Effect of sample holding time on bioaccessibility and sediment ecotoxicological assessments

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.

Assessing the Influence of Organic Carbon, Aging Time and Temperature on Bioaccessibility of Bifenthrin

Tenax extraction, a measure of chemical desorption rates from sediments, was used to evaluate the bioaccessibility of bifenthrin in two different sediments exposed to three temperatures aged over a 56-d holding period. A 24-h single-point Tenax extraction was used and parent 14C-bifenthrin and polar metabolites were quantified in the sediment and Tenax. Bioaccessibility of bifenthrin was inversely related to the organic carbon (OC) content in the sediment, holding time, and temperature. Sequestration of the bifenthrin into slowly desorbing fractions within the sediment appears to have decreased degradation of the parent compound into metabolites and decreased the amount of parent compound bioaccessible for uptake by the Tenax. These results suggest that the environmental risk of bifenthrin to aquatic species is greatest immediately after the pesticide enters a waterbody after runoff, for low-OC content sediments, and in areas or seasons where water temperatures are colder.

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 (F_{26, 567} = 97.291, p = 2.00 × 10^-16), Tenax age (F_{6, 567} = 14.735, p = 1.12 × 10^-15), and the interaction of these two terms (F_{156, 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 (F_{6, 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.

Bioavailability of legacy and current-use pesticides in juvenile Chinook salmon habitat of the Sacramento River watershed: Importance of sediment characteristics and extraction techniques

The Sacramento River watershed, California, provides important rearing and migratory habitat for several species of conservation concern. Studies have suggested significant benefits for juvenile fish rearing in floodplain habitats of the watershed compared to the mainstem Sacramento River. However, the potential for contaminant exposure in each of these two habitats is poorly understood. Consequently, the present study aimed to determine the distribution and occurrence of bioavailable pesticides within two known salmon habitats using a suite of approaches including exhaustive chemical extraction, single-point Tenax extraction (SPTE) and ex situ passive sampling. Sediment samples were collected from sites within both habitats twice annually in 2019 and 2020, with inundation of the floodplain and high flows for both areas in 2019 and low flow conditions observed in 2020. Sediment characteristics including total organic carbon, black carbon and particle size distribution were determined to elucidate the influence of physical characteristics on pesticide distribution. Using exhaustive extractions, significantly greater sediment concentrations of organochlorines were observed in the floodplain compared to the Sacramento River in both years, with bioaccessible organochlorine concentrations also significantly greater in the floodplain (ANOVA, p < 0.05). Using both SPTEs and exhaustive extractions, significantly fewer pesticides were detected across both sites under low flow conditions as compared to high flow conditions (Poisson regression, p < 0.05). Sediment characteristics including percent fines and black carbon had significant positive relationships with total and bioaccessible pyrethroid and organochlorine concentrations. Fewer analytes were detected using low-density polyethylene (LDPE) passive samplers as compared to SPTEs, suggesting greater sensitivity of the Tenax technique for bioavailability assessments. These findings suggest that threatened juvenile fish populations rearing on the floodplain may have greater exposure to organochlorines than fish inhabiting adjacent riverine habitats, and that pesticide exposure of resident biota may be exacerbated during high-flow conditions.

Assessing endocrine disruption in freshwater fish species from a "hotspot" for estrogenic activity in sediment

Little is known about sediment-bound exposure of fish to endocrine disrupting chemicals (EDC) under field conditions. This study aimed to investigate potential routes of EDC exposure to fish and whether sediment-bound contaminants contribute towards exposure in fish. Tench (Tinca tinca) and roach (Rutilus rutilus) as a benthic and pelagic living fish species, respectively, were sampled at the Luppe River, previously described as a "hotspot" for accumulation of EDC in sediment. A field reference site, the Laucha River, additionally to fish from a commercial fish farm as reference were studied. Blackworms, Lumbriculus variegatus, which are a source of prey for fish, were exposed to sediment of the Luppe River and estrogenic activity of worm tissue was investigated using in vitro bioassays. A 153-fold greater estrogenic activity was measured using in vitro bioassays in sediment of the Luppe River compared the Laucha River. Nonylphenol (NP; 22 mg/kg) was previously identified as one of the main drivers of estrogenic activity in Luppe sediment. Estrogenic activity of Luppe exposed worm tissue (14 ng 17β-estradiol equivalents/mg) indicated that food might act as secondary source to EDCs. While there were no differences in concentrations of NP in plasma of tench from the Luppe and Laucha, vitellogenin, a biomarker for exposure to EDCs, was induced in male tench and roach from the Luppe River compared to both the Laucha and cultured fish by a factor of 264 and 90, respectively. However, no histological alterations in testis of these fish were observed. Our findings suggest that sediments substantially contribute to the overall EDC exposure of both benthic and pelagic fish but that the exposure did not impact gonad status of the fish.

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.

Understanding the bioavailability of pyrethroids in the aquatic environment using chemical approaches

Pyrethroids are a class of commonly used insecticides and are ubiquitous in the aquatic environment in various regions. Aquatic toxicity of pyrethroids was often overestimated when using conventional bulk chemical concentrations because of their strong hydrophobicity. Over the last two decades, bioavailability has been recognized and applied to refine the assessment of ecotoxicological effects of pyrethroids. This review focuses on recent advances in the bioavailability of pyrethroids, specifically in the aquatic environment. We summarize the development of passive sampling and Tenax extraction methods for assessing the bioavailability of pyrethroids. Factors affecting the bioavailability of pyrethroids, including physicochemical properties of pyrethroids, and quality and quantity of organic matter, were overviewed. Various applications of bioavailability on the assessment of bioaccumulation and acute toxicity of pyrethroids were also discussed. The final section of this review highlights future directions of research, including development of standardized protocols for measurement of bioavailability, establishment of bioavailability-based toxicity benchmarks and water/sediment quality criteria, and incorporation of bioavailability into future risk assessment and management actions.

Impact of holding time on toxicity change of urban road dust during runoff process

During runoff process, the urban road dust (URD) passes through the road-side gutters and detention tanks, where it gets hold for a certain period of time, hours to weeks, before making its way into the water bodies. A part of the water-exchangeable toxicants are leached by the water, and some strongly bound toxicants remain attached to the URD. Toxicity of urban runoff is dependent on holding time, water volume, and the type and composition of the wet road dust (WeRD) and leachate. However, there are no studies that have elucidated the manner in which toxicities of the WeRD and leachate vary during prolonged holding in the runoff processes. The main objectives of this research were to, i) identify the distribution of toxicants in the WeRD and leachate, and ii) evaluate the change in toxicity during prolonged holding. The URD samples that were collected from residential road, arterial road and highways in Tokyo, Japan, were mixed with moderately hard water in varying ratios (1:2 to 1:16) and were held for a certain time (1h to 5days) before centrifuging into the WeRD and leachate. Toxicity test was conducted with ostracod Heterocypris incongruens direct contact test. Toxicity of both the WeRD and leachate from residential area was not significantly greater than the 20% lethal limit. Toxicity of the WeRD from other stations initially decreased, further reached a minimum corresponding to the critical holding time, and it subsequently increased again. Toxicity of the arterial leachate gradually increased, whereas that of the highway leachate gradually decreased during 5days holding. Unionized ammonia and zinc were confirmed as one of the possible toxicants. This study proposes and verifies a model for the toxicity change of the WeRD during prolonged holding.