Aquatic herbicides and the control of water weeds

Water ResearchVol.9. pp. I to 15.PergamonPress1975Printedtn GreatBritain.

REVIEW PAPER

AQUATIC HERBICIDES AND THE CONTROL OF WATER WEEDS M. P. BROOKER Department of Applied Biology, University of Cambridge. Downing Street. Cambridge, U.K. and R. W. EDWARDS Department of Applied Biology. University of Wales Institute of Science & Technology. Cathays Park. Cardiff. U.K. (Received 17 July 1974)

Abstract--The application of herbicides for the control of aquatic plants produces two groups of effects. The primary or direct effects result from the spectrum of toxic action of the herbicide itself on aquatic and, after abstraction, terrestrial organisms. The secondary or indirect effects result from the death of the plants and consequent changes in the physical, chemical and biological nature of a treated water body, changes which may also interfere with abstracted uses. Such effects are reviewed, particularly where they constrain other water resource uses or differ from effects resulting from cutting and removal. Concerning direct effects, the losses of aquatic herbicides from water and their toxicity to mammals, aquatic fauna and crop plants are considered together with the implications of different methods of herbicide application. Possible methods of removing aquatic herbicides from water supplies are described. The major ecological changes following the use of aquatic herbicides are indirect resulting from the destruction of the aquatic plants. The death and decay of submerged aquatic plants is likely to perturb the oxygen-carbon dioxide balance of the water and other changes in water quality may occur. Loss of habitat and changes in available food resources may result in changes in the aquatic fauna. Replacement growths of plants (macro- or micro-) may cause problems in relation to drainage functions, water abstractions and recreational facilities. INTRODUCTION Growths of aquatic plants, by impeding water flow and increasing siltation, can cause problems in the operation and maintenance of flood control, navigation and water supply systems. Profuse growths of aquatic plants can also interfere with angling and other waterbased recreation and weed masses when detached from their substrate can block streams, pipes and jets. Some of the problems caused by growths of aquatic weeds and methods available for their control are described by Mitchell (1974). In earlier years weed growths were controlled by hand-cutting, but recently tae dwindling availability and increased cost of labour have brought about both a widespread use of aquatic herbicides and mechanisation of cutting operations for emergent and submerged weeds. Robinson (197t) estimated that 30 per cent of main river systems in the U.K. (approx. 10,300 kin) were subject to weed control operations by River Authorities and that virtually all those water courses under the auspices of Internal Drainage Boards (approx. 32,300 km), and a minority of farm

ditches, were subject to annual weed clearance. A survey of Internal Drainage Boards revealed that 63 per cent used both mechanical and chemical methods of weed control, 33 per cent used only mechanical methods and 2 per cent practised no weed control at all (Robson, personal communication). It has been estimated that in an effort to control bankside vegetation and aquatic weeds in the U.K. in 1972 £6 million was spent on weed cutting and £2.6 million was spent on herbicide use (Newbold, in press). In Essex the cost of using herbicides to control emergent aquatic plants is in the order of 50-75 per cent of standard hand methods, representing a substantial saving together with earlier completion of the control programme (Brooker and Baird, 1974). However, Robinson (1971) reported that the use of herbicides in Kent did not greatly reduce the overall cost of maintenance operations but did ensure that land drainage channels were ready to function at greater efficiency earlier than otherwise would be the case. The aquatic herbicides which have been introduced

M. P. BROOKERand R. W. EDWARDS

Table I. Chemicals cleared for use as aquatic herbicides by the Pesticides Safety Precautions Scheme

Herbicide Chlorthiamid 2.4-D Datapon Dichlobenil Diquat Maleic hydrazide Paraquat Terbutryne

Use

Maximum permitted concentration in treated water (mg 1- ~J

Minimum interval between treatment and irrigation Idays)

3.0 5'0 30'0 30 2"0 2'0 2-0

2S 21 35 28 10 21 l0

0"I

84

Submerged Bank weeds Emergent Submerged Sub merged Bank grasses Submerged Emergent (with dalapon) Submerged and algae

have been selected not only for their phytotoxicity but also for their low toxicity to aquatic animals and to potential terrestrial target-organisms, such as farm animals and plant crops, which could be exposed to water containing these herbicides after abstraction. It must not be assumed, however, that indirect effects of herbicide use. resulting from weed destruction, are unimportant or that cutting techniques and herbicides have essentially the same ecological effects. This review examines evidence for the actual and potential effects of herbicide use, particularly where such effects constrain other water-resource uses or differ from those resulting from alternative weed-control methods, principally cutting and subsequent removal.

Herbicides used in freshwaters Details of the procedures for official clearance and approval ofaquatic herbicides in the U.K. and instructions for their use are well documented (Robinson, 1969; Fryer and Makepeace, 1971; Makepeace, 1971; Robson, 1973), Only eight chemicals are cleared under the Pesticides Safety Precaution Scheme (P.S.P.S.) for use in or near water and such clearance limits both maximal concentration and minimal interval between

I ....................

I .......... d wAttn

OS!

t

l .......... I O~G4NtS~S

Fig. I. Effects of herbicide application for the control of aquatic plants.

herbicide treatment and use of the water for irrigation or potable supply (Table l). Whilst it is not likely that the maximum or even recommended doses will be frequently exceeded, for over-use represents waste or profit reduction, the safeguards concerning the safe-interval are inadequate, particularly in channels which have complex and intermittent flow patterns. In such channels the whereabouts of a water-mass contaminated with herbicide after spraying would be difficult to determine and it is unlikely that potential abstractors would be aware of all herbicide applications in their catchment area.

Classification of effects of herbicide application The application of a herbicide to a water body for the control of aquatic plants produces two groups of effects (Fig. l). Primary effects result from the direct action of the herbicide on the target plant species (A ~), other aquatic organisms (A:) and systems after water abstraction (A3). The secondary or indirect effects result from the death of the plants and may influence in situ resources (B 0, e.g. aquatic animal species of conservation interest, or abstracted uses (B,). Generally, research into the effects of aquatic herbicides has concentrated on primary or direct effects and toxicity data have largely been acquired from short-term acute tests. This imbalance understandably develops from the pesticide clearance arrangements where particular pesticides are examined individually and the more generalised secondary or indirect effects of herbicide usage resulting from weed-kill are considered analagous to effects of other methods of weed eradication. Such an assumption is erroneous for cutting methods facilitate weed removal, thus avoiding the consequences of in situ decay, and a much easier spatial pattern of weed control. Furthermore. whilst acute toxicity studies may be adequate for assessing potential danger to terrestrial organisms, which will generally

Aquatic herbicides and the control of water weeds Table 2. Acute toxicity of aquatic herbicides to mammals (From Martin 19721 Herbicide Chlorthiamid 2.4-D Dalapon Dichlobenil Diquat Maleic h.vdrazide Paraquat Terbutr}ne

Oral 1_D 50 Img kg- t bod? weight) 500-757 37~805 7570-9330 2056-3160 100-231 2340-6950 25-150 2400-5000

receive herbicide doses over short periods of time. they are unlikely to be adequate for aquatic non-target organisms which may be directly exposed to herbicidesinks, such as sediments, for substantial parts of their life-cycles. Direct effects

After abstraction waler may be used, either with or without treatment, by biological systems or for industrial processes. It is convenient to classify effects in relation to the broad use rather than the degree or type of treatment lbr, in practice, treatment processes are usually designed to remove suspended particulate material and to disinfect rather than to remove soluble organic substances. Thus, their effects, with respect to herbicides, are generally limited .to the removal of herbicide fractions absorbed to particulates and only where soluble organics are removed using, [or example, activated carbon, will soluble herbicide fractions be removed too. Although herbicides and their breakdown products may taint water supplies directly (Sigworth 1965) problems generally arise after disinfection with chlorine or ozone. Such taints may also cause the rejection of water supplied, without treatment, to farm animals although no information is available on the extent of this problem. (i) Potable water supply. At the doses normally recommended for use in the field (Table 1) aquatic herbicides are not acutely toxic to mammalian species (Table 2), although paraquat is a scheduled poison. An average man of 75 kg body weight would have to consume about 250 1. of water containing the maximum permissible concentration of paraquat (2.0mg l-t. Table 1) to reach a dose equivalent to the oral LD 50 (Table 2~. Toxicity data on chronic exposure to mammals are presented by the manufacturers of herbicides to the P.S.P. Committee and clearance is subject to assurance of safety from long-term exposure, but such data

3

remain confidential and onl.~ available from individual herbicide manufacturers to water authorities and other "'interested parties." Table 3 summarizes published results of chronic mammalian toxicity studies with aquatic herbicides. Such studies inclt, de. for some herbicides, assessments ofcarcino- and teratogenicity. Several methods are available for the removal of herbicides from water IFoy and Bingham. 1969: Kearney et al.. 1969). Faust and Aly 11964) have reported the experimental removal of 2.4-D from water using activated carbon and Faust and Zarins (1969) have demonstrated that 1'0 mg 1- ~ of diquat and paraquat were reduced to 0"l mg 1-~ at 20:C in 30 rain by 82 and 44 mg 1- ~ of activated carbon respectively--well within the normal operational conditions of a watertreatment plant. Clay minerals (e.g. bentonite) have been used to absorb both paraquat and diquat before tlocculation of such minerals (Coats et al., 1966; Faust and Zarins, 1969). Kearney et al. (19691, on the basis of small scale laboratory experiments with trichlorobenzoic acid (TBA), suggested the use of high intensity u.v. irradiation to de-contaminate herbicide residues in water. The volatility of dichlobenil provides a basis for its removal from water. Few data have been published on herbicides in relation to problems of taint although the risks have been acknowledged (Croll, 1972). Sigworth (1965) tested thirty-four pesticides for odour thresholds: the concentrations at which the odour of 2,4-D (acid) and dalapon were just detectable were 3"13 and 23-20 mg I- ~ respectively, above the concentrations likely to be present in surface waters following herbicide application. However, the phenolic derivatives of 2,4-D, with chlorination, are converted to 2,4-dichlorophenol which gives rise to odour and taste problems at concentrations of 2 and 8 #g 1-~ respectively (Frank, 1972). Indeed, Faust et al. 11961) have reported that 2,4-dichlorophenol is present as an impurity of commercial formulations of 2,4-D and whilst this compound is likely to break down as readily as 2,4-D it must not be assumed that tastes result solely from disinfection. (it) Industrial water supply. There can be no general requirements concerning the quality of industrial water. Food processing, cosmetic, pharmaceutical and similar industries clearly need water at least of comparable quality to potable supply. Packaging materials if manufactured using water containing traces of 2,4-D may transfer taints and odours to packaged foods and drinks. Steel manufacture is vulnerable to appreciable concentrations of certain metals in process water and copper sulphate, although not cleared under P.S.P.S., is widely recommended as an algicide. In the U.S.A. it is currently the only herbicide used to any extent in

Paraquat

Maleic hydrazide

Diquat

Dalapon

Dichlobcnil

2,4-D

Herbicide

Rat

Rat Rat Rat Rat

2 g day- ~ during pregnancy 100mgkg - ~ d -~ f o r 2 y r

60 mg kg- t d - ~ from day 3 to 14 of pregnancy 235 mg kg-- J d - ~ for 2 months 240 mg kg- i d- 1 for 2 months 15 mg kg -~ d - t for 2 yr 50mgkg-td-t for2yr

Single i.p. dose of 6.5 mg kg- ~ during day 7-14 of pregnancy Single i.p. dose of 13 mg kg- ~ during day 5-14 of pregnancy

4 doses equiwflent to 2500, 2000, 1000 and 667 mg kg- ~ on days I, 7, 14 and 21 after birth

None Bi-lateral opacities of lenses Bone deformation and reduction in weight of embryos Interrupted most pregnancies

Rat

Rat

Malformation of costal cartilages of embryos Interrupted most pregnancies

None; incidence of carcinomata similar to controls Mouse Significantly high incidence of hepatomas at 49--51 weeks

Rat

Rat

Dog Dog Rat

None Decrease in weight gain None Increase in gain of kidney weight

None; no evidence for carcinogenic effect Mouse None

Man Dog Rat

1.7mgkg - ~ d -~ f o r 4 y r 1 5 m g k g - t d -1 Single intra peritoneal (i.p.) dose of 7 mg kg- t during day 6-11 of pregnancy Single i.p. dose of 14 mg kg- t during day 6-14 of pregnancy 5 0 0 m g k g - I w k - ~ for2yr

Effect

None Toxic No pathological change. Decrease in liver glycogen and blood catalase Sheep None; no mallormation of embryos

Target

500 g day- ~ for 3 weeks 20 mg kg-I d 50mgkg-ld-'for lyr

Dose

Table 3. Chronic toxicity of aquatic herbicides to mammals

;~ 7~

Khcra aml Whitta (1969)

Khera and Whitta {1969)

Khcra and W hitta (1969)

l!pstein el al. (1967)

Barnes el al. (1957)

m

"~ ;~

,--,

"0

~-"

Clark and Hurst (1970) Chu'k and Hurst (I 97(I) Khera and Whitta (1969)

Davis el al. (1970) Davis el al. (1970) Martin (19721 Martin (19721

Van Gcnderen and Van l:,sch (19681

Van Genderen alld V;lll I!sch (196N)

Binns and Jolmsoll (1970)

I)avis et al. 11970) McKce and Wolf(1963) Smith and Isom ( 19671

Reference

4-

Aquatic herbicides and the control of ~ater ~eeds water subsequently abstracted for potable supply {Frank, 1972). l iiil lrriyation and jilrmstock. There are tour major elements to be considered in relation to safety of water for crop irrigation and farmstock: {a) the dissipation of the herbicide by decay, absorption or dilution. [b) the method of application of the herbicide both to the aquatic system and agricultural crop. tel the distribution of herbicide-treated water in relation to abstractions. {d} susceptibility of the target organisms. {a) The differences in minimal interval between application of herbicide and use of irrigation water {Table I) predominantly reflect differences of stability and rate of loss of herbicide fi'om the aqueous phase by sorption: such behaviour is clearly influenced by site factors, e.g. water depth, temperature. Mullison (1970) has reviewed the dynamics of herbicides used in or near water in the U.S.A. and Kearney and Kaufman (1969) have collected data on the degradation of a wide range of herbicides. Most herbicides are susceptible to degradation by microorganisms though studies have generally been confined to terrestrial systems. Several workers (Audus, 1964; Kearney and Kaufman, 1969: Wright, 1971) cite examples of soil bacteria and fungi capable of degrading a number of herbicides used in aquatic situations including 2,4-D, dalapon, paraquat, diquat and dichlobenil. Robson (1966, 1968) concluded that 2.4-D amine in water and mud was broken down by microorganisms and that some adaptation of these organisms occurred. Little or no breakdown took place in the period immediately following treatment and this lag phase was followed by rapid degradation of the herbicide: a second application was degraded immediately. Hemmer and Faust {I969} have now described the kinetics of the breakdown of 2,4-D by aquatic microorganisms and De Marco et al. (1967) reported that microbial decomposition of 2,4-D was inhibited by a decrease in both temperature and dissolved oxygen. Although several soil organisms have been shown to breakdown paraquat (Burns and Audus, 1970; Anderson and Drew, 1972). Fry et al. (1973) in a study of microbial populations in a reservoir treated with paraquat were unable to isolate any aquatic microorganisms capable of degrading this herbicide. Photochemical decomposition of 2,4-D in aqueous solution has been reported (Aly and Faust, 1964; Tutass. 1966). Paraquat is also broken down by u.v. light and whilst this degradation may be of practical significance in terrestrial application, the absorption properties of the aqueous solution of the herbicide in

5

u.v. light make it unlikel? that photolysis will be an important pathway of degradation in aquatic systems {Slade. 1965, 1966). Losses of herbicides b~ volatilisation may also occur. Beynon and Wright 11968) reported that 85 per cent of dichlobenil applied to a field was lost by evaporation and. although dichlobenil is stable in pure water, under practical conditions it is likely to t.ndergo some volatilisation. The use of a granular formulation helps to reduce such losses (Verloop, 1972). The bipyridilium compounds {paraquat and diquat) arc lost quickly from water probably by first binding reversibly to the organic fraction of the mud and then becoming irreversibly adsorbed to the clay fraction (Burns and Audus. 1970) where the herbicides are thought to be unavailable to biological systems (Funderburk, 1969). Other herbicides e.g. dichlobenil, accumulate in mud but remain biologically active in this phase. In practice, these physico-chemical and biological mechanisms of loss of herbicides from water occur concurrently and observations on rates of loss in the field rarely apportion losses. 2,4-D disappears fairly rapidly from water and mud: Schultz (1973) reported that residues of 2.4-D in water, initially treated with 2 mg 1- ~. declined to less than 0-I mg I- ~ after 35 days and the concentration in the mud was 0.1 mg k g - t after 14 day's. Dichlobenil. the closely related compound chlorthiamid (which breaks down to dichlobenil), and terbutryne are more persistent and much less is known of the breakdown processes involved with these compounds. Dichlobenil has been detected in water and mud 100 and 312 days respectively after treatment (Frank, 1972) and terbutryne, applied at a rate of 0-1 mg l- 1. was still present in the water (0.02 mg 1- ~) after about 180 days while the concentration in the mud after 133 days was 0.18mgl -~ (Van Der Weij et al., 1971). On the other hand the bipyridilium compounds disappear rapidly from water and are generally not detectable after two weeks (Yeo, 1967; Way et al., 1971: Brooker and Edwards. 1973a) and proportions of up to 64 per cent of the original application of paraquat have been recovered from mud deposists tip to eight months after application (Brookcr and Edwards, 1973a)although, unlike dichlobenil and terbutryne, in this phase the herbicide is biologically inactive. (b) The purpose of herbicide application will also influence the final concentration in the water. Herbicides intended to control submerged aquatic plants are applied directly to the water and in these circumstances the final concentration of herbicide after application is likely to approach the theoretical maximum. Where herbicides are applied for control of ditchbank

Furrow

Furrow

Furrow Furrow

I:urrow

Soybean

Corn

Sngar beet Col'n

F'ield beans

Sprinkler

Soybeans

Furrow Furrow

Furrow

Ratabagas Soybean

Sprinkler

Maize

Soybeans

Furrow

Furrow

Maize

Furrow

Sprinkler

Sugar beet

Corn

1-12

Furrow

Stlgar beet

Corn

3-03

Furrow

Sugar beet (seedling)

2'72

0.54 68.06

5.45

0-54

6-05 5,45

3-03

0.60

"~

2 _~

2

2

3 2

3

3

2

I" 12

2

3

2

2

3

3

3

2

~

Volume* (ha-cm)

3.03

1.12

3.03

2.24

7.26

Furrow

Red Mexican beans (seedling)

2.24

Rate* (kg ha- ~)

Furrow

Irrigation

Red Mexican beans {seedling)

Crop

* 5"45 kg ha- t in 2 ha-era is equiwdent to 10 mg I - t

Diqnat

Dichlobcnil

Dalapon

2,4-D

Herbicide

None (irowlh suppressed

None

Some stunting. No reduction in yield

Maturity dehlyed. No reduction ill yield

None Maturity delayed. Reduced yield and quality

Significant decrease in yield

None

None

Seed quality impaired

None

Injury to roots and foliage: no decrease in root yield Increase in fresh weight of foliage and roots. Increased sugar yield None

Lethal to many seedlings

Seed damage. Delayed matnrity. 40'~;~ redt,ction in yield

Top growth and root injury. No reduction in yield

Eflbct

Table 4. Ell"cots of aquatic herbicides in irrigation water on crop plants

]~rtlllS et ,d. (1')(,4) Ih'uns el al. (1904)

Bruns el ol. (1972)

Bruns et aL 11972)

llruns el al. (1972)

Bruns alld Dawson (1959) Bruns eta/. (1972)

I]lttns and Dawson (1959 I

Ill'tillS and Dawson (1959)

l]runs alld ('arlile (1971)

Brtms :rod ('al'lile (1971)

Ihuns and ('arlilc 11971)

Brtms and ('arlilc (1971)

Ih'uns and CaHile (1971)

Bruns and Carlile 11971)

Bruns (1957)

Ih'tms (1954)

Ih'ulls 11954)

Reference

:~

~.

~,, m

"-~

Aquatic herbicides and the control of water weeds

7

plants (e.g. 2,4-D) or for emergent aquatic plants (e.g. and stockwatering over comparatively wide areas in dalapon) the amount of herbicide actually entering the which aquatic herbicides have been recently applied. (d) Table 4 summarises the pt, blished data on the water course is likely to be a small proportion of that applied. For example, Brooker {unpublished data) effects of irrigation water, contaminated with aquatic detected a maximum concentration of 70/,~g 1- 1 in the herbicides, on crop plants. Under the recommended water of a drainage channel treated with dalapon at a conditions for use (Table 1) the concentrations which rate of 25 kg acid equivalent ha-1. The maximum will be present [section (b!] are unlikely to be a risk to irrigated crop plants. In trials in Holland estabtheoretical concentration was 15 mg 1-~, over 200 times the recorded value. Clearly, contamination of lished potatoes, tomatoes, lettuce and strawberries water courses is likely to be less than the predicted tolerated 1.0 mg 1- t dichlobenil in irrigation water at maximum concentration when herbicides are used for 301. m--" {0"3 kg ha- t) gi',en lbur times during the emergent or ditchbank control and an appreciation of summer. Sugar beets were completely killed at 1-0 mg this situation should bring about a reduction in the im- 1- 1 but survived 0-2 mg 1- ~. In the U.S.A. weekly irrigation for 12 weeks with water which had an initial posed time interval between application and water use. Bartley and Gangstad (1973) studied residues of 2,4- concentration of 0'2 mg 1- i dichlobenil was generally D in 19 canals in the U.S.A. following ditchbank spray- safe for seeded crops whereas transplanted crops and ing. Peak concentrations were less than 50 ,ug l- t in 12 turf tolerated initial concentrations of 0'4 and 0"8 mg canals, 50-100/.ig l- t in 5 canals and above 100 ~eg I-1 1-1 (Pieters and De Boer. 1971). Howe and Wright in 2 canals. Frank et al. (1970) reported maximum con- (1965) reported that water treated with paraquat at the centrations of 365 l~g 1- 1 dalapon in drainage ditches recommended rate could be used for furrow irrigation in the U.S.A. immediately and for overhead irrigation after seven days (cf. Table l). However. some crop plants may be Even where high concentrations of herbicides occur in irrigation water, crops may be protected by herbi- particularly sensitive to herbicides and this was highcide inactivation (e.g. 2,4-D, dichlobenil) using acti- lighted in the U.K. in 1971 when an industrial disvated carbon, either applied directly to the crop or to charge of 2,3,6-trichlorobenzoic acid (T.B.A3, a herbithe pumping system (Arle et al., 1948: Ahrens. 1967; cide similar in action to 2.4-D. contaminated a public Lucas and Hammer, 1967). st, pply which when used to irrigate tomato crops caused serious damage {Hills. 1973). The tomato plants {c) Where herbicides have been used to control were sensitive to concentrations ofT.B.A, as low as 0-1 aquatic plants it is necessary to have some knowledge ~g I- 1. of the treatment history of the abstracted water before Certain herbicides retain their phytotoxicity lbr use. In ponds and reservoirs with minimal water replacement such history is generally easy to ascertain. several months, e.g. dichlobenil, terbutryne, even when But in flowing systems, particularly complex articu- adsorbed by sediments and damage to terrestrial crops lated systems with multi-directional flow, such as could be caused by transfer of herbicide sorbed onto many agricultural drainage systems, the origin of spoil dredged from drainage channels and distributed on neighbouring agricultural land. abstracted water is difficult to determine. The toxic hazards of aquatic herbicides to farmstock In simple uni-directional non-pulsed systems it should be possible to predict the change in peak con- depend on the acute toxicity of the chemical (Table 2). centration of a water-soluble conservative substance the concentration in the water and the maximum water with time provided the water velocity is known (Owens consumption of the animal (Swan, 1967). Palmer and et al., 1969). On the same basis, if decay' and sorption Radeleff (1969) reported that a yearling cow (250 kg) behaviour are known, it should be possible to predict tolerated 25 mg dichlobenil kg- 1 body weight tbr ten the change in peak concentration of non-conservative days without ill-eflact and this was equivalent to a herbicides. Studies of downstream dissipation of herbi- daily water intake of 6250 1. containing I mg 1- ~ dichcides (Demint, 1970; Bartley and Hattrup. 1970) and lobenil. Palmer (1972) describes the toxicity of 45 insecticides (Wallace et al., 1973) have been carried out organic herbicides to cattle, sheep and chickens. in flowing watercourses using dyes to help elucidate Despite the apparent safety of aquatic herbicides to dispersion patterns. The successful use of dyes as farm animals, provision is increasingly made for their tracers in flowing waters offers a simple method of watering from public supplies. This avoids the possiidentifying the movement of herbicides and makes bility of danger from the contamination of natural possible the isolation of individual parts of an irriga- water by a variety of chance spillages, discharges or tion channel if there is a possibility of contamination toxic blooms. The separation of the drainage and water(Demint. 1970). In complex articulated systems it may ing function of channels also provides much greater be necessary to prohibit abstraction for irrigation freedom to optimize water levels for drainage and

M.P. BROOKERand R. W. EDWARDS

$

Table 5, Acute toxicity of herbicides to fish (from Tooby, 1971) LC 50 (mgl-~l Herbicide Chlorthiamid* 2,4-D (tri-ethanolamine salt) Dalapon Dich[obeni[ Diquat Diquat Mateic h~drazide Paraquat Paraquat Terbutryne4.

24 h 41 125 711 14.5 72 90 4000 235 127 --

48 h Water Species --

N.s.

R,h.

105 490 I2.3 37 70 -160 56 62

S S S S H S H S S

R.h. S.g. R.h. R.h. S.g, R.h. R.h. R.h. R.h.

* Martin (1972). 4"Tyson (pets. comm.). S = soft water; H --- hard water; N.s. = not specified; R.h, = Rasbora heteromorpha (harlequin fish); S.g. = Sahno yairdnerii (rainbow trout). avoids damage to channel banks caused by farm stock at drinking sites. Uptake of herbicides by terrestrial animals is not restricted to that in drinking water; herbicide residues in crop plants, animals and animal products (e.g. eggs and milk) must also be considered. Bartley and Gangstad (1973) reported that maximum residues of 2,4-D

and dalapon in food crops did not exceed 330 and 1250 .ug kg-~ respectively after irrigation with water containing up to 1.125 mg I- ~ (2,4-D) and 11.250 mg 1- 1 (dalapon) although no application volume is reported. These residues are within the statutory limits for these crops in the U.S.A. (Bartley and Gangstad. 1973). Cows fed 1000 mg 2.4-D kg- ~ in their diet for two weeks followed by one week of untreated forage had residues in their milk ranging from <0"05 to 0.09 mg I- L and in cream of 0-05 mg 1- ~ (Leng, 1972). Dairy cows fed dalapon at a rate equivalent to 3 g kg- Lbased on a dry weight intake of forage produced milk with a maximum residue of 2.45 mg I- L dalapon after seven days and no odours were detected in the milk: there were no effects in respect to milk production, butter fat, body weight or behaviour (Fertig and Schreiber, 1961). (iv) Aquatic non-target organisms. The acute toxicity of aquatic herbicides to fish and some invertebrates is well documented (Hughes and Davis, 1963, 1967; McKee and Wolf, 1963; Cope, 1965, 1966: Sanders and Cope, 1966. 1968; Alabaster, 1969: Wilson and Bond. 1969; Mullison, 1970: Sanders. 1970: Kemp et al., 1971; Tooby, 1971) and is illustrated in Tables 5 and 6. Generally, the concentrations of herbicide used for weed control are unlikely to create an acute hazard to the aquatic fauna although dichlobenil is much more toxic to some indigenous fish species than was anticipated when it was first cleared for use under P.S.P,S.

Table 6. Acute toxicity of herbicides to aquatic invertebrates LC 50(mg 1-1 ) Herbicide 2.4-D

Dalapon

Dichlobenil

Diquat

Paraquat

Species

Pteronarcys californica Daphnia pulex Simocephalus serrulatus P. californica S. serrulatus D. pulex H yalella azeteca Callibaetis sp. Limnephilus sp, Enallagma sp. P. californica D. pulex S. serrulatus H. azeteca Callibaetis sp. Limnephilus sp. Enallagma sp. S. serrulatus D. pule.*:

48 h

96 h

['8 3"2

4-9 --

100

16"0 11"00

12-5 15"2 23"3 24"2 8.4 3-7 5"8 0-12 65"0 > 100 > 100 0'45 0"24

8'5 12"0 13.0 20"7

0.048 33"0 > 100 > 100

Reference Walker (1971) Walker (1971) Walker (1971) Sanders and Cope (1968) Walker (1971) Walker (1971) Wilson and Bond (1969) Wilson and Bond (1969) Wilson and Bond (1969) Wilson and Bond (1969) Cope (1966) Cope (1966) Cope (1966) Wilson and Bond (1969) Wilson and Bond (1969) Wilson and Bond (1969) Wilson and Bond (1969) Walker (1971) Walker (1971)

Aquatic herbicides and the control of water weeds IToob~. personal communicationl. Paraquat is particularly toxic to ,tmphipods (e.g. Hyallela azeteca, Table 61 and Brooker and Edwards [1974) reported that the incipient LC 50 of paraquat to the isopod .4sellus meridianus was 0.24 mg 1- t though field studies indicated that populations of A. meridianus were not directl? affected by paraquat application (1.0 mg 1-t) to a reservoir for weed control. Earnest (1971) reported that bluegills became distressed within three hours of paraquat application (I.0 mg 1-t) and many deaths occurred: this sensitivity is not confirmed by toxicity studies on other fish species (Alabaster. 1969: Brooker and Edwards. 19741. Copper sulphate which is often used as an algicide is toxic to fish at concentrations below those commonly recommended for algal control Tooby (1971} reported that the maximum concentrations (mg l - t ) of copper sulphate in which a variety of fish can survive are: trout, 0.14; carp. 0-33: goldfish, 0-5; and perch, 0.67. Howe,mr, it should be noted that the toxicity of copper is greatly influenced by water hardness, the 48h LC 50 to rainbow trout being about 0.05 mg 1- t in soft water (20 mg 1- t as CaCO3) and about 0.4 mg l - t in hard water (500 mg l - t as CaCOa) (Brown, 1968). Few Long term studies have been made Of the effects of herbicides on aquatic organisms and the effects on eggs and juveniles have also been neglected. Cope (1965} reported that bluegills treated with 0-6 mg 1- t dichlobenil developed pathological symptoms in gills after four days and the condition of the gills had deteriorated further after 63 days. Pathological disorders were found in bluegills exposed to propylene glycol butyl ether esters of 2,4-D (10 mg 1- t) and spawning was delayed by 2 weeks at 5 and 10 mg 1- t Concentrations of the amine salt of 2,4-D (the formulation approved for use in water) up to 25 mg 1- t had no effects on the eggs or fry of the bluegill (Hiltibran, 1967) and bluegill fingerlings were not harmed by diquat at 3-0 mg 1-~ (Gilderhus, 1967). The same author reported that diquat at 3'0 mg 1- ' was toxic to all stages of Daphnia and that at 1.0 mg 1- ~ no development of adults occurred. However, there was no evidence from field trials that paraquat (I.0 mg 1-t) had similar effects on Daphnia {Brooker and Edwards, 1974). Dichlobenil at 1'0 mg l-* did not affect fish spawning or hatching of eggs (Spencer-Jones, 1974). Indirect efJi.,cts

Whilst the ecological changes resulting from the use of herbicides to control emergent aquatic plants have not been intensively studied, those for submerged plants have been well documented (Walker. 1963: Fish, 1966: Pokorny et al., 1971 ; Walsh et al.. 1971 ; Way et

9

al., 1971: Simpson and Pimentel. 1972: Brooker and Edwards. t973a and b. 1974: Newbold, in press: Owens and Marls, in preparation). Some of the changes resulting from the destruction of submerged and emergent plants are likely to be ver~ similar iTable 7). Changes of particular relevance to the aquatic fauna are shown in Fig. 2. ti) Oxygen-carbon dioxide balance. The immediate result of the application of a herbicide to control submerged plants is a reduction in community photosynthesis (Heuss, 1971: Brooker and Edwards, 1973b: Owens and Marls, in preparation). For example, the bipyridilium compounds and terbutryne interfere directly with the photosynthetic mechanism of the plants, this interference, together with possible enhanced microbial respiration, resulting in a reduction in the net utilisation of carbon dioxide and a decreased net oxygen production. Brooker and Edwards (1973a) reported that three days alter paraquat application to control submerged angiosperms the pH of the water fell from 9-2 to 8.1 and this was associated with increased bicarbonate alkalinity and the presence of free carbon dioxide in the water. Wojtalik et al. (1971) also reported a large decrease in pH (2'1 units) over the period fourteen days after the application of 2+4-D to a reservoir to control Myriophylh,m. Apart from the effects of reduced pH on the aquatic fauna, quality changes of abstracted water must be considered and, where such changes are adverse, temporary buffering might be necessary. Table 7. Predicted major ecological effects resulting from the control of submerged and emergent plants with herbicides Submerged (a) Loss of substrate, change of habitat (b) Plants decay in situ

(c) Immediate loss of photosynthetic oxygen production in water; possible rapid replacement e.g. phytoplankton (d) Little effect on terrestrial fauna

Emergent Loss of substrate. change of habitat Some plants decay in situ but generally removed to banks or burned Increase in photosynthetic oxygen production in water e.g. photoplankton, submerged macrophytes

Severe efti:ct on components of terrestrial fauna, e.g. nesting sites of birds like the reed bunting and reed warbler

10

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Fig. 2. Effects of herbicide application and the destruction of submerged plants likely to be of consequence in determining faunal changes. Where large masses of plant material are treated with herbicides so much oxygen may be required for aerobic decay processes, especially when plant death is rapid, that deoxygenation of the water may occur. These conditions are aggravated by the reduction in community photosynthesis at such times. Several workers have reported low ( < 2.0 mg I- t) oxygen conccntrations in reservoirs and lakes following weed control with herbicides (Walker, 1963: Edwards, 1968: Pokorn? ct ~d.. 1971: Van Der Weij t't al., 1971) and fish kills were recorded in some cases. The toxic effect of low oxygen concentrations will be potentiated by associated high concentrations of carbon dioxide. Other workers (Fish, 1966; Wojtalik et al., 1971; Brooker and Edwards, 1973a) reported some reduction in oxygen concentrations of the water following herbicide application but this was not sufficient to affect aquatic organisms. Brooker (1974) has produced a nomograph by which the risk of deoxygenation and of associated fishery damage in herbicide application may be assessed from plant biomass and water depth. The European Standards for Drinking Water (World Health Organisation, 1970) recommended 5 mg I - t dissolved oxygen as the minimum for potable supply to prevent taste and odour problems caused by reduced substances associated with low oxygen tensions (Guivcr. 1972; Steel, 1972) and to minimise the corrosive properties of the water (James, 1971). During the periods of plant decay following herbicide application the concentration of dissolved organic material and suspended detrital material in the water is likely to increase the water treatment required to prepare

water for uses such as boiler Ieed supply and for the pharmaceutical industry. (ii) P l a n t replacement. The death and decay of macrophytes in a water body make available for release large amounts of nutrients {Kormondy, 1968: Boyd, 1970: Jewell, 1970; Nichols and Keeney, 1973). Some workers (Fish, 1966; Walsh et al., 1971: Simpson and Pimentel. 1972; Brooker and Edwards, 1973a) have reported that where deoxygenation does not take place no general increase in nutrient concentrations in the water occurs following the successful control of submerged plants. Pokorny et al. (1971) recorded increases of N H : N from trace amounts to 0.62 mg 1- t 19 days after herbicide treatment and of PO+-P from 0.24 to 0.87 mg I- z after 15 days: Walker (1963) recorded increases of total inorganic nitrogen and PO,~-P of 0.501-05 mg 1- t and 0.01-0-13 mg 1- t respectively. In both these studies severe deoxygenation occurred and it is possible that changes in the redox potential at the mud surface could have accounted for increases in concentration of these nutrients (Mortimer, 1971). Such increases in water used for irrigation may benefit crop plant growth (Rhoades and Bernstein, 1971) but are unlikely to be of major economic significance since they are small in comparison with recommended rates of fertilizer application. Release of nutrients from decaying plants and the increased light available following weed destruction (Wojtalik et aL. 1971; Brooker. 1972) might stimulate the development of planktonic algae (Pokorny et al., 1971 ; Walsh et al., 1971; Way et al.. 1971) or resistant macrophytes. Brooker and Edwards (1973a) and

Aquatic herbicides and the control of water weeds Mathews (1967) reported rapid colonisation of lakes b~ macrophytic Characeae after control of angiosperms with bipyridilium herbicides. No herbicide is capable of controlling all plant species at the doses recommended for use and it is to be expected that in favourable conditions following herbicide application growths of replacement species will develop. The replacement of a susceptible macrophyte may simply reconstitute the original problem to a greater or lesser degree but the development of a "'bloom" of planktonic algae could have severe implications both for in situ use and after abstraction. Certain blue-green algae produce exudates or decay products which can be toxic to fish and livestock (Davidson, 1959; Gorham, 1964) and after abstraction and chlorination may impart undesirable tastes and odours to water supplies (Bays, 1969). Increased concentrations of particulate material, resulting from both the decay of the macrophytes and from algal growths, may overload filters (Bays, 1969; Ridley, 1970). damage or block conveyance systems and irrigation equipment, and may adversely affect surface soil structure by filling soil pores and decreasing permeability to air and water (Rhoades and Bernstein, 197 I). (iii) E~,ct of plato death on tile aquatic fluma (a) Bemhic inrertehrates. Several workers have reported increases in the density of benthic invertebrates following the use of various herbicides for the control of submerged macrophytes (Walker, 1963; Harp and Campbell, 1964; Van Der Weij et al., 1971 ; Brooker and Edwards, 1974) probb.bly as a result of the increased availability of detritus associated with the death and decay of the plants. In general, however, the status of most species of benthic invertebrates does not change as a result of herbicide use (Hilsenhoff, 1966; Smith and Isom, 1967; Pokorny et al., 1971; Brooker and Edwards, 1974). (b) Invertebrates associated with ttle sediments and the macrophytes. Brooker and Edwards (1974) reported no significant changes in the density of these invertebrates (e.g. Asellus, Clod;on. Caelzis) resulting from the application of paraquat for weed control. Asellus held in cages in a lake treated with paraquat (0-5 mg 1-~) suffered mortalities (Way et al., 1971) but death could have been a result of severe deoxygenation (Edwards. 1968). (c) Zooplallkton. The effects of herbicidal control of aquatic plants on the zooplankton vary. Total zooplankton numbers declined in a reservoir treated with paraquat and some species of Cladocera were eliminated (Pokorny et ,d., 1971) but Van Der Weij (1971), in trials with mercaptotriazines, observed no detrimental effects on zooplankton numbers and this

l|

accords with observations of other workers I Pierce, 1966. 1967. 1968: Simpson and Pimental. 1972). Brooker and Edwards (1974t reported that those planktonic invertebrates normally found in equal abundance in weed beds and open water were unaffected by paraciuat application and subsequent weed death but the population growth of those species generally more abundant in weed beds than in open water was severel.v restricted. On the other hand the successful application of 1-0 mg 1- 1 dichlobenil to control macrophytes in a pond resulted in an increase in the density of zooplankters and this was associated with a "'bloom" of phytoplankton (Walsh et al.. 1971). (d) Aquatic incertehrates associated with ttle weeds. The most dramatic effects of plant destruction are on the fauna closely associated with the macrophytes, many invertebrates (e.g. molluscs, trichopterans. [epidopterans, chironomids) being lost or reduced in density (Walker, 1963: Hilsenhoff, 1966: Brooker and Edwards. 19741. In the study of Brooker and Edwards (1974) these effects were discernible in the year after herbicide treatment although there had been considerable recovery in plant status. The degree and period of effect, which may have important implications with respect to conservation and fisheries, will clearly be influenced by the degree of dependence of the invertebrate species on a particular macrophyte, the timing of plant death in relation to the life-cycle of the species, the availability of alternative refuges, the dispersion characteristics of the species and the rate of recovery of the plants. (e) Invertebrates of tile margim~l cegetatiolz. Where herbicides are applied to control submerged plants (e.g. diquat, dichlobenil) emergent marginal vegetation is not affected and nor are those invertebrates associated with these plants (Brooker and Edwards, 1974). Data are not available on the effects on the aquatic fauna of the use of herbicides (e.g. dalapon) to control emergent plants but clearly subsequent changes in habitat are likely to be important in this respect (Table 7). (f) Fish. Changes in the invertebrate fauna will generally be reflected in the diet of omnivorous and carnivorous fish. Brooker and Edwards (1974) reported changes in the diet of the eel following macrophyte control which were consistent with changes in the invertebrate community. Fish with more restricted feeding habits than the eel may be adversely affected. Reports on the effect of use of herbicides for weed control on fish productivity are conflicting: in some instances production increased, in others it decreased (Bennett, 1971). For those fish which attach their adhesive eggs to macrophytes the destruction of these plants early in

I2

M.P. BROOKERand R. W. EDWARDS

the growing season could seriously affect spawning success. Subsequently the absence of aquatic plants might increase predation on fry a n d small fish since shelter would be depleted. Certain p r o b l e m s of herbicide use in relation to fisheries m a n a g e m e n t are described by Brooker a n d Edwards (1973c/. (gl Arifauna. Some consideration should be given to wild fowl when herbicides are used for aquatic plant control since many of the food resources of these species [e.g. aquatic macrophytes and invertebrates) are likely to be lost, Other avian species often closely associated with the aquatic habitat are reed warbler (Acrocephalus scirpaceus), sedge warbler (A. schoenohaemts), reed bunting (Emberica schoeniclus), bearded tit {Pamlru,s hiarmicus), and snipe (Gullina~o gallineffo) (Haslam 1973). Those birds nesting in emergent aquatic vegetation (e.g. warblers) are likely to be particularly susceptible to chemical methods of weed control where the plants may be effectively cleared for a period of up to four years (e.g. Phra~.lmites--dalaponl eliminating potential nesting sites. Conventional clearance by h a n d [when there is a single a u t u m n cut) allows summer re-growth of emergent plants a n d nesting can take place. Where herbicides are used on a wide scale it should be possible to provide "refuges' for such bird species by retaining some hand-cleared areas. Unfortunately field studies on these aspects of aquatic herbicide use have not been undertaken. Acknowled.qements--The attthors are grateful to the Directors of the Water Research Centre and the Weed Research Organisation for the use of their" information services. M.P.B. who is a Research Fellow at Wolfson College, Cambridge and is sponsored by Imperial Tobacco Ltd. wishes to thank Professor J. W. L. Beament and Professor A. N. Worden for the use of facilities at the Department of Applied Biology. Cambridge and at Huntingdon Research Centre respectively.

REFERENCES

A hrens J. I. (1967). Further studies with activated carbon for herbicide detoxification in soils. Weed Abstr. 16, No. 2390. Alabaster J. S. (1969). Survival of fish in 164 herbicides, insecticides, fungicides, wetting agents and miscellaneous substances. Int. Pest. Cont. March-April. A ly A. O. and Faust S. D. (1964). Studies on the fate of 2,4-D and ester derivatives in natural surface waters. J. agric. Fd. Chem. 12, 541-546. Anderson J. R. and Drew E. A. (1972). Growth characteristics of a species of Lipomyces and its degradation of paraquat. J. gen. Mierohiol. 70, 43-58. Arle H. F.. Leonard O. A. and Harris V. C. (1948). Inactivation of 2,4-D on sweet potato slips with activated charcoal. Science. Lond. 107, 247. Audus L. J. (1964). Herbicide behaviour in soil--II Interactions with soil organisms. In: The Physiology & Bio-

chemistr~ of Herbicides {Edited b} L. J. AudusJ. 163206. Academic. Barnes J. M. et aL 11957). The non-toxicit-, of mateic hydrazide for mammalian tissues..Vature. Lond. 180, 62-64. Bartley and Gangstad E. O. 119731. Environmental aspects of aquatic plant control. ASCE National Water Resources Engineering Meeting. January 20-February 2, 1973. Washington D.C. 28pp. Bartley T. R. and Hattrup A. R. {1970). 2.4-D contamination and persistence in irrigation water. Proc. West. Soc. Weed Sci. 23. t0-33. Bays L. R. (19691. Pesticide pollution and the effects on the biota of Chew Valley Lake. Wat. Treat. Exam. 18, 295-326. Bennett G. W. (197l). M amzgement of Lakes aml Ponds. Van Nostrand Reinhold 375 pp. Beynon K. J. and Wright A. N. 11968). Breakdown of the herbicide t'~C-chlorthiamid. J. Sci. Fd. Ayric. 19, 723-32. Binns W. and Johnson A. E. 11970). Chronic and teratogenic effects of 2,4-D and atrazine to sheep. Proc. 25th N. cent. Weed Control Conf I00. Boyd C. E. (19701. Losses of mineral nutrients during decomposition of Typha latiJblia. Arch. Hydrobiol. 66, 511-517. Brooker M. P. {1972). The ecological effbcts of the use of a herbicide (paraquat) Jbr weed cop~rrol, in a fisheries reserroir. Ph.D. thesis, University of Wales. Brooker M. P. (1974). The risk of deoxygenation of water in herbicide application for aquatic weed control. J. lnstn. War. Engrs. 28, 206--210. Brooker M. P. and Baird J. H. t1974). "'Cost" evaluation of watercourse management in Essex. Surveyor CXLIV, No. 4285, 34-37. Brooker M. P. and Edwards R. W. (1973a1. Effects of the herbicide paraquat on the ecology of a reservoir--I Botanical and chemical aspects. Freshwat. Biol. 3, 157-175. Brooker M. P. and Edwards R. W. {1973b). Effects of the herbicide paraquat on the ecology of a reservoir--If Community metabolism. Freshwat. Biol. 3, 383-389. Brooker M. P. and Edwards R. W. (1973c). The use of a herbicide in a fisheries reservoir. J. l~zst. Fisl,. Mgmt. 4, 102-108. Brooker M. P. and Edwards R. W. (1974). Effects of the herbicide paraquat on the ecology of a reservoir--Ill Fauna and general discussion. Freshwat. Biol. 4, 311-335. Brown V. M. (1968). The calculation of the acute toxicity of mixtures of poisons to rainbow trout. Water Res. 2, 723733. Bruns V. F. (1954). The response of certain crops to 2.4-dichlorophenoxyacetie acid in irrigation water--I Red Mexican beans. Weeds 3, 359-76. Bruns V. F. (1957). The response of certain crops to 2.4-dichlorophenoxyacetic acid in irrigation water--II Sugarbeets Weeds, 5, 250-258. Bruns V. F. and Carlisle B. L, ( 1971 ). Effect of silvex and 2.4D in irrigation water on certain crops. Weed Ahstr. 20, No. 1394. Bruns V. F. and Dawson J. H. (1959]. Effects of DCB, DCBxylene mixtures, amitrol and sodium salt of dalapon in irrigation water on corn and rutabagas. Weeds 7, 333340. Bruns V. F.. Hodgson J. M. and Arle A. F. (1972). Response of several crops to six herbicides in irrigation water. U.S. Dept. A,qr. Tech. Bul. 1461, Bruns V. F.. Yeo R. R. and Arle H. F. [1964). Tolerance of certain crops to several aquatic herbicides in irrigation water. U.S. Dept. Ayr. Tech. Bul. 1299.

Aquatic herbicides and the control of water weeds Burns R. G. and Audus L. J. ( 1970~. Distribution and breakdo~ n of paraquat in soil. Weed Res. 10, 49-58. Clark D. G. and Hurst E. W. 11970). The toxicity of diquat. Br. J. ind. ),led. 27, 51-53. Coats G. E.. Funderburk H. H.. Lawrence J. H. and Davis D. E. (19661. Factors affecting persistence and inactivation of diquat and paraquat. Weed Res. 6, 58-66. Cope O. B. {1965). Some response of freshwater fish to herbicides. Proc. 6th Weed Control Conf 8, 439-449. Cope O. B. ( 19661. Contamination of the freshwater ecosystem b~ pesticides. J. appl. Ecol. ISuppl.)3, 517-523. Croll B, T. (1972). Organic pollutants in water. J. Soc. War. Treat. Exam. 21,213-288. Davidson F. F. 11959). Poisoning of wild and domestic animals by a toxic bloom of Nostoe riculare Kultz. J. Am. War. Wks. Ass. 51, 1277-87. Davis T. R. A., Burg A. W., Neumeyer J. L, Butters K. M. and Wasler B. D. [1970). Water Quality Criteria Data Book. Vol. 2. Organic Chemieul Pollution of Freshwater. Dc Marco J.. S.~mons J. M, and Robeck G. G. (19671. Behaviour of synthetic organics in stratified impoundments. J. Am. Wat. Wks Ass. 59, 965-976. Dcrnint R. J. (1970). Use of dye as a model of herbicide dissipation in irrigation water. Proc. West. Soc. Weed Sci. 23, 45-51. Earnest R. D. (1971). Effects of paraquat on fish in a Colorado farm pond. Progt:e. Fish. Cult. 3, 27-31. Ed~vards R. W. (1968). Plants as oxygenators in rivers. IVater Rt's. 2, 243-248. Epstein S. S. et aL (1967). Carcinogenicity of the herbicide maleic hydrazide. Nature, Loml. 215, 1388-1390. Faust S. D. and Aly O. M. (1964). Water pollution by organic pesticides. J. Am. War. Wks. Ass. 56, 267-279. Faust S. D., Younger R. R., Tucker R. T. and Aly O. M. (1961). Observations on the occurrence and persistence of 2,4-D and 2,4-dichlorophenol in lake water. Proc. N. E. Weed Control Conf 16, 459-465. Faust S. D. and Zarins A. (1969). Interaction of diquat and paraquat with clay minerals and carbon in aqueous stations. Residue Rev. 29, 15 I- 170. Fertig S. N. and Schreiber M. M. (1961), Effects of dalapon ingestion on performance of dairy cattle and levels of resi -; due in milk. J. agric. Fd. Chem. 9, 369-374. Fish G. R. (1966). Some effects of the destruction of aquatic weeds in Lake Rotoiti, New Zealand. Weed Res, 6, 350358. Foy C. L. and Bingham S. W. (1969). Some research approaches towards minimizing herbicidal residues in the environment. Residue Rev. 29, 105-135. Frank P. A. (1972). Herbicidal residues in aquatic environment. In: Fate of organic pesticides in the aquatic environment. Advances in Chemistry Series No. 11, 138--148. Frank P. A., Demint R. J. and Comes R. D. (1970). Herbicides in irrigation water following canal-bank treatment for weed control. Weed Science 18, 687-692. Fr.~ J. C.. Brooker M. P. and Thomas P. L. (1973). Changes in the microbial populations of a reservoir treated with the herbicide paraquat. Water Res. 7, 395-407. Fr3er J. D. and Makepeace R. J. (1970). Weed Cono'ol Handhook. 2. Blackwell, London. Funderburk H. H. (1969). Diquat and paraquat. Degradation ~fherhicides (Edited by Kearney P. C. and Kaufman D. D.~, Marcel Dekker, New York. 283-288. Gilderhus P. A. (1967). Effects of diquat on bluegills and their food organisms. Progce. Fish. Cult. 29, 67-74.

t3

Gorham P. R. (t964). Toxic algae as a public health hazard. J. Am. War. W'ks. Ass. 56, 148t-88. Guiver K. (1972). Pollution control in rivers serving as sources for public water supply. J. Soc. }Vtzt. Treat. Exanz. 21, 187-201. Harp G. L. and Campbell R. S. (1964). Effects of the herbicide silvex on benthos of a farm pond. J. Wihtl. Mgmt. 28, 307-317. Haslam S. M. {1973). The management of British wetlands --11. Conservation. d. Enciron. M~lmt. I, 345-361. Hemmet R. B. and Faust S. D. (1969). Biodegradation kinetics of 2.4-dichlorophenoxyacetic mud by aquatic microorganisms Residue Rev. 29, 191-207. Heuss K. (1971). Der einfluss yon herbiziden auf aquatische biozonozen und deren physiologische leistungen. Proc. Eur. Weed Res. Coun. 3rd int. Syrup. Aquatic Weeds. 139146. Hills L. D. (1973). Thalidomide tomatoes. Ecologist 3, 393. Hilsenhoff W. L. (1966). Effect of diquat on aquatic insects and related animals. J. econ. Ent. 59, 1520-1521. Hiltibran. R. C. (1967). Effects of some herbicides on fertilised fish eggs and fry. Trans. Amer. Fish. Soc. 96, 414--416. Howe D. J. T. and Wright N. (1965). The toxicity of paraquat and diquat. Proc. 18th N.Z. Weed Control Conf 105114. Hughes J. S. and Davis J. T. (1963). Variations in toxicity to bluegill sunfish of phenoxy herbicides, Weeds 11, 5053. Hughes J. S. and Davis J. T. (1967). Effects of selected herbicides on bluegill sunfish. Proc. 18th a. Conf S. East Ass. Game Fish. Comm 480-482. James G. V. ( 197 I). Water Treatment. Technical Press, 31 l PP. Jewell W. J. (1970). Aquatic weed decay: dissolved oxygen utilisation and nitrogen and phosphorus regeneration. J. War. Poll. Control Fed. 43, 1475-1467. Kearney P. C. and Kaufman D. D. (Editor) (1969). Degradation of Herbicides. Marcel Dekker, New York. 394 pp. Kearney P. G., Woolson E. A.. Plimmer J. R. and lsensee A. R. (1969). Decontamination of pesticides in soils. Residue Rev, 29, 137-149. Kemp H. T., Abrams J. P. and Overbeck R. C. ( 1971). Water Quality Criteria Data Book. Vol. 3. Effects of Chemicals on Aquatic Life. 528 pp. Khera K. S. and Whitta L. L. (1969). Embryopathic effects of diquat and paraquat in the white rat. Weed Abst. 18, No. 951. Kormondy E. J. (t968). Weight loss of cellulose and aquatic macrophytes in a Carolina Bay Limnol. Oceanogr. 13, 522-526. Leng M. L. (1972). Residues in milk and meat and safety to livestock from the use of phenoxy herbicides in pasture and rangleland. Down to Earth. 28, 12-20. Lucas E. H. and Hammer C. L. (1967). Inactivation of 2,4-D by adsorption on charcoal. Science, New York 105, 340. Makepeace P. J. (1971). The official clearance and approval of aquatic herbicides in the United Kingdom. Proc. E,o'. Weed Res. Counc. 3rd int. Syrup. Aquatic Weeds. 305-312. Martin H.(Ed.l(1972).Pesticide Manual.. 3rd Edition British Crop Protection Council. M athews L. J. (1967). Further results of spraying lake weeds. Roturua and Waikato Water Weeds: Problems and the Search for a Solution (Edited by V. J. Chapman and C. A. Bell) pp. 76. University of Auckland, N.Z. McKee J. E. and Wolf H. W. (Ed.) (1963). Water Quality Cri-

14

M.P. BROOKERand R. W. EDW'.~,Rt~S

tcriu. The Resources Agenc? of California State Water Qualit? Board. Sacramento, California Pub. Np. 3-A. Mitchell D. S. i19"41..4quatic ceqetation uml its use und control. UNESCO. Paris. 135 pp. Mortimer C. H. 11971 ~. Chemical exchanges between sediments and water in the Great Lakes--speculations on probable regulating mechanisms. LimnoL Oceanogr. 16, 3~7-404. Mullison W. R. [ 1970). Effects of herbicides on water and its inhabitants. |li:ed Science 18. 738-750. Newbold C. tin press). Herbicides in aquatic s~stems. Biol. CooL,ere. Nichols D. S. and Keeney D. R. 11973). Nitrogen and phosphorus release from decaying water milfoil. Hy&'obioloyia 42, 509-525. Owens M. and Marls P. J. (in preparation). Some ecological eff,:cts of the use of paraquat for weed control in a small lake. Ot~ens M.. Knowles G. and Clark A. (1969). The prediction of the distribution of dissolved oxygen in rivers. Adv. War. Poll. Res. 4, 125-137. Palmer J. S. 11972). Toxicit~ of 45 organic herbicides to ~;attle. sheep and chickens. U.S,D..4./A.R.S. Production Research Report. No. t37. Palmer J. S. and Radeleff R. D. (1969). The toxicity of some organic herbicides to cattle, sheep and chickens. U.S,D.A./ 4.R.S. Production Rese,o'ch Report No. 106. Pierce M. A. (1966). Application of fenac to four small ponds on Vassar Campus. Proc. N. East Vv'eed Control Coal 20, 470-475. Pierce M. E. 11967). Study of a second year application of fcnac to two small ponds on Vassar Campus. Proc. N. East Weed Comrol Conf 21,530-533. Pierce. M. E. [ 1968). The effect of several herbicides on eight test areas in Nobska Pond, Woods Hole, Massachusetts. Proc. ,V. East Weed Control Cot~ 22, 195-203. Pieters A. J. and De Boer F. G. 11971). Dichlobenil in the aquatic environment. Proc. Eur..Weed Res. Coun. 3r,I ira. Syrup. Aquatic Weeds. 183-193. Pokorny J.. Mentberger J., Losos B., Hartman P., and Hetesa J. (1971t. Changes in hydrochemical and hydrobiological rotations occurring when Elodea was controlled with paraquat. Proc. Eur. Weed Res. Cottn. 3rd int. Syrup. Aquatic Weeds. 217-229. Rhoades J. D. and Bernstein L. (1971). Chemical, physical and biological characteristics of irrigation and soil water. Water and Water Pollution Handbook, Vol. 1 (Edited by L. L. Ciccio), 141-222. Marcel Dekker, N. York. Ridley J. E. A. (1970j. The biology and management of eutrophic reservoirs. Wut. Treat. Exam. 19, 374-399. Robinson G. W. (1969). The use of herbicides in the maintenance of land drainage channels of Romney Marsh. J. llzstn H,'ttt. En~lrs. 23, 159-176. Robinson G. W. 11971~. Practical aspects of chemical control of weeds in land drainage channels in England and Wales. Proc. Eur. Weed Res. Coum 3rd Int. Syrup. Aquatic Weeds 297-302. Robson T. O. (1966). Some studies of the persistence of 2,4D in natural surface waters in Britain. Proc. 8th Br. Weed Control Coql~ 594-597. Robson T. O. (1968). Some studies of the persistence of 2,4D in natural surface waters. Proc. 9th Brit. Weed Control Cm!12 404-40,',I. Robson T. O. (19731. The control ofaquatic plants. Ministry of Agriculture, Fisheries and Food. Bulletin No. 194. Sanders H. O. (1970). Toxicities of some herbicides to six

species of freshwater crustaceans. J. Wut. Pollut. Control Fed. 42, 154-1--15511. Sanders H. O. and Cope O. B. ~1966~. Toxicities of several pesticides to tx~o species of cladocerans. Trons. Am. Fish. Soc. 95, 165-169. Sanders H. O. and Cope O, B. i 1068). The relative toxicities of several pesticides to naiads of three species of stoneflies. Limnol. Oceanogr. 13, I 12- l 17. Schultz D. P. 119731. Dynamics of a salt of (2.4-D dichlorophenoxyl acetic acid in fish. water and hydrosoL J. ayric. Fd. Chem. 21, 1S6--192. Sigworth G. A. 119651. Identification and removal of herbicides and pesticides. J. Ant. ~2lt. Wks. Ass. 57, 1016-1022. Simpson R. L. and Pimentel D. (1972). Ecological effects of the aquatic herbicide fenae on small ponds. Search A qric., Cornell Unic. 2. I0. 1-39. Slade P. t1965~. Photochemical degradation of paraquat. Nature, Lond. 207, 515-516. Slade P. (1966). The fate of paraquat applied to plants. Weed Res. 6, 158-167. Smith G. E. and lsom B. G. (1967). Investigations of effects of large-scale applications of 2,4-D on aquatic fauna and water quality. Pest. Monit. 3. !, 16-21. Spencer-Jones. D. H. (1974). Dichlobenil--a means of controlling aquatic weeds. J. Inst. Fish. Motor. 5, 10-15. Steel J. A, {1972). The application of fundamental limnological research in water supply system design and management. Syrup. Zool. Soc. Lond. (19731. 29, 41-67. Swan A. A. B. {1967). Toxicological problems in the control of water weeds. European Weed Research Council Symposium (Oldenburg). 161-167. Tooby T. E. 11971). The toxicity of aquatic herbicides to freshwater organisms-a brief review. Proc, Eur. Weed Res. Court. 3rd int. Syrup. Aquatic Weeds. 197 I, 129-137. Tutass H. (t966). Photodecomposition of 2,4-D Proc. 18th a. Cal(fi Weed Conf 13-14. Van Genderen H. and Van Esch. G. J. (1968). Toxicology of the herbicide dichlobenil (2.6-dichlorobenzonitrile) and its main metabolites. Fd. Cosmet. Toxieol. 6, 261-269. Van Der Weij H. G.. Hoogers B. J. and Blok E. (1971). Mercaptotroazines compared with diuron for aquatic weed control in stagnant water. Proe. E,n'. Weed Rex. Co,re. 3rd int. Syrup. Aquatic H,'eeds 149-160. Verloop A. (1972). Fate of the herbicide dichlobeniI in plants and soil in relation to its biological activity. Residue Rev. 43, 55-103. Wallace R. R.. Merritt W. F. and West A. S. (1973). Dispersion and transport of rhodamine B dye and methoxychlor in running water: a preliminary study. Environ. Pollut. 5, 11-18. Walker. C. R. (19711. The toxicological effects of herbicides and weed control on fish and other organisms in the aquatic ecosystem. Proc. Eur. Weed Res. Coun. 3rd int. Syrup. Aquatic Weeds. 119-127. Walker. C. R. (19631. Toxicological effects of herbicides on the fish environment. Proc. Ann. Air. Wat. Poll. Cop~ 8, 17-34. Walsh G. E.. Miller C. W. and Heitmuller P. T. (1971). Uptake and effects of dichlobeni[ in a small pond. Bull Environ. Contain. ToxicoL 6, 279-288. Way J. M.. Newman J. F.. Moore N. W. and Knaggs F. W. ( 1971 ). Some Ecological effects of the use of paraquat for the control of weeds in small lakes. J. appl. Ecol. 8, 509532. Wilson D, C. and Bond C. E. 119691. The effects of the herbicide diquat and dichlobenil (Casoron) on pond inverte-

Aquatic herbicides and the control of ~ater ~eeds brates. Part 1. Acute toxicit?. Trwts. 4m. Fi,dL Soc. 98, 43s-443. Wojtalik T. A.. Hall T. F. and Hill L. O. 1197l i. Monitoring ecological conditions associated ~ith ~ide-scalc application of DMA 2.4-D to aquatic environments. Pest. Mo~rit..I. 4, 18->2{}3. World Health Organization 119701. European Standards for

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Drinking Water. 2nd ~:dition Gcnc~,a. The Organisation. 1970. Wright S. J. L. q1971~. Degradation of herbicides b~ soil micro-organisms. S.vmp. Soc. .4ppt. Bcict. I, 233-254. Yeo R. R. I lOOTI. Dissipation of diquat and paraquat and the effects on aquatic ~ccds and fish. lVL'ed* 15. 42 -46.