Mixture toxicity of the antifouling compound irgarol to the marine phytoplankton species Dunaliella tertiolecta

This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations > or = 0.27 micro g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC50 = 0.7 micro g/L; chlorothalonil 96 h EC50 = 64 micro g/L; atrazine 96 h EC50 = 69 micro g/L; 2,4-D 96 h EC50 = 45,000 micro g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.     

Mixture Toxicity of the Antifouling Compound Irgarol to the Marine Phytoplankton Species Dunaliella tertiolecta

This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations ≥ 0.27 μ g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC₅₀ = 0.7 μ g/L; chlorothalonil 96 h EC₅₀ = 64 μ g/L; atrazine 96 h EC₅₀ = 69 μ g/L; 2,4-D 96 h EC₅₀ = 45,000 μ g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.     

A comparison of mixture toxicity assessment: examining the chronic toxicity of atrazine, permethrin and chlorothalonil in mixtures to Ceriodaphnia cf. dubia

Pesticides predominantly occur in aquatic ecosystems as mixtures of varying complexity, yet relatively few studies have examined the toxicity of pesticide mixtures. Atrazine, chlorothalonil and permethrin are widely used pesticides that have different modes of action. This study examined the chronic toxicities (7-d reproductive impairment) of these pesticides in binary and ternary mixtures to the freshwater cladoceran Ceriodaphnia cf. dubia. The toxicity of the mixtures was compared to that predicted by the independent action (IA) model for mixtures, as this is the most appropriate model for chemicals with different modes of action. Following this they were compared to the toxicity predicted by the concentration addition (CA) model for mixtures. According to the IA model, the toxicity of the chlorothalonil plus atrazine mixture conformed to antagonism, while that of chlorothalonil and permethrin conformed to synergism. The toxicity of the atrazine and permethrin mixture as well as the ternary mixture conformed to IA implying there was either no interaction between the components of these mixtures and/or in the case of the ternary mixture the interactions cancelled each other out to result in IA. The synergistic and antagonistic mixtures deviated from IA by factors greater than 3 and less than 2.5, respectively. When the toxicity of the mixtures was compared to the predictions of the CA model, the binary mixture of chlorothalonil plus atrazine, permethrin plus atrazine and the ternary mixture all conformed to antagonism, while the binary mixture of chlorothalonil plus permethrin conformed to CA. Using the CA model provided estimates of mixture toxicity that did not markedly underestimate the measured toxicity, unlike the IA model, and therefore the CA model is the most suitable to use in ecological risk assessments of these pesticides.     

Pesticide storage and release in unsaturated soil in Illinois, USA.

The chemical fate and movement of pesticides may be subject to transient storage in unsaturated soils during periods of light rainfall, and subsequent release into shallow groundwater by increased rainfall. The objective of this study was to conduct field-scale experiments to determine the relative importance of transient storage and subsequent release of agrichemicals from the vadose zone into potential aquifers. Two field-scale experiments were conducted under a rain exclusion shelter. In the 1x experiment, atrazine and chlorpyrifos were applied at application-rate equivalents (1.6 kg ha(-1) and 1.3 kg ha(-1), respectively). In the 4x experiment, atrazine was applied in an amount that was four times greater than that usually applied to fields (6.7 kg ha(-1)). Water was either applied to simulate rain or withheld to simulate dry periods. In the 1x experiment, atrazine was detected in the water samples whereas chlorpyrifos was not detected in the majority of the samples. The dry period imposed on the treatment plot did not appear to result in storage of the chemicals, whereas the wet period resulted in greater leaching of atrazine, although the concentrations remained less than the Maximum Contaminant Level of 3 microg L(-1). Both chemicals were detected in soil samples collected from a 20- to 30-cm depth, but it appeared that both chemicals dissipated before the field experiment was concluded. It appeared that the one-time application of atrazine and chlorpyrifos at the label rates did not result in a sufficient mass to be stored and flushed in significant concentrations to the saturated zone. When atrazine was applied at 4x and a longer drought period was imposed on the treatment plot, the resulting concentrations of dissolved atrazine were still less than 3 microg L(-1) . Atrazine was detected in only the near-surface (0 to 15 cm) soil samples and the herbicide dissipated before the onset of the dry period in the treatment plot. The results of this field study demonstrated that atrazine and chlorpyrifos were not sufficiently persistent to be stored and then released in significantly large concentrations to the saturated zone. The dissipation half-life of atrazine in the 4x application was about 44 days. This study, in addition to others, suggested that atrazine may be less persistent in surface soil than has been generally reported.     

Constructed wetlands for mitigation of atrazine-associated agricultural runoff

Atrazine was amended into constructed wetlands (59-73x14x0.3 m) for the purpose of monitoring transport and fate of the pesticide to obtain information necessary to provide future design parameters for constructed wetlands mitigation of agricultural runoff. Following pesticide amendment, a simulated storm and runoff event equal to three volume additions was imposed on each wetland. Targeted atrazine concentrations were 0 microg/l (unamended control), 73 microg/l, and 147 microg/l. Water, sediment, and plant samples were collected weekly for 35 days from transects longitudinally distributed throughout each wetland and were analyzed for atrazine using gas chromatography. Between 17 and 42% of measured atrazine mass was within the first 30-36 m of wetlands. Atrazine was below detection limits (0.05 microg/kg) in all sediment and plant samples collected throughout the duration of this study. Aqueous half lives ranged from 16 to 48 days. According to these data, conservative buffer travel distances of 100-280 m would be necessary for effective runoff mitigation.     

Examining the joint toxicity of chlorpyrifos and atrazine in the aquatic species: Lepomis macrochirus, Pimephales promelas and Chironomus tentans

The joint toxicity of chlorpyrifos and atrazine was compared to that of chlorpyrifos alone to discern any greater than additive response using both acute toxicity testing and whole-body residue analysis. In addition, acetylcholinesterase (AChE) inhibition and biotransformation were investigated to evaluate the toxic mode of action of chlorpyrifos in the presence of atrazine. The joint toxicity of atrazine and chlorpyrifos exhibited no significant difference in Lepomis macrochirus compared to chlorpyrifos alone; while studies performed with Pimephales promelas and Chironomus tentans, did show significant differences. AChE activity and biotransformation showed no significant differences between the joint toxicity of atrazine and chlorpyrifos and that of chlorpyrifos alone. From the data collected, the combination of atrazine and chlorpyrifos pose little additional risk than that of chlorpyrifos alone to the tested fish species.     

Toxicity of uranium and copper individually, and in combination, to a tropical freshwater macrophyte (Lemna aequinoctialis)

Copper (Cu) and uranium (U) are of potential ecotoxicological concern to tropical freshwater biota in northern Australia, as a result of mining activities. Few data are available on the toxicity of U, and no data are available on the toxic interaction of Cu and U, to freshwater biota. This study determined the toxicity of Cu and U individually, and in combination, to a tropical freshwater macrophyte, Lemna aequinoctialis (duckweed), in a synthetic soft water (27 degrees C; pH, 6.5; hardness, 40 mg CaCO3 l-1, alkalinity, 16 mg CaCO3 l-1), typical of many fresh surface waters in coastal northern Australia. The growth rate of L. aequinoctialis decreased with increasing Cu or U concentrations, with the concentration of Cu inhibiting growth by 50% (EC50) being 16+/-1.0 microg l-1, with a minimum detectable effect concentration (MDEC) of 3.2 microg l-1. The concentration of U inhibiting growth by 50% (EC50) was 758+/-35 microg l-1 with a MDEC of 112 microg l-1. The EC50 value for the exposure of L. aequinoctialis to equitoxic mixtures of Cu and U was significantly (P0.05) higher than one toxic unit (1.35; 95% confidence interval, 1.18-1.52), indicating that the combined effects of Cu and U are less than additive (antagonistic). Therefore, inhibition of the growth rate of L. aequinoctialis was reduced when Cu and U were present in equitoxic mixtures, relative to individual metal exposures. Since non-additive (e.g. antagonistic) interactions of metal mixtures cannot be predicted using current mixture models, these results have important potential implications for the protection of freshwater ecosystems through the derivation of national water quality guidelines.     

Influence of Lead on Atrazine Uptake by Rice (Oryza sativa L.) Seedlings from Nutrient Solution (7 pp)

Background Atrazine is a widely used herbicide, and its persistence in soil and water causes environmental concerns. In the past, plat uptake processes are mainly investigated for single contaminants. However, in many cases, contaminants co-exist in environmental matrix, such as soil, and plant uptake of one contaminant may be influenced by its co-existing ones.Methods The uptake of atrazine by rice seedlings (Oryza sativa L.) from nutrient solution through the roots was investigated in a solution culture, over an exposure period of 4 weeks. Atrazine accumulation in plant tissues was determined by gas chromatography, and lead was determined using atomic absorption spectrometry.Results and Discussion With different ratios of atrazine and Pb2+ concentrations in solution, the observed atrazine concentrations in shoots and roots varied significantly. In atrazine-Pb2+ mixture systems, the added Pb2+ either increased or decreased the concentrations or BCFs of atrazine in seedlings (relative to those without Pb2+), depending on the atrazine-Pb2+ ratio in nutrient solution. The enhanced atrazine uptake results presumably from atrazine-Pb2+ complex formation. The reduced atrazine uptake, which occurred mainly at high atrazine concentrations, is attributed to atrazine toxicity that inhibited seedling growth and transpiration. Conclusion The formation of atrazine-Pb2+ complex both in the solution and within plant tissues may affect the accumulation of both contaminants by rice plants.     

Effects of herbicide and insecticide interaction on soil entomofauna under maize crop

The aim of this study was to evaluate the impact of the herbicide mixture nicosulfuron + atrazine, with or without the insecticide chlorpyrifos, onto soil entomofauna under maize crop. The treatments, applied 25 days after maize emergence, were represented by a weeded control without insecticide and herbicide, a weeded control with chlorpyrifos, and mixtures of nicosulfuron + atrazine, with or without chlorpyrifos. Arthropods populations, on the soil surface, as well as inside the soil under maize, were principally represented by mites (Arachnida: Acari), decomposer collembolans (Hexapoda:Parainsecta:Collembola) and predator ants (Hymenoptera:Formicidae). The nicosulfuron + atrazine mixture with chlorpyrifos and the isolated chlorpyrifos reduced the population dynamics of all insect groups on the soil surface compared to the weeded control. In the soil, mite and ant populations were reduced after application of the herbicide mixture with chlorpyrifos and of the isolated chlorpyrifos.     

Toxicity of fipronil and its enantiomers to marine and freshwater non-targets

Fipronil is a phenylpyrazole insecticide used in agricultural and domestic settings for controlling various insect pests in crops, lawns, and residential structures. Fipronil is chiral; however, it is released into the environment as a racemic mixture of two enantiomers. In this study, the acute toxicity of the (S,+) and (R,-) enantiomers and the racemic mixture of fipronil were assessed using Simulium vittatum IS-7 (black fly), Xenopus laevis (African clawed frog), Procambarus clarkii (crayfish), Palaemonetes pugio (grass shrimp), Mercenaria mercenaria (hardshell clam), and Dunaliella tertiolecta (phytoplankton). Results showed that S. vittatum IS-7 was the most sensitive freshwater species to the racemic mixture of fipronil (LC50 = 0.65 microg/L) while P. pugio was the most sensitive marine species (LC50 = 0.32 microg/L). Procambarus clarkii were significantly more sensitive to the (S,+) enantiomer while larval P. pugio were significantly more sensitive to the (R,-) enantiomer. Enantioselective toxicity was not observed in the other organisms tested. Increased mortality and minimal recovery was observed in all species tested for recovery from fipronil exposure. These results indicate that the most toxic isomer of fipronil is organism-specific and that enantioselective toxicity may be more common in crustaceans than in other aquatic organisms.     

Lethal and sub-lethal effects of the fungicide chlorothalonil on three life stages of the grass shrimp,Palaemonetes pugio

Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) is the second most widely used fungicide in the United States. Due to the widespread use of chlorothalonil, it is important to investigate the effects chlorothalonil may have on estuarine species such as the grass shrimp, Palaemonetes pugio. This study examined the toxicity of chlorothalonil to three life-history stages (embryo, larvae, adult) of the grass shrimp. Also, molting frequency, growth response and metamorphosis from a larval life cycle pulsed exposure assay were examined as sub-lethal indicators of chlorothalonil exposure. Results showed embryos were the least sensitive with a 96-h Median Lethal Concentration (LC50) of 396.0 microg/L (95% Confidence Interval [CI] 331.3-472.4 microg/L). The adult 96-h LC50 was 152.9 microg/L (95% CI 120.3-194.5 microg/L). Larvae were the most sensitive to chlorothalonil exposure with a 96-h LC50 of 49.5 microg/L (95% CI 44.4-55.27 microg/L). In the life cycle pulsed exposure assay, all surviving larvae in the treatments required significantly more molts to reach postlarvae than the control. Other measured parameters showed differences between treatments and control but there was no statistical significance. This research demonstrated that chlorothalonil is highly toxic to grass shrimp and that larval grass shrimp would be the most appropriate life stage to use for chlorothalonil risk assessments since that stage is the most sensitive.     

Toxicity of carbaryl, diquat dibromide, and fluoranthene, individually and in mixture, to larval grass shrimp, Palaemonetes pugio

This study examined the toxicity of two pesticides (carbaryl and diquat dibromide) and one polycyclic aromatic hydrocarbon (fluoranthene), both singly and in mixture, to grass shrimp larvae (Palaemonetes pugio). These three chemicals are all present in coastal environments and can easily enter estuarine ecosystems. Fluoranthene was the most toxic chemical with a 96-h LC50 value of 32.45 microg/L, followed by carbaryl (43.02 microg/L) and diquat dibromide (1624 microg/L). In the chemical mixture tests, the binary carbaryl/diquat dibromide mixture and the ternary carbaryl/diquat dibromide/fluoranthene mixture had additive results.     

Combined toxic impacts of thiamethoxam and four pesticides on the rare minnow (Gobiocypris rarus)

To examine pesticide mixture toxicity to aqueous organisms, we assessed the single and combined toxicities of thiamethoxam and other four pesticides (chlorpyrifos, beta-cypermethrin, tetraconazole, and azoxystrobin) to the rare minnow (Gobiocypris rarus). Data from 96-h semi-static toxicity assays of various developmental phases (embryonic, larval, juvenile, and adult phases) showed that beta-cypermethrin, chlorpyrifos, and azoxystrobin had the highest toxicities to G. rarus, and their LC₅₀ values ranged from 0.0031 to 0.86 mg a.i. L^?1, from 0.016 to 6.38 mg a.i. L^?1, and from 0.39 to 1.08 mg a.i. L^?1, respectively. Tetraconazole displayed a comparatively high toxicity, and its LC₅₀ values ranged from 3.48 to 16.73 mg a.i. L^?1. By contrast, thiamethoxam exhibited the lowest toxic effect with LC₅₀ values ranging from 37.85 to 351.9 mg a.i. L^?1. Rare minnow larvae were more sensitive than embryos to all the pesticides tested. Our data showed that a pesticide mixture of thiamethoxam–tetraconazole elicited synergetic toxicity to G. rarus. Moreover, pesticide mixtures containing beta-cypermethrin in combination with chlorpyrifos or tetraconazole also had synergetic toxicities to fish. The majority of pesticides are presumed to have additive toxicity, while our data emphasized that the concurrent existence of some chemicals in the aqueous circumstance could cause synergetic toxic effect, leading to severe loss to the aqueous environments in comparison with their single toxicities. Thence, the synergetic impacts of chemical mixtures should be considered when assessing the ecological risk of chemicals.

     

Influence of the pesticides glyphosate,chlorpyrifos and atrazine on growth parameters of nonochratoxigenic Aspergillus section Nigri strains isolated from agricultural soils

This investigation was undertake to determine the effect of glyphosate, chlorpyrifos and atrazine on the lag phase and growth rate of nonochratoxigenic A. niger aggregate strains growing on soil extract medium at ?0.70, ?2.78 and ?7.06 MPa. Under certain conditions, the glyphosate concentrations used significantly increased micelial growth as compared to control. An increase of about 30% was observed for strain AN 251 using 5 and 20 mg L^?1 of glyphosate at ?2.78 MPa. The strains behaved differently in the presence of the insecticide chlorpyrifos. A significant decrease in growth rate, compared to control, was observed for all strains except AN 251 at ?2.78 MPa with 5 mg L^?1. This strain showed a significant increase in growth rate. With regard to atrazine, significant differences were observed only under some conditions compared to control. An increase in growth rate was observed for strain AN 251 at ?2.78 MPa with 5 and 10 mg L^?1 of atrazine. By comparison, a reduction of 25% in growth rate was observed at ?7.06 MPa and higher atrazine concentrations. This study shows that glyphosate, chlorpyrifos and atrazine affect the growth parameters of nonochratoxigenic A. niger aggregate strains under in vitro conditions.     

Feasibility of constructed wetlands for removing chlorothalonil and chlorpyrifos from aqueous mixtures

Chlorpyrifos (an insecticide) and chlorothalonil (a fungicide) are transported in stormwater runoff and can be lethal to receiving aquatic system biota. This study determined removal rates of chlorpyrifos and chlorothalonil in simulated stormwater runoff treated in constructed wetland mesocosms. Using sentinel species, Ceriodaphnia dubia and Pimephales promelas, observed declines in toxicity of the simulated runoff after treatment were 98 and 100%, respectively. First order removal rates were 0.039/h for chlorpyrifos and 0.295/h for chlorothalonil in these experiments. Constructed wetland mesocosms were effective for decreasing concentrations of chlorpyrifos and chlorothalonil in simulated stormwater runoff, and decreasing P. promelas and C. dubia mortality resulting from these exposures. The results from this study indicate that constructed wetlands could be part of an efficient mitigation strategy for stormwater runoff containing these pesticides.     

Lack of effects of atrazine on estrogen-responsive organs and circulating hormone concentrations in sexually immature female Japanese quail (Coturnix coturnix japonica)

The widely used herbicide, atrazine, has been reported to exhibit reproductive toxicity in rats and amphibians. The present studies investigate toxicity of atrazine in Japanese quail and its ability to influence reproduction in sexually immature females. Atrazine was administered in the diet at concentrations from 0.001 to 1000 ppm (approximately 109 mg kg-1 per day) or systemically via daily subcutaneous injections (1 and 10 mg kg-1) or Silastic implants. Atrazine did not cause overt toxicity in sexually immature female quail (no effects on change in body weight, feed intake, mortality or on circulating concentrations of the stress hormone, corticosterone). It was hypothesized that if atrazine were to have estrogenic activity or to enhance endogenous estrogen production, there would be marked increases in the weights of estrogen sensitive tissues including the oviduct, the liver and the ovary together with changes in gonadotropin secretion. However, atrazine had no effect on either liver or ovary weights. Atrazine in the diet increased oviduct weights at 0.1 and 1 ppm in some studies. These effects were not consistently observed and were not significant when data from studies were combined. Systemic administration of atrazine had no effect on oviduct weights. Dietary (concentrations from 0.001 to 1000 ppm) and systemically administered atrazine had no effect on circulating concentrations of luteinizing hormone (LH). The present studies provide evidence for a lack of general or reproductive toxicity of atrazine in birds.     

Synergistic effects caused by atrazine and terbuthylazine on chlorpyrifos toxicity to early-life stages of the zebrafish Danio rerio

This study examined the effects of three widely used pesticides that have been previously detected in aquatic systems neighbouring agricultural fields on the early-life stages of the zebrafish Danio rerio. Tests involving single exposures and binary combinations of the s-triazine herbicides (atrazine and terbuthylazine) and the organophosphate insecticide chlorpyrifos were performed. Several endpoints, such as swimming behaviour, morphological abnormalities and mortality, were studied. In addition, the inhibition of acetylcholinesterase (AChE) activity was investigated in order to evaluate the mode of action and toxicity of chlorpyrifos in the presence of these herbicides. Results indicate that both binary mixtures elicited synergistic responses on the swimming behaviour of zebrafish larvae. Moreover, although the herbicides were not effective inhibitors of the AChE on their own, a synergistic inhibition of the enzyme activity was obtained by exposure to mixtures with chlorpyrifos. We observed a correlation between impairment of swimming behaviour of the larvae and inhibition of AChE activity. This study supports previous studies concerning the risk assessment of mixtures since the toxicity may be underestimated when looking only at the single toxicants and not their mixtures.     

Effect of surfactants at low concentrations on the sorption of atrazine by natural sediment.

A series of experiments were carried out to determine the effect of surfactants at low concentrations on the sorption of atrazine by natural sediments. With surfactant concentrations ranging from 0 to 20 mg/ L, anionic and cationic surfactants appreciably reduce the adsorption of atrazine, while nonionic surfactant decreases the adsorption of atrazine at concentrations equal to or less than 1 mg/L and increases adsorption at higher concentrations. Desorption of atrazine in the presence of different sodium dodecylbenzene sulfonate (SDBS) concentrations shows that a portion of the bound pesticide resists desorption in the SDBS free system. However, the addition of SDBS accelerates the desorption of atrazine. Furthermore, the nature of sediment and the contacting sequence of SDBS, at 10 mg/L, with the sediment, also influence the adsorption of atrazine. The conclusions in this study could be explained partially by the effect of the type and concentration of surfactants and the characteristics of sediments.     

Pesticide fate in tropical wetlands of Brazil: an aquatic microcosm study under semi-field conditions

A contamination of off-site aquatic environments with pesticides has been observed in the tropics, yet only sparse information exists about pesticide fate in such ecosystems. The objective of our semi-field study was to elucidate the fate of alachlor, atrazine, chlorpyrifos, endosulfan, metolachlor, profenofos, simazine, and trifluralin in the aqueous environment of the Pantanal wetland (MT, Brazil). To this aim, water and water/sediment microcosms of two sizes (0.78 and 202 l) were installed in the outskirts of this freshwater lagoon environment and pesticide dissipation was monitored for up to 50 d after application. The physical-chemical water conditions that developed in the microcosms were reproducible among field replicates for both system sizes. Pesticide dissipation was substantially enhanced for most pesticides in small microcosms relative to the large ones (reduced DT(50) by a factor of up to 5.3). The presence of sediment in microcosms led to increased persistence of chlorpyrifos, endosulfan, and trifluralin in the test systems, while for polar pesticides (alachlor, atrazine, metolachlor, profenofos, and simazine) a lesser persistence was observed. Atrazine, simazine, metolachlor, and alachlor were identified as the most persistent pesticides in large water microcosms (DT(50) > or = 47 d); in large water/sediment systems endosulfan beta, atrazine, metolachlor, and simazine showed the slowest dissipation (DT(50) > or = 44 d). A medium-term accumulation in the sediment of tropical ecosystems can be expected for chlorpyrifos and endosulfan isomers (11-35% of applied amount still extractable at 50 d after application). We conclude that the persistence of the studied pesticides in aquatic ecosystems of the tropics is not substantially lower than during summer in temperate regions.     

Analysis of pesticide runoff from mid-Texas estuaries and risk assessment implications for marine phytoplankton

During 1993, estuarine surface water samples were collected from the mid-Texas coast (Corpus Christi to Port Lavaca, TX). Agricultural watershed areas as well as tidal creeks immediately downstream were chosen as sampling sites along with adjoining bay sampling stations. Collections were made throughout the growing season (February to October 1993) before and after periods of significant (> 1.25 cm) rainfall. All samples were initially screened for the presence of pesticides using enzyme-linked immunosorbent assay (ELISA) test kits (EnviroGard) for triazine herbicides and carbamate insecticides. All samples were extracted and then analyzed using gas chromatography (GC) for quantification of atrazine. Only samples testing positive for carbamate insecticides via ELISA were further extracted for GC analysis to quantify aldicarb and carbofuran. Additionally, laboratory toxicity tests using phytoplankton were examined from published, peer-reviewed literature and compared with the atrazine field levels found in Texas. Results of ELISA screening indicated the presence of triazine herbicides in nearly all samples (>93%). GC analysis further confirmed the presence of atrazine concentrations ranging from <0.01-62.5 microg/L. Screening tests also found detectable levels of carbamate insecticides (aldicarb and carbofuran) that were also confirmed and quantified by GC. Comparison of measured concentrations of atrazine compared with published toxicity tests results indicated that there was a potential environmental risk for marine/estuarine phytoplankton in surface waters of Texas estuaries, particularly when the chronic nature of atrazine exposure is considered.