Use of carboxylesterase activity to remove pyrethroid-associated toxicity to Ceriodaphnia dubia and Hyalella azteca in toxicity identification evaluations

Increases in the use and application of pyrethroid insecticides have resulted in concern regarding potential effects on aquatic ecosystems. Methods for the detection of pyrethroids in receiving waters are required to monitor environmental levels of these insecticides. One method employed for the identification of causes of toxicity in aquatic samples is the toxicity identification evaluation (TIE); however, current TIE protocols do not include specific methods for pyrethroid detection. Recent work identified carboxylesterase treatment as a useful method for removing/detecting pyrethroid-associated toxicity. The present study has extended this earlier work and examined the ability of carboxylesterase activity to remove permethrin- and bifenthrin-associated toxicity to Ceriodaphnia dubia and Hyalella azteca in a variety of matrices, including laboratory water, Sacramento River (CA, USA) water, and Salinas River (CA, USA) interstitial water. Esterase activity successfully removed 1,000 ng/L of permethrin-associated toxicity and 600 ng/L of bifenthrin-associated toxicity to C. dubia in Sacramento River water. In interstitial water, 200 ng/L of permethrin-associated toxicity and 60 ng/L of bifenthrin-associated toxicity to H. azteca were removed. The selectivity of the method was validated using heat-inactivated enzyme and bovine serum albumin, demonstrating that catalytically active esterase is required. Further studies showed that the enzyme is not significantly inhibited by metals. Matrix effects on esterase activity were examined with municipal effluent and seawater in addition to the matrices discussed above. Results confirmed that the esterase retains catalytic function in a diverse array of matrices, suggesting that this technique can be adapted to a variety of aquatic samples. These data demonstrate the utility of carboxylesterase treatment as a viable step to detect the presence of pyrethroids in receiving waters.     

Whole-sediment toxicity identification evaluation tools for pyrethroid insecticides: I. Piperonyl butoxide addition

Piperonyl butoxide (PBO) is a synergist used in some pyrethroid and pyrethrin pesticide products and has been used in toxicity identification evaluations (TIEs) of water samples to indicate organophosphate or pyrethroid-related toxicity. Methods were developed and validated for use of PBO as a TIE tool in whole-sediment testing to help establish if pyrethroids are the cause of toxicity observed in field-collected sediments. Pyrethroid toxicity was increased slightly more than twofold in 10-d sediment toxicity tests with Hyalella azteca exposed to 25 microg/L of PBO in the overlying water. This concentration was found to be effective for sediment TIE use, but it is well below that used in previous water and pore-water TIEs with PBO. The effect of PBO on the toxicity of several nonpyrethroids also was tested. Toxicity of the organophosphate chlorpyrifos was reduced by PBO, and the compound had no effect on toxicity of cadmium, DDT, or fluoranthene. Mixtures of the pyrethroid bifenthrin and chlorpyrifos were tested to determine the ability of PBO addition to identify pyrethroid toxicity when organophosphates were present in a sample. The PBO-induced increase in pyrethroid toxicity was not seen when chlorpyrifos was present at or above equitoxic concentrations with the pyrethroid. In the vast majority of field samples, however, the presence of chlorpyrifos does not interfere with use of PBO to identify pyrethroid toxicity. Eleven field sediments or soils containing pyrethroids and/or chlorpyrifos were used to validate the method. Characterization of the causative agent as determined by PBO addition was consistent with confirmation by chemical analysis and comparison to known toxicity thresholds in 10 of the 11 sediments.     

Causes of water toxicity to Hyalella azteca in the New River, California, USA

The New River (CA, USA) was created in 1905 to 1907 when the Colorado River washed out diversionary works and flowed into the Salton Basin, creating the Salton Sea. Approximately 70% of the river's current flow is agricultural wastewater from the Imperial Valley. The river is contaminated with pesticides, industrial organic chemicals, metals, nutrients, bacteria, and silt. Monitoring for the State of California Surface Water Ambient Monitoring Program has indicated persistent water column toxicity to the epibenthic amphipod Hyalella azteca. Four toxicity identification evaluations (TIEs), along with chemical analyses, were performed, and the results indicated multiple and varying causes of toxicity. The first two TIEs characterized the causes of toxicity as a combination of metals and organics, but only the second sample contained enough total copper to contribute to toxicity. The third TIE used an emerging method for characterizing and identifying toxicity caused by pyrethroid pesticides. This TIE characterized organics as the cause of toxicity, and a carboxylesterase enzyme treatment further identified the cause of toxicity as pyrethroids. The final TIE used the enzyme and Phase II procedures to identify cypermethrin as the cause of toxicity. The TIE results demonstrate the evolving causes of toxicity in the New River and should assist regulators with implementing the total maximum daily load process for pesticides, particularly pyrethroids. Further research will determine if pyrethroids and other New River contaminants are having an impact on the Salton Sea.     

Inhibition of aquatic toxicity of pyrethroid insecticides by suspended sediment

The use of pyrethroid insecticides is increasing in both agricultural and urban environments. Although pyrethroids display very high acute toxicities to water column organisms in laboratory tests, environmental water samples typically contain suspended sediment (SS) that can reduce the freely dissolved concentration of pyrethroids, hence their bioavailability. Consequently, phase distribution could play an important role in pyrethroid aquatic toxicology. In this study, we evaluated the effect of SS on the acute toxicity of four widely used pyrethroid insecticides to Ceriodaphnia dubia. In all assays, median lethal concentrations (LC50s) consistently increased with increasing SS, demonstrating the pronounced inhibitory effects of SS on pyrethroid toxicity. The LC50s in the 200 mg/L SS solutions were 2.5 to 13 times greater than those measured in sediment-free controls. Solid-phase microextraction (SPME) was used to determine the apparent distribution coefficient Kd for the pyrethroids in the water samples. Under the assumption that only the freely dissolved fraction is bioavailable, the measured Kd was used to predict C. dubia LC50s in the water samples. The predicted LC50s were within a factor of two of the measured values for 95% of the treatments. Results from this study suggest that the inhibitory effect of SS can be highly significant and must be considered in estimating exposures to pyrethroids in aquatic systems. The SPME methodology could be used effectively to measure bioavailable concentration and to predict the actual ecotoxicologic effects of pyrethroids.     

Whole sediment toxicity identification evaluation tools for pyrethroid insecticides: III. Temperature manipulation

Since the toxicity of pyrethroid insecticides is known to increase at low temperatures, the use of temperature manipulation was explored as a whole-sediment toxicity identification evaluation (TIE) tool to help identify sediment samples in which pyrethroid insecticides are responsible for observed toxicity. The amphipod Hyalella azteca is commonly used for toxicity testing of sediments at a 23 degrees C test temperature. However, a temperature reduction to 18 degrees C doubled the toxicity of pyrethroids, and a further reduction to 13 degrees C tripled their toxicity. A similar response, though less dramatic, was found for 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), and dissimilar temperature responses were seen for cadmium and the insecticide chlorpyrifos. Tests with field-collected sediments containing pyrethroids and/or chlorpyrifos showed the expected thermal dependency in nearly all instances. The inverse relationship between temperature and toxicity provides a simple approach to help establish when pyrethroids are the principal toxicant in a sediment sample that could be used as a supplemental tool in concert with chemical analysis or other TIE manipulations. The phenomenon appears to be, in part, a consequence of a reduced ability to biotransform the toxic parent compound at cooler temperatures. The strong dependence of pyrethroid toxicity on temperature has important ramifications for predicting their environmental effects, and the standard test temperature of 23 degrees C dramatically underestimates risk to resident fauna during the cooler months.     

Role of piperonyl butoxide in the toxicity of chlorpyrifos to Ceriodaphnia dubia and Xenopus laevis

The use of chemical inhibitors/inducers is one of the strategies employed to determine whether a particular metabolic pathway is involved in the metabolism of a xenobiotic. The objective of this study was to assess the role of piperonyl butoxide (PBO) on the toxicity of an organophosphorus insecticide, chlorpyrifos (CPF) to two species, Ceriodaphnia dubia (waterflea) and Xenopus laevis (South African clawed frog). Chlorpyrifos was highly toxic to C. dubia (48-h LC50: 0.05 microg/L) in comparison with X. laevis (96-h LC50: 2410 microg/L). Piperonyl butoxide at 200 microg/L reduced the toxicity of chlorpyrifos to C. dubia by a factor of 6. Piperonyl butoxide at 3000 microg/L also reduced the toxicity of CPF to X. laevis with respect to mortality and malformations. Acetylcholinesterase (AChE) activity was used as a biomarker to further assess the role of PBO in chlorpyrifos toxicity. X. laevis exposed to CPF and PBO exhibited a biphasic response in terms of AChE activity with an initial increase in the AChE activity followed by a drastic decrease. The results from the present study indicate that C. dubia and X. laevis have the capability to metabolize chlorpyrifos via cytochromes P450 mediated reactions. The results also indicate that the use of the biomarker AChE is useful in determining metabolic processes of organophosphorus insecticides, which require metabolic activation.     

Effect of piperonyl butoxide on permethrin toxicity in the amphipod Hyalella azteca

Piperonyl butoxide (PBO) is a synergist of pyrethroid pesticides found in many products for structural pest control, mosquito control, and home and garden uses. Because both PBO and pyrethroid residues potentially co-occur in urban creeks, this study determined if environmental levels of PBO were capable of synergizing pyrethroids in the environment. Three types of toxicity tests were conducted with the amphipod Hyalella azteca to determine the minimum PBO concentration required to increase toxicity of the pyrethroid permethrin: Sediment was spiked with permethrin only; permethrin and overlying water spiked with PBO; and permethrin, PBO, and overlying water spiked with PBO. In tests with PBO added to both water and sediment, PBO concentrations of 2.3 microg/L in water and 12.5 microg/kg in sediment reduced the permethrin median lethal concentration (LC50) nearly 50% to 7.3 mg/kg organic carbon (OC). Higher concentrations of PBO increased permethrin toxicity up to sevenfold. In exposures with PBO in water alone, 11.3 microg/L was required to increase permethrin toxicity. Urban creek sediments from California and Tennessee, USA, had PBO concentrations in the low microg/kg range; only one water sample was above the detection limit of 0.05 microg/L. Wetlands in northern California also were sampled after application of pyrethrins and PBO for mosquito abatement. Sediment and water PBO concentrations within 12 h of abatement spraying peaked at 3.27 microg/kg and 0.08 microg/L, respectively. These results suggest that environmental PBO concentrations rarely, if ever, reach concentrations needed to increase pyrethroid toxicity to sensitive organisms, though available data on environmental levels are very limited, and additional data are needed to assess definitively the risk.     

Isomer selectivity in aquatic toxicity and biodegradation of bifenthrin and permethrin

Synthetic pyrethroids are widely used insecticides, and contamination of surface aquatic ecosystems by pyrethroid residues from runoff is of particular concern because of potential aquatic toxicity. Pyrethroids also are chiral compounds consisting of multiple stereoisomers. In the present study, we evaluated the diastereomer and enantiomer selectivity of cis-bifenthrin (cis-BF) and permethrin (PM) in their aquatic toxicity and biodegradation. The 1R-cis enantiomer was the only enantiomer in cis-BF showing toxicity against Ceriodaphnia dubia. Incubation with pesticide-degrading bacteria showed that the trans diastereomer of PM was selectively degraded over the cis diastereomer, whereas the 1S-cis enantiomer in cis-BF or cis-PM was preferentially degraded over the corresponding 1R-cis enantiomer. The enantioselectivity was significantly greater for cis-PM than for cis-BF and also varied among different strains of bacteria. Isomer selectivity may be a common phenomenon in both aquatic toxicity and biodegradation of pyrethroids, and this should be considered when assessing ecotoxicological risks of these compounds in sensitive ecosystems.     

Identifying the cause and source of sediment toxicity in an agriculture-influenced creek

Del Puerto Creek, an agriculturally influenced stream in northern California, USA, with a history of sediment toxicity, was used as a case study to determine the feasibility of using sediment toxicity testing and chemical analysis to identify the causative agent for the toxicity and its sources. Testing with the amphipod Hyalella azteca confirmed historical toxicity and identified a point along the creek at which there was an abrupt increase in sediment toxicity that persisted for at least 6 km downstream. Three recently developed whole sediment toxicity identification evaluation manipulations, temperature reduction, piperonyl butoxide addition, and esterase addition, were applied to sediment from one site and were suggestive of a pyrethroid as the cause for toxicity. Utilizing published median lethal concentration (LC50) values in a toxic unit analysis, the pyrethroid insecticide bifenthrin was identified as the primary contributor to toxicity in nearly all sites at which toxicity was observed, with occasional additional contributions from the pyrethroids lambda-cyhalothrin, esfenvalerate, and cyfluthrin. Most agricultural drains discharging to Del Puerto Creek contained bifenthrin in their sediments at concentrations near or above acutely toxic concentrations. However, only one drain contained sediments with bifenthrin concentrations approaching the concentrations measured in creek sediments. This fact, along with the proximity of that particular discharge to the location in the creek with the highest concentrations, suggested that one drain may be responsible for much of the toxicity and pyrethroid residues in creek sediments. The methods employed in this study are likely to be of considerable value in total maximum daily load efforts in Del Puerto Creek or other California surface water bodies known to have pyrethroid-related aquatic toxicity.     

Ecotoxicologic impacts of agricultural drain water in the Salinas River, California, USA

The Salinas River is the largest of the three rivers that drain into the Monterey Bay National Marine Sanctuary in central California (USA). Large areas of this watershed are cultivated year-round in row crops, and previous laboratory studies have demonstrated that acute toxicity of agricultural drain water to Ceriodaphnia dubia is caused by the organophosphate (OP) pesticides chlorpyrifos and diazinon. We investigated chemical contamination and toxicity in waters and sediments in the river downstream of an agricultural drain water input. Ecological impacts of drain water were investigated by using bioassessments of macroinvertebrate community structure. Toxicity identification evaluations were used to characterize chemicals responsible for toxicity. Salinas River water downstream of the agricultural drain was acutely toxic to the cladoceran Ceriodaphnia dubia, and toxicity to C. dubia was highly correlated with combined toxic units (TUs) of chlorpyrifos and diazinon. Laboratory tests were used to demonstrate that sediments in this system were acutely toxic to the amphipod Hyalella azteca, a resident invertebrate. Toxicity identification evaluations (TIEs) conducted on sediment pore water suggested that toxicity to amphipods was due in part to OP pesticides; concentrations of chlorpyrifos in pore water sometimes exceeded the 10-d mean lethal concentration (LC50) for H. azteca. Potentiation of toxicity with addition of the metabolic inhibitor piperonyl butoxide suggested that sediment toxicity also was due to other non-metabolically activated compounds. Macroinvertebrate community structure was highly impacted downstream of the agricultural drain input, and a number of macroinvertebrate community metrics were negatively correlated with combined TUs of chlorpyrifos and diazinon, as well as turbidity associated with the drain water. Some macroinvertebrate metrics were also correlated with bank vegetation cover. This study suggests that pesticide pollution is the likely cause of ecological damage in the Salinas River, and this factor may interact with other stressors associated with agricultural drain water to impact the macroinvertebrate community in the system.     

Evidence of pesticide impacts in the Santa Maria River watershed, California, USA

The Santa Maria River provides significant freshwater and coastal habitat in a semiarid region of central California, USA. We conducted a water and sediment quality assessment consisting of chemical analyses, toxicity tests, toxicity identification evaluations, and macroinvertebrate bioassessments of samples from six stations collected during four surveys conducted between July 2002 and May 2003. Santa Maria River water samples collected downstream of Orcutt Creek (Santa Maria, Santa Barbara County, CA, USA), which conveys agriculture drain water, were acutely toxic to cladocera (Ceriodaphnia dubia), as were samples from Orcutt Creek. Toxicity identification evaluations (TIEs) suggested that toxicity to C. dubia in Orcutt Creek and the Santa Maria River was due to chlorpyrifos. Sediments from these two stations also were acutely toxic to the amphipod Hyalella azteca, a resident invertebrate. The TIEs conducted on sediment suggested that toxicity to amphipods, in part, was due to organophosphate pesticides. Concentrations of chlorpyrifos in pore water sometimes exceeded the 10-d median lethal concentration for H. azteca. Additional TIE and chemical evidence suggested sediment toxicity also partly could be due to pyrethroid pesticides. Relative to an upstream reference station, macroinvertebrate community structure was impacted in Orcutt Creek and in the Santa Maria River downstream of the Creek input. This study suggests that pesticide pollution likely is the cause of ecological damage in the Santa Maria River.     

Use and toxicity of pyrethroid pesticides in the Central Valley, California, USA

The use of pyrethroid insecticides is increasing for agriculture, commercial pest control, and residential consumer use. In addition, there is a trend toward the use of newer and more potent compounds. Little is known about the toxicity of sediment-associated pyrethroid residues to aquatic organisms, yet recent work has shown they commonly are found in aquatic sediments in the heavily agricultural Central Valley of California, USA. Minimal data exist on the sensitivity of standard sediment toxicity testing species to pyrethroids, despite two or more decades of agricultural use of these compounds. Sediment concentrations causing acute toxicity and growth impairment to the amphipod Hyalella azteca were determined for six pyrethroids in three sediments, ranging from 1.1 to 6.5% organic carbon (OC). In order of decreasing toxicity of sediment-associated residues, the compounds tested were bifenthrin (average 10-d median lethal concentration [LC50] = 0.18 microg/g OC), lambda-cyhalothrin (0.45 microg/g OC), deltamethrin (0.79 microg/g OC), esfenvalerate (0.89 microg/g OC), cyfluthrin (1.08 microg/g OC), and permethrin (4.87 microg/g OC). In a sediment containing about 1% OC, most pyrethroids, except permethrin, would be acutely toxic to H. azteca at concentrations of 2 to 10 ng/g dry weight, a concentration only slightly above current analytical detection limits. Growth typically was inhibited at concentrations below the LC50; animal biomass on average was 38% below controls when exposed to pyrethroid concentrations roughly one-third to one-half the LC50. Survival data are consistent with current theory that exposure occurs primarily via the interstitial water rather than the particulate phase. A reanalysis of previously reported field data using these toxicity data confirms that the compounds are exceeding concentrations acutely toxic to sensitive species in many agriculture-dominated water bodies.     

Evaluating the risk to aquatic ecosystems posed by leachate from tire shred fill in roads using toxicity tests, toxicity identification evaluations, and groundwater modeling

The risk to adjacent aquatic systems posed by leachates from scrap tires used in engineering applications has not been characterized adequately. Toxicity testing, toxicity identification evaluation (TIE), and groundwater modeling were used to determine the circumstances under which tire shreds could be used as roadbed fill with negligible risk to aquatic organisms in adjacent water bodies. Elevated levels of iron, manganese, and several other chemicals were found in tire shred leachates. However, chronic toxicity tests with Ceriodaphnia dubia and fathead minnows (Pimephales promelas) showed no adverse effects caused by leachates collected from tire shreds installed above the water table. Exposure to leachates collected from tire shreds installed below the water table resulted in significant reductions to both survival and reproduction in C. dubia. The TIE results indicated that exposure to soluble metals (likely ferrous iron primarily) and the formation of iron hydroxide precipitates on this invertebrate species likely were the causes of the observed effects. The available chemistry data show that iron concentrations in the affected groundwater decreased substantially within a short distance (0.61 m) downgradient of tire shred fill. Based on geochemical modeling, the use of tire shreds in applications below the water table is appropriate in settings where dissolved oxygen is greater than 2.0 mg/L, pH is greater than 5.8, and a downgradient buffer of approximately 3.0 m exists between the fill and the surface water. For settings with lower dissolved oxygen concentrations or lower pH, results of groundwater modeling indicate that a greater buffer distance (approximately 11 m) is needed to dilute the leachate to nontoxic levels under various soil and groundwater conditions solely through advection and dispersion processes.     

Toxicity of Stormwater Runoff After Dormant Spray Application of Diazinon and Esfenvalerate (Asana®) in a French Prune Orchard,Glenn County,California, USA

Organophosphate pesticides (OPs), in particular diazinon and chlorpyrifos, have frequently been detected in toxic concentrations in waterways draining agricultural and urban areas in California’s Sacramento and San Joaquin River watersheds (US Geological Survey 1997, Werner et al. 2000). Toxicity has in part been linked to stormwater runoff of OP pesticides applied during the dormant season on stonefruit and almond orchards (Foe and Sheipline 1993; Kuivila and Foe 1995). State Water Quality Plans have now been implemented by regulatory agencies to prevent movement of OPs into surface water, and growers have reduced the application of OPs. Simultaneously, the use of so-called reduced-risk alternatives, such as pyrethroid insecticides and Bacillus thuringiensis bloom sprays, has increased dramatically (Epstein et al. 2000).

Best management practices (BMPs) are aimed at reducing off-site movement of pesticides into surface waters. Pyrethroid pesticides, among them the widely used esfenvalerate (Asana®) are considerably more hydrophobic (solubility in water: 0.4 μg/L) than the relatively soluble OP pesticide diazinon (solubility in water: 40,000 μg/L; Extoxnet 2001). Although runoff of pyrethroids is believed to be minimal thus reducing pesticide impact on surface waters, esfenvalerate has been shown to be toxic to fish at extremely low concentrations (≤ 1 ug/L; Haya 1989; Clark et al. 1989; Lozano et al. 1992), and potentially poses a significantly higher risk to these organisms than OP pesticides. In addition, its potential to bioaccumulate and bioconcentrate is high (Smith and Stratton 1986). A second recommended method for reducing toxic runoff from orchards is the use of different orchard floor cover crops. Cover crops are believed to enhance water infiltration (Hargrove 1991).

This study was performed to measure the effectiveness of these two BMPs in reducing the toxicity of Stormwater runoff. Experiments were carried out in a French prune orchard at the Talbot-Vereschagin Ranch, Glenn County, California.

     

Acetylcholinesterase inhibition in estuarine fish and invertebrates as an indicator of organophosphorus insecticide exposure and effects

The majority of insecticides currently in use are organophosphorus, carbamate, and synthetic pyrethroid compounds. Organophosphorus insecticides (OPs) produce toxicity by inhibiting the cholinesterase enzymes in the nervous system. Monitoring of acetylcholinesterase (AChE) inhibition has been widely used in terrestrial and freshwater aquatic systems as an indicator of OP exposure and effects. This review describes the use of AChE inhibition as a biomarker in the estuarine environment, discusses the relationship between AChE inhibition and other manifestations of OP toxicity, and highlights areas where additional research is needed. A variety of studies with estuarine fish have suggested that brain AChE inhibition levels of > 70% are associated with mortality in most species. Selected species, however, appear capable of tolerating much higher levels (> 90%) of brain inhibition. Sublethal effects on stamina have been reported for some estuarine fish in association with brain AChE inhibition levels as low as 50%. Most studies suggest, however, that these effects are observed only when brain AChE inhibition is at near-lethal levels. A number of field studies have successfully used AChE inhibition in fish as a biomarker in the estuarine environment. The use of AChE inhibition as a biomarker in estuarine invertebrates has been less well studied. Although AChE inhibition has been measured in the tissues of a variety of invertebrate species following OP exposure, the relationship between AChE inhibition and lethality is less distinct. Additional work is needed in both fish and invertebrates to better explain species-specific differences in the relationship between AChE inhibition and mortality and to investigate other physiological perturbations associated with AChE inhibition.     

Toxicity of storm-water runoff after dormant spray application in a french prune orchard, Glenn County, California, USA: temporal patterns and the effect of ground covers

Organophosphorous (OP) insecticides, especially diazinon, have been detected routinely in surface waters of the Sacramento and San Joaquin River watersheds, coincident with rainfall events following their application to dormant orchards during the winter months. Preventive best management practices (BMP) aim at reducing off-site movement of pesticides into surface waters. Two proposed BMPs are: The use of more hydrophobic pyrethroid insecticides believed to adsorb strongly to organic matter and soil and the use of various types of ground cover vegetation to increase the soil's capacity for water infiltration. To measure the effectiveness of these BMPs, storm water runoff was collected in a California prune orchard (Glenn County, CA, USA) during several rainstorms in the winter of 2001, after the organophosphate diazinon and the pyrethroid esfenvalerate were applied to different orchard sections. We tested and compared acute toxicity of orchard runoff from diazinon- and esfenvalerate-sprayed sections to two species of fish (Pimephales promelas, Onchorhynchus mykiss) and three aquatic invertebrates (Ceriodaphnia dubia, Simocephalus vetelus, Chironomus riparius), and determined the mitigating effect of three ground cover crops on toxicity and insecticide loading in diazinon-sprayed orchard rows. Runoff from the esfenvalerate-sprayed orchard section was less toxic to waterflea than runoff from the diazinon-sprayed section. However, runoff from the orchard section sprayed with esfenvalerate was highly toxic to fish larvae. Samples collected from both sections one month later were not toxic to fish, but remained highly toxic to invertebrates. The ground cover crops reduced total pesticide loading in runoff by approximately 50%. No differences were found between the types of vegetation used as ground covers.     

Solid-phase sediment toxicity identification evaluation in an agricultural stream

The lower Santa Maria River watershed provides important aquatic habitat on the central California coast and is influenced heavily by agricultural runoff. As part of a recently completed water quality assessment, we conducted a series of water column and sediment toxicity tests throughout this watershed. Sediment from Orcutt Creek, a tributary that drains agricultural land, consistently was toxic to the amphipod Hyalella azteca, which is a resident genus in this river. Toxicity identification evaluations (TIEs) were conducted to determine cause(s) of toxicity. We observed no toxicity in sediment interstitial water even though concentrations of chlorpyrifos exceeded published aqueous toxicity thresholds for H. azteca. In contrast to interstitial water, bulk sediment was toxic to H. azteca. In bulk-phase sediment TIEs, the addition of 20% (by volume) coconut charcoal increased survival by 41%, implicating organic chemical(s). Addition of 5% (by volume) of the carbonaceous resin Ambersorb 563 increased survival by 88%, again suggesting toxicity due to organic chemicals. Toxicity was confirmed by isolating Ambersorb from the sediment, eluting the resin with methanol, and observing significant toxicity in control water spiked with the methanol eluate. A carboxylesterase enzyme that hydrolyzes synthetic pyrethroids was added to overlying water, and this significantly reduced toxicity to amphipods. Although the pesticides chlorpyrifos, DDT, permethrin, esfenvalerate, and fenvalerate were detected in this sediment, and their concentrations were below published toxicity thresholds for H. azteca, additivity or synergism may have occurred. The weight-of-evidence suggests toxicity of this sediment was caused by an organic contaminant, most likely a synthetic pyrethroid.     

Probabilistic risk assessment of cotton pyrethroids: I. Distributional analyses of laboratory aquatic toxicity data

This is the first in a series of five papers that assess the risk of the cotton pyrethroids in aquatic ecosystems in a series of steps ranging from the analysis of effects data through modeling exposures in the landscape. Pyrethroid insecticides used on cotton have the potential to contaminate aquatic systems. The objectives of this study were to develop probabilistic estimates of toxicity distributions, to compare these among the pyrethroids, and to evaluate cypermethrin as a representative pyrethroid for the purposes of a class risk assessment of the pyrethroids. The distribution of cypermethrin acute toxicity data gave 10th centile values of 10 ng/L for all organisms, 6.4 ng/L for arthropods, and 380 ng/L for vertebrates. For bifenthrin, cyfluthrin, lambda-cyhalothrin, and deltamethrin, the 10th centile values for all organisms were 15, 12, 10, and 9 ng/L, respectively, indicating similar or somewhat lower toxicity than cypermethrin. For tralomethrin and fenpropathrin, the 10th centiles were <310 and 240 ng/L, respectively. The distribution of permethrin toxicity to all organisms, arthropods, and vertebrates gave 10th centiles of 180, 76, and 1600 ng/L, respectively, whereas those for fenvalerate were 37, 8, and 150 ng/L. With the exception of tralomethrin, the distributions of acute toxicity values had similar slopes, suggesting that the variation of sensitivity in a range of aquatic nontarget species is similar. The pyrethroids have different recommended field rates of application that are related to their efficacy, and the relationship between field rate and 10th centiles showed a trend. These results support the use of cypermethrin as a reasonable worst-case surrogate for the other pyrethroids for the purposes of risk assessment of pyrethroids as a class.     

Identifying the causes of oil sands coke leachate toxicity to aquatic invertebrates

A previous study found that coke leachates (CL) collected from oil sands field sites were acutely toxic to Ceriodaphnia dubia; however, the cause of toxicity was not known. Therefore, the purpose of this study was to generate CL in the laboratory to evaluate the toxicity response of C. dubia and perform chronic toxicity identification evaluation (TIE) tests to identify the causes of CL toxicity. Coke was subjected to a 15-d batch leaching process at pH 5.5 and 9.5. Leachates were filtered on day 15 and used for chemical and toxicological characterization. The 7-d median lethal concentration (LC50) was 6.3 and 28.7% (v/v) for pH 5.5 and 9.5 CLs, respectively. Trace element characterization of the CLs showed Ni and V levels to be well above their respective 7-d LC50s for C. dubia. Addition of ethylenediaminetetraacetic acid significantly (p?≤?0.05) improved survival and reproduction in pH 5.5 CL, but not in pH 9.5 CL. Cationic and anionic resins removed toxicity of pH 5.5 CL only. Conversely, the toxicity of pH 9.5 CL was completely removed with an anion resin alone, suggesting that the pH 9.5 CL contained metals that formed oxyanions. Toxicity reappeared when Ni and V were added back to anion resin-treated CLs. The TIE results combined with the trace element chemistry suggest that both Ni and V are the cause of toxicity in pH 5.5 CL, whereas V appears to be the primary cause of toxicity in pH 9.5 CL. Environmental monitoring and risk assessments should therefore focus on the fate and toxicity of metals, especially Ni and V, in coke-amended oil sands reclamation landscapes.     

农药混剂联合毒性评价

用Ｈａｒｒｉｓ法研究了３类杀虫剂（有机磷,拟除虫菊酯和氨基甲酸酯）的二元混剂对大鼠的急性毒性联合作用,涉及的有机磷类农药有：甲基对硫磷,乐果,甲胺磷,辛硫磷,敌敌畏,丙溴磷,马拉硫磷,水胺硫磷;拟除虫菊酯类农药有：高效氯氰菊酯,氰戊菊酯,甲氰菊酯,溴氧菊酯：氨基甲酸酯类农药有：灭多威,异丙威,速灭威等。