Methodological and Environmental Impacts on Bioaccessibility Estimates Provided by Single-Point Tenax Extractions.

Single-point Tenax extractions (SPTEs) of hydrophobic organic contaminants provide estimates of bioaccessibility through consistent measures of the chemical concentration initially in the rapidly desorbing fraction in sediment (C rapT0), such that a constant ratio is expected between SPTE and C rapT0 (C T /C rapT0, where T is the duration of the SPTE). As environmental factors (i.e., aging time and organic carbon content) and contaminant hydrophobicity can affect the C rapT0, the utility of the SPTEs as exposure estimates hinges on the consistency of the C T /C rapT0 ratio. Individually these factors have little impact on the ability of SPTEs to represent bioaccumulation, but the effect of these factors in combination, as well as SPTE methodological variation on the C T /C rapT0 ratio is poorly understood. The current study evaluated how environmental and methodological variation-expressed as varying Tenax to organic carbon mass (Tenax:OC) ratios-impacts the C 24h/C rapT0 ratio of pyrethroids in laboratory-spiked sediments. A multiple regression analysis was used to examine the impact of organic carbon, pyrethroid hydrophobicity, Tenax mass, and aging time on the C 24h/C rapT0 ratio. Only aging time of the pyrethroids in sediment significantly affected the C 24h/C rapT0 ratio with a slight decline of -0.0027/d in the C 24h/C rapT0 ratio, and this decline was considered negligible as a consistent C 24h/C rapT0 ratio of 1.46 ± 0.03 was observed across all experimental treatments. This result further demonstrates the consistency of SPTEs to estimate bioaccessibility of hydrophobic contaminants in sediment and subsequent exposure.

Bioaccumulation of highly hydrophobic organohalogen flame retardants from sediments: application of toxicokinetics and passive sampling techniques.

Highly hydrophobic organohalogen flame retardants (HHOFRs) are found ubiquitously in the environment; therefore, a better understanding of their bioavailability is needed. In the current study, bioaccumulation testing using the oligochaete, Lumbriculus variegatus, and passive sampling (solid-phase microextraction (SPME)) were performed to study the bioaccumulation potential of HHOFRs, including decabromodiphenyl ether (deca-BDE), decabromodiphenyl ethane (DBDPE), and dechlorane plus (DP), in laboratory-spiked and field-collected sediments. The HHOFRs were bioavailable to L. variegatus even though their biota-sediment accumulation factors were low (0.016 ± 0.002 to 0.48 ± 0.082 g organic carbon/g lipid, syn-DP > anti-DP > deca-BDE > DBDPE). Hydrophobicity and stereoisomerism affected HHOFR bioavailability. Meanwhile, HHOFR concentrations on the SPME fibers (Cf) correlated with those in biota (Cb), suggesting the potential application of SPME in bioavailability prediction for those compounds. The log Cf to log Cb correlation for deca-BDE and DP had a greater intercept than that for polychlorinated biphenyls (data obtained from the literature) although the slopes were similar, while data for DBDPE fell on the regression line for PCBs, implying some uncertainty in application of SPMEs across chemical classes. The increasing sorptive ability of proteins for HHOFRs in comparison to the less-brominated BDEs suggested that protein-binding should be considered when estimating bioaccumulation potential of HHOFRs in benthic invertebrates.

Can SPME fiber and Tenax methods predict the bioavailability of biotransformed insecticides?

Recent studies recognize the ability of chemical techniques such as solid phase microextraction (SPME) fibers and Tenax extraction to predict bioavailability more effectively than exhaustive chemical extractions for sediment-associated organic contaminants. While the majority of research using these techniques studied legacy compounds such as PCBs and PAHs, there is great potential for these methods to work well for highly toxic, rapidly biotransformed compounds such as pyrethroid insecticides. The current study compared the ability of the two techniques to predict the bioavailability of permethrin and bifenthrin to two benthic invertebrates (Lumbriculus variegatus and Hexagenia sp.). In addition, variations in the application of the two techniques, specifically duration and conditions of exposure of the SPME fibers and duration of extraction with Tenax, were explored. The SPME fiber concentrations correlated strongly to both 6 and 24 h Tenax concentrations. The SPME fiber concentrations and 6 h and 24 h Tenax extractable concentrations correlated with both the parent permethrin and bifenthrin concentrations in the tissues of both species at steady state. Parent compound tissue concentrations for both species could be predicted with a single relationship for individual pyrethroids. This demonstrated the potential value of these methods to predict the bioavailability of compounds subject to biotransformation and application to multiple species.

Bioavailability of hydrophobic organic contaminants in sediment with different particle-size distributions.

Few studies have been conducted examining the distribution of different-sized particles in sediment and its potential impact on bioavailability of sediment-associated contaminants. In the current study, three sediments composed of different particle sizes, i.e., fine (0-180 µm), combined (0-500 µm), and coarse (180-500 µm), were used to evaluate the bioaccumulation potential and toxicokinetic rates of four hydrophobic organic contaminants (HOCs) including two polychlorinated biphenyls (PCB-101 and PCB-118), a metabolite of an organochlorine insecticide (p,p'-DDE), and a polybrominated diphenyl ether (BDE-47) to the benthic oligochaete Lumbriculus variegatus. Two chemical approaches, Tenax extraction and matrix-solid phase microextraction (SPME), were also used to measure bioavailability of the sediment-associated HOCs. The uptake and elimination rates of HOCs by L. variegatus from coarse sediment were greater than those from fine sediment, although the biota-sediment accumulation factors (BSAFs) were not significantly different among sediments with different particle sizes. The freely dissolved HOC concentrations measured by matrix-SPME were greater in coarse sediment, however, no difference was found in uptake and desorption rates for the matrix-SPME and Tenax extraction measurements. Although BSAFs in L. variegatus were the same among sediments, kinetic rates of HOCs for organisms and freely dissolved HOC concentrations were lower in fine sediment, suggesting that sediment ingestion may also play a role in organism uptake, especially for HOCs in fine sediment.

Toxicity of anionic polyacrylamide formulations when used for erosion control in agriculture.

Addition of anionic polyacrylamide (PAM) to agricultural irrigation water can dramatically reduce erosion of soils. However, the toxicity of PAM to aquatic life, while often claimed to be low, has not been thoroughly evaluated. Five PAM formulations, including two oil-based products, one water-based product, one granular product and one tablet product, were evaluated for acute and/or chronic toxicity to five species commonly used for freshwater toxicity testing [Hyalella azteca (Saussure), Chironomus dilutus (Shobanov et al.), Ceriodaphnia dubia (Richard), Pimephales promelas (Rafinesque), and Selenastrum capricornutum (Printz)]. When applied as an oil-based product, acute toxicity was seen to four of the five species at concentrations less than the 10 mg/L that is often used for erosion control. Toxicity was diminished, but still remained, after passage of the irrigation water across an agricultural field, indicating a potential impact to nearby surface waters. Results from the non-oil-based products indicated minimal toxicity associated with PAM even at concentrations 10 times those used in agriculture when applied in the granular form, as a tablet, or in a water-based liquid. These data suggest that other agents in the oil-based products, such as surfactants or emulsifiers, rather than the PAM itself, contribute to the toxicity. Care is required in selecting an appropriate PAM formulation when the potential exists for entry of tailwater to nearby surface waters.

Can Tenax Extraction Be Used as a Surrogate Exposure Metric for Laboratory-Based Bioaccumulation Tests Using Marine Sediments?

The Tenax technique was used as an alternative exposure metric to assess the bioavailability of polychlorinated biphenyls (PCBs) from contaminated marine sediments. The sediments used were collected from 2 Superfund sites, New Bedford Harbor (MA, USA) and Gould Island (RI, USA). No sieving was conducted for either sediment after arrival, and sediments were stored in stainless steel drums at 2.8 to 4.0 °C in the dark until use. Exhaustive chemical extractions, single-point 24-h Tenax extractions, and 14-d bioaccumulation tests using the amphipod Leptocheirus plumulosus were conducted for both sediments. The sum of 119 PCB congeners from total exhaustive chemical extraction in the New Bedford Harbor and Gould Island sediments were 1084 and 188.2 µg/g organic carbon, respectively. The PCB concentrations from the bioaccumulation tests and Tenax extractions showed that both exposure metrics followed a similar trend in amount and distribution of PCB congeners. The results from both exposure metrics were fit into a log-log linear regression, and then compared with a previously developed log-log linear model for freshwater organisms. The results showed that although the marine data fell within the prediction intervals of the freshwater linear model, the marine regression followed a lower trajectory due to the differences in both the slopes and intercepts between the marine and freshwater regressions. The present study showed a strong relationship between Tenax and marine invertebrate PCB concentrations. Environ Toxicol Chem 2019;38:1188-1197. © 2019 SETAC.

Survey of bioaccessible pyrethroid insecticides and sediment toxicity in urban streams of the northeast United States.

Pyrethroids are a class of widely-used insecticides that can be transported from terrestrial applications to aquatic systems via runoff and tend to sorb to organic carbon in sediments. Pyrethroid occurrence is detrimental to stream ecosystems due to toxicity to sediment-dwelling invertebrates which are particularly at risk of pyrethroid exposure in urban streams. In this work, 49 streams located in watersheds in the northeastern United States were surveyed for nine current-use pyrethroids using two extraction methods. Total sediment concentrations were determined by exhaustive chemical extraction, while bioaccessible concentrations were determined by single-point Tenax extraction. Total and bioaccessible pyrethroid concentrations were detected in 76% and 67% of the sites, and the average sum of pyrethroids was 232 ng/g organic carbon (OC) for total and 43.8 ng/g OC for bioaccessible pyrethroids. Bifenthrin was the most commonly detected pyrethroid in streambed sediments. Sediment toxicity was assessed using 10-d Hyalella azteca bioassays, and 28% and 15% of sediments caused a decrease in H. azteca biomass and survival, respectively. A temperature-based focused toxicity identification evaluation was used to assess pyrethroids as the causal factor for toxicity. The concentrations of pyrethroids was only weakly correlated with the degree of urban land use. Sediment toxicity was predicted by total and bioaccessible pyrethroid concentrations expressed as toxic units. This work suggests that bioaccessibility-based methods, such as Tenax extraction, can be a valuable tool in assessing sediment toxicity.

Effects of type and quantity of organic carbon on the bioaccessibility of polychlorinated biphenyls in contaminated sediments.

Organic carbon principally controls sorption and desorption of hydrophobic organic compounds in sediments. We investigated the effects of organic carbon type and quantity on compound bioaccessibility. The desorption of 21 polychlorinated biphenyl (PCB) congeners was determined in spiked sediments amended with black carbon, humic acid, and sawdust at either 3 or 6% organic carbon. Desorption parameters were determined using Tenax sequential extractions and then modeled as operationally defined rapid, slow, and very slow fractions and rate constants. The effects of the amendments on PCB bioaccumulation were also evaluated using Lumbriculus variegatus. The lowest and highest PCB bioaccessibilities were observed in the black carbon and sawdust amendments, respectively. The total amount of PCBs desorbed ranged from 3 to 27% for the black carbon amendments, 12 to 55% for humic acid amendments, 16 to 80% for sawdust amendments, and 35 to 89% for controls. The results also showed that desorption of PCBs was slower in 6% amendments than 3% amendments, and this finding was most evident in humic acid and black carbon amendments. Overall, the trend in PCB bioaccumulation was similar to what was found for compound desorption in that the highest PCB bioaccumulation was observed in controls and sawdust amendments, whereas humic acid and black carbon amendments showed lower bioaccumulation. Finally, the 24-h single-point Tenax and bioaccumulation data were fit to a Tenax regression model. The PCB bioaccumulation was effectively predicted by the model, with 80% of the data falling within the 95% confidence intervals. Environ Toxicol Chem 2018;37:1280-1290. © 2018 SETAC.

Effect of sample holding time on bioaccessibility and sediment ecotoxicological assessments.

The ecotoxicological effects of hydrophobic organic compound (HOC) contamination in sediment are often assessed using laboratory exposures of cultured invertebrates to field-collected sediment. The use of a sediment holding time (storage at 4 °C) between field sampling and the beginning of the bioassay is common practice, yet the effect of holding time on the reliability of bioassay results is largely unknown, especially for current-use HOCs, such as pyrethroid insecticides. Single-point Tenax extraction can be used to estimate HOC concentrations in the rapidly desorbing phase of the organic carbon fraction of sediment (i.e., bioaccessible concentrations), which relate to sediment toxicity and bioaccumulation in invertebrates. In this study, repeated measurements of bioaccessible concentrations (via Tenax), were made as a function of sediment holding time using pyrethroid-contaminated field sediment, and Hyalella azteca 10-d survival and growth was measured concurrently for comparison. Similarly, bioaccessible concentrations and 14-d bioaccumulation were measured in Lumbriculus variegatus as a comparison using the legacy HOCs, polychlorinated biphenyls (PCBs). While the bioaccessible and bioaccumulated PCB concentrations did not change significantly through 244 d of holding time, the bioaccessible pyrethroid concentrations were more varied. Depending on when pyrethroid-contaminated sediments were sampled, the bioaccessible pyrethroid concentrations showed first-order loss with half-lives ranging from 3 to 45 d of holding, or slower, linear decreases in concentrations up to 14% decrease over 180 d. These findings suggest that at least for some contaminants in sediments, holding the sediments prior to bioassays can bias toxicity estimates.

The robustness of single-point Tenax extractions of pyrethroids: Effects of the Tenax to organic carbon mass ratio on exposure estimates.

Use of Tenax extractable concentrations to estimate biological exposure to hydrophobic organic contaminants is well documented, yet method variation exists between studies, specifically in the ratio of Tenax mass to organic carbon mass in the sediment (Tenax:OC ratio) being extracted. The effects of this variation on exposure estimates are not well understood. As Tenax is theoretically in direct competition with organic carbon for freely dissolved chemical in sediment interstitial water, varying the Tenax:OC ratio could impact single-point Tenax extraction (SPTE) exposure estimates. Therefore, the effects of varying Tenax:OC ratios on SPTE pyrethroid concentrations from field-contaminated and laboratory-spiked sediments were compared to bioaccumulation by Lumbriculus variegatus. The Tenax:OC ratio had minimal effect on SPTE pyrethroid concentrations. The SPTE pyrethroid concentrations obtained using the highest and lowest Tenax:OC ratios ranged from 0.85- to 3.91-fold different, which is unlikely to contribute substantial error to bioaccessibility estimates. Comparisons to Tenax exposure endpoints from previous research reveal the variation in these endpoints is likely due to toxicokinetic and toxicodynamic differences; processes common to exposure estimates provided by any chemical extraction technique. As the pyrethroid concentrations in the experimental sediments caused toxicity to L. variegatus, thus affecting bioaccumulation, the SPTE concentrations overestimated bioaccumulation. However, SPTE concentrations strongly correlated with growth inhibition regardless of the Tenax:OC ratio, providing accurate estimates of the correct exposure endpoint. Tenax masses of 0.500-0.800 g should provide sufficient Tenax to achieve Tenax:OC ratios of at least 5:1, which will provide accurate exposure estimates while retaining the ease of conducting SPTEs.

Tenax extraction of sediments to estimate desorption and bioavailability of hydrophobic contaminants: a literature review.

Characterizing sediment-associated hydrophobic contaminants is problematic, because assessing the total amount of a compound available for chemical exchange with an organism is difficult. To address this, contaminant concentrations have been normalized for specific sediment characteristics (including organic C content) or the chemical activity has been estimated using passive samplers. Another approach to assess compound availability is to determine the extent of readily desorbed compound using resin extractions of sediment slurries. The present paper reviews the literature that uses Tenax® TA, a 2,6-diphenylene-oxide polymer as an extraction tool to measure bioavailability of hydrophobic organic contaminants in sediment. Some work has assessed the extent of desorption with sequential extractions to characterize the maximum rate and pool sizes for different desorbing fractions of bound contaminant. As such, the rapidly desorbing fraction has been well correlated with the extent of degradation, bioaccumulation, and toxicity of hydrophobic contaminants. A shortcut to measuring the full desorption curve to determine the rapidly desorbing compound is to use a single-point extraction, with 6 h or 24 h extractions being the most common. The Tenax extraction has been shown to be effective with laboratory-spiked sediments, field-collected sediments, laboratory-exposed organisms, field-collected organisms, and studies among laboratories. Furthermore, a literature-based model has described the bioaccumulation of polychlorinated biphenyls from independently measured field-collected sediments. Despite the success of this approach, applying the Tenax method to manage contaminated sediments is limited by the absence of a standard set of conditions to perform the extractions, as well as standard methods for using field sediments.

Tenax extraction as a simple approach to improve environmental risk assessments.

It is well documented that using exhaustive chemical extractions is not an effective means of assessing exposure of hydrophobic organic compounds in sediments and that bioavailability-based techniques are an improvement over traditional methods. One technique that has shown special promise as a method for assessing the bioavailability of hydrophobic organic compounds in sediment is the use of Tenax-extractable concentrations. A 6-h or 24-h single-point Tenax-extractable concentration correlates to both bioaccumulation and toxicity. This method has demonstrated effectiveness for several hydrophobic organic compounds in various organisms under both field and laboratory conditions. In addition, a Tenax bioaccumulation model was developed for multiple compounds relating 24-h Tenax-extractable concentrations to oligochaete tissue concentrations exposed in both the laboratory and field. This model has demonstrated predictive capacity for additional compounds and species. Use of Tenax-extractable concentrations to estimate exposure is rapid, simple, straightforward, and relatively inexpensive, as well as accurate. Therefore, this method would be an invaluable tool if implemented in risk assessments.

Validation of an extraction method for Cry1Ab protein from soil.

Corn expressing insecticidal proteins derived from Bacillus thuringiensis (Bt corn) has increased in usage in the United States from 8% of total corn acreage in 1996 to 67% in 2012. Because of this increase, it is important to be able to monitor the fate and transport of the insecticidal Bt proteins to evaluate environmental exposure and effects. Accurate and validated methods are needed to quantify these proteins in environmental matrices. A method to extract Bt Cry1Ab proteins from 3 soil types using a 10× phosphate-buffered saline with Tween buffer and a commercially available enzyme-linked immunosorbent assay (ELISA) was validated through a series of 6 tests. The validation process for Cry1Ab extractions in soil has not yet been reported in the scientific literature. The extraction buffer and each soil matrix were tested and validated for the ELISA. Extraction efficiencies were 41%, 74%, and 89% for the 3 soil types and were significantly correlated with the organic matter content of the soil. Despite low recoveries, consistent results with low coefficients of variation allowed for accurate measurements. Through validating this method with 3 different soils, a sensitive, specific, precise, and accurate quantification of Bt Cry1Ab was developed. The validation process can be expanded and implemented in other environmental matrices, adding consistency to data across a wide range of samples.

Application of a Tenax model to assess bioavailability of polychlorinated biphenyls in field sediments.

Recent literature has shown that bioavailability-based techniques, such as Tenax extraction, can estimate sediment exposure to benthos. In a previous study by the authors, Tenax extraction was used to create and validate a literature-based Tenax model to predict oligochaete bioaccumulation of polychlorinated biphenyls (PCBs) from sediment; however, its ability to assess sediment remediation was unknown. The present study further tested the Tenax model by examining the impacts of remediation on surface sediment concentrations, Tenax extractable concentrations, and tissue concentrations of laboratory-exposed Lumbriculus variegatus. Tenax extractable concentration was an effective exposure metric to evaluate changes in Lumbriculus exposure preremediation and postremediation, with 75% of the postremediation data corresponding to the Tenax model. At nondredged sites, bioaccumulation was better predicted by the Tenax model, with 86% of the data falling within the 95% confidence intervals, than at dredged sites, for which only 64% of the data fit the Tenax model. In both pre- and postdredge conditions, when the model failed, it was conservative, predicting higher PCB concentrations than observed in the oligochaetes, particularly for the postdredge data. The present study advances understanding of the applicability of the Tenax model for use when examining systems that may have undergone significant disturbances. The Tenax model provides a unique tool for quickly quantifying potential exposure to benthic organisms.

Bioavailability-based toxicity endpoints of bifenthrin for Hyalella azteca and Chironomus dilutus.

Recent studies have determined that techniques, such as solid phase microextraction (SPME) fibers and Tenax beads, can predict bioaccumulation and potentially could predict toxicity for several compounds and species. Toxicity of bifenthrin was determined using two standard sediment toxicity tests with the benthic species Hyalella azteca and Chironomus dilutus in three reference sediments with different characteristics. The objectives of the current study were to establish bioavailability-based median lethal concentrations (LC50) and median effect concentrations (EC50) of the pyrethroid insecticide bifenthrin, compare their ability to assess toxicity to the use of whole sediment concentrations, as well as to make comparisons of the concentrations derived using each method in order to make assessments of accuracy and extrapolation potential. Four metrics were compared including SPME fiber concentration, pore water concentration derived using SPMEs, 6 h Tenax extractable concentration, and 24 h Tenax extractable concentration. The variation among the LC50s and EC50s in each sediment derived using bioavailability-based methods was comparable to variation among organic carbon normalized sediment concentrations, but improved over whole sediment concentrations. There was a significant linear relationship between SPME or Tenax and organic carbon normalized sediment concentrations. Additionally, there was a significant relationship between the SPME and Tenax concentrations across sediments. The significant linear relationship between SPME and Tenax concentrations further demonstrates that these bioavailability-based endpoints are interrelated. This study derived bioavailability-based benchmarks that may prove to be more accurate than sediment-based ones in predicting toxicity across sediment types.

Using SPME fibers and Tenax to predict the bioavailability of pyrethroids and chlorpyrifos in field sediments.

The presence of pyrethroids in both urban and agricultural sediments at levels lethal to invertebrates has been well documented. However, variations in bioavailability among sediments make accurate predictions of toxicity based on whole sediment concentrations difficult. A proposed solution to this problem is the use of bioavailability-based estimates, such as solid phase microextraction (SPME) fibers and Tenax beads. This study compared three methods to assess the bioavailability and ultimately toxicity of pyrethroid pesticides including field-deployed SPME fibers, laboratory-exposed SPME fibers, and a 24-h Tenax extraction. The objective of the current study was to compare the ability of these methods to quantify the bioavailable fraction of pyrethroids in contaminated field sediments that were toxic to benthic invertebrates. In general, Tenax proved a more sensitive method than SPME fibers and a correlation between Tenax extractable concentrations and mortality was observed.

A comparison of exposure methods for SPME-based bioavailability estimates.

The ability of polydimethlysiloxane coated solid phase microextraction (SPME) fibers to predict bioavailability has been documented for a number of species and compounds. There are also a variety of established methods for establishing SPME-based bioavailability estimates; however, factors such as time until equilibrium and exposure regimen could affect fiber concentrations and have not yet been thoroughly tested. Exposure time may influence SPME fiber concentrations at equilibrium. Co-exposure of the fibers with different animals or the invertebrate species used could yield different estimates than those acquired using a shaker table system to achieve equilibrium between the sediment and SPME fibers. The current study examined the effects of time and exposure method (shaker table versus co-exposure with test species) on SPME fiber concentrations for two hydrophobic compounds: permethrin and p,p'-dichlorodiphenyldichloroethylene (DDE). An additional experiment with permethrin determined whether animal densities or fiber number influenced fiber concentrations. There were significant differences between the time required for SPME fibers to reach equilibrium when co-exposed with different species or separately, but fiber concentrations at equilibrium among treatments for both compounds were similar. Furthermore, among the 12 variations in species and fiber densities, there were no significant differences among treatments indicating that neither the route of exposure, animal density, nor fiber volume influenced SPME fiber estimates. This demonstrated that SPME fiber concentrations at equilibrium were not affected by exposure conditions, increasing their versatility in environmental assessments.

Application of a Tenax model to assess bioavailability of PCBs in field sediments.

Bioavailability has been estimated in the past using equilibrium partitioning-based biota-sediment accumulation factors. These values are not always reliable using field-collected sediments, however, likely due to varying amounts of different organic carbons, particularly black carbon, in sediments. Therefore, improving approaches to better evaluate contaminant bioavailability in sediment are needed. In the present study, a literature-based model was constructed that relied on both laboratory-exposed and field-collected oligochaete bioaccumulation data. The model system used 24-h Tenax extraction data paired with bioaccumulation tests using oligochaetes to establish the ability and utility of the biomimetic extraction. The model was then tested to confirm its utility and reliability to estimate bioavailability of oligochaetes exposed to polychlorinated biphenyl (PCB) contaminated sediments from the Ottawa River in Ohio, USA. The model correctly identified the bioaccumulation of PCBs for 94.9% of the data and 97% of the dioxin-like congeners. The mono- and di-substituted chlorinated biphenyls were the least well described, but the estimates were conservative, for example, the model overpredicted bioaccumulation. Thus, the Tenax model was robust and reliable across a wide range of sediment characteristics for estimating PCB bioaccumulation in oligochaetes.

Determining modifications to bifenthrin toxicity and sediment binding affinity from varying potassium chloride concentrations in overlying water.

Bifenthrin, a current-use pyrethroid insecticide, has been repeatedly identified as a major contributor to toxicity in urban and residential stream sediment. Within an urban stream multiple stressors exist. However, other than pesticides, the influence of secondary stressors on bifenthrin toxicity has not been studied. The goal of this project was to study how dissolved ions, based on the model salt KCl, influence bifenthrin toxicity. The presence of these dissolved ions could influence bifenthrin toxicity either through joint action as a secondary toxicant or through changing the partitioning or bioavailability of bifenthrin between the sediment matrix and overlying water or pore water. The first objective was to determine if mixtures of bifenthrin and KCl, a commonly utilized reference toxicant, display additive toxicity to the benthic invertebrates Hyalella azteca and Chironomus dilutus using concentration addition and independent action mathematical models. The second objective of the present study was to examine how KCl dissolved in the overlying water influences partitioning and bioavailability of a pyrethroid (bifenthrin). Joint toxicity of bifenthrin and KCl was less than predicted by both concentration addition and independent action models. However, both models predicted the joint toxicity within a factor of two. Partitioning of bifenthrin was not significantly influenced by KCl concentrations based on K(oc) determinations and desorption to Tenax beads. This indicates that the fate and bioavailability of bifenthrin are not likely different in aquatic environments with varying dissolved ion concentrations. Therefore, the toxicological interaction that results in the antagonistic joint action between bifenthrin and KCl is likely due to the physiological effects of exposure to hypertonic solutions of KCl rather than alterations to bifenthrin bioavailability.

Desorption of hydrophobic compounds from laboratory-spiked sediments measured by Tenax absorbent and matrix solid-phase microextraction.

Tenax extraction and matrix solid-phase microextraction (matrix-SPME) were used to study desorption of hydrophobic contaminants (HOC) from sediments. 14C-labeled hexachlorobiphenyl, DDE, permethrin, chlorpyrifos, and phenanthrene were individually spiked into sediments differing in physical characteristics. Sequestration of the HOCs into sediment was observed for all compounds, and desorption was described by rapid, slow, and very slow rates. The freely dissolved HOC concentration in the sediment porewater was estimated by matrix-SPME, and serial sampling was used to ensure equilibrium was achieved among sediment, porewater and matrix-SPME fiber. Differences in partitioning of the HOCs between sediment and porewater for the different sediments were reduced by replacing the HOC concentration in sediment with the rapidly desorbing fraction. The significantly lower porewater concentration determined from matrix-SPME, than predicted from equilibrium partitioning theory (EPT), showed that only a small fraction of sediment HOCs were available for equilibrium and the predictability of EPT can be improved with the consideration of sequestration in sediment. A good correlation was noted between sediment concentration in the rapidly desorbing fraction measured by Tenax extraction, and SPME fiber concentration as determined by matrix-SPME. Thus, the two methods both tracked the readily desorbed contaminant equally well though Tenax extraction measures the accessible pool, and matrix-SPME measures the chemical activity of the HOCs.