The effect of salinity fluctuation in freshwater streams on the fecundity of post-diapause Chironomus dilutus.

Much scientific research dedicated to understanding the effects of freshwater salinization caused by road de-icing salts has utilized static exposures, with many tests conducted at winter or spring temperatures. While relevant for lentic ecosystems, pulsed patterns of salinity occur in lotic environments, particularly in summer months where precipitation can decrease elevated salinity levels caused by retention of residual salts. The current study aimed to evaluate the effects of pulsed patterns of salinity on the emergence, sex ratio, and fecundity of Chironomus dilutus over two generations of laboratory exposure. Three road de-icing salt treatments, including a control, modeled after environmental monitoring data of two local streams, were used to determine the ecological effects of periodic declines in salinity on C. dilutus at summer temperatures. No significant effects were observed on emergence success or sex ratios within or across generations, but fecundity of C. dilutus in the high salt treatment was reduced regardless of generation (P < 2e-16), possibly due to increased osmoregulatory stress caused by increased salinities. The intermediate and decreasing salinities may account for the lack of negative effects on emergence success and sex ratios by protecting sensitive life stages. More research is needed on long-term effects of reduced fecundity on population viability. The current study suggests more research using a similar experimental design is needed to fully evaluate the influence of road de-icing salts in lotic environments, as static laboratory exposures may not accurately reflect environmental changes in salinity.

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison.

This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practical guidance for standardized passive sampling, and advance the use of passive sampling in regulatory decision making by increasing confidence in the use of the technique. The study was performed by a consortium of 11 laboratories and included experiments with 14 passive sampling formats on 3 sediments for 25 target chemicals (PAHs and PCBs). The resulting overall interlaboratory variability was large (a factor of ∼10), but standardization of methods halved this variability. The remaining variability was primarily due to factors not related to passive sampling itself, i.e., sediment heterogeneity and analytical chemistry. Excluding the latter source of variability, by performing all analyses in one laboratory, showed that passive sampling results can have a high precision and a very low intermethod variability (

The Value of Using Multiple Metrics to Evaluate PCB Exposure.

Current methods for evaluating exposure in ecosystems contaminated with hydrophobic organic contaminants typically focus on sediment exposure. However, a comprehensive environmental assessment requires a more holistic approach that not only estimates sediment concentrations, but also accounts for exposure by quantifying other pathways, such as bioavailability, bioaccumulation, trophic transfer potential, and transport of hydrophobic organic contaminants within and outside of the aquatic system. The current study evaluated the ability of multiple metrics to estimate exposure in an aquatic ecosystem. This study utilized a small lake contaminated with polychlorinated biphenyls (PCBs) to evaluate exposure to multiple trophic levels as well as the transport of these contaminants within and outside of the lake. The PCBs were localized to sediments in one area of the lake, yet this area served as the source of PCBs to aquatic invertebrates, emerging insects, and fish and terrestrial spiders in the riparian ecosystem. The Tenax extractable and biota PCB concentrations indicated tissue concentrations were localized to benthic invertebrates and riparian spiders in a specific cove. Fish data, however, demonstrated that fish throughout the lake had PCB tissue concentrations, leading to wider exposure risk. The inclusion of PCB exposure measures at several trophic levels provided multiple lines of evidence to the scope of exposure through the aquatic and riparian food web, which aids in assessing risk and developing potential future remediation strategies.

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.

Avoidance behavior of Hyalella azteca in response to three common-use insecticides.

Non-target organisms in aquatic environments may experience lethal or sublethal effects following exposure to contaminants. Most protocols and regulations, however, are designed to provide protection from lethal effects and are thus based on conventional estimates of population lethality. The relative lack of reliable behavioral endpoints makes it challenging to implement regulations that are similarly protective against sublethal toxicity. The objective of this study was to quantify the avoidance behavior of Hyalella azteca when exposed to three insecticides-bifenthrin (B), chlorpyrifos (C), and permethrin (P)-at a range of estimated lethal concentrations. A two-choice behavioral arena was used for each chemical to quantify H. azteca activity and time spent in either uncontaminated sediment or sediment spiked at concentrations reflecting estimated 48-h lethal concentrations (LC50, LC25, and LC10). For all three insecticides, naïve H. azteca demonstrated a preference for the uncontaminated sediment over the contaminated sediment at the LC50 (B: 312 ng/gOC; C: 1265 ng/gOC; P: 5042 ng/gOC) and LC25 (B: 230 ng/gOC; C: 859 ng/gOC; P: 3817 ng/gOC), spending significantly more time in the uncontaminated side of the arena. H. azteca did not avoid sediment at LC10 (B: 204 ng/gOC; C: 609 ng/gOC; P: 1515 ng/gOC) levels, indicating the existence of a potential threshold of detection. Despite the lack of substrate preference at this exposure level, H. azteca were nevertheless more active (i.e., increased zone-switching) when exposed to bifenthrin at the LC10, suggesting a possible irritation response (e.g., movement after exposure) to this chemical. Our results provide evidence that H. azteca exhibit innate avoidance responses to sediments contaminated with common insecticides at concentrations below those represented by traditional toxicological endpoints (e.g., LC50). The sensitivity and ease with which this behavioral endpoint can be assayed demonstrates the potential utility of behavioral endpoints in toxicological assessments using model organisms.

Evaluating the trophic transfer of PCBs from fish to humans: Insights from a synergism of environmental monitoring and physiologically-based pharmacokinetic modeling.

Accumulation of polychlorinated biphenyls (PCBs) within fish tissues has prompted many states to issue consumption advisories. In Pennsylvania such advisories suggest one meal per month for most game species harvested from Lake Erie; however, these advisories do not account for the emergent properties of regional PCB mixtures, and the downstream accumulation of PCB congeners into human tissues is poorly documented. This study aimed to demonstrate the utility of pairing environmental monitoring with pharmacokinetic modeling for the purpose of estimating dietary PCB exposure in humans. We qualified and quantified the PCB congeners present in the filets of five Lake Erie fish species and used these data to estimate exposure under consumption scenarios that matched or exceeded the advisories. Physiologically-based pharmacokinetic (PBPK) modeling was then employed to predict PCB accumulation within seven tissue compartments of a hypothetical man and woman over 10 years. Twenty-one congeners were detected between the five fish species at concentrations ranging from 56.0 to 411.7 ng/g. Predicted accumulation in human tissues varied based on tissue type, the species consumed, biological sex, and fish-consumption rate. Notably, steady-state concentrations were higher in fatty tissue compartments ("Fat" and "Liver") and across all tissues in women compared to men. This study serves as a preliminary blueprint for generating predictions of site-specific and tissue-specific exposure through the integration of environmental monitoring and pharmacokinetic modeling. Although the details may vary across applications, this simple approach could complement traditional exposure assessments for vulnerable communities in the Great Lakes region that continue to suffer from legacy contamination.

Determining the reusability of Tenax beads (60-80 mesh) in estimates of bioaccessibility using single-point extractions.

Single-point Tenax extractions are a viable means of estimating bioaccessibility of hydrophobic organic contaminants in sediment, soil, and intestinal fluids. One advantage of this extraction technique is that after thorough cleaning and drying, Tenax beads can be reused in subsequent extractions with the assumption that no changes in bioaccessibility estimates will occur. This assumption of reusability, however, has not been tested. Therefore, the objective of the current study was to evaluate the reusability of Tenax beads by comparing bioaccessible polychlorinated biphenyl (PCB) concentrations measured by differently aged Tenax beads. New Tenax beads (60-80 mesh) were aged through 24 h single-point Tenax extractions of clean sand 0, 1, 5, 10, 15, 20, and 25 times. The aged Tenax was then used to extract 27 PCB congeners from laboratory spiked sediment and the bioaccessible PCB concentrations were compared. Despite significant effects of PCB congener (F26, 567 = 97.291, p = 2.00 × 10-16), Tenax age (F6, 567 = 14.735, p = 1.12 × 10-15), and the interaction of these two terms (F156, 567 = 1.711, p = 4.79 × 10-6) on bioaccessible concentrations measured by Tenax, the significance was due to two PCB congeners that showed large variation during analytical quantification. For the remaining 25 congeners, no differences in bioaccessible PCB concentrations were found between differently aged Tenax, suggesting repeated use did not impact bioaccessible estimates provided by Tenax. Scanning electron microscope imaging revealed no significant changes in the visible surface area of the Tenax beads after aging (F6, 203 = 1.434, p = 0.203), suggesting no significant changes in the Tenax phase volume resulting in consistent estimates of bioaccessibility through repeated use. Given the strong correlations between single-point Tenax extractable and tissue concentrations, providing data to detail the reusability of Tenax in repeated extractions further demonstrates the applicability of this extraction technique in risk assessment.

A comparison of activated carbon remediation success in floodplain soils contaminated with DDT and its metabolites using ex situ and in situ experimentation.

Remediation of hydrophobic organic contaminants using activated carbon is an effective means by which to clean up contaminated areas. Predicting remediation success using laboratory experimentation with soil, however, is unclear. Current remediation efforts involving activated carbon addition to floodplain soils downstream of the Velsicol Chemical Corporation Superfund Site (VCCSS) have offered the opportunity to directly compare in situ activated carbon remediation with laboratory experimentation. The objective of the current study was to compare bioaccumulation of DDT, DDD, and DDE (DDX) residues by earthworms (Eisenia fetida) exposed to laboratory-aged (LA) or field-aged (FA) soils from four locations. Samples were evaluated at 0-, 3-, and 9-months post-remediation to determine the ability of laboratory studies to predict in situ remediation. Floodplain soils downstream from the VCCSS were amended with 2% by weight activated carbon in the field and the laboratory, and then aged for 3- or 9-months. At 0-, 3-, and 9-months bioaccumulation assays were conducted with LA and FA soils and tissue concentrations were compared within study sites. In both LA and FA soils, activated carbon caused significant reductions (37.01-92.94%) in bioaccumulated DDX in earthworms. Field-collected worms showed a similar trend in reduction of bioaccumulated DDX, suggesting activated carbon remediation was successful in reducing bioavailable DDX for native organisms within the floodplain soils. The rate of reduction in bioavailable DDX, however, was significantly faster in LA soils (ß = -0.189, p < 0.0001) compared to FA soils (ß = -0.054, p < 0.0038). Differences in temperature and methods of activated carbon incorporation between LA and FA soils may account for the differences in remediation rate, suggesting laboratory experiments may overpredict the extent or speed in which remediation occurs in the field. Therefore, use of laboratory studies in predicting success of activated carbon remediation may be most effective when conditions mimic field remediation as closely as possible.

Utility of normalizing Tenax extractable concentrations for phase volume in application as an environmental screening tool.

Bioaccessibility-based extraction tools, such as single-point Tenax extractions (SPTEs), provide cost-effective and accurate estimates of bioaccumulation and toxicity of hydrophobic organic contaminants during environmental sampling. Use of SPTEs as a screening tool in risk assessment is hindered by the requirement for normalization of extractable concentrations for organic carbon (OC). Normalizing SPTE concentrations for the volume of Tenax used during the extraction could improve the applicability of this methodology by removing the system dependence when applying SPTE concentrations to estimates of bioaccumulation. The objective of this study was to examine the utility of Tenax phase volume normalization in place of OC normalization when using SPTEs to estimate bioaccumulation. No significant differences were observed between the slope of regression lines generated between SPTE concentrations normalized for either Tenax phase volume or OC (p = 0.410), but slight improvement of the regression was noted when using phase volume normalization (R2 = 0.829) compared to OC normalization (R2 = 0.740). Replacing OC normalization with phase volume normalization in use of SPTEs more accurately represents the partition of the chemical to the Tenax during the SPTE, improves estimates of bioaccumulation, and expands the use of SPTEs as a rapid assessment tool for determining bioaccumulation during screening of contaminated environments.

Bridging the Information Gap Between Science and Society: A Solution to Nonpoint Source Contamination?

The dissemination of information associated with scientific achievement serves to advance research and guide future experimentation. In the sphere of environmental science, such advancements aim to better characterize harmful chemicals and the factors that influence in situ toxicity, which is central to the protection of the environments upon which humans depend. While some information regarding the dangers associated with common anthropogenic contaminants reaches wider audiences, the nuance of this information is often lost, potentially leading to ineffective solutions, specifically as it relates to nonpoint source contamination. Bridging the divide between scientific research, regulatory implementation, and product innovation is imperative in order to find meaningful and lasting environmental solutions. Road de-icing salts are applied to impervious surfaces to protect human health and maintain the efficient transportation of goods by roadways during winter months. The toxicity of these salts in freshwater ecosystems is well understood and researched within the scientific community. Tentative regulations and solutions developed to mitigate the environmental damage caused by road de-icing salts, however, perfectly represent the disconnect between the scientific community and the general public. Here, we use road de-icing salt as an example of how such a disconnect can manifest in the form of ineffective solutions and regulatory standards, and we present a general framework by which environmental scientists can more effectively bridge the gap between the scientific community and society at large. Integr Environ Assess Manag 2020;16:415-420. © 2020 SETAC.

Toxicity testing of "eco-friendly" de-icing formulations using Chironomus dilutus.

An influx of chloride ions from road de-icing solutions can result in toxicological effects to organisms in terrestrial and aquatic environments. As such, "eco-friendly" de-icing alternatives are sought to mitigate environmental impacts of de-icing impervious surfaces, while maintaining human safety. While many alternative de-icers are economically impractical for municipal use, the residential commercial market is flooded with de-icing formulations claiming to be "eco-friendly". Given the little regulation and guidance that surrounds eco-labeling, the meaning of "eco-friendly" remains unclear in the context of biological systems. The objective of the current study was to determine the toxicity of three "eco-friendly" de-icing formulations to Chironomus dilutus using 10 d toxicity tests. The toxicity of these three formulations was compared to a traditional formulation composed entirely of chloride salts. Two of the "eco-friendly" de-icers demonstrated LC50s of 6.61 and 6.32 g/L, which were similar in toxicity to the traditional sodium chloride formulation with a LC50 6.29 g/L. The comparable toxicities of these formulations is likely due to the presence of chloride salts in each of the "eco-friendly" de-icers. The third "eco-friendly" formulation, a urea-based de-icer, demonstrated toxicity an order of magnitude higher than that of the traditional formulation with an LC50 of 0.63 g/L. While C. dilutus may not have been the intended endpoint in consideration when marketing these products as "eco-friendly", consideration of how eco-labeling is utilized and the role of environmental scientists in determining the meaning of such claims must be considered to ensure continued and future protection of the environment.

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.

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.

Do pyrethroid-resistant Hyalella azteca have greater bioaccumulation potential compared to non-resistant populations? Implications for bioaccumulation in fish.

The recent discovery of pyrethroid-resistant Hyalella azteca populations in California, USA suggests there has been significant exposure of aquatic organisms to these terrestrially-applied insecticides. Since resistant organisms are able to survive in relatively contaminated habitats they may experience greater pyrethroid bioaccumulation, subsequently increasing the risk of those compounds transferring to predators. These issues were evaluated in the current study following toxicity tests in water with permethrin which showed the 96-h LC50 of resistant H. azteca (1670 ng L-1) was 53 times higher than that of non-resistant H. azteca (31.2 ng L-1). Bioaccumulation was compared between resistant and non-resistant H. azteca by exposing both populations to permethrin in water and then measuring the tissue concentrations attained. Our results indicate that resistant and non-resistant H. azteca have similar potential to bioaccumulate pyrethroids at the same exposure concentration. However, significantly greater bioaccumulation occurs in resistant H. azteca at exposure concentrations non-resistant organisms cannot survive. To assess the risk of pyrethroid trophic transfer, permethrin-dosed resistant H. azteca were fed to fathead minnows (Pimephales promelas) for four days, after which bioaccumulation of permethrin and its biotransformation products in fish tissues were measured. There were detectable concentrations of permethrin in fish tissues after they consumed dosed resistant H. azteca. These results show that bioaccumulation potential is greater in organisms with pyrethroid resistance and this increases the risk of trophic transfer when consumed by a predator. The implications of this study extend to individual fitness, populations and food webs.

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.