Development of toxicity identification evaluation procedures for pyrethroid detection using esterase activity

Recent agrochemical usage patterns suggest that the use of organophosphate (OP) pesticides will decrease, resulting in a concomitant increase in pyrethroid usage. Pyrethroids are known for their potential toxicity to aquatic invertebrates and many fish species. Current toxicity identification evaluation (TIE) techniques are able to detect OPs, but have not been optimized for pyrethroids. Organophosphate identification methods depend upon the use of piperonyl butoxide (PBO) to identify OP-induced toxicity. However, the use of PBO in TIE assays will be confounded by the co-occurrence of OPs and pyrethroids in receiving waters. It is necessary, therefore, to develop new TIE procedures for pyrethroids. This study evaluated the use of a pyrethroid-specific antibody, PBO, and carboxylesterase activity to identify pyrethroid toxicity in aquatic toxicity testing with Ceriodaphnia dubia. The antibody caused significant mortality to the C. dubia. Piperonyl butoxide synergized pyrethroid-associated toxicity, but this effect may be difficult to interpret in the presence of OPs and pyrethroids. Carboxylesterase activity removed pyrethroid-associated toxicity in a dose-dependent manner and did not compromise OP toxicity, suggesting that carboxylesterase treatment will not interfere with TIE OP detection methods. These results indicate that the addition of carboxylesterase to TIE procedures can be used to detect pyrethroids in aquatic samples.     

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.     

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.     

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.     

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.     

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.     

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.     

Causes of Sediment Toxicity to <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> in San Francisco Bay,California

Since the San Francisco Regional Monitoring Program (RMP) sampling began, elutriate samples prepared with sediment from the Grizzly Bay monitoring station have been consistently toxic to bivalve larvae (Mytilus galloprovincialis). An investigation into the cause of toxicity was initiated with a Phase I Toxicity Identification Evaluation (TIE) using bivalve embryos. TIE results and chemical analyses of elutriate samples suggested that divalent metals were responsible for the observed toxicity. Following the initial characterization of trace metals as toxicants, additional TIEs were performed on elutriates prepared from three additional Grizzly Bay samples collected between 1997 and 2001. Additional TIEs included ethylenediamine tetraacetic acid (EDTA) treatments in a sediment-water interface (SWI) exposure system, and the use of a cation exchange column with serial elution of sample fractions with hydrochloric acid of increasing normality. EDTA significantly reduced toxicity in overlying water in the SWI system. The cation exchange column reduced both toxicity and concentrations of trace metals, and serial elution of the column added back both toxicity and specific metals contained in individual acid fractions. Chemical analyses of three elutriate samples demonstrated copper concentrations were within the range toxic to bivalves. Results of Phase I TIEs, additional Phase II treatments, SWI exposures, and metals analyses indicate the potential for metal toxicity in sediments from this estuarine site. When combined with the results of standard TIE methods, a solid-phase cation extraction and elution approach identified copper as the most probable cause of toxicity.     

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.     

Effect of aging on desorption kinetics of sediment-associated pyrethroids

Pyrethroids are insecticides commonly used in both agricultural and urban environments. Residues of pyrethroids frequently are found in bed sediments of regions such as California (USA), and as such, sediment toxicity from pyrethroid contamination is an emerging concern. Pyrethroids are highly hydrophobic, and toxicity from sediment-borne pyrethroids is expected to depend closely on their desorption rate. In the present study, we evaluated the effect of aging on desorption kinetics of sediment-borne pyrethroids. Two sediments spiked with four pyrethroids were incubated for 7, 40, 100, and 200 d at room temperature. Desorption measured using sequential Tenax extractions was well described by a three-compartment model. The estimated rapid desorption fraction (F(rapid)) decreased quickly over time and was accompanied by an increase of the very slow desorption fraction. The aging effect on desorption kinetics followed a first-order model, with half-lives for the decrease in F(rapid) for all four pyrethroids in both sediments ranging from two to three months. When coupled with degradation, the estimated half-lives of the rapidly desorbing fraction (and, thus, the potentially bioavailable concentration) were two months or less for all four pyrethroids. Two field-contaminated sediments displayed distinctively different desorption kinetics. The sediment with fresh residues exhibited rapid desorption, and the sediment containing aged residues was highly resistant to desorption. The observation that desorption of pyrethroids decreased quickly over contact time implies that the bioavailability of sediment-borne pyrethroids may diminish over time and that use of nonselective extraction methods may lead to overestimating the actual sediment toxicity from pyrethroid contamination.     

The behavior and identification of toxic metals in complex mixtures: Examples from effluent and sediment pore water toxicity identification evaluations

Toxicity caused by heavy metals in environmental samples can be assessed by performing a suite of toxicity identification evaluation (TIE) methods. The behavior of metals during TIEs can vary greatly according to sample matrix. Some approaches and precautions in using TIE to identify metal toxicants in a sample are discussed, using case studies from three effluent and one sediment TIEs. These approaches include responses of metals that erroneously suggest the presence of other toxicants, the bioavailability of metals retained by glass-fiber filtration, and cautionary steps in Phase III to avoid dilution water effects on sample toxicity.Mention of trade names does not constitute endorsement by the U.S. Environmental Protection Agency.     

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.     

Marine sediment toxicity identification evaluation methods for the anionic metals arsenic and chromium

Marine sediments accumulate a variety of contaminants and, in some cases, demonstrate toxicity because of this contamination. Toxicity identification evaluation (TIE) methods provide tools for identifying the toxic chemicals causing sediment toxicity. Currently, whole-sediment TIE methods are not available for anionic metals like arsenic and chromium. In the present paper, we describe two new anion-exchange resins used in the development of whole-sediment TIE methods for arsenic and chromium. Resins were shown to reduce whole-sediment toxicity and overlying water concentrations of the anionic metals. Sediment toxicity, expressed as the median lethal concentration, was reduced by a factor of two to a factor of nearly six between amended sediment treatments containing resin and those without resin. Aqueous concentrations of arsenic and chromium in the toxicity exposures decreased to less than the detection limits or to concentrations much lower than those measured in treatments without resin. Interference studies indicated that the anion-exchange resins had no significant effect on concentrations of the representative pesticide endosulfan and minimal effects on concentrations of ammonia. However, the anion-exchange resins did significantly reduce the concentrations of a selection of cationic metals (Cd, Cu, Ni, Pb, and Zn). These data demonstrate the utility of anion-exchange resins for determining the contribution of arsenic and chromium to whole-sediment toxicity. The present results also indicate the importance of using TIE methods in a formal TIE structure to ensure that results are not misinterpreted. These methods should be useful in the performance of marine whole-sediment TIEs.     

Whole-sediment toxicity identification evaluation tools for pyrethroid insecticides: II. Esterase addition

An esterase enzyme capable of catalyzing the hydrolysis of the ester bond common to all pyrethroid insecticides has been proposed as a toxicity identification evaluation procedure for the compounds when present in water samples. It appeared to show promise in previous applications to pore water and in one published application to bulk sediment. The present study was designed to provide the additional validation of the technique when applied to whole sediment, demonstrating its efficacy and specificity to pyrethroids. When added to the overlying water in a standard sediment toxicity test with the amphipod Hyalella azteca, the enzyme reduced toxicity of pyrethroid-spiked laboratory sediments. The technique had no effect on toxicity of DDT or chlorpyrifos, but it dramatically reduced the toxicity of cadmium, presumably by complexation of the cadmium with dissolved organic matter rather than by enzymatic activity. Esterase addition consistently reduced pyrethroid-related toxicity in 12 tests with field-collected sediments. The procedure, however, also results in substantial changes in water quality, provides an undesirable nutritional benefit to the test organisms exposed to the esterase, and achieves a substantial fraction of the protective capability simply by complexation of the pyrethroids with the esterase or the microbial growth that the esterase promotes. The esterase addition technique has potential for whole-sediment application, but further development of procedures and confirmation by independent lines of evidence are needed to reduce the potential for misinterpretation of results.     

Assessment of supercritical fluid extraction use in whole sediment toxicity identification evaluations

Supercritical fluid extraction (SFE) with pure CO(2) was assessed as a confirmatory tool in phase III of whole sediment toxicity identification evaluations (TIEs). The SFE procedure was assessed on two reference sediments and three contaminated sediments by using a combination of toxicological and chemical measurements to quantify effectiveness. Sediment toxicity pre- and post-SFE treatment was quantified with a marine amphipod (Ampelisca abdita) and mysid (Americamysis bahia), and nonionic organic contaminants (NOCs) polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were measured in sediments, overlying waters, and interstitial waters. In general, use of SFE with the reference sediments was successful, with survival averaging 91% in post-SFE treatments. Substantial toxicity reductions and contaminant removal from sediments and water samples generated from extracted sediments of up to 99% in two of the contaminated sediments demonstrated SFE effectiveness. Furthermore, toxicological responses for these SFE-treated sediments showed comparable results to those from the same sediments treated with the powdered coconut charcoal addition manipulation. These data demonstrated the utility of SFE in phase III of a whole sediment TIE. Conversely, in one of the contaminated sediments, the SFE treatments had no effect on sediment toxicity, whereas sediment concentrations of PCBs and PAHs were reduced. We propose that, for some sediments, the SFE treatment may result in the release of otherwise nonbioavailable cationic metals that subsequently cause toxicity to test organisms. Overall, SFE treatment was found to be effective for reducing the toxicity and concentrations of NOCs in some contaminated sediments. However, these studies suggest that SFE treatment may enhance toxicity with some sediments, indicating that care must be taken when applying SFE and interpreting the results.     

Chemical availability and sediment toxicity of pyrethroid insecticides to Hyalella azteca: application to field sediment with unexpectedly low toxicity

Tenax extraction is a simple, inexpensive approach to estimate the bioavailability of hydrophobic organic contaminants from sediment. In the present study, a single-point Tenax extraction was evaluated regarding its correlation with the acute toxicity to Hyalella azteca using field-collected sediments in California, USA. Pyrethroids were believed to be the primary contributor to the observed toxicity, and a significant correlation existed between the expected toxicity (given pyrethroid concentrations) and the mortality at most sampling sites. A small subset of sites, however, showed unexpectedly low toxicity to H. azteca despite high concentrations of pyrethroids. These samples were evaluated by Tenax extraction with the expectation that this procedure, which qualifies bioavailable instead of total pyrethroid concentration in sediment, would better explain the anomalously low toxicity. The term bioavailable toxic unit was proposed to link sediment toxicity with chemical availability, and the toxicity in the 17 selected sediments was better explained using Tenax extraction. The r2 value of the regression between sediment toxicity and toxic unit for the 17 sediments increased from 0.24 to 0.60 when the Tenax-extractable concentration was used in place of the total concentration. Results also showed that adsorption to sand particles might play a controlling role in pyrethroid bioavailability and, in turn, sediment toxicity to benthic invertebrates.     

Analysis of pyrethroids in sediment pore water by solid-phase microextraction

Sediment toxicity from trace contamination of pyrethroid insecticides is an emerging water quality concern. Pyrethroids are highly hydrophobic, and their sediment toxicity is related to the freely dissolved concentration in pore water. Solid-phase microextraction (SPME) was evaluated as a selective method to analyze free concentrations of eight pyrethroids in sediment pore water, and SPME measurements were compared to total pore-water concentrations measured using a conventional liquid-liquid extraction (LLE) method. Free pore-water concentrations detected by SPME (C(w-SPME)) were 4.1 to 37% of the total concentration given by LLE (C(w-LLE)) in pore water prepared from a freshwater sediment and only 3.2 to 13.3% in the pore water of a marine sediment. The difference suggested predominant partitioning of pyrethroids into the dissolved organic matter phase in pore water. The method detection limits of the SPME method were lower than the 10th percentile of the reported median lethal concentrations for aquatic organisms, with relative standard deviation <20% as determined over 200 analyses. The SPME method was further used to analyze field-contaminated sediment samples. Those analyses showed that the phase distribution of pyrethroids in sediment was influenced by sediment type and other conditions. Our results show that SPME provides a sensitive, reproducible, and practical method for screening sediment toxicity from potential pyrethroid contamination.     

Measuring pyrethroids in sediment pore water using matrix-solid phase microextraction

Pyrethroids are hydrophobic insecticides commonly used in both agricultural and urban environments. Their high toxicity to aquatic organisms, including benthic invertebrates, and detection in the sediment at many locations in California, U.S.A., have spawned interest in understanding their bioavailability in bed sediments. A recent study showed good correlation between uptake of 14C-permethrin in Chironomus tentans and solid-phase microextraction (SPME) fibers in sediments. The present study was directed at the development of an SPME technique applicable to trace levels of nonlabeled pyrethroids in sediment. Disposable polydimethylsiloxane fibers were used to detect freely dissolved pore-water concentrations of bifenthrin, fenpropathrin, cis-permethrin, trans-permethrin, cyfluthrin, cypermethrin, and esfenvalerate under agitated and static conditions. Partition equilibrium between fiber and sediment was reached in <5 d when the samples were agitated on a shaker at low speed, while much longer times (>23 d) were needed without agitation. Polydimethylsiloxane to water partition ratios (K(PDMS)) of the seven pyrethroids were measured separately and ranged from 2.83 x 10(5) to 1.89 x 10(6). When applied to field-contaminated sediments, agitated matrix-SPME was able to detect pore-water concentrations as low as 0.1 ng/L. The method developed in the present study may be coupled with bioassays to gain mechanistic understanding of factors affecting pyrethroid toxicities, and applied to field samples to better predict sediment toxicities from pyrethroid contamination.     

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.     

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.