbicide were found in water from a bore in the vicinity of such a railway track in Baden-Wiirttemberg, F.R.G. (Milde et al., 1982). The range of the concentrations measured is given in Table 4. In The Netherlands, groundwater samples were taken from 21 bores, used for public water supply, and situated within about 100 m of railway tracks. The water was analysed for bromacil and amitrol (Vogelaar et al., 1987). In none of the samples could amitrol be detected (limit of detection 0.1 ttg l-1 ). In 4 of the bores, with depths between 15 and 40 m, bromacil was found in the concentration range given in Table 4. Results of some other measurements of bromacil in bores near railway tracks in The Netherlands, including higher concentrations, were released to the press, but detailed reports have not been published. Dinoseb was analysed in groundwater after application as a selective herbicide at comparatively low rates (a few kg ha -1) in a potato crop on low to moderately humic soil in Drenthe, The Netherlands (Loch, 1987). Occasionally, low concentrations were found in the upper groundwater, however, after
Country, area
F.R.G., four states Netherlands, Noord-Brabant Bromacil F.R.G., Baden-Wiirttemberg Bromacil Netherlands, three provinces Dinoseb Netherlands, Drenthe Isoproturon F.R.G., two states Mecoprop F.R.G., Baden-Wtirttemberg Mecoprop F.R.G., Baden-Wtirttemberg Mecoprop F.R.G., four states Molinate Italy, Pavia Phenoxyalkanoic U.K., acids East Anglia 2,4,5-T F.R.G., Baden-Wtirttemberg 2,3,6-TBA Sweden, MalmShus TCA Sweden, MalmShus
Bentazone Bentazone
Compound
5
Tile-drain water Tile-drain water
Not given 31 0.85-1.0 8
<0.05<0.1 -
Range
12.5 670
up to 79 370 -1270
Jernl~s(1985) Jernl~sandKlingspor (1981)
Roth (1987)
Hurle et al. (1987)
u p t o 17
< 0.02-
Loch (1987) IPS (1987) Hurle etal. (1987)
IPS (1987) Bern etal.(1983) Croll (1986)
0.03
<0.1 < 0.05< 0.02-
0.9 < 0.05
Vogelaaret al. (1987)
IPS (1987) Janssenand PuCker (1987) Mildeetal. (1982)
Reference
<0.050.37 0.05- 154 < 0.2 0.4
9.2 0.08 0.6
<0.1 -
1.8
0.85 1.0
0.2
About 30 up to 147
0.12 0.2
Average
Concentration (#g 1-1 )
Bores Various 42 <0.1 Bores 41 Upper (?)groundwater Not given More than 15 Bores Not given ?
Spring
1- 2 Various
Upper groundwater Bores Bores, Springs
24 32 50
21
15-40
Bores
35 26
No. of samples
About 15
Various Below 3
Depth (m)
Upper (?) groundwater
Bores Upper groundwater
Sampled
Concentrations of herbicides (other than triazines) measured in shallow and deep groundwater
TABLE 4
378
application at a comparatively high rate (8.3 kg h a - 1 ) as a defoliant, distinctly higher concentrations were measured (Table 4). After application in late summer, the highest concentrations in the upper groundwater were already measured in the subsequent autumn and winter. Water samples taken from 161 bores in 6 states of F.R.G. were analysed for isoproturon (IPS, 1987). In only 5 of the bores (in 2 states), the herbicide was detected and the concentrations were very low (Table 4). Groundwater and water from springs, both used for public water supply in Baden-Wiirttemberg, F.R.G., were sampled and analysed for mecoprop by Hurle et al. (1987). This herbicide could be measured in 8 out of 50 samples (Table 4). In water from another spring in this state, mecoprop was found in 2 out of 5 samples at a very low concentration (Table 4). Analyses for mecoprop were also made for 142 samples from 95 bores in various states of F.R.G. (IPS, 1987). In water from 20 bores, a residue of mecoprop was detected at least once, but only in one bore was the concentration above 0.1 ttg 1-1. The results for these bores are summarized in Table 4. Around 300 bores for water supply were sampled in Pavia, Italy, and analysed for molinate (Berri et al., 1983). The area was intensively cropped with rice and maize. The results of the analyses are given in Table 4. In 13% of the bores, molinate was found, usually at concentrations between 0.05 and 3 ttg 1-1. However in a few bores, concentrations were up to 20 #g 1-1 and in one well (10-m deep) 154ttg 1-1. Samples were taken from groundwater (via boreholes) in East Anglia, U.K., in areas with arable farming in which phenoxyalkanoic acid herbicides were used on a large scale (Croll, 1986 ). Only low concentrations of these herbicides (among which mecoprop, further not specified) were found (Table 4). Substantial concentrations were measured (Table 4) of the herbicide 2,4,5T in water extracted from an aquifer below a forest area in Baden-Wiirttemberg, F.R.G. (Roth, 1987). The herbicide TBA was applied in mid October to 8 experimental plots (0.25 ha each) in MalmShus, Sweden, at rates of 0.2 and 0.6 kg ha-1. Three months after application, the tile-drain water from each of the plots was sampled and analysed (Jernl~s, 1985). Substantial concentrations were found (Table 4) and the total amounts leached during those 3 months corresponded to about 10% of that applied. The herbicide TCA was applied (April) to an experimental field with humic sand soil in MalmShus, Sweden, at rates ranging from 20 to 60 kg ha-1. Samples were taken from the water flowing from tile-drains at a depth of 0.85-1.0 m (Jernl~s and Klingspor, 1981 ). About a month after application, comparatively high concentrations could be measured in the water by spectrometry (Table 4). In drain water from irrigated fields, residues were detected throughout the summer.
379
Fumigants and their admixtures The soil fumigant 1,3-dichloropropene is widely used in areas with intensive agriculture and horticulture in western Europe. Besides the (Z) and (E) isomers of 1,3-dichloropropene, the mixtures contained substantial amounts of other volatile chlorinated hydrocarbons. For example, the content of 1,2-dichloropropane in some mixtures was around 25%. After this compound was detected in deep groundwater in 1984 (Hoogsteen, 1986), the authorities in some countries established a maximum content of 0.5% for 1,2-dichloropropane in the fumigant mixtures. A further reduction in this limit is under consideration. Presumably, the concentrations of 1,2-dichloropropane currently found in deep groundwater, originate from application of fumigants with a high content of this admixture a few tens of years ago. In Schleswig-Holstein, F.R.G., residues of 1,2-dichloropropane were detected in groundwater sampled from bores for public water supply (IPS, 1987 ). In water from 5 bores (out of 13 ), this compound was measured at least once. The results for these bores are summarized in Table 5. Industrial discharge may have contributed to this contamination. In a survey started in 1984, residues of 1,2-dichloropropane were measured in deep groundwater (25-40 m) pumped for public water supply in Drenthe, The Netherlands (van Beek, 1986; Hoogsteen, 1986). The concentrations in 3 catchment areas ranged up to 9.3/zg l- 1 (Table 5 ). The highest concentrations were measured for bores fed by water percolating through areas with arable farming, including potato growing. In these areas, dichloropropene mixtures had been used since 1968. The concentration of 1,2-dichloropropane in the extracted water can be drastically reduced in airstrip-column installations (Hoogsteen, 1986). Water samples were taken at various depths (7-68 m) in bores installed in areas of Drenthe, The Netherlands, in which the fields had been fumigated regularly with 1,3-dichloropropene (Janssen and Puijker, 1987). In 24 (depth to 35 m) out of 52 samples, 1,2-dichloropropane could be measured (Table 5). Two other admixtures of the fumigant, 1,2,2-trichloropropane and 1,2,3-trichloropropane, were also detected (Table 5), although in fewer samples and at lower concentrations. The isomers of 1,3-dichloropropene could not be detected in the water samples (detection limit 0.05/zg l-1). Similarly, the fumigant methyl isothiocyanate, the transformation product of metham-sodium (also used on a large scale), was not detected at this limit (Janssen and Puijker, 1987). Some potato fields with humic and peaty sand soils in Niedersachsen, F.R.G., were fumigated with 1,3-dichloropropene at a rate of about 125 1 ha -1 in November. The upper groundwater below the fields (water table at about 2 m) was sampled at various times after installation of observation wells (Stock et al., 1987a,b). The results of the analyses for 1,3-dichloropropene are summa-
Country, area
1,2-dichloropropane F.R.G., Schleswig-Holstein 1,2-dichloropropane Netherlands, Drenthe 1,2-dichloropropane Netherlands, Drenthe 1,3-dichloropropene F.R.G., Niedersachsen 1,3-dichloropropene F.R.G., Niedersachsen 1,3-dichloropropene F.R.G., Schleswig-Holstein 1,3-dichloropropene F.R.G., Schleswig-Holstein 1,3-dichloropropene Netherlands, Drenthe 1,3-dichloropropene Netherlands, Zuid-HoUand 1,2,2-trichloroNetherlands, propane Drenthe 1,2,3-trichloroNetherlands, propane Drenthe
Compound
25 -40 7 -68 1 - 2 1.7- 2.3 1 - 5 1 - 4
Bores Bores Upper groundwater Upper groundwater Upper groundwater
1 - 2 1 - 3 7 -68 7 -68
Upper groundwater Upper groundwater Bores Bores
Bores for irrigation 11 and 24
various
Depth (m)
Bores
Sampled
52
52
92
20
9
14
8 8 80
52
24
40
1.0
0.06
<0.6
5.7
0.23
0.6
2530 2
8.5
2.2
0.8
5.1
5 -
5
-8620
<0.05-
< 0.05-
<0.6 -
< 0.5 -
< 0.02-
<0.02-
9.1
0.9
2.5
80
0.89
3.2
<0.1 - 803
<1
<0.05- 165
up to 9.3
<0.05-
No. of Concentration (pg 1-1 ) samples Average Range
Concentrations of fumigants and their admixtures measured in shallow and deep groundwater
TABLE 5
Janssen and Puijker (1987)
van der Pas and Leistra (1987) Janssen and Puijker (1987)
Loch (1987)
Rexilius and Schmidt (1982)
Rexilius and Schmidt (1982)
Stock et al. (1987b)
Stock et al. (1987a,b)
van Beek ( 1986 ) Hoogsteen (1986) Janssen and Puijker (1987)
IPS (1987)
Reference
c~ Oo Q
381 rized in Table 5. In winter after the application, concentrations up to around 8000/~g 1-1 were found below one of the fields. In the course of time, the concentrations decreased, but after several months (in May) they were still substantial. Under a second field, the concentrations were much lower (Table 5). In another study in Niedersachsen, F.R.G., the upper groundwater was sampled with 80 observation wells installed in 37 potato fields and these samples were also analysed for 1,3-dichloropropene (Stock et al., 1987b). In the area with humic and peaty sand soils, the water table was between 1.0 and 4.1 m. The results of these measurements are given in Table 5. In slightly more than half the samples, no 1,3-dichloropropene was detected. In 18% of the samples, the concentrations were above 0.5/~g 1-1. Substantial concentrations were measured only in the first year after application. Two fields with sandy soil in Schleswig-Holstein, F.R.G., were fumigated with 1,3-dichloropropene mixture (rate about 230 1 ha -1) at the end of October. Some of the fields were then sprinkler irrigated with 40 m m of water. For 140 days after application, samples were taken from the upper groundwater of the fields and these were analysed for 1,3-dichloropropene (Rexilius and Schmidt, 1982 ). The concentrations were in the range 0.02-3.2 #g l-1 (Table 5). In 2 bores for irrigation (11 and 24 m deep) 10-25 m from the fumigated fields, the concentrations of 1,3-dichloropropene were somewhat lower (Table 5). Many water samples were collected from 23 bores in Schleswig-Holstein, F.R.G., in an area in which 1,3-dichloropropene had been used for many years (Rexilius, 1987). The samples were analysed by gas chromatography at a detection limit of 0.001/~g 1-1 and in none of the 1332 samples could residues of the fumigant be detected. Fields in Drenthe, The Netherlands, with low to moderately humic sand soil, were fumigated repeatedly with 1,3-dichloropropene in the autumn (rate about 200 kg h a - 1). In the subsequent years, the upper groundwater under the fields was analysed for 1,3-dichloropropene (Loch, 1987). In the summer following application, substantial concentrations of this fumigant were measured (Table 5 ). In subsequent months, the concentrations beneath two fields declined to < 1 and 3/~g l-1, respectively, and they declined further to < 0.5/~g 1-1 in the following year. This decline could result from transformation of this fumigant in the groundwater zone. However, such field measurements do not provide much certainty about that. Three fields with sandy soil in Zuid-Holland, The Netherlands, were fumigated with 1,3-dichloropropene (rates 290-350 kg h a - 1) in summer, after which samples were taken from the water-saturated subsoil at monthly intervals up to 3 months after application (van der Pas and Leistra, 1987). Neglecting adsorption onto the subsoil material with hardly any organic matter, the concentrations in the upper groundwater could be calculated. The results for the layer 1-3-m deep are summarized in Table 5. Only in a few of the samples was a low residue found, mainly in the first 2 months.
382 TABLE 6 Concentrations of insecticides and nematicides in groundwater Compound
Country, area
Sampled
Depth (m)
No. of samples
Concentration (pg l - 1)
Reference
Average Range Aldicarb Lindane Oxamyl
Netherlands, Drenthe F.R.G., Baden-Wiirttemberg Netherlands, Drenthe
Upper groundwater Spring
1- 2
Observation bores
7-15
4 3 8
43 0.04 < 0.1
4.5 -130 0.010.08 < 0.1 0.2
Loch (1987) Hurle et al. (1987) Janssen and Puijker ( 1987 )
Insecticides and nematicides Aldicarb was applied to a low-humic sand soil in Drenthe, The Netherlands, at the planting of a potato crop. The application rate was comparatively low: 1.5 kg ha -1 (Loch, 1987). A concentration of 130/~g 1-1 (sum of the two oxidation products) was measured in the upper groundwater below the field in October. In the subsequent year (3 measurements), the concentrations were lower (average 15/lg 1-1), but after an initial decline they increased again (Table 6 ). In Noord-Brabant, The Netherlands, an aldicarb residue (22/~g 1-1; more than 90% sulfone) was measured in the upper groundwater (2 m below the soil surface) (Smelt et al., 1983 ). A rate of aldicarb of 5.3 kg ha-1 was applied to this sandy soil (pH 4.3) 18 months before. Water samples from a spring in Baden-Wiirttemberg, F.R.G., were analysed for lindane (Hurle et al., 1987). In 3 samples, the insecticide was detected at a very low concentration (Table 6). Observation bores (7-15-m deep) were installed in an agricultural area in Drenthe, The Netherlands, that also serves as a catchment area for public water supply (Janssen and Puijker, 1987). In this area, oxamyl was used on a limited scale. In 2 out of the 8 samples taken from the bores, oxamyl was detected at a low concentration (Table 6). TRANSFORMATIONIN THE GROUNDWATERZONE When a pesticide residue leaches to the upper groundwater, the question arises whether this residue is further transformed in the groundwater zone or not. Almost all bores for public water supply reach into aquifers at a depth of at least a few tens of metres. The travel time of the water from the upper
383 groundwater to the bore is usually at least a few tens of years, so there is ample time for further transformation of the residue. Even if transformation is slow, with a half-life of, for example, a few years, the decrease in concentration by transformation is considerable. Only a few studies have been made on the transformation of pesticide residues in subsoil material. Some studies on the transformation of carbamoyloxime pesticides can serve as examples of some early steps in research in that area. The toxic oxidation products of aldicarb, its sulfoxide and sulfone, were incubated at I0 ° C in materials from i to 2 m depth within the groundwater zone of 4 fields. The subsoils were in anaerobic condition and this was maintained during incubation (Smelt et al., 1983). The times for 50% transformation of the sulfoxide in the 4 subsoil materials were 6, 2, 3 and 27 days. The corresponding values for the sulfone were 6, 7, 8 and 131 days. The lowest transformation rates were measured for a subsoil with a redox potential of 310 mV (highest in this series) and with a comparatively low pH of 5.0. After one of the anaerobic subsoils had been sterilized, transformation was not much retarded. This indicates that the transformation is catalysed by soil constituents in reduced state (Smelt et al., 1983 ). The rates of transformation in the aerobic materials from above the water table in the same profiles were much lower than those in the anaerobic materials. The rates of transformation of oxamyl and methomyl in the 4 anaerobic subsoils were even faster: about 10% of the amount applied or less remained after i day (Smelt et al., 1983 ). In a follow-up study oxamyl was incubated at 20 °C in 3 water-saturated subsoils, two with a fairly low and one with a high redox potential (Bromilow et al., 1986). Transformation in the two subsoils with low redox potential was very rapid: it was largely completed within i day. On the other hand, transformation of oxamyl in the subsoil with high redox potential (500-600 mV) was very slow: for an incubation period of 120 days, there was no clear transformation. Similarly, there was no distinct transformation of the oxidation products of aldicarb in a period of 72 days in this watersaturated aerobic subsoil. In incubation studies, ferrous ions occurring frequently in reduced subsoil conditions proved to be involved in the rapid transformation of carbomoyloximes. The reaction mechanisms and the products formed have been studied by Bromilow et al. (1986). Studies on the rate of hydrolysis of pesticides in water are interesting because they may provide a lower limit of the possible transformation rates in the groundwater zone. However the pH-buffer used in many studies may have an effect on this rate. Some studies on the soil fumigant 1,3-dichloropropene are discussed here as examples. It is remarkable that in various deep bores, in which the admixture 1,2-dichloropropane was detected, no 1,3-dichloropropene could be detected (Table 5). There is not much difference in the adsorption behavior of these corn-
384
pounds in soils and subsoils. This suggests that 1,3-dichloropropene may be transformed in the groundwater zone. Studies on its transformation in watersaturated subsoil materials have not yet been published, but some reports about its hydrolysis have appeared. The rate of hydrolysis of the (Z) and (E) 1,3-dichloropropenes in water with citrate/phosphate buffer at pH 5.5 and 7.5 was studied by van Dijk (1974). The value of the pH had only a small effect. The half-lives of the (Z) and (E) isomers at 2 ° C were about 95 and 75 days and those at 15 ° C were about 10 and 12 days, respectively. The hydrolysis of the (Z) and (E) isomers of 1,3-dichloropropene in sterile phosphate-buffered water in the dark was studied by McCall (1987). The rate of hydrolysis decreased with decreasing temperature, as expected, and at 10 ° C the corresponding half-life was 51 days. The hydrolysis products, the (Z) and (E) isomers of 3-chloroallylalcohol, were measured to be formed at similar rates and they were stable to further hydrolysis (in 30 days). TOXICOLOGICAL EVALUATION AND LIMIT VALUES
In 1984, the maximum admissible concentration of 0.1 #g 1-1 for pesticide residues in drinking water (Directive of the European Communities) was incorporated in Dutch legislation. In F.R.G., it was incorporated in 1986, but its implementation was postponed until 1989 to provide time for further development of the analytical procedures to allow for measurement well below the limit value (Friesel, 1986). If one relies only on chemical analysis, field measurements should be made for about 300 pesticides plus their main metabolites. In other West European countries, there is considerable resistance to the incorporation of the EC directive for pesticides into the national legislation. The main argument is lack of a toxicological basis for this limit. The evaluation of the risk of pesticide residues in drinking water (and thus in groundwater) for public health can be much improved in western Europe. Extensive toxicological data are available for almost any pesticide approved nowadays. The procedure for the establishment of an acceptable daily intake (ADI) of residue through foodstuffs is generally accepted. Its value is derived from the no-observed-effect level in long-term toxicity studies, which is multiplied by a safety factor (e.g. 0.01 ). A fraction of the ADI is then reserved for possible residues of a pesticide in drinking water. Such evaluation procedures are followed by the US Environmental Protection Agency and by the World Health Organization (WHO, 1984, 1987). In the WHO procedure, 1% of the ADI was reserved for possible residues of bio-accumulating pesticides (e.g. some chlorinated hydrocarbons) in drinking water (WHO, 1984) and 10% of the ADI was reserved for a series of herbicides (WHO, 1987). For many pesticides, the toxicologically based guideline values (Table 7) are well above the maxim u m admissible concentration of 0.1 ]~g l-1 in the European directive.
385 TABLE 7 Guideline values derived by the World Health Organization for pesticide residues in drinking water (WHO, 1984, 1987) Pesticide
Guideline values (~g 1-1)
Atrazine Bentazone 2,4-D Lindane MCPA Methoxychlor Metolachlor Pendimethalin Pyridate Simazine Trifluralin
2 25 100 3 0.5 30 5 17 60 17 170
The value of 0.1 #g 1-1 in the European directive could be considered as a threshold value for further evaluation and for taking measures to reduce contamination. If this value is exceeded (in measurements or estimates), the toxicological significance of the residue has first to be evaluated. In some West European countries, a procedure including toxicological evaluation is being developed as a basis for decisions for short-term and long-term improvement (H~isselbarth, 1987). The toxicological significance of a measured residue is important when one considers ways of abandoning groundwater extraction or of purifying the water, which are often accompanied by high costs. Further the residue can then be an element in weighing the agricultural benefit and the risk of the use of that pesticide in the registration procedure. Measures may be necessary to reduce transfer to groundwater, but these will only exert their effect after many years. Predictive procedures, including the use of well-tested computational models for transport and transformation, together with the measurement of reliable physico-chemical data, should be preferred for evaluating the potential pollution hazard of pesticides under various scenarios. GENERAL DISCUSSION
The list of pesticide residues found in groundwater is already quite long and its length may be expected to increase as measurements continue. Most attention has been paid to the leaching of the parent compounds to groundwater; only in a few studies have some transformation products also been considered. One should realize that transformation products may leach to the groundwater even if the parent compound does not. This may be illustrated by the leaching
386
measurements of Scheunert et al. (1987), who applied [14C]buturon (3 kg h a - 1) to a field lysimeter (0.6-m deep). Over a period of 12 years they did not detect the parent compound in the percolation water, but the sum of the transformation products (expressed as buturon equivalent) ranged from 25 ttg 1-1 after I year to about 0.5 #g 1-1 after 12 years. In various instances, measurements have been made in areas with a high risk, for example with intensive application of a pesticide and with vulnerable soils. Fortunately, there were many measuring series in which pesticides have not been detected in groundwater. However the pesticide application history in the catchment areas and the soil conditions are often not very well known in monitoring studies. This makes the translation of the results to other areas difficult. More detailed studies (measurements or simulations) on field scale, starting from the application of a pesticide, remain necessary. Such studies may also indicate whether there are other sources of contamination, besides regular use in agriculture. The measurement of extremely low concentrations of pesticides in groundwater requires special techniques and procedures for sampling and analysis. Contamination of the bore hole down to groundwater with soil from higher layers should be prevented. Several volumes of a bore hole should be discarded before the water sample is taken. All glassware, equipment and chemicals used for sampling, extraction and analysis should be free from interfering substances. Zero-control samples should be included in the procedure to check for such substances. The method of analysis should be sensitive and the detection method as specific as possible. To confirm the identity of traces, at least two different methods of analysis should be used. Interfering substances in the samples may be very different, depending on the origin of the samples. In various studies reviewed here, contamination of samples and interference by other substances cannot be excluded. Single high values are especially open to suspicion; repeated measurements for a bore at various times are to be preferred. The establishment of extremely low limits for groundwater is a great impetus for the further development of sensitive and specific analytical procedures: even a fraction of such a limiting value should be detectable. Estimates on the leaching of pesticides from the root zone often started from laboratory data for the compounds and from knowledge obtained from computer modeling of the leaching process (Leistra, 1986 ). Various pesticides that were expected to leach were found later at comparatively high concentrations in shallow groundwater (e.g. aldicarb and 1,3-dichloropropene). However, for some pesticides (e.g. dinoseb), unexpectedly high concentrations were found. The cause of such deviation must be investigated, for instance inferior basic data or particular field conditions. Another category of pesticides that was considered to present little risk of leaching, is found at very low levels in shallow groundwater. The fraction of the amount applied leaching to groundwater is often very low: only about 0.1% or less (Boesten, 1987). Presumably, com-
387 plications in the transport in the root zone play a part. After heavy rain, a fraction of the water may pass very quickly through larger voids in the soil, carrying a small fraction of the original amount. The nature and magnitude of such complicating phenomena call for further research (Boesten, 1987). In general, it turns out that checking the behavior of pesticides under field conditions is very useful in the registration procedure. Little is known about the further transformation of pesticide residues in the groundwater zone, so much research remains to be done. Transformation studies with subsoil materials allow predictions to be made about the concentrations of compounds in the deeper groundwater which is to be pumped up (Leistra, 1986). Conditions in groundwater zones differ greatly from those in root zones. As the range of conditions in the groundwater zone is wide (Leistra, 1987 ), studies with various subsoils are needed. Little is known about the relationship between the bio-geochemical condition in the groundwater zones and the transformation rates. Hydrolysis, catalysis and microbial activity may play a part. Thus it is essential that the conditions in the field be simulated as closely as possible in incubation studies. If the European Directive is transposed into stringent limiting values, it will often be necessary for considerable further transformation of the residues in the groundwater zone to take place.
REFERENCES Berri, A., Allievi,C. and Burzi, F., 1983. Residui di atrazina e molinate nelle acque di falda di zone agricole sottoposte a diserbo. Acqua-Aria, 3: 259-264. Boesten, J.J.T.I.,1987. Leaching of herbicides to groundwater: A review of important factorsand of availablemeasurements. Proceedings British Crop Protection Conference -- Weeds, British Crop Protection Council, London, pp. 559-568. Bromilow, R.H., Briggs, G.G., Williams, M.R., Smelt, J.H., Tuinstra, L.G.M.Th. and Traag, W.A., 1986. The role of ferrous ions in the rapid degradation of oxamyl, methomyl and aldicarb in anaerobic soils.Pestic. Sci., 17: 535-547. Council of the European Communities, 1980. Directive of the Council of 15 July 1980 relatingto the quality of water intended for human consumption. The OfficialJournal of the European Communities L229, 30 August 1980, pp. 11-29. Croll, B.T., 1986. The effectof the agriculturaluse of herbicides on fresh waters. In: J.F. de L.G. Solbd (Editor), Effects of Land Use on Fresh Waters. EllisHorwood, Chichester, pp. 201-209. Friesel,P., 1986. Grundwasserqualitiitsbeeintriichtigungen durch die Anwendung von Pflanzenschutz- und Sch~idlingsbekKmpfungsmitteln (PSM). Bundesgesundheitsblatt, 29: 424-427. Galassi, S. and Leoni, Y., 1987. The problem of atrazine in drinking water in Italy. In: Papers European Conference "Impact of agriculture on water resources". Deutscher Verein des Gasund Wasserfaches, Eschborn, pp. 219-230. H~isselbarth,U., 1987. Zur Erfassung und Bewertung von Pflanzenbehandlungs- und Sch~idlingsbek~impfungsmitteln in Trinkwiissern entsprechend der Novelle der Trinkwasserverordnung. In: G. Milde and P. Friesel (Editors), Schriftenreihe des Vereins fiirWasser-, Boden- und Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 45-50. Hoogsteen, K.J., 1986. Microverontreiniging in drie waterwingebieden. Water, 19: 48-52. Hurle, K., Giessl, H. and Kirchhoff, J., 1987. 0ber das Vorkommen einiger ausgew~ihlter Pflan-
388 zenschutzmittel im Grundwasser. Schriftenreihe des Vereins for Wasser-, Boden- und Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 169-190. IPS, 1987. Pflanzenschutzwirkstoffe und Trinkwasser. Ergebnisse einer Untersuchungsreihe der Pflanzenschutzindustrie. Industrieverband Pflanzenschutz, Frankfurt/Main, 36 pp. Janssen, H.M.J. and Puijker, L.M., 1987. Bestrijdingsmiddelen in grondwater. In: C.G.E.M. van Beek (Editor), Landbouw en drinkwatervoorziening. Mededeling No. 99, KIWA, Nieuwegein, The Netherlands, Chapter 9, 19 pp. Jernl~s, R., 1985. Leaching of 2,3,6-TBA from a sandy soil. Weeds Weed Control, 26: 197-208. Jernl~s, R. and Klingspor, P., 1981. Leaching of TCA from arable fields. Weeds Weed Control, 22: 120-128. Leistra, M., 1986. Modelling the behaviour of organic chemicals in soil and groundwater. Pestic. Sci., 17: 256-264. Leistra, M., 1987. Transformation rates of carbamoyl oxime pesticides in soils and subsoils: Consequences for groundwater quality. In: W. van Duijvenbooden and H.G. van Waegeningh (Editors), Vulnerability of Soil and Groundwater to Pollutants. TNO Committee on Hydrological Research, The Hague, pp. 787-796. Loch, J.P.G., 1987. Vulnerability of groundwater to pesticide leaching. In: W. van Duijvenbooden and H.G. van Waegeningh (Editors), Vulnerability of Soil and Groundwater to Pollutants. TNO Committee on Hydrological Research, The Hague, pp. 797-807. McCall, P.J., 1987. Hydrolysis of 1,3-dichloropropene in dilute aqueous solution. Pestic. Sci., 19: 235-242. Meinert, G. and H~ifner, M., 1987. MSglichkeiten und Probleme bei der Anwendung von Pflanzenbehandlungsmitteln in Wasserschutgebieten. Schriftenreihe des Vereins for Wasser-, Bodenund Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 51-63. Milde, G., Pribyl, J., Kiper, M. and Friesel, P., 1982. Problems of pesticide use and the impact on groundwater. Memoires Prague Congress, Intern. Assoc. Hydrogeol. 1. Novinar Publ. House, Prague, pp. 249-260. Plant Protection Service, 1987. Bestrijdingsmiddelen en waterwingebieden. Bericht No. 3, Wageningen, The Netherlands, 4 pp. Rexilius, L., 1987. Anwendung von Bodenentseuchungsmitteln im Baumschulengebiet des Kreises Pinneberg (Schleswig-Holstein) im Hinblick auf Kontaminations-miiglichkeiten yon Grundund Trinkwasser- Eine Bestandsaufnahme. Schriftenreihe des Vereins for Wasser-, Bodenund Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 225-243. Rexilius, L. and Schmidt, H., 1982. Untersuchungen zum Versickerungsverhaltens von 1,3-Dichiorpropen und Methylisothiocyanat auf Baumschulfl~ichen. Nachrichtenbl. Dtsch. Pflanzenschutzdienst (Berlin), 34: 161-165. Roth, M., 1987. Grundwasserbelasting durch Pflanzenschutzmittel in Baden-Wtirttemberg. Konzeption-Ergebnisse-Ausblick. Schriftenreihe des Vereins fOr Wasser-, Boden- und Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 143-148. Scheunert, I., Korte, F. and Reiml, D., 1987. Applikationsuntersuchungen von Pflanzenbehandlungsmitteln im System Pflanze/Boden in Lysimetern unter Einsatz 14C-markierter Substanzen und der besonderen Berticksichtigung des Leaching-Verhaltens. Schriftenreihe des Vereins for Wasser-, Boden- und Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 313-322. Schiavon, M. and Jacquin, F., 1973. Etude de la prdsence d'atrazine dans les eaux de drainage. Comptes Rendus des journ~es d'6tudes sur les herbicides, Columa, Versailles, pp. 35-43. Smelt, J.H., Dekker, A., Leistra, M. and Houx, N.W.H., 1983. Conversion of four carbamoyl oximes in soil samples from above and below the soil water table. Pestic. Sci., 14: 173-181. Snegaroff, J., 1979. La pollution des eaux par les triazines herbicides dans le secteur du marais charentais. Phytiatr.-Phytopharm., 28: 249-261. Stock, R., Friesel, P. and Milde, G., 1987a. Grundwasserkontamination dutch Pflanzenbehand-
389 lungsmittel in der Niederen Geest Schleswig-Holsteins und im Emsland. Schriftenreihe des Vereins fiir Wasser-, Boden- und Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 209-223. Stock, R., Friesel, P., Milde, G. and Ahlsdorf, B., 1987b. Grundwasserqualita'ts-beeinfliissungdurch Planzenschutzmittel. In: Impact of Agriculture on Water Resources. Deutscher Verein des Gasund Wasserfaches. Eschborn, F.R.G., pp. 239-265. Van Beek, C.G.E.M., 1986. Grondontsmetting en de openbare drinkwatervoorziening. In: Lezingen Kongres Grondontsmetting nu en in de toekomst. Agriben, Etten-Leur, The Netherlands, pp. 15-16. Van der Pas, L.J.T. and Leistra, M., 1987. Movement and transformation of 1,3-dichloropropene in the soil of flower-bulb fields. Arch. Environ. Contam. Toxicol., 16: 417-422. Van Dijk, H., 1974. Degradation of 1,3-dichloropropenes in the soil. Agro-Ecosystems, 1: 193-204. Vogelaar, A.J., van Beek, C.G.E.M., Puijker, L.M. and Janssen, H.M.J., 1987. De aanwezigheid van de bestrijdingsmiddelen bromacil en amitrol in het grondwater onttrokken op enkele geselekteerde winningen. Report SWO-87.329, KIWA, Nieuwegein, 27 pp. Werner, G., 1987. Strategien und Ergebnisse der 0berwachung der Rohwasserqualit~t von Grundwasserf6rderungsanlagen auf Kontamination durch Pflanzenbehandlungsmittel. Schriftenreihe des Vereins fiir Wasser-, Boden- und Lufthygiene 68. Gustav Fischer, Stuttgart, pp. 149167. WHO, 1984. Guidelines for drinking-water quality. Vol. 1. Recommendations. World Health Organization, Geneva, Switzerland, 130 pp. WHO, 1987. Drinking-water quality: Guidelines for selected herbicides. Environmental Health 27. World Health Organization, Regional Office for Europe, Copenhagen, Denmark, 23 pp.
369
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
P e s t i c i d e C o n t a m i n a t i o n of G r o u n d w a t e r in Western E u r o p e M. LEISTRA and J.J.T.I. BOESTEN
Institute for Pesticide Research, P.O. Box 650, 6700 AR Wageningen (The Netherlands) (Accepted for publication 19 May 1989)
ABSTRACT Leistra, M. and Boesten, J.J.T.I., 1989. Pesticide contamination of groundwater in western Europe. Agric. Ecosystems Environ., 26: 369-389. In recent years, many measurements have been made of residues of pesticides in shallow and deep groundwater in western Europe. Some triazine herbicides and their transformation products have been detected most frequently. The average concentration in measuring series for deep groundwater was usually below 0.1 ]~g 1-1, and the highest values were usually below 0.5 ]~g 1-1. The concentrations of mecoprop in deep groundwater ranged up to 0.6/~g l - 1 and those of bentazone to almost 1.0/~g l - 1. Some other herbicides were found at comparatively high concentrations and the highest values were found for TBA and TCA in tile-drain water. The soil fumigant 1,3-dichloropropene was mainly found in shallow groundwater, but its admixture 1,2-dichloropropane was also found in deep groundwater (range up to 10 ]~gl - 1, sometimes even higher). Residues of the nematicides aldicarb and oxamyl have been measured in shallow and intermediate groundwater, but measurements for deep groundwater are still lacking. Some carbamoyl-oximes were incubated in subsoil materials to study their transformation and their rate of transformation in anaerobic subsoils was surprisingly high. The maximum admissible concentration of 0.1 pg l - 1 in a Directive of the European Communities of 1980 is the subject of much debate, because a toxicological basis is lacking.
INTRODUCTION
The interest of registration authorities in the possible contamination of groundwater by pesticides dates from the beginning of the 1970s. In some countries, notably F.R.G. and The Netherlands, official working groups were established then to evaluate the risk of pesticide residues leaching from the root zone to the upper groundwater. In the course of years, many pesticides have been evaluated and for several of them a substantial leaching of residues was considered to be possible. A national warning system was set up in these countries to prevent the use of potentially hazardous pesticides in the protection zone of groundwater extractions. In various regions, this protection was un0167-8809/89/$03.50
© 1989 Elsevier Science Publishers B.V.
370 fortunately difficult to achieve. The interest of the public, the drinking-water companies and the public authorities was awakened by the detection, in the early 1980s, of pesticide residues in deep groundwater, pumped for public water supply. Since then, research has been extended and the efficiency of the protection of catchment areas has been improved. The most recent "black list" in The Netherlands, of 31 pesticides whose residues might leach to the upper groundwater, is given in Table 1. In addition, there is a list of 17 compounds whose residues may leach from the root zone when applied under particular conditions, such as during winter or in greenhouses (Plant Protection Service, 1987 ). A similar "black list" of pesticides in the F.R.G. contained about 70 pesticides in 1985. At the time these lists were compiled, only laboratory data were usually available, for example those on adsorption/mobility and on transformation of the pesticides in soil. Only a few pesticides had been subjected to field trials or to monitoring. The number of measurements in the field has strongly increased in recent years. As a result of improved sensitivity in analytical techniques, ever lower concentrations of pesticides can now be measured, leading to a substantial number of positive measurements. As the evaluation of the risk of leaching is intensified, such lists of pesticides presenting a risk to groundwater quality may be expected to grow. In some western European countries, the risk of leaching to groundwater plays a major part in the registration procedure. In a Directive, the Council of the European Communities (1980) established a maximum admissible concentration of 0.1/~g 1-1 for any pesticide in drinking water. Further, the upper limit for the sum of the concentrations of pesticides and related chemicals was set at 0.5/zg l - 1. The value of 0.1/lg 1-1 was chosen because it represented a detection limit in chemical analysis. The idea was that pesticide residues should not be present in drinking water (H~sselbarth, 1987). Since groundwater is seldom purified, the Directive also applies to groundwater pumped for consumption. The member countries were obliged to incorporate this Directive into their national legislation within a few years. A toxicoTABLE1 Pesticides whoseuse is not allowedin groundwaterprotectionareas in The Netherlands {Plant Protection Service, 1987) Alachlor Aldicarb Alloxydim-sodium Asulam Benazolin Benazolin-ethyl Bentazone Borates
Bromacil Fluroxypyr Chloralhydrate Glufosinate-ammonium Chlorthal-dimethyl Hexazinone Dicamba Lenacil 1,3-dichloropropene Metalaxyl Dikegulac-sodium Metazachlor E n d o t h a l - s o d i u m Methomyl Ethiofencarb Metolachlor
Propachlor Propoxur Sodiumarsenite TCA Thiofanox Triclopyr Vamidothion
371 logical basis for this limit is missing: the vast amount of toxicological research on the presently approved pesticides is completely neglected. Consequently, the enormous differences in mammalian toxicity of the various pesticides are not accounted for. Measurements of residues above the Community's limit have raised great concern among distributors and consumers. Expensive measures have sometimes been taken to keep the residue below this detection limit. This contribution surveys the results of measurements of pesticide residues in shallow and deep groundwater in western Europe. The conditions that may be relevant for residues in a particular situation are indicated. For a few pesticides, information about their transformation in the groundwater zone is discussed. Finally, a few ways of improving the evaluation of the risk of a pesticide for groundwater quality are indicated. MEASUREMENTSIN GROUNDWATER
Triazines in the upper groundwater Samples were taken from groundwater (via boreholes) in areas with arable farming in East Anglia, U.K. and they were analysed for atrazine (Croll, 1986). In some areas with sandy soils and a shallow water table, low concentrations were found (Table 2). The concentrations of simazine were, on average, about 0.25 times those of atrazine. In the period December-May, tile-drain water samples were taken from a field with alluvial clay soil in Charente Maritime, France, on which atrazine and simazine had been applied repeatedly for a maize crop (rate 1.25 kg h a - 1). Upon drying, this soil showed clear shrinkage fissures. The residues of the herbicides were analysed (Snegaroff, 1979) and the results of the measurements are given in Table 2. The concentrations of atrazine and simazine were almost the same and rather high. Atrazine was applied in spring at a rate of 1.25 kg h a - 1to 2 fields in Lorraine, France, one with a clay soil and the other with a clay loam soil, with tile-drains at a depth of about 0.9 m. In the first 9 months following application the tiledrain water was sampled and analysed for atrazine (Schiavon and Jacquin, 1973). The results are summarized in Table 2. These soils also showed clear shrinkage fissures, through which water flowed quickly after heavy rainfall. This could explain the comparatively high concentrations of atrazine in the drain water. After repeated annual applications of atrazine to 2 maize fields in BadenWiirttemberg, F.R.G., Hurle et al. (1987) collected water from tile-drains 0.81.0-m deep. They found concentrations between 0.2 and 2.3 #g 1-1 (Table 2 ). In the years after the application had stopped, the concentration of atrazine in drain water gradually decreased. Two years after the last application, the
U.K., East Anglia France, Charente Maritime France, Lorraine F.R.G., Baden-Wtirttemberg F.R.G., Schleswig-Holstein F.R.G., Schleswig-Holstein Netherlands, Noord-Brabant Netherlands, Noord-Brabant F.R.G., Baden-Wiirttemberg Netherlands, Noord-Brabant France, Charente Maritime F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg
Atrazine
Desethylterbuthylazine
Terbuthylazine
Terbuthylazine
Simazine
Simazine
Desethyl-atrazine
Desethyl-atrazine
Atrazine
Atrazine
Atrazine
Atrazine
Atrazine Atrazine
Atrazine
Country, area.
Compound
Tile-drain water
Tile-drain water
Tile-drain water
Tile-drain water
Tile-drain water
Upper groundwater
Tile-drain water
Upper groundwater
Upper groundwater
Upper groundwater
Upper groundwater
Tile-drain water Tile-drain water
Tile-drain water
Upper groundwater
Sampled
0.8-1.0
0.8-1.0
0.8-1.0
0.8-1.0
Not given
Below 3
0.8-1.0
1 -2
Below 3
0.5-5
0.5-3
0.9 0.8-1.0
Not given
Not given
Depth (m)
3
9
5
9
11
17
8
25
29
44
24
11 9
> 24 11
No. of samples
0.05
0.4
0.49
0.4
22
<0.1
0.04
0.22
0.1
0.74
16 0.6
27
Average
-46
0.2 -35
-
0.02- 0.07
<0.1 - 1.0
0.06- 1.92
<0.1 - 1.2
12
<0.1
<0.02- 0.17
<0.08- 0.58
<0.1 - 0.8
0.01-17.5
<0.05- 6.75
6 -29 0.2 - 2.3
12
< 0.2 - 0.5
Range
Concentration (P4~1-1 )
Residues of triazine herbicides measured in the upper groundwater and in tile-drain water of treated fields
TABLE 2
Hurle et al. (1987)
Meinert and H~ifner (1987)
Hurle et al. (1987)
Meinert and H~fner (1987)
Snegaroff (1979)
Janssen and Puijker (1987)
Hurle et al. (1987)
Loch (1987)
Janssen and Puijker (1987)
Stock et al. (1987a,b)
Stock et al. (1987a,b)
Schiavon and Jacquin ( 1973 ) Hurle et al. (1987)
Snegaroff (1979)
Croll (1986)
Reference
bO
373 transformation product desethyl-atrazine could still be measured in the water. Terbuthylazine, used as an alternative to atrazine, could be measured in the tile-drain water in the first few months after application, together with its transformation product desethyl-terbuthylazine (Table 2 ). In tile-drain water and in water from shallow bores in grape-growing areas in Rheinland-Pfalz, F.R.G., the concentrations of atrazine and simazine varied between 0.01 and 0.03 #g l-1 (Hurle et al., 1987). In the upper groundwater of a forest area, no residues of these triazines could be found. The upper groundwater was collected from below maize fields in SchleswigHolstein, F.R.G., that had been treated for several years with atrazine (1-1.5 kg h a - 1) (Stock et al., 1987a,b). Most fields had humic sand soils. The results of 24 analyses for 6 observation wells in the period May-March are summarized in Table 2. Observation wells (44) were installed in 33 maize fields with sandy soil, on which atrazine had been regularly used at a dose of about 1 kg ha-1. The upper groundwater in these wells was analysed for atrazine (Stock et al., 1987a,b). The results of these measurements are also given in Table 2. Samples were taken from shallow groundwater in a catchment area in NoordBrabant, The Netherlands, in which atrazine is used in maize, grown in crop rotation (Janssen and Puijker, 1987). With the detection limit at 0.1/~g l-1, atrazine could be measured in 7 out of 29 samples (Table 2). The transformation product desethyl-atrazine was found at lower concentrations (Table 2), while desisopropyl-atrazine could not be detected. Under continuous maize on humic sand soil in Noord-Brabant, The Netherlands, the upper groundwater was sampled for atrazine analysis (Loch, 1987). This herbicide had been applied almost yearly in the spring (rate 0.5-1.2 kg ha -1), In nearly all of the samples (25) a low concentration of atrazine was found (Table 2). An arable field with sandy loam soil in Baden-Wiirttemberg, F.R.G., was treated with simazine (0.5 kg ha-1) and with terbuthylazine (0.74 kg ha-1) in April. Tile-drains were situated at a depth of 0.8-1.0 m. In the year following application, samples of drain water were taken and analysed by gas chromatography (Meinert and Hiifner, 1987). The concentration of the two triazines measured 9 times are summarized in Table 2. Already in May, after heavy rainfall, the compounds were detected in the drain water and their concentrations had increased considerably by the end of June.
Triazines in deep groundwater In the period 1983-1985, many water samples were taken from 11 groundwater bores and springs in Baden-Wiirttemberg, F.R.G., and they were analysed for residues of triazine herbicides (Hurle et al., 1987 ). One series of samples was taken in limestone areas and another in sedimentary areas. The catchment areas of these bores and springs were used mainly for agriculture,
374
with a substantial use of atrazine in maize. Atrazine could be detected (Table 3) in the majority of 238 groundwater samples. In some of the samples, desethyl-atrazine was also detected. When simazine was detected, its concentration was usually distinctly lower than that of atrazine. Water from a spring in Baden-Wiirttemberg, F.R.G., was sampled and analysed for some triazines (Hurle et al., 1987). The catchment area of this spring was used mainly for agriculture. The average concentrations of atrazine and simazine were below 0.1/zg 1-1 (Table 3). The concentrations of desethylatrazine were even lower (Table 3) and desethyl-simazine was found in only 1 out of 13 samples, at 0.03/~g l - 1. A series of 40 groundwater extraction sites in Baden-Wfirttemberg, F.R.G., was selected on the basis of the vulnerability of their catchment areas: intensive use of herbicides and low-adsorptive soil in the top layers (Roth, 1987). The maximum concentrations of atrazine and simazine measured in 120 water samples in 1984 are given in Table 3. In a subsequent measuring series of 155 samples from groundwater extraction sites, carried out in 1985, atrazine exceeded the 0.1/~g 1-1 level only twice (Roth, 1987). Samples were taken from bores producing groundwater from an aquifer in the Valley of the Danube, F.R.G. This water was analysed for residues of atrazine and simazine (Werner, 1987). The catchment areas were used for agriculture with maize as one of the crops. In 4 bores, the concentrations of atrazine ranged up to 0.06 #g 1-1 but in one bore they were distinctly higher (Table 3). The concentrations of simazine (applied on a much smaller scale) were substantially lower (Table 3). When the concentration of atrazine was comparatively high, the desethyl and desisopropyl transformation products were also detected. Their concentrations were somewhat lower (desethyl) or much lower (desisopropyl) than those of atrazine. Water samples were also taken from a large spring in a limestone area. The concentrations of atrazine and simazine measured by gas chromatography (Werner, 1987) are summarized in Table 3. The concentrations of the desethyl and desisopropyl transformation products of atrazine were about 0.6 and 0.2 times those of atrazine itself. In 1985, nine springs used for drinking water in Rheinland-Pfalz, F.R.G., were sampled and analysed for triazine residues by Hurle et al. (1987). On a large fraction of the catchment area, crops were grown. Atrazine and simazine were detected in most of the samples (Table 3). The average concentration of the transformation product desethyl-atrazine was somewhat higher and that of desethyl-simazine was much lower (Table 3). Groundwater samples were taken from 24 bores used for public water supply in 3 states of F.R.G. and they were analysed for atrazine (IPS, 1987). In 14 bores (most up to 20-m deep) in the 3 states, atrazine was detected at least once and its concentration range is given in Table 3. The highest concentrations were measured for areas with intensive agriculture. In 5 out of 20 bores for public water supply in 2 federal states, simazine was detected at least once
Country, area
F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg
F.R.G., Baden-Wiirttemberg F.R.G., Rheinland-Pfalz F.R.G., three states Italy,Pavia F.R.G., Baden-Wfirttemberg F.R.G., Rheinland-Pfalz F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg F.R.G., Baden-Wiirttemberg
F.R.G., Baden-Wiirttemberg F.R.G., Rheinland-Pfalz F.R.G., two states F.R.G., Rheinland-Pfalz
Compound
Atrazine Atrazine Atrazine Atrazine
Atrazine Atrazine Atrazine Atrazine Desethyl-atrazine Desethyl-atrazine Simazine Simazine Simazine
Simazine Simazine Simazine Desethyl-simazine
Spring Springs Bores Springs
Springs Bores Bores Spring Springs Spring Bores Bores
Spring
Bores, Springs Spring Bores Bores
Sampled
238 13 120 52 13 18 9 93 313 13 9 13 120 52 13 18 9 36 9
No. of samples
0.06 <0.1 0.01
0.02 0.09 0.03
0.06 <0.1
0.08 0.07
Average <0.01-0.76 <0.01-0.35 up to 0.4 <0.01-0.06 0.1 -0.3 0.1 -0.3 <0.01-0.29 <0.05-0.26 <0.05-4 <0.02-0.10 <0.02-0.44 <0.01-0.15 up to 0.2 < 0.01-0.015 0.02-0.08 up to 0.1 0.01-0.15 <0.05-0.14 <0.02-0.06
Range
Concentration (pg l - 1)
Werner (1987) Hurle et al. (1987) IPS (1987) Hurle et al. (1987)
Werner (1987) Hurle et al. (1987) IPS (1987) Berri et al. {1983) Hurle et al. (1987) Hurle et al. (1987) Hurle et al. (1987) Roth (1987) Werner ( 1987 )
Hurle et al. (1987) Hurle et al. (1987) Roth (1987) Werner (1987)
Reference
Concentrations of triazine herbicides and their transformation products in water samples taken from groundwater bores and springs. Depths of the extractions were rarely indicated (see text)
TABLE 3
e~
376 (IPS, 1987). The results for these bores are summarized in Table 3. Only one sample had more than 0.1 pg 1-1. About 2000 bores for public water supply in Lombardia, Italy, were analysed for atrazine (Galassi and Leoni, 1987). Of these bores, 14% exceeded 0.1 ttg l-1 and 1.4% exceeded 1.0 ttg l-1. Water from about 1000 private bores (shallower) was also analysed and was generally found to have higher concentrations. About 300 bores used for supplying drinking water were sampled in an area in the Province of Pavia in Italy and analysed for atrazine (Berri et al., 1983). The area was intensively cropped with rice and maize. The results of the analyses are summarized in Table 3. In 67% of the bores, atrazine was detected at concentrations between 0.05 and 4 pg l - 1. The proportion of the bores in which atrazine was found decreased from 73% of those up to 20-m deep to 59% of those between 20 and 40-m deep and to 27% of those deeper than 40 m.
Herbicides (other than triazines) in shallow and deep groundwater Groundwater samples were taken from 141 bores used for public water supply in 4 states of F.R.G. (IPS, 1987). In 11 of these bores, bentazone was measured at least once. The results of the measurements for these bores are summarized in Table 4. In a catchment area in Noord-Brabant, The Netherlands, in which bentazone was applied to maize and other crops, the upper groundwater was sampled and analysed for residues of this herbicide (Janssen and Puijker, 1987). In 10 out of 26 samples, this compound could be measured (Table 4) at a detection limit of 0.1 pg 1-1. The concentrations of the transformation product anthranilic acid isopropylamide were below this detection limit. Bromacil is used on a large scale for weed control on railway tracks. Residues of this herbicide were found in water from a bore in the vicinity of such a railway track in Baden-Wiirttemberg, F.R.G. (Milde et al., 1982). The range of the concentrations measured is given in Table 4. In The Netherlands, groundwater samples were taken from 21 bores, used for public water supply, and situated within about 100 m of railway tracks. The water was analysed for bromacil and amitrol (Vogelaar et al., 1987). In none of the samples could amitrol be detected (limit of detection 0.1 ttg l-1 ). In 4 of the bores, with depths between 15 and 40 m, bromacil was found in the concentration range given in Table 4. Results of some other measurements of bromacil in bores near railway tracks in The Netherlands, including higher concentrations, were released to the press, but detailed reports have not been published. Dinoseb was analysed in groundwater after application as a selective herbicide at comparatively low rates (a few kg ha -1) in a potato crop on low to moderately humic soil in Drenthe, The Netherlands (Loch, 1987). Occasionally, low concentrations were found in the upper groundwater, however, after
Country, area
F.R.G., four states Netherlands, Noord-Brabant Bromacil F.R.G., Baden-Wiirttemberg Bromacil Netherlands, three provinces Dinoseb Netherlands, Drenthe Isoproturon F.R.G., two states Mecoprop F.R.G., Baden-Wtirttemberg Mecoprop F.R.G., Baden-Wtirttemberg Mecoprop F.R.G., four states Molinate Italy, Pavia Phenoxyalkanoic U.K., acids East Anglia 2,4,5-T F.R.G., Baden-Wtirttemberg 2,3,6-TBA Sweden, MalmShus TCA Sweden, MalmShus
Bentazone Bentazone
Compound
5
Tile-drain water Tile-drain water
Not given 31 0.85-1.0 8
<0.05<0.1 -
Range
12.5 670
up to 79 370 -1270
Jernl~s(1985) Jernl~sandKlingspor (1981)
Roth (1987)
Hurle et al. (1987)
u p t o 17
< 0.02-
Loch (1987) IPS (1987) Hurle etal. (1987)
IPS (1987) Bern etal.(1983) Croll (1986)
0.03
<0.1 < 0.05< 0.02-
0.9 < 0.05
Vogelaaret al. (1987)
IPS (1987) Janssenand PuCker (1987) Mildeetal. (1982)
Reference
<0.050.37 0.05- 154 < 0.2 0.4
9.2 0.08 0.6
<0.1 -
1.8
0.85 1.0
0.2
About 30 up to 147
0.12 0.2
Average
Concentration (#g 1-1 )
Bores Various 42 <0.1 Bores 41 Upper (?)groundwater Not given More than 15 Bores Not given ?
Spring
1- 2 Various
Upper groundwater Bores Bores, Springs
24 32 50
21
15-40
Bores
35 26
No. of samples
About 15
Various Below 3
Depth (m)
Upper (?) groundwater
Bores Upper groundwater
Sampled
Concentrations of herbicides (other than triazines) measured in shallow and deep groundwater
TABLE 4
378
application at a comparatively high rate (8.3 kg h a - 1 ) as a defoliant, distinctly higher concentrations were measured (Table 4). After application in late summer, the highest concentrations in the upper groundwater were already measured in the subsequent autumn and winter. Water samples taken from 161 bores in 6 states of F.R.G. were analysed for isoproturon (IPS, 1987). In only 5 of the bores (in 2 states), the herbicide was detected and the concentrations were very low (Table 4). Groundwater and water from springs, both used for public water supply in Baden-Wiirttemberg, F.R.G., were sampled and analysed for mecoprop by Hurle et al. (1987). This herbicide could be measured in 8 out of 50 samples (Table 4). In water from another spring in this state, mecoprop was found in 2 out of 5 samples at a very low concentration (Table 4). Analyses for mecoprop were also made for 142 samples from 95 bores in various states of F.R.G. (IPS, 1987). In water from 20 bores, a residue of mecoprop was detected at least once, but only in one bore was the concentration above 0.1 ttg 1-1. The results for these bores are summarized in Table 4. Around 300 bores for water supply were sampled in Pavia, Italy, and analysed for molinate (Berri et al., 1983). The area was intensively cropped with rice and maize. The results of the analyses are given in Table 4. In 13% of the bores, molinate was found, usually at concentrations between 0.05 and 3 ttg 1-1. However in a few bores, concentrations were up to 20 #g 1-1 and in one well (10-m deep) 154ttg 1-1. Samples were taken from groundwater (via boreholes) in East Anglia, U.K., in areas with arable farming in which phenoxyalkanoic acid herbicides were used on a large scale (Croll, 1986 ). Only low concentrations of these herbicides (among which mecoprop, further not specified) were found (Table 4). Substantial concentrations were measured (Table 4) of the herbicide 2,4,5T in water extracted from an aquifer below a forest area in Baden-Wiirttemberg, F.R.G. (Roth, 1987). The herbicide TBA was applied in mid October to 8 experimental plots (0.25 ha each) in MalmShus, Sweden, at rates of 0.2 and 0.6 kg ha-1. Three months after application, the tile-drain water from each of the plots was sampled and analysed (Jernl~s, 1985). Substantial concentrations were found (Table 4) and the total amounts leached during those 3 months corresponded to about 10% of that applied. The herbicide TCA was applied (April) to an experimental field with humic sand soil in MalmShus, Sweden, at rates ranging from 20 to 60 kg ha-1. Samples were taken from the water flowing from tile-drains at a depth of 0.85-1.0 m (Jernl~s and Klingspor, 1981 ). About a month after application, comparatively high concentrations could be measured in the water by spectrometry (Table 4). In drain water from irrigated fields, residues were detected throughout the summer.
379
Fumigants and their admixtures The soil fumigant 1,3-dichloropropene is widely used in areas with intensive agriculture and horticulture in western Europe. Besides the (Z) and (E) isomers of 1,3-dichloropropene, the mixtures contained substantial amounts of other volatile chlorinated hydrocarbons. For example, the content of 1,2-dichloropropane in some mixtures was around 25%. After this compound was detected in deep groundwater in 1984 (Hoogsteen, 1986), the authorities in some countries established a maximum content of 0.5% for 1,2-dichloropropane in the fumigant mixtures. A further reduction in this limit is under consideration. Presumably, the concentrations of 1,2-dichloropropane currently found in deep groundwater, originate from application of fumigants with a high content of this admixture a few tens of years ago. In Schleswig-Holstein, F.R.G., residues of 1,2-dichloropropane were detected in groundwater sampled from bores for public water supply (IPS, 1987 ). In water from 5 bores (out of 13 ), this compound was measured at least once. The results for these bores are summarized in Table 5. Industrial discharge may have contributed to this contamination. In a survey started in 1984, residues of 1,2-dichloropropane were measured in deep groundwater (25-40 m) pumped for public water supply in Drenthe, The Netherlands (van Beek, 1986; Hoogsteen, 1986). The concentrations in 3 catchment areas ranged up to 9.3/zg l- 1 (Table 5 ). The highest concentrations were measured for bores fed by water percolating through areas with arable farming, including potato growing. In these areas, dichloropropene mixtures had been used since 1968. The concentration of 1,2-dichloropropane in the extracted water can be drastically reduced in airstrip-column installations (Hoogsteen, 1986). Water samples were taken at various depths (7-68 m) in bores installed in areas of Drenthe, The Netherlands, in which the fields had been fumigated regularly with 1,3-dichloropropene (Janssen and Puijker, 1987). In 24 (depth to 35 m) out of 52 samples, 1,2-dichloropropane could be measured (Table 5). Two other admixtures of the fumigant, 1,2,2-trichloropropane and 1,2,3-trichloropropane, were also detected (Table 5), although in fewer samples and at lower concentrations. The isomers of 1,3-dichloropropene could not be detected in the water samples (detection limit 0.05/zg l-1). Similarly, the fumigant methyl isothiocyanate, the transformation product of metham-sodium (also used on a large scale), was not detected at this limit (Janssen and Puijker, 1987). Some potato fields with humic and peaty sand soils in Niedersachsen, F.R.G., were fumigated with 1,3-dichloropropene at a rate of about 125 1 ha -1 in November. The upper groundwater below the fields (water table at about 2 m) was sampled at various times after installation of observation wells (Stock et al., 1987a,b). The results of the analyses for 1,3-dichloropropene are summa-
Country, area
1,2-dichloropropane F.R.G., Schleswig-Holstein 1,2-dichloropropane Netherlands, Drenthe 1,2-dichloropropane Netherlands, Drenthe 1,3-dichloropropene F.R.G., Niedersachsen 1,3-dichloropropene F.R.G., Niedersachsen 1,3-dichloropropene F.R.G., Schleswig-Holstein 1,3-dichloropropene F.R.G., Schleswig-Holstein 1,3-dichloropropene Netherlands, Drenthe 1,3-dichloropropene Netherlands, Zuid-HoUand 1,2,2-trichloroNetherlands, propane Drenthe 1,2,3-trichloroNetherlands, propane Drenthe
Compound
25 -40 7 -68 1 - 2 1.7- 2.3 1 - 5 1 - 4
Bores Bores Upper groundwater Upper groundwater Upper groundwater
1 - 2 1 - 3 7 -68 7 -68
Upper groundwater Upper groundwater Bores Bores
Bores for irrigation 11 and 24
various
Depth (m)
Bores
Sampled
52
52
92
20
9
14
8 8 80
52
24
40
1.0
0.06
<0.6
5.7
0.23
0.6
2530 2
8.5
2.2
0.8
5.1
5 -
5
-8620
<0.05-
< 0.05-
<0.6 -
< 0.5 -
< 0.02-
<0.02-
9.1
0.9
2.5
80
0.89
3.2
<0.1 - 803
<1
<0.05- 165
up to 9.3
<0.05-
No. of Concentration (pg 1-1 ) samples Average Range
Concentrations of fumigants and their admixtures measured in shallow and deep groundwater
TABLE 5
Janssen and Puijker (1987)
van der Pas and Leistra (1987) Janssen and Puijker (1987)
Loch (1987)
Rexilius and Schmidt (1982)
Rexilius and Schmidt (1982)
Stock et al. (1987b)
Stock et al. (1987a,b)
van Beek ( 1986 ) Hoogsteen (1986) Janssen and Puijker (1987)
IPS (1987)
Reference
c~ Oo Q
381 rized in Table 5. In winter after the application, concentrations up to around 8000/~g 1-1 were found below one of the fields. In the course of time, the concentrations decreased, but after several months (in May) they were still substantial. Under a second field, the concentrations were much lower (Table 5). In another study in Niedersachsen, F.R.G., the upper groundwater was sampled with 80 observation wells installed in 37 potato fields and these samples were also analysed for 1,3-dichloropropene (Stock et al., 1987b). In the area with humic and peaty sand soils, the water table was between 1.0 and 4.1 m. The results of these measurements are given in Table 5. In slightly more than half the samples, no 1,3-dichloropropene was detected. In 18% of the samples, the concentrations were above 0.5/~g 1-1. Substantial concentrations were measured only in the first year after application. Two fields with sandy soil in Schleswig-Holstein, F.R.G., were fumigated with 1,3-dichloropropene mixture (rate about 230 1 ha -1) at the end of October. Some of the fields were then sprinkler irrigated with 40 m m of water. For 140 days after application, samples were taken from the upper groundwater of the fields and these were analysed for 1,3-dichloropropene (Rexilius and Schmidt, 1982 ). The concentrations were in the range 0.02-3.2 #g l-1 (Table 5). In 2 bores for irrigation (11 and 24 m deep) 10-25 m from the fumigated fields, the concentrations of 1,3-dichloropropene were somewhat lower (Table 5). Many water samples were collected from 23 bores in Schleswig-Holstein, F.R.G., in an area in which 1,3-dichloropropene had been used for many years (Rexilius, 1987). The samples were analysed by gas chromatography at a detection limit of 0.001/~g 1-1 and in none of the 1332 samples could residues of the fumigant be detected. Fields in Drenthe, The Netherlands, with low to moderately humic sand soil, were fumigated repeatedly with 1,3-dichloropropene in the autumn (rate about 200 kg h a - 1). In the subsequent years, the upper groundwater under the fields was analysed for 1,3-dichloropropene (Loch, 1987). In the summer following application, substantial concentrations of this fumigant were measured (Table 5 ). In subsequent months, the concentrations beneath two fields declined to < 1 and 3/~g l-1, respectively, and they declined further to < 0.5/~g 1-1 in the following year. This decline could result from transformation of this fumigant in the groundwater zone. However, such field measurements do not provide much certainty about that. Three fields with sandy soil in Zuid-Holland, The Netherlands, were fumigated with 1,3-dichloropropene (rates 290-350 kg h a - 1) in summer, after which samples were taken from the water-saturated subsoil at monthly intervals up to 3 months after application (van der Pas and Leistra, 1987). Neglecting adsorption onto the subsoil material with hardly any organic matter, the concentrations in the upper groundwater could be calculated. The results for the layer 1-3-m deep are summarized in Table 5. Only in a few of the samples was a low residue found, mainly in the first 2 months.
382 TABLE 6 Concentrations of insecticides and nematicides in groundwater Compound
Country, area
Sampled
Depth (m)
No. of samples
Concentration (pg l - 1)
Reference
Average Range Aldicarb Lindane Oxamyl
Netherlands, Drenthe F.R.G., Baden-Wiirttemberg Netherlands, Drenthe
Upper groundwater Spring
1- 2
Observation bores
7-15
4 3 8
43 0.04 < 0.1
4.5 -130 0.010.08 < 0.1 0.2
Loch (1987) Hurle et al. (1987) Janssen and Puijker ( 1987 )
Insecticides and nematicides Aldicarb was applied to a low-humic sand soil in Drenthe, The Netherlands, at the planting of a potato crop. The application rate was comparatively low: 1.5 kg ha -1 (Loch, 1987). A concentration of 130/~g 1-1 (sum of the two oxidation products) was measured in the upper groundwater below the field in October. In the subsequent year (3 measurements), the concentrations were lower (average 15/lg 1-1), but after an initial decline they increased again (Table 6 ). In Noord-Brabant, The Netherlands, an aldicarb residue (22/~g 1-1; more than 90% sulfone) was measured in the upper groundwater (2 m below the soil surface) (Smelt et al., 1983 ). A rate of aldicarb of 5.3 kg ha-1 was applied to this sandy soil (pH 4.3) 18 months before. Water samples from a spring in Baden-Wiirttemberg, F.R.G., were analysed for lindane (Hurle et al., 1987). In 3 samples, the insecticide was detected at a very low concentration (Table 6). Observation bores (7-15-m deep) were installed in an agricultural area in Drenthe, The Netherlands, that also serves as a catchment area for public water supply (Janssen and Puijker, 1987). In this area, oxamyl was used on a limited scale. In 2 out of the 8 samples taken from the bores, oxamyl was detected at a low concentration (Table 6). TRANSFORMATIONIN THE GROUNDWATERZONE When a pesticide residue leaches to the upper groundwater, the question arises whether this residue is further transformed in the groundwater zone or not. Almost all bores for public water supply reach into aquifers at a depth of at least a few tens of metres. The travel time of the water from the upper
383 groundwater to the bore is usually at least a few tens of years, so there is ample time for further transformation of the residue. Even if transformation is slow, with a half-life of, for example, a few years, the decrease in concentration by transformation is considerable. Only a few studies have been made on the transformation of pesticide residues in subsoil material. Some studies on the transformation of carbamoyloxime pesticides can serve as examples of some early steps in research in that area. The toxic oxidation products of aldicarb, its sulfoxide and sulfone, were incubated at I0 ° C in materials from i to 2 m depth within the groundwater zone of 4 fields. The subsoils were in anaerobic condition and this was maintained during incubation (Smelt et al., 1983). The times for 50% transformation of the sulfoxide in the 4 subsoil materials were 6, 2, 3 and 27 days. The corresponding values for the sulfone were 6, 7, 8 and 131 days. The lowest transformation rates were measured for a subsoil with a redox potential of 310 mV (highest in this series) and with a comparatively low pH of 5.0. After one of the anaerobic subsoils had been sterilized, transformation was not much retarded. This indicates that the transformation is catalysed by soil constituents in reduced state (Smelt et al., 1983 ). The rates of transformation in the aerobic materials from above the water table in the same profiles were much lower than those in the anaerobic materials. The rates of transformation of oxamyl and methomyl in the 4 anaerobic subsoils were even faster: about 10% of the amount applied or less remained after i day (Smelt et al., 1983 ). In a follow-up study oxamyl was incubated at 20 °C in 3 water-saturated subsoils, two with a fairly low and one with a high redox potential (Bromilow et al., 1986). Transformation in the two subsoils with low redox potential was very rapid: it was largely completed within i day. On the other hand, transformation of oxamyl in the subsoil with high redox potential (500-600 mV) was very slow: for an incubation period of 120 days, there was no clear transformation. Similarly, there was no distinct transformation of the oxidation products of aldicarb in a period of 72 days in this watersaturated aerobic subsoil. In incubation studies, ferrous ions occurring frequently in reduced subsoil conditions proved to be involved in the rapid transformation of carbomoyloximes. The reaction mechanisms and the products formed have been studied by Bromilow et al. (1986). Studies on the rate of hydrolysis of pesticides in water are interesting because they may provide a lower limit of the possible transformation rates in the groundwater zone. However the pH-buffer used in many studies may have an effect on this rate. Some studies on the soil fumigant 1,3-dichloropropene are discussed here as examples. It is remarkable that in various deep bores, in which the admixture 1,2-dichloropropane was detected, no 1,3-dichloropropene could be detected (Table 5). There is not much difference in the adsorption behavior of these corn-
384
pounds in soils and subsoils. This suggests that 1,3-dichloropropene may be transformed in the groundwater zone. Studies on its transformation in watersaturated subsoil materials have not yet been published, but some reports about its hydrolysis have appeared. The rate of hydrolysis of the (Z) and (E) 1,3-dichloropropenes in water with citrate/phosphate buffer at pH 5.5 and 7.5 was studied by van Dijk (1974). The value of the pH had only a small effect. The half-lives of the (Z) and (E) isomers at 2 ° C were about 95 and 75 days and those at 15 ° C were about 10 and 12 days, respectively. The hydrolysis of the (Z) and (E) isomers of 1,3-dichloropropene in sterile phosphate-buffered water in the dark was studied by McCall (1987). The rate of hydrolysis decreased with decreasing temperature, as expected, and at 10 ° C the corresponding half-life was 51 days. The hydrolysis products, the (Z) and (E) isomers of 3-chloroallylalcohol, were measured to be formed at similar rates and they were stable to further hydrolysis (in 30 days). TOXICOLOGICAL EVALUATION AND LIMIT VALUES
In 1984, the maximum admissible concentration of 0.1 #g 1-1 for pesticide residues in drinking water (Directive of the European Communities) was incorporated in Dutch legislation. In F.R.G., it was incorporated in 1986, but its implementation was postponed until 1989 to provide time for further development of the analytical procedures to allow for measurement well below the limit value (Friesel, 1986). If one relies only on chemical analysis, field measurements should be made for about 300 pesticides plus their main metabolites. In other West European countries, there is considerable resistance to the incorporation of the EC directive for pesticides into the national legislation. The main argument is lack of a toxicological basis for this limit. The evaluation of the risk of pesticide residues in drinking water (and thus in groundwater) for public health can be much improved in western Europe. Extensive toxicological data are available for almost any pesticide approved nowadays. The procedure for the establishment of an acceptable daily intake (ADI) of residue through foodstuffs is generally accepted. Its value is derived from the no-observed-effect level in long-term toxicity studies, which is multiplied by a safety factor (e.g. 0.01 ). A fraction of the ADI is then reserved for possible residues of a pesticide in drinking water. Such evaluation procedures are followed by the US Environmental Protection Agency and by the World Health Organization (WHO, 1984, 1987). In the WHO procedure, 1% of the ADI was reserved for possible residues of bio-accumulating pesticides (e.g. some chlorinated hydrocarbons) in drinking water (WHO, 1984) and 10% of the ADI was reserved for a series of herbicides (WHO, 1987). For many pesticides, the toxicologically based guideline values (Table 7) are well above the maxim u m admissible concentration of 0.1 ]~g l-1 in the European directive.
385 TABLE 7 Guideline values derived by the World Health Organization for pesticide residues in drinking water (WHO, 1984, 1987) Pesticide
Guideline values (~g 1-1)
Atrazine Bentazone 2,4-D Lindane MCPA Methoxychlor Metolachlor Pendimethalin Pyridate Simazine Trifluralin
2 25 100 3 0.5 30 5 17 60 17 170
The value of 0.1 #g 1-1 in the European directive could be considered as a threshold value for further evaluation and for taking measures to reduce contamination. If this value is exceeded (in measurements or estimates), the toxicological significance of the residue has first to be evaluated. In some West European countries, a procedure including toxicological evaluation is being developed as a basis for decisions for short-term and long-term improvement (H~isselbarth, 1987). The toxicological significance of a measured residue is important when one considers ways of abandoning groundwater extraction or of purifying the water, which are often accompanied by high costs. Further the residue can then be an element in weighing the agricultural benefit and the risk of the use of that pesticide in the registration procedure. Measures may be necessary to reduce transfer to groundwater, but these will only exert their effect after many years. Predictive procedures, including the use of well-tested computational models for transport and transformation, together with the measurement of reliable physico-chemical data, should be preferred for evaluating the potential pollution hazard of pesticides under various scenarios. GENERAL DISCUSSION
The list of pesticide residues found in groundwater is already quite long and its length may be expected to increase as measurements continue. Most attention has been paid to the leaching of the parent compounds to groundwater; only in a few studies have some transformation products also been considered. One should realize that transformation products may leach to the groundwater even if the parent compound does not. This may be illustrated by the leaching
386
measurements of Scheunert et al. (1987), who applied [14C]buturon (3 kg h a - 1) to a field lysimeter (0.6-m deep). Over a period of 12 years they did not detect the parent compound in the percolation water, but the sum of the transformation products (expressed as buturon equivalent) ranged from 25 ttg 1-1 after I year to about 0.5 #g 1-1 after 12 years. In various instances, measurements have been made in areas with a high risk, for example with intensive application of a pesticide and with vulnerable soils. Fortunately, there were many measuring series in which pesticides have not been detected in groundwater. However the pesticide application history in the catchment areas and the soil conditions are often not very well known in monitoring studies. This makes the translation of the results to other areas difficult. More detailed studies (measurements or simulations) on field scale, starting from the application of a pesticide, remain necessary. Such studies may also indicate whether there are other sources of contamination, besides regular use in agriculture. The measurement of extremely low concentrations of pesticides in groundwater requires special techniques and procedures for sampling and analysis. Contamination of the bore hole down to groundwater with soil from higher layers should be prevented. Several volumes of a bore hole should be discarded before the water sample is taken. All glassware, equipment and chemicals used for sampling, extraction and analysis should be free from interfering substances. Zero-control samples should be included in the procedure to check for such substances. The method of analysis should be sensitive and the detection method as specific as possible. To confirm the identity of traces, at least two different methods of analysis should be used. Interfering substances in the samples may be very different, depending on the origin of the samples. In various studies reviewed here, contamination of samples and interference by other substances cannot be excluded. Single high values are especially open to suspicion; repeated measurements for a bore at various times are to be preferred. The establishment of extremely low limits for groundwater is a great impetus for the further development of sensitive and specific analytical procedures: even a fraction of such a limiting value should be detectable. Estimates on the leaching of pesticides from the root zone often started from laboratory data for the compounds and from knowledge obtained from computer modeling of the leaching process (Leistra, 1986 ). Various pesticides that were expected to leach were found later at comparatively high concentrations in shallow groundwater (e.g. aldicarb and 1,3-dichloropropene). However, for some pesticides (e.g. dinoseb), unexpectedly high concentrations were found. The cause of such deviation must be investigated, for instance inferior basic data or particular field conditions. Another category of pesticides that was considered to present little risk of leaching, is found at very low levels in shallow groundwater. The fraction of the amount applied leaching to groundwater is often very low: only about 0.1% or less (Boesten, 1987). Presumably, com-
387 plications in the transport in the root zone play a part. After heavy rain, a fraction of the water may pass very quickly through larger voids in the soil, carrying a small fraction of the original amount. The nature and magnitude of such complicating phenomena call for further research (Boesten, 1987). In general, it turns out that checking the behavior of pesticides under field conditions is very useful in the registration procedure. Little is known about the further transformation of pesticide residues in the groundwater zone, so much research remains to be done. Transformation studies with subsoil materials allow predictions to be made about the concentrations of compounds in the deeper groundwater which is to be pumped up (Leistra, 1986). Conditions in groundwater zones differ greatly from those in root zones. As the range of conditions in the groundwater zone is wide (Leistra, 1987 ), studies with various subsoils are needed. Little is known about the relationship between the bio-geochemical condition in the groundwater zones and the transformation rates. Hydrolysis, catalysis and microbial activity may play a part. Thus it is essential that the conditions in the field be simulated as closely as possible in incubation studies. If the European Directive is transposed into stringent limiting values, it will often be necessary for considerable further transformation of the residues in the groundwater zone to take place.
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