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.

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.

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.

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.

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.

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.

Optimization of Tenax extraction parameters for polychlorinated biphenyls in contaminated sediments.

Tenax extraction is a chemical technique used to provide a rapid estimate of exposure to chemicals from contaminated sediments. However, an absence of standardization has limited the implementation of Tenax extraction in regulatory venues. In the current study, the operational parameters of extraction solvent volume, Tenax sorption rate from water, and Tenax:OC (organic carbon) ratios were investigated employing polychlorinated biphenyls (PCBs) as model compounds. The highest extraction efficiency of the analytes from Tenax resulted from a 10mL extraction volume. Recoveries of PCBs from spiked-sediment ranged from 79% to 100% with relative standard deviations between 1% and 9%. For the Tenax sorption rate from water, 0.01g of Tenax cleared >95% of the initial solution concentration of individual PCBs from 40mL of water in less than 30min. This Tenax mass is capable of clearing PCBs from the 40mL of water 413 times in 24h. Thus, a 24h single-point Tenax extraction would be sufficient to remove all of the desorbing PCBs from a contaminated sediment. Finally, the influence of the Tenax:OC ratio becomes more evident as the hydrophobicity of the compound and OC content (%) of the sediment increases. To obtain more reliable Tenax extractable concentrations, a minimum Tenax:OC ratio of 5:1 is suggested to conduct single-point Tenax extractions. In summary, a solvent volume of 10mL extracted the compounds efficiently from the Tenax, and the rapid sorption from water using at least the minimum Tenax:OC ratio should lead to good measures of rapidly desorbing compound and thus represent bioaccessibility.

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.