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Exposure of the earthworm, Lumbricus terrestris, to diazinon, and the relative risk to passerine birds
Soil Biel. Biochem. Vol. 29, No. 314, pp. 717-720, 1997 0 1997 ElsevierScience Ltd. Al1rights reserved
PII: s0038-0717(!36)001!3!3-x
Printed in Great Britain 0038-0717/97$17.00+ 0.00
EXPOSURE OF THE EARTHWORM, LUMBRICUS TERRESTRIS, TO DIAZINON, AND THE RELATIVE RISK TO PASSERINE BIRDS G. L. STEPHENSON,‘*
C. D. WREN,’ 1. C. J. MIDDELRAAD’ E. WARNER’
and J.
‘Ecological Services for Planning Ltd, 361 Southgate Dr., Guelph, Ontario, Canada NlG 3M5 and ‘Eco North, RR 1, Rosseau, Ontario, Canada P2A 2X8 (Accepted
23 July 1996)
Summary-Laboratory experiments were conducted to determine the acute lethality of diazinon to the earthworm, Lumbrinrs terrestris, in a sandy loam soil. The 7-d and 21d LCS,,Swere both approximately 43 mg kg-’ soil (dry wt). Earthworms were also placed into test containers with the same type of soil, which were then placed into established field plots, and replicates of three were sprayed once with either 0 (control), 0.5, 1 or 2 times the recommended application rate of 7.5 kg a.i. ha-‘. NO acute mortality was attributed to these spraying regimes. The half-life of diazinon in soil in the laboratory and field experiments was between 4 and 21 d. At al1 treatment levels, the bioconcentration factors ranged from 0.8 to 2.9, and from 0.7 to 2.3 in the laboratory and field experiments, respectively. The potential hazard to worm-eating birds was estimated using the equation MDD = SC x BCF x FC, where MDD is the mean daily dose (mg d-‘), SC is the soil concentration (mg kg-‘), BCF is the bioconcentration factor for diazinon in worms, and FC is the estimate of the daily food consumption of the birds (kg d-‘). Calculations using both the laboratory and field data indicate that diazinon, when applied at the recommended application rate, does not pose an acute hazard to adult birds eating worms from sprayed areas. The potential for sublethal effects or hazard to sensitive life stages (e.g. hatchlings and fledglings) was not assessed. 0 1997 Elsevier Science Ltd
INTRODUCTION Diazinon is an organophosphorus insecticide used for lawn and turf care. It is used on turf for the
control of insect pests such as the black fairway beetle (Ataenius spretulus), hairy chinch bug (Blissus leucopterus hirtus), sod webworm (Parapediasia sp. and Pediasia sp.), ants and white grubs (Phyllophaga sp.) (OMAF, 1990; Fushtey and Sears, 1981). It is also used to control insect pests in fruit, vegetable and field crops, grasslands and ornamentals. Diazinon applied to turf has been implicated in incidences of bird poisonings in both Canada and the United States (Stone and Gradoni, 1985; Eisler, 1986; USEPA, 1986). Twenty-three different bird species have been killed by exposure to diazinon (USEPA, 1986) with waterfowl species most frequently affected. Diazinon has also been reported to have killed songbirds (e.g. American robin, Turdus migratorius; European starling, Sturnus vulgaris; red-winged blackbird, Agelaius phoeniceus; and house sparrow, Passer domesticus; USEPA, 1986). Most songbird deaths have been associated with ingestion of vegetation sprayed with diazinon. *Author for correspondence.
However, soil invertebrates, including earthworms, often comp& a significant portion of a passerine’s diet. Therefore, in order to estimate the relative risk of diazinon use on turf to passerine birds, experiments were designed to assess diazinon toxicity to, and bioaccumulation in, the earthworm commonly known as the Canadian night crawler or dew worm, Lumbricus terrestris, and these data were subsequently combined with pharmacokinetic data in a preliminary risk assessment.
MATERIALS AND METHODS Laboratory experiments
An appropriate aliquot of a diazinon (Basudin R 500 EC) stock solution and a predetermined amount of distilled water were added to 1500 g of Fox sand which had been weighed and placed into a stainless-steel bowl. The Fox sand had been collected from Delhi, Ontario, dried for 2 h at room temperature, and passed through a double sieve with S- and 2-mm mesh. The contents (i.e. soil, water and diazinon) in the bowl were thoroughly mixed with a stainless-steel spatula and the mixture was placed into a 2-1 glass test container. The treatments consisted of four test concentrations (10, 40, 80 and 160 mg diazinon kg-’ soil dry wt), and a
717
G. L.
718
Stephenson et al
negative control of distilled water, with 15 test containers per treatment. Ten worms were sorted, weighed, and randomly placed into each test container. The test containers were randomly placed onto a table in a room with a constant temperature (17 k l”C), and the fluorescent lights were kept on to ensure that the worms penetrated the soil. The worms and soil in replicates of three were sampled on day 4, 7, 14 and 21. Worm (alive or dead) and soil samples were collected, weighed, labelled and chemical analysis. frozen for subsequent Bioconcentration factors (BCF) in each replicate were determined by dividing the worm tissue concentration by the ambient concentration in the soil.
Field experiment
Test containers, which were made with flexible corrugated drainage tiles with vinyl fly screens fixed over both ends, contained 750 g of Fox sand, as wel1 as 10 worms that had been acclimated to the Fox sand in the laboratory prior to use in the field experiments. The test containers with soil and worms were randomly placed into prepared holes in outside plots, where they would be exposed to natural climatic conditions. The top of each test container was fitted with a 7.4 cm dia plug of bluegrass sod. Spray applications of diazinon (Basudin R 500 EC) in distilled water were applied to the surface of each test container with a continental E-Z sprayer. The treatments consisted of three test concentrations (0.5, 1.0 or 2.0 times the application rate of 7.5 kg a.i. ha-‘) and a negative control (i.e. distilled water only), with 12 test containers per treatment. Water was applied evenly to the surface of each test container and surrounding soil in the field plots within 8 h of the diazinon application. Three test containers from each treatment were sampled on days 4, 7, 14 and 21. The contents were shaken from each test container and the worms were separated into living and dead subsamples, rinsed to remove soil particles, placed onto blotting paper to remove excess water and weighed. Subsamples of worm tissue, which included the gut content, and Tabje 1. Diazinon concentrations
Treatment Soil
Nomina1 concentration (mg kg-’ wil) Day 0
Control 40
80 160
Control 10 40 80 160
NA, not analysed.
Diazinon analysis
Frozen soil (60-290 g) and pooled worm (2456 g) samples were thawed, and the worm samples masticated in the sample bag using a glass pestle. A 25-g subsample of soil and a lO-g subsample of worm slurry (i.e. including gut contents) were extracted with 100 ml of a mixture of acetonitrile and water (8515) in a 250-ml Erlenmyer flask, and shaken for 30 min at high speed on an Eberbach horizontal shaker. The solvent mixture was passed through a Whatman No. 4 filter and placed into a 50-ml, screw-top, glass, test tube. The solution from the worm subsample was then placed into a freezer for 12 h at -20°C to separate water and fat fractions. After freezing, the acetonitrile layer (top) was decanted. Anhydrous granular sodium sulphate (10 g) was used to dry both the soil and worm liquid extracts which were concentrated under vacuum (Buchi Rotovap 55°C 3.733 kPa vacuum) to approximately 1-2 ml, and this volume was retained for clean-up. Clean-up and GC analytic variables were the same for both types of samples. For clean-up, raw extracts were eluted through a glass column (16 mm i.d. x 90 mm) packed with 2 g charcoal-celite (1:4). The eluting solvent consisted of 50 ml acetonitriletoluene (3:l). The eluate was evaporated to low volume under vacuum (rotovap) and exchanged into 2,2,4_trimethylpentane (2.5 ml) for determination with gas chromatography (GC). Extracts were analysed using a 30 m x 0.25 mm J&W DB-1701 capillary column (film thickness 0.25 urn) on a Varian 3600 GC equipped with SPI (septum-equipped programmable injector) and TSD (thermionic specific detector). GC conditions were as follows: initial temperature, 90°C; hold time, 1 min; increase to 200°C at 20” min-‘; hold time, 0 min; increase to 250°C at 10”min-‘; hold time, 0.5 min. SPI conditions were as follows: initial temperature, 90°C; increasing to 250°C at 100” min-‘;
(mg kg-’ wet wt) in wils and warms of the laboratory experiment. Worm bioconcentration presented in parentheses
10
WOllllS
soil were collected and frozen for subsequent chemical analysis.
Measured concentrations (mg kg-’ wet wt) Day 4
Day 21
< 0.025 4.32 20.83 50.34 102.48 0.064 12.70 (2.9) 36.39 (1.7) 57.40 (1.1) 84.19 (0.8)
0.025 2.63 15.41 NA NA < 0.025 4.15 (1.5) NA NA NA
factors are
Diazinon toxicity and risk to birds Table 2. Diazinon concentration
719
(mg kg-’ wet wt) in wils and worms of the field experiment. Worm bioconcentration sented in parentheses
factors are pre-
Dose
Day 1
Day 21
Soil
Control 0.5 x AR l.OxAR 2.0 x AR
Womls
Control 0.5 x AR
i 0.025 0.34 0.61 1.81 < 0.025 (0) 0.78 (2.3) 1.05 (1.7) 3.16 (1.7)
0.13 0.38 0.56 1.61 < 0.025 (0) 0.26 (0.7) 0.53 (0.9) 1.34 (0.8)
l.OxAR 2.0 x AR AR, application rate
hold time, 12.10 min. formed manually.
Injections
(1 ul) were per-
RESULTS
The laboratory experiments indicated that a threshold LC~O of approximately 43 mg kg-’ was reached by day 7 (Probit; Systat, 1987). The measured concentrations of diazinon in soil by day 4 were generally lower than the nomina1 concentrations, and the diazinon concentrations in the soils decreased with time (Table 1). There was a strong positive correlation between diazinon concentration in the soil with that in the worm tissue. In the field experiment, mortality in the control group was on average less than 10%. There was little mortality in any of the treatments so no LC~~ was determined. The concentration of diazinon in soil was relatively constant during the 21-d test (Table 2). There was a measureable increase in the diazinon concentration in the soils in the control treatment suggesting there may have been some migration of the diazinon from the treated test containers. The test containers were positioned approximately 45 cm apart.
T
-
DISCUSSION
In both the field and laboratory experiments, diazinon was measurable after 21 d of application. The half-life of diazinon was between 4 and 21 d. This range is consistent with that reported in a review by Branham and Wehner (1985). Generally, diazinon does not move readily in soil and rarely penetrates below 1.3 cm (Kuhr and Tashiro, 1978; Branham and Wehner, 1985; Troino and Garretson, 1988). However, heavy precipitation during the field experiment may have facilitated movement of the chemical from the treated test containers to the controls. Diazinon is routinely applied to turf to control insect pests at a rate of 7.5 kg a.i. ha-’ (OMAF,
3.0
RZ = 0.996
z
3
The concentration of diazinon in the worms was greater than that in the soil at day 7 (Table 2); however, by day 21 a decrease in tissue residues to concentrations below or equal to that in the soil had occurred. There was a strong positive correlation (R2 values were 0.995 and 0.989 for 7 and 21 d exposures, respectively) between worm-body residues and the measured soil concentrations of diazinon (Fig. 1).
2.5
ab== 0.142 1.657
5 ?? 1)-. *.*-
Day 21 R==0.989 a = 0.019 b = 1.171
0
0.5
I .o
1.5
2.0
2.5
Measured diazinon concentration (mg/kg soil) Fig. 1. Whole-body diazinon concentrations in L. terrestris regressed against measured diazinon concentrations in soil in the field experiment.
G. L. Stephenson et al.
720
1990). At the recommended application rate (1 x AR), the measured soil concentration was 0.609 mg kg-’ wet wt on day 7. From the laboratory experiments, the 7 and 21-d LC~~ was approximately 43 mg kg-’ which was comparable to the LC~~S reported by Lanno et al. (1997). Therefore. the estimated margin of safety for earthworm acute mortality at the recommended application rate is 71.7 (LC~~ divided by soil concentration; USEPA, 1992). Conversely, the recommended application rate must be exceeded 71.7-fold before acute mortality to Lumbricus terrestris is expected. The results of our field experiment demonstrate that diazinon is not acutely toxic to earthworms at the recommended application rate or at twice this rate. The hazard assessment used in this study followed a logica1 approach utilizing empirical data generated from field and laboratory experiments and a simplistic model to estimate the expected exposure of worm-eating birds to diazinon applied to turf. The bioaccumulation results show that on day 7, the concentrations of diazinon in the worms were 1.05 and 3.1 mg kg-’ wet wt at 1 and 2 times the recommended AR, respectively. The average weight of a worm used in the experiments was 5.5 g wet wt. The acute LD5$ of diazinon for the house sparrow and the red-winged blackbird are 7.5 and respectively, or 0.195 and 3.2 mg kg-‘, assuming an average 0.208 mg bird-‘, respectively, weight of 26 and 65 g for the sparrow and blackbird, respectively (USEPA, 1986). The amount of food (i.e. number of warms) that must be eaten bv an adult house sparrow to meet the LC~~ dose can be estimated by multiplying the LD50 of 0.195 mg bird-’ by the concentration in the food at 1 and 2 x AR. The number of worms that would equal the LD50 at 1 and 2 x AR is 34 and 11, respectively. For the red-winged blackbird the equivalent would be 36 and 11.6 worms for the two application
rates,
respectively.
The ootential hazard to worm-eatina birds was estimated using the equation MDD = SC x BCF x FC, where MDD is the mean daily dose (mgd-‘), SC is the soil concentration (mg kg-]), BCF is the bioconcentration factor for dia&&‘in worms, and FC is the estimate of the daily food consumption of the birds (kg dd’), 1
assuming
that
the
food
ingested
as a per
cent
of
body weight per day was 20 and 15% for the house snarrow -and red-winged blackbird. resnectivelv (Renaga, 1973; Dunniñg, 1984). The MDDs for í and 2 x AR for the house sparrow and the redwinged blackbird were 5.46 and 16.42, and 10.29 and 30.9 ug d-‘, respectively. A margin of safety
(MOS) was estimated by dividing the acute LD50 for each species by the mean daily dose at each AR. The respective values for the two application rates (1 and 2 x AR) for the house sparrow and redwinged blackbird were 35.6 and 11.9, and 20.3 and 6.8, respectively. A MOS > I indicates that acute toxicity is not expected. Our results indicate that at the application rate of 7.5 kg ha-‘, there is little risk of acute toxicity of diazinon to worm-eating birds under standard conditions given the presumptions in the text.
REFERENCES Branham B. E. and Wehner D. J. (1985) Fate of diazinon applied to thatched turf. Journul of Agronomics 77, lol104. Dunning J. G. Jr (1984) Body weights of 686 species of North American birds. Western Bird Banding Association Monograph, No. 1. Eisler R. (1986) Diazinon hazards to fish, wildlife and invertebrates: a synoptic review. U.S. Fish and Wildltye Service Biology Report 85. United States Fish and Wildlife Service. Washington. Fushtey S. G and Sears M. K. (1981) Turfgrass diseases and insect pests (descriptions, illustrations and controls). OMAF Publication 162. Ontario Ministry of Agriculture and Food, Toronto, Ontario, Canada. Kenaga E. E. (1973) Factors to be considered in the evaluation of the toxicity of pesticides to birds in their environment. Environmental Quality and Safety 2, 166181. Kuhr R. J. and Tashiro H. (1978) Distribution and persistence of chlorpyrifos and diazinon applied to turf. Bulletin of Environmental Contamination and Toxicology 20, 652-656. Lanno R. P., Stephenson G. L. and Wren C. D. (1997) Applications of toxicity curves in assessing the toxicity of diazinon and oentachloronhenol to Lumbricus terrestris in natura1 soils. Soil kology & Biochemistry 29, 689-692. OMAF (1990) Recommendations for turfgrass management. OMAF Publication SM. Ontario Ministry of Agriculture and Food, Toronto, Ontario, Canada. Stone W. B. and Gradoni P. B. (1985), Wildlife mortalitv related to the use of the pesticide diazinon. Northeastern Environmental Science 4,30-38. Systat (1987) Nonlin Probit Model ~- maximum likelihood estimation, p 624. The System ,for Statistics. p.624. Svstat. Evanston. IL. Trdno J. and Garretson C. (1988) Soil distribution of
simazine, diazinon and bromide in sandy soil after exposure to 1985-86 rains in Fresno County. Californiu Department of Agriculture and Food, Sacramento, CA. USEPA (1986) Diazinon .- Position Document 4. Intent to cancel reaistrations and denial of annlications for
registration of pesticide products containurg diazinon; review. conclusion of special United -- States
Environmental -Protection Agency, __. Washmgton, D.C. USEPA (1992) Framework for Ecological Risk Assessment EPA\630\R-92\001. United States Environmental Protection Agency, Washington, D.C
PII: s0038-0717(!36)001!3!3-x
Printed in Great Britain 0038-0717/97$17.00+ 0.00
EXPOSURE OF THE EARTHWORM, LUMBRICUS TERRESTRIS, TO DIAZINON, AND THE RELATIVE RISK TO PASSERINE BIRDS G. L. STEPHENSON,‘*
C. D. WREN,’ 1. C. J. MIDDELRAAD’ E. WARNER’
and J.
‘Ecological Services for Planning Ltd, 361 Southgate Dr., Guelph, Ontario, Canada NlG 3M5 and ‘Eco North, RR 1, Rosseau, Ontario, Canada P2A 2X8 (Accepted
23 July 1996)
Summary-Laboratory experiments were conducted to determine the acute lethality of diazinon to the earthworm, Lumbrinrs terrestris, in a sandy loam soil. The 7-d and 21d LCS,,Swere both approximately 43 mg kg-’ soil (dry wt). Earthworms were also placed into test containers with the same type of soil, which were then placed into established field plots, and replicates of three were sprayed once with either 0 (control), 0.5, 1 or 2 times the recommended application rate of 7.5 kg a.i. ha-‘. NO acute mortality was attributed to these spraying regimes. The half-life of diazinon in soil in the laboratory and field experiments was between 4 and 21 d. At al1 treatment levels, the bioconcentration factors ranged from 0.8 to 2.9, and from 0.7 to 2.3 in the laboratory and field experiments, respectively. The potential hazard to worm-eating birds was estimated using the equation MDD = SC x BCF x FC, where MDD is the mean daily dose (mg d-‘), SC is the soil concentration (mg kg-‘), BCF is the bioconcentration factor for diazinon in worms, and FC is the estimate of the daily food consumption of the birds (kg d-‘). Calculations using both the laboratory and field data indicate that diazinon, when applied at the recommended application rate, does not pose an acute hazard to adult birds eating worms from sprayed areas. The potential for sublethal effects or hazard to sensitive life stages (e.g. hatchlings and fledglings) was not assessed. 0 1997 Elsevier Science Ltd
INTRODUCTION Diazinon is an organophosphorus insecticide used for lawn and turf care. It is used on turf for the
control of insect pests such as the black fairway beetle (Ataenius spretulus), hairy chinch bug (Blissus leucopterus hirtus), sod webworm (Parapediasia sp. and Pediasia sp.), ants and white grubs (Phyllophaga sp.) (OMAF, 1990; Fushtey and Sears, 1981). It is also used to control insect pests in fruit, vegetable and field crops, grasslands and ornamentals. Diazinon applied to turf has been implicated in incidences of bird poisonings in both Canada and the United States (Stone and Gradoni, 1985; Eisler, 1986; USEPA, 1986). Twenty-three different bird species have been killed by exposure to diazinon (USEPA, 1986) with waterfowl species most frequently affected. Diazinon has also been reported to have killed songbirds (e.g. American robin, Turdus migratorius; European starling, Sturnus vulgaris; red-winged blackbird, Agelaius phoeniceus; and house sparrow, Passer domesticus; USEPA, 1986). Most songbird deaths have been associated with ingestion of vegetation sprayed with diazinon. *Author for correspondence.
However, soil invertebrates, including earthworms, often comp& a significant portion of a passerine’s diet. Therefore, in order to estimate the relative risk of diazinon use on turf to passerine birds, experiments were designed to assess diazinon toxicity to, and bioaccumulation in, the earthworm commonly known as the Canadian night crawler or dew worm, Lumbricus terrestris, and these data were subsequently combined with pharmacokinetic data in a preliminary risk assessment.
MATERIALS AND METHODS Laboratory experiments
An appropriate aliquot of a diazinon (Basudin R 500 EC) stock solution and a predetermined amount of distilled water were added to 1500 g of Fox sand which had been weighed and placed into a stainless-steel bowl. The Fox sand had been collected from Delhi, Ontario, dried for 2 h at room temperature, and passed through a double sieve with S- and 2-mm mesh. The contents (i.e. soil, water and diazinon) in the bowl were thoroughly mixed with a stainless-steel spatula and the mixture was placed into a 2-1 glass test container. The treatments consisted of four test concentrations (10, 40, 80 and 160 mg diazinon kg-’ soil dry wt), and a
717
G. L.
718
Stephenson et al
negative control of distilled water, with 15 test containers per treatment. Ten worms were sorted, weighed, and randomly placed into each test container. The test containers were randomly placed onto a table in a room with a constant temperature (17 k l”C), and the fluorescent lights were kept on to ensure that the worms penetrated the soil. The worms and soil in replicates of three were sampled on day 4, 7, 14 and 21. Worm (alive or dead) and soil samples were collected, weighed, labelled and chemical analysis. frozen for subsequent Bioconcentration factors (BCF) in each replicate were determined by dividing the worm tissue concentration by the ambient concentration in the soil.
Field experiment
Test containers, which were made with flexible corrugated drainage tiles with vinyl fly screens fixed over both ends, contained 750 g of Fox sand, as wel1 as 10 worms that had been acclimated to the Fox sand in the laboratory prior to use in the field experiments. The test containers with soil and worms were randomly placed into prepared holes in outside plots, where they would be exposed to natural climatic conditions. The top of each test container was fitted with a 7.4 cm dia plug of bluegrass sod. Spray applications of diazinon (Basudin R 500 EC) in distilled water were applied to the surface of each test container with a continental E-Z sprayer. The treatments consisted of three test concentrations (0.5, 1.0 or 2.0 times the application rate of 7.5 kg a.i. ha-‘) and a negative control (i.e. distilled water only), with 12 test containers per treatment. Water was applied evenly to the surface of each test container and surrounding soil in the field plots within 8 h of the diazinon application. Three test containers from each treatment were sampled on days 4, 7, 14 and 21. The contents were shaken from each test container and the worms were separated into living and dead subsamples, rinsed to remove soil particles, placed onto blotting paper to remove excess water and weighed. Subsamples of worm tissue, which included the gut content, and Tabje 1. Diazinon concentrations
Treatment Soil
Nomina1 concentration (mg kg-’ wil) Day 0
Control 40
80 160
Control 10 40 80 160
NA, not analysed.
Diazinon analysis
Frozen soil (60-290 g) and pooled worm (2456 g) samples were thawed, and the worm samples masticated in the sample bag using a glass pestle. A 25-g subsample of soil and a lO-g subsample of worm slurry (i.e. including gut contents) were extracted with 100 ml of a mixture of acetonitrile and water (8515) in a 250-ml Erlenmyer flask, and shaken for 30 min at high speed on an Eberbach horizontal shaker. The solvent mixture was passed through a Whatman No. 4 filter and placed into a 50-ml, screw-top, glass, test tube. The solution from the worm subsample was then placed into a freezer for 12 h at -20°C to separate water and fat fractions. After freezing, the acetonitrile layer (top) was decanted. Anhydrous granular sodium sulphate (10 g) was used to dry both the soil and worm liquid extracts which were concentrated under vacuum (Buchi Rotovap 55°C 3.733 kPa vacuum) to approximately 1-2 ml, and this volume was retained for clean-up. Clean-up and GC analytic variables were the same for both types of samples. For clean-up, raw extracts were eluted through a glass column (16 mm i.d. x 90 mm) packed with 2 g charcoal-celite (1:4). The eluting solvent consisted of 50 ml acetonitriletoluene (3:l). The eluate was evaporated to low volume under vacuum (rotovap) and exchanged into 2,2,4_trimethylpentane (2.5 ml) for determination with gas chromatography (GC). Extracts were analysed using a 30 m x 0.25 mm J&W DB-1701 capillary column (film thickness 0.25 urn) on a Varian 3600 GC equipped with SPI (septum-equipped programmable injector) and TSD (thermionic specific detector). GC conditions were as follows: initial temperature, 90°C; hold time, 1 min; increase to 200°C at 20” min-‘; hold time, 0 min; increase to 250°C at 10”min-‘; hold time, 0.5 min. SPI conditions were as follows: initial temperature, 90°C; increasing to 250°C at 100” min-‘;
(mg kg-’ wet wt) in wils and warms of the laboratory experiment. Worm bioconcentration presented in parentheses
10
WOllllS
soil were collected and frozen for subsequent chemical analysis.
Measured concentrations (mg kg-’ wet wt) Day 4
Day 21
< 0.025 4.32 20.83 50.34 102.48 0.064 12.70 (2.9) 36.39 (1.7) 57.40 (1.1) 84.19 (0.8)
0.025 2.63 15.41 NA NA < 0.025 4.15 (1.5) NA NA NA
factors are
Diazinon toxicity and risk to birds Table 2. Diazinon concentration
719
(mg kg-’ wet wt) in wils and worms of the field experiment. Worm bioconcentration sented in parentheses
factors are pre-
Dose
Day 1
Day 21
Soil
Control 0.5 x AR l.OxAR 2.0 x AR
Womls
Control 0.5 x AR
i 0.025 0.34 0.61 1.81 < 0.025 (0) 0.78 (2.3) 1.05 (1.7) 3.16 (1.7)
0.13 0.38 0.56 1.61 < 0.025 (0) 0.26 (0.7) 0.53 (0.9) 1.34 (0.8)
l.OxAR 2.0 x AR AR, application rate
hold time, 12.10 min. formed manually.
Injections
(1 ul) were per-
RESULTS
The laboratory experiments indicated that a threshold LC~O of approximately 43 mg kg-’ was reached by day 7 (Probit; Systat, 1987). The measured concentrations of diazinon in soil by day 4 were generally lower than the nomina1 concentrations, and the diazinon concentrations in the soils decreased with time (Table 1). There was a strong positive correlation between diazinon concentration in the soil with that in the worm tissue. In the field experiment, mortality in the control group was on average less than 10%. There was little mortality in any of the treatments so no LC~~ was determined. The concentration of diazinon in soil was relatively constant during the 21-d test (Table 2). There was a measureable increase in the diazinon concentration in the soils in the control treatment suggesting there may have been some migration of the diazinon from the treated test containers. The test containers were positioned approximately 45 cm apart.
T
-
DISCUSSION
In both the field and laboratory experiments, diazinon was measurable after 21 d of application. The half-life of diazinon was between 4 and 21 d. This range is consistent with that reported in a review by Branham and Wehner (1985). Generally, diazinon does not move readily in soil and rarely penetrates below 1.3 cm (Kuhr and Tashiro, 1978; Branham and Wehner, 1985; Troino and Garretson, 1988). However, heavy precipitation during the field experiment may have facilitated movement of the chemical from the treated test containers to the controls. Diazinon is routinely applied to turf to control insect pests at a rate of 7.5 kg a.i. ha-’ (OMAF,
3.0
RZ = 0.996
z
3
The concentration of diazinon in the worms was greater than that in the soil at day 7 (Table 2); however, by day 21 a decrease in tissue residues to concentrations below or equal to that in the soil had occurred. There was a strong positive correlation (R2 values were 0.995 and 0.989 for 7 and 21 d exposures, respectively) between worm-body residues and the measured soil concentrations of diazinon (Fig. 1).
2.5
ab== 0.142 1.657
5 ?? 1)-. *.*-
Day 21 R==0.989 a = 0.019 b = 1.171
0
0.5
I .o
1.5
2.0
2.5
Measured diazinon concentration (mg/kg soil) Fig. 1. Whole-body diazinon concentrations in L. terrestris regressed against measured diazinon concentrations in soil in the field experiment.
G. L. Stephenson et al.
720
1990). At the recommended application rate (1 x AR), the measured soil concentration was 0.609 mg kg-’ wet wt on day 7. From the laboratory experiments, the 7 and 21-d LC~~ was approximately 43 mg kg-’ which was comparable to the LC~~S reported by Lanno et al. (1997). Therefore. the estimated margin of safety for earthworm acute mortality at the recommended application rate is 71.7 (LC~~ divided by soil concentration; USEPA, 1992). Conversely, the recommended application rate must be exceeded 71.7-fold before acute mortality to Lumbricus terrestris is expected. The results of our field experiment demonstrate that diazinon is not acutely toxic to earthworms at the recommended application rate or at twice this rate. The hazard assessment used in this study followed a logica1 approach utilizing empirical data generated from field and laboratory experiments and a simplistic model to estimate the expected exposure of worm-eating birds to diazinon applied to turf. The bioaccumulation results show that on day 7, the concentrations of diazinon in the worms were 1.05 and 3.1 mg kg-’ wet wt at 1 and 2 times the recommended AR, respectively. The average weight of a worm used in the experiments was 5.5 g wet wt. The acute LD5$ of diazinon for the house sparrow and the red-winged blackbird are 7.5 and respectively, or 0.195 and 3.2 mg kg-‘, assuming an average 0.208 mg bird-‘, respectively, weight of 26 and 65 g for the sparrow and blackbird, respectively (USEPA, 1986). The amount of food (i.e. number of warms) that must be eaten bv an adult house sparrow to meet the LC~~ dose can be estimated by multiplying the LD50 of 0.195 mg bird-’ by the concentration in the food at 1 and 2 x AR. The number of worms that would equal the LD50 at 1 and 2 x AR is 34 and 11, respectively. For the red-winged blackbird the equivalent would be 36 and 11.6 worms for the two application
rates,
respectively.
The ootential hazard to worm-eatina birds was estimated using the equation MDD = SC x BCF x FC, where MDD is the mean daily dose (mgd-‘), SC is the soil concentration (mg kg-]), BCF is the bioconcentration factor for dia&&‘in worms, and FC is the estimate of the daily food consumption of the birds (kg dd’), 1
assuming
that
the
food
ingested
as a per
cent
of
body weight per day was 20 and 15% for the house snarrow -and red-winged blackbird. resnectivelv (Renaga, 1973; Dunniñg, 1984). The MDDs for í and 2 x AR for the house sparrow and the redwinged blackbird were 5.46 and 16.42, and 10.29 and 30.9 ug d-‘, respectively. A margin of safety
(MOS) was estimated by dividing the acute LD50 for each species by the mean daily dose at each AR. The respective values for the two application rates (1 and 2 x AR) for the house sparrow and redwinged blackbird were 35.6 and 11.9, and 20.3 and 6.8, respectively. A MOS > I indicates that acute toxicity is not expected. Our results indicate that at the application rate of 7.5 kg ha-‘, there is little risk of acute toxicity of diazinon to worm-eating birds under standard conditions given the presumptions in the text.
REFERENCES Branham B. E. and Wehner D. J. (1985) Fate of diazinon applied to thatched turf. Journul of Agronomics 77, lol104. Dunning J. G. Jr (1984) Body weights of 686 species of North American birds. Western Bird Banding Association Monograph, No. 1. Eisler R. (1986) Diazinon hazards to fish, wildlife and invertebrates: a synoptic review. U.S. Fish and Wildltye Service Biology Report 85. United States Fish and Wildlife Service. Washington. Fushtey S. G and Sears M. K. (1981) Turfgrass diseases and insect pests (descriptions, illustrations and controls). OMAF Publication 162. Ontario Ministry of Agriculture and Food, Toronto, Ontario, Canada. Kenaga E. E. (1973) Factors to be considered in the evaluation of the toxicity of pesticides to birds in their environment. Environmental Quality and Safety 2, 166181. Kuhr R. J. and Tashiro H. (1978) Distribution and persistence of chlorpyrifos and diazinon applied to turf. Bulletin of Environmental Contamination and Toxicology 20, 652-656. Lanno R. P., Stephenson G. L. and Wren C. D. (1997) Applications of toxicity curves in assessing the toxicity of diazinon and oentachloronhenol to Lumbricus terrestris in natura1 soils. Soil kology & Biochemistry 29, 689-692. OMAF (1990) Recommendations for turfgrass management. OMAF Publication SM. Ontario Ministry of Agriculture and Food, Toronto, Ontario, Canada. Stone W. B. and Gradoni P. B. (1985), Wildlife mortalitv related to the use of the pesticide diazinon. Northeastern Environmental Science 4,30-38. Systat (1987) Nonlin Probit Model ~- maximum likelihood estimation, p 624. The System ,for Statistics. p.624. Svstat. Evanston. IL. Trdno J. and Garretson C. (1988) Soil distribution of
simazine, diazinon and bromide in sandy soil after exposure to 1985-86 rains in Fresno County. Californiu Department of Agriculture and Food, Sacramento, CA. USEPA (1986) Diazinon .- Position Document 4. Intent to cancel reaistrations and denial of annlications for
registration of pesticide products containurg diazinon; review. conclusion of special United -- States
Environmental -Protection Agency, __. Washmgton, D.C. USEPA (1992) Framework for Ecological Risk Assessment EPA\630\R-92\001. United States Environmental Protection Agency, Washington, D.C