Fate and effects of sediment-associated polycyclic musk HHCB in subtropical freshwater microcosms.

Galaxolide (HHCB) is used as a fragrance ingredient in household and personal care products, and has been ubiquitously detected in the environment. Here we investigated the fate of HHCB in subtropical freshwater microcosms, and evaluated effects of sediment-associated HHCB on a biological community consisting of algae, Daphnia, benthic macroinvertebrates and bacteria. The concentrations of sediment-associated HHCB did not change significantly during a 28 days exposure period, but HHCB accumulated in worms with biota-sediment accumulation-factor (BSAF) values in the range of 0.29-0.66 for Branchiura sowerbyi and 0.94-2.11 for Limnodrilus hoffmeisteri. There was no significant effects of HHCB (30 µg/g dry weight (dw) sediment) on chlorophyll-a content, sediment bacterial community composition, and survival and growth of benthic macroinvertebrates. However, the presence of benthic macroinvertebrates altered the sediment bacterial community structure relative to microcosms without introduced organisms. The findings of this study suggest that a single high-dose of HHCB, over 28 days, at environmentally relevant concentrations would not impose direct toxicological risks to aquatic organisms such as benthic macroinvertebrates.

Bioaccumulation and Biotransformation of Triclosan and Galaxolide in the Freshwater Oligochaete Limnodrilus hoffmeisteri in a Water/Sediment Microcosm.

Personal care products are widely used in our daily life in considerable quantities and discharged via the down-the-drain route to aquatic environments, resulting in potential risks to aquatic organisms. We investigated bioaccumulation and biotransformation of two widely used personal care products, triclosan (TCS) and galaxolide (HHCB) spiked to sediment, in the oligochaete worm Limnodrilus hoffmeisteri in water/sediment microcosms. After 7 days of sediment exposure to 3.1 µg of TCS or HHCB/g of dry weight sediment, the accumulation of TCS and HHCB in L. hoffmeisteri reached equilibrium, at which point the biota-sediment accumulation factors (BSAFs) were 2.07 and 2.50 for TCS and HHCB, respectively. The presence of L. hoffmeisteri significantly accelerated the dissipation of the levels of TCS and HHCB in the microcosms, with approximately 9.03 and 2.90% of TCS and HHCB, respectively, eliminated from the water/sediment systems after exposure for 14 days in the presence of worms. Two biotransformation products, methyl triclosan and triclosan O-sulfate, were identified for TCS in worm tissue, whereas only methyl triclosan was identified in the sediment. Unlike TCS, no evidence of biotransformation products was found for HHCB in either worm tissue or sediment. These experiments demonstrate that L. hoffmeisteri biotransformed TCS through methylation and sulfation, whereas HHCB biotransformation was undetectable.

Bioaccumulation and effects of sediment-associated gold- and graphene oxide nanoparticles on Tubifex tubifex.

With the development of nanotechnology, gold (Au) and graphene oxide (GO) nanoparticles have been widely used in various fields, resulting in an increased release of these particles into the environment. The released nanoparticles may eventually accumulate in sediment, causing possible ecotoxicological effects to benthic invertebrates. However, the impact of Au-NPs and GO-NPs on the cosmopolitan oligochaete, Tubifex tubifex, in sediment exposure is not known. Mortality, behavioral impact (GO-NP and Au-NP) and uptake (only Au-NP) of sediment-associated Au-NPs (4.9±0.14nm) and GO-NPs (116±0.05nm) to T. tubifex were assessed in a number of 5-day exposure experiments. The results showed that the applied Au-NP concentrations (10 and 60µg Au/g dry weight sediment) had no adverse effect on T. tubifex survival, while Au bioaccumulation increased with exposure concentration. In the case of GO-NPs, no mortality of T. tubifex was observed at a concentration range of 20 and 180µg GO/g dry weight sediment, whereas burrowing activity was significantly reduced at 20 and 180µg GO/g dry weight sediment. Our results suggest that Au-NPs at 60µg Au/g or GO-NPs at 20 and 180µg GO/g were detected by T. tubifex as toxicants during short-term exposures.

Polycyclic Aromatic Acids Are Primary Metabolites of Alkyl-PAHs-A Case Study with Nereis diversicolor.

Although concentrations of alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) in oil-contaminated sediments are higher than those of unsubstituted PAHs, only little attention has been given to metabolism and ecotoxicity of alkyl-PAHs. In this study we demonstrated that metabolism of alkyl-PAHs primarily forms polycyclic aromatic acids (PAAs). We generalize this to other alkyl-PAHs, based on literature and the present study of the metabolism of 1-methylphenanthrene, 3,6-dimethylphenanthrene, and 1-, 2-, 3-, and 6-methylchrysene related to their unsubstituted parent PAHs. Also, we observed that body burdens and production of PAAs was related to the position of the methyl group, showing the same isomer specific preferences as for microbial degradation of alkyl-PAHs. We detected a high production of PAAs, and larger metabolism of alkyl-PAHs than their unsubstituted parent PAHs. We therefore propose that carboxylic acid metabolites of alkyl-PAHs have the potential of constituting a new class of contaminants in marine waters that needs attention in relation to ecological risk assessments.

The Importance of Including Variable Exposure Concentrations When Assessing Toxicity of Sediment-Associated Pharmaceuticals to an Amphipod.

Pharmaceuticals have been classified as an environmental concern due to their increasing consumption globally and potential environmental impact. We examined the toxicity of sediment-associated diclofenac and citalopram administered as both single compounds and in a mixture to the sediment-living amphipod Corophium volutator. This laboratory-based study addressed the following research questions: (1) What is the toxicity of sediment-associated diclofenac and citalopram to C. volutator? (2) Can the mixture effect be described with either of the two mixture models: concentration addition (CA) or independent action (IA)? (3) What is the importance of the choice of (i) exposure measure (start concentration, time-weighted average [TWA], full exposure profile) and (ii) effect model (concentration-response vs. the toxicokinetic-toxicodynamic model general unified threshold model for survival in its reduced form [GUTS-RED]) for the derived effect concentration values? Diclofenac was more toxic than citalopram to C. volutator as a single compound (10-day exposure). Diclofenac exposure to C. volutator provided median lethal concentrations (LC50s) within the same range (11 µg g-1 dry wt sediment) using concentration-response based on TWA and both GUTS-RED models. However, concentration-response based on measured start concentrations provided an approximately 90% higher LC50 (21.6 ± 2.0 µg g-1 dry wt sediment). For citalopram, concentration-response parameters were similar regardless of model or concentration used (LC50 85-97 µg g-1 dry wt sediment), however, GUTS-RED with the assumption of individual tolerance resulted in a lower LC50 (64.9 [55.3-74.8] µg g-1 dry wt sediment). The mixture of diclofenac and citalopram followed the CA quite closely, whereas the result was synergistic when using the IA prediction. In summary, concentration-response based on TWA and GUTS-RED provided similar and reasonably good fits compared to the data set. The implications are that GUTS-RED will provide a more flexible model, which, in principle, can extend beyond the experimental period and make predictions based on variable exposure profiles (toxicity at different time frames and at different variable exposure scenarios) compared to concentration-response, which provides contaminant toxicity at one point in time. Environ Toxicol Chem 2024;00:1-11. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of Nereis diversicolor on the transformation of 1-methylpyrene and pyrene: transformation efficiency and identification of phase I and II products.

Transformation of nonsubstituted and alkyl-substituted polycyclic aromatic hydrocarbons (PAHs) by the benthic invertebrate Nereis diversicolor was compared in this study. Pyrene and 1-methylpyrene were used as model compounds for nonsubstituted and alkyl-substituted PAHs, respectively. Qualitative and quantitative analyses of metabolites and parent compounds in worm tissue, water, and sediment were performed. Transformation of 1-methylpyrene generated the benzylic hydroxylated phase I product, 1-pyrenecarboxylic acid that comprised 90% of the total metabolites of 1-methylpyrene, and was mainly found in water extracts. We tentatively identified 1-methylpyrene glucuronides and 1-carbonylpyrene glycine as phase II metabolites not previously reported in literature. Pyrene was biotransformed to 1-hydroxypyrene, pyrene-1-sulfate, pyrene-1-glucuronide, and pyrene glucoside sulfate, with pyrene-1-glucuronide as the most prominent metabolite. Transformation of 1-methylpyrene (21% transformed) was more than 3 times as efficient as pyrene transformation (5.6% transformed). Because crude oils contain larger amounts of C1-C4-substituted PAHs than nonsubstituted PAHs, the rapid and efficient transformation of sediment-associated 1-methylpyrene may result in a high exposure of water-living organisms to metabolites of alkyl-substituted PAHs, whose toxicities are unknown. This study demonstrates the need to consider fate and effects of substituted PAHs and their metabolites in risk assessments.

When and How to Conduct Ecotoxicological Tests Using Natural Field-Collected Sediment.

In recent years, the sediment compartment has gained more attention when performing toxicity tests, with a growing emphasis on gaining more ecological relevance in testing. Though many standard guidelines recommend using artificially formulated sediment, most sediment studies are using natural sediment collected in the field. Although the use of natural field-collected sediment contributes to more environmentally realistic exposure scenarios and higher well-being for sediment-dwelling organisms, it lowers comparability and reproducibility among studies as a result of, for example, differences in the base sediment depending on sampling site, background contamination, particle size distribution, or organic matter content. The aim of this methodology contribution is to present and discuss best practices related to collecting, handling, describing, and applying natural field-collected sediment in ecotoxicological testing. We propose six recommendations: (1) natural sediment should be collected at a well-studied site, historically and by laboratory analysis; (2) larger quantities of sediment should be collected and stored prior to initiation of an experiment to ensure a uniform sediment base; (3) any sediment used in ecotoxicological testing should be characterized, at the very least, for its water content, organic matter content, pH, and particle size distribution; (4) select spiking method, equilibration time, and experimental setup based on the properties of the contaminant and the research question; (5) include control-, treated similarly to the spiked sediment, and solvent control sediment when appropriate; and (6) quantify experimental exposure concentrations in the overlying water, porewater (if applicable), and bulk sediment at least at the beginning and the end of each experiment. Environ Toxicol Chem 2023;00:1-10. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Particles as carriers of matter in the aquatic environment: Challenges and ways ahead for transdisciplinary research.

A diverse array of natural and anthropogenic particles found in the aquatic environment, can act as carriers of co-transported matter (CTM), such as nutrients, genetic material and contaminants. Thus, understanding carrier particle transport will increase our understanding of local and global fluxes of exogenous CTM (affiliated with the particle) and endogenous CTM (an inherent part of the particle). In the present contribution, researchers from multiple disciplines collaborated to provide perspectives on the interactions between carrier particles and CTM, and the fundamentals of transport of particles found in the aquatic environment and the generic spherical smooth particles, often used to make predictions about particle behavior in suspension. Evidently, the particles in the aquatic environment show a great variety of characteristics and vary greatly from each other as well as from the generic particle. However, in spite of these differences, many fundamental concepts apply to particles in general. We emphasize the importance of understanding the basic concepts of transport of particle-associated CTM, and the main assumptions in the generic-founded models, which are challenged by the diverging characteristics of particles found in the aquatic environment, as paramount moving forward. Additionally, we identified the need for a conceptual and semantic link between different scientific fields of particle research and initiated the formation of a consistent terminology. Disciplinary and organizational (academic and funding) barriers need to be overcome to enable individual researchers to move beyond their knowledge sphere, to stimulate future interdisciplinary collaborations and to avoid research silos. Hereby, we can foster faster and better progress of evolving research fields on new and emerging anthropogenic carrier particles, and stimulate the development of solutions to the technological and environmental challenges.

Biodynamics and adverse effects of CuO nanoparticles and CuCl2 in the oligochaete T. tubifex: Cu form influence biodynamics in water, but not sediment.

The use of copper oxide (CuO) NPs results in the release of these particles into the aquatic environment. Here, the particles settle out and accumulate in the sediment. However, little is known about the biodynamics of sediment-associated NPs in benthic organisms. We compared the toxicity and biodynamics of CuO NPs (7 nm) and dissolved Cu (CuCl2) in the sediment-dwelling oligochaete, Tubifex tubifex, to gain insights into the relative importance of metal form (CuCl2 vs CuO NPs) and exposure route (water vs sediment). Isotopically enriched 65Cu was used as a tracer to distinguish background from newly accumulated 65Cu in worms. For each exposure route, we conducted three experiments: one uptake, one elimination, and one longer-term net accumulation experiment to parameterize uptake and elimination of 65CuCl2 and 65CuO NPs in T. tubifex. 65Cu accumulation was detected for both 65CuCl2 and 65CuO NPs regardless of whether T. tubifex were exposed in sediment- or water-only setups. Water exposures to 65CuCl2 resulted in tail trauma whereas limited effects were seen for sediment exposures or exposures to 65CuO NPs via either exposure route. Uptake rate constants and accumulation of 65Cu in T. tubifex were higher following 65CuCl2 exposure than 65CuO NPs, in water, but not in sediment. Thus, the relative importance of exposure route and Cu form for uptake dynamics is not straightforward suggesting that findings on bioaccumulation and toxicity in water exposures cannot be directly extrapolated to sediment.

Influence of Aging on Bioaccumulation and Toxicity of Copper Oxide Nanoparticles and Dissolved Copper in the Sediment-Dwelling Oligochaete Tubifex tubifex: A Long-Term Study Using a Stable Copper Isotope.

For engineered metal nanoparticles (NPs), such as copper oxide (CuO) NPs, the sediment is recognized as a major compartment for NP accumulation. Sediment-dwelling organisms, such as the worm Tubifex tubifex, will be at particular risk of metal and metal NP exposure. However, a range of complex transformation processes in the sediment affects NP bioavailability and toxicity as the contamination ages. The objective of this study was to examine bioaccumulation and adverse effects of CuO NPs in T. tubifex compared to dissolved Cu (administered as CuCl2) and the influence of aging of spiked sediment. This was done in a 28-day exposure experiment with T. tubifex incubated in clean sediment or freshly spiked sediment with different concentrations of dissolved Cu (up to 230 µg g-1 dw) or CuO NPs (up to 40 µg g-1 dw). The experiment was repeated with the same sediments after it had been aged for 2 years. To obtain a distinct isotopic signature compared to background Cu, both Cu forms were based on the stable isotope 65Cu (>99%). The 28-day exposure to sediment-associated dissolved 65Cu and 65CuO NPs resulted in a clear concentration-dependent increase in the T. tubifex 65Cu body burden. However, despite the elevated 65Cu body burdens in exposed worms, limited adverse effects were observed in either of the two experiments (e.g., above 80% survival in all treatments, low or no effects on the growth rate, feeding rate, and reproduction). Organisms exposed to aged sediments had lower body burdens of 65Cu than those exposed to freshly spiked sediments and we suggest that aging decreases the bioavailability of both 65Cu forms. In this study, the use of a stable isotope made it possible to use environmentally realistic Cu concentrations and, at the same time, differentiate between newly accumulated 65Cu and background Cu in experimental samples despite the high background Cu concentrations in sediment and T. tubifex tissue. Realistic exposure concentrations and aging of NPs should preferably be included in future studies to increase environmental realism to accurately predict the environmental risk of metal NPs.

Dietary uptake and effects of copper in Sticklebacks at environmentally relevant exposures utilizing stable isotope-labeled 65CuCl2 and 65CuO NPs.

Copper oxide nanoparticles (CuO NPs) accumulating in sediment can be taken up by invertebrates that serve as prey for fish. Thus, it is likely that the latter are exposed to CuO NPs via the gut. However, to this day it is unknown if CuO NPs can be taken up via the gastrointestinal tract and if and in which tissues/organs they accumulate. To address this knowledge gap, we synthesized CuO NPs enriched in the stable isotope 65Cu and incorporated them at low concentration (5 µg 65Cu g-1 ww food) into a practical diet prepared from worm homogenate, which was then fed to Three-spined Stickleback (Gasterosteus aculeatus) for 16 days. For comparison, fish were exposed to a diet spiked with a 65CuCl2 solution. Background Cu and newly taken up 65Cu in fish tissues/organs including gill, stomach, intestine, liver, spleen, gonad and carcass and feces were quantified by ICP-MS. In addition, expression levels of genes encoding for proteins related to Cu uptake, detoxification and toxicity (ctr-1, gcl, gr, gpx, sod-1, cat, mta and zo-1) were measured in selected tissues using RT-qPCR. The obtained results showed that feces of fish fed 65CuO NP-spiked diet contained important amounts of 65Cu. Furthermore, there was no significant accumulation of 65Cu in any of the analyzed internal organs, though 65Cu levels were slightly elevated in liver. No significant modulation in gene expression was measured in fish exposed to 65CuO NP-spiked diet, except for metallothionein, which was significantly upregulated in intestinal tissue compared to control fish. Altogether, our results suggests that dietary absorption efficiency of CuO NPs, their uptake across the gastrointestinal barrier into the organism, and effects on Cu-related genes is limited at low, environmentally relevant exposure doses (0.2 µg 65Cu -1 fish ww day-1).

Investigation of the fate and effects of acetyl cedrene on Capitella teleta and sediment bacterial community.

The fate of the fragrance material, acetyl cedrene (AC), in sediment was examined in a 16 day laboratory experiment using the sediment microbial community subjected to the following treatments: AC (nominal concentration; 0 and 50 microg g(-1) dw sediment) and macrofaunal worms (with/without Capitella teleta (formerly Capitella sp. I)). Furthermore effects of AC on microbial respiration in the system were determined by examining CO(2) flux. T-RFLP (terminal restriction fragment length polymorphism) was used to analyze PCR (polymerase chain reaction) amplified 16S DNA gene fragments from the sediments to detect changes in the structure and diversity of the bacterial community. In addition, survival of C. teleta in sediment was determined. Lastly, we examined how the interactions between microbes and C. teleta in the sediment affected the above-mentioned parameters. The results showed that there was an interaction between worm treatment and time of sampling on the loss of AC from the sediment. This was caused by AC loss initially being fastest in the sediment with C. teleta present, but at experimental termination there was no significant difference between the two treatments (i.e., with/without worms) in the amount of AC remaining in the sediment. Survival of C. teleta was significantly reduced by AC at experimental termination, but neither microbial respiration nor structure and diversity of the bacterial community were significantly affected.

Effects of sediment-associated Cu on Tubifex tubifex - Insights gained by standard ecotoxicological and novel, but simple, bioturbation endpoints.

Sediments serve as both source and sink of contaminants (e.g., Cu) and biologically important materials (e.g., metals, nutrients). Bioturbation by benthic organisms is ecologically relevant as bioturbation affects the physio-chemical characteristics of sediments, thus altering nutrient and contaminant distribution and bioavailability. We examined the effects of sediment-associated Cu on T. tubifex with conventional toxicity endpoints, such as mortality and growth, and less commonly used non-destructive endpoints, such as bioturbation and feeding. An experimental approach was developed to examine the applicability of simple methods to detect effects on bioturbation and feeding. Two experiments were conducted with 7-day exposures to uncontaminated or Cu-spiked natural sediment at six Cu concentrations to examine Cu bioaccumulation and effects. Endpoints included worm mortality, feeding rate and growth (experiment A) and worm bioturbation (particle diffusion and maximum penetration depth, experiment B). A microparticle tracer was placed on the sediment surface and vertical particle transport was followed over time. Adverse effects were detected for all endpoints (bioturbation, feeding rate, growth and survival): a slight positive effect at the lowest Cu concentrations followed by adverse effects at higher concentrations indicating hormesis. These simple, non-destructive endpoints, provided valuable information and demonstrated that sediment-associated contaminants, such as Cu, can influence bioturbation activity, which in turn may affect the distribution of sediment-bound or particulate pollutants, such as the plastic microparticles studied here. Thus, we suggest to use simple endpoints, such as bioturbation and feeding rate, in ecotoxicity testing since these endpoint account for the influence of interactions between pollutants and benthos and, thus, increase ecological relevance.

Development of metal adaptation in a tropical marine zooplankton.

Tropical marine ecosystems are highly vulnerable to pollution and climate change. It is relatively unknown how tropical species may develop an increased tolerance to these stressors and the cost of adaptations. We addressed these issues by exposing a keystone tropical marine copepod, Pseudodiaptomus annandalei, to copper (Cu) for 7 generations (F1-F7) during three treatments: control, Cu and pCu (the recovery treatment). In F7, we tested the "contaminant-induced climate change sensitivity" hypothesis (TICS) by exposing copepods to Cu and extreme temperature. We tracked fitness and productivity of all generations. In F1, Cu did not affect survival and grazing but decreased nauplii production. In F2-F4, male survival, grazing, and nauplii production were lower in Cu, but recovered in pCu, indicating transgenerational plasticity. Strikingly, in F5-F6 nauplii production of Cu-exposed females increased, and did not recover in pCu. The earlier result suggests an increased Cu tolerance while the latter result revealed its cost. In F7, extreme temperature resulted in more pronounced reductions in grazing, and nauplii production of Cu or pCu than in control, supporting TICS. The results suggest that widespread pollution in tropical regions may result in high vulnerability of species in these regions to climate change.

Benthic invertebrate and microbial biodiversity in sub-tropical urban rivers: Correlations with environmental variables and emerging chemicals.

Urban rivers often function as sinks for various contaminants potentially placing the benthic communities at risk of exposure. We performed a comprehensive biological survey of the benthic macroinvertebrate and bacterial community compositions in six rivers from the suburb to the central urban area of Guangzhou city (South China), and evaluated their correlations with emerging organic contaminants, heavy metals and nutrients. Overall, the benthic macroinvertebrate community shifted from molluscs to oligochaete from the suburban to the central urban rivers that receive treated and untreated sewage. An exception was the site in the Sha River where chironomids were most abundant. The differences in macroinvertebrate community assemblages were significantly associated with chromium, total phosphorus, galaxolide, triclosan and sand content in the sediment. There was no significant difference in benthic macroinvertebrate composition between the dry and wet season. As assessed by double constrained ordination, sexual reproduction was the only trait of benthic macroinvertebrates that showed a significant correlation with pollution variables, as it was significantly positively correlated with chromium and total phosphorus. This suggests that r-strategist occurs in polluted sampling sites. The benthic bacterial community composition showed a significant difference between seasons and among the Liuxi River, Zhujiang River and central urban rivers. The differences in community composition of the benthic bacteria were significantly correlated with galaxolide, total phosphorus, lead and triclosan. These results suggest that input of treated and untreated sewage significantly altered the benthic macroinvertebrate and bacterial community compositions in urban rivers.

Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I.

A life table response experiment lasting 120 d was used to investigate the effects of the synthetic polycyclic musk HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8-hexamethylcyclopenta-gamma-2-benzopyrane; 0, 1.5, 26, 123, and 168 mg/kg dry wt sediment) on the life history of the infaunal polychaete Capitella species I. The HHCB exposure showed no detectable effects on adult survival, age at first reproduction, length of the reproductive period, number of broods, individual worm body volumes, or body size-specific egestion rates. In contrast, HHCB significantly affected juvenile survival (>or=123 mg/kg), maturation time (168 mg/kg), total number of eggs produced (>or=26 mg/kg), and brood size (>or=123 mg/kg) and marginally increased time between breeding attempts (>or=26 mg/kg). A declining trend was observed for population growth rate with increasing HHCB concentrations, but differences between the control and exposed groups were not significant. Thus, despite detectable effects of HHCB on individual life-history traits, the results suggest that environmentally realistic concentrations of HHCB are not likely to reduce the growth rate of Capitella sp. I populations.

Effects of the polycyclic musk HHCB on individual- and population-level endpoints in Potamopyrgus antipodarum.

Although the polycyclic musk 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[gamma]-2-benzopyran (HHCB) is frequently detected in aquatic sediments, very little is known about its effects on sediment-feeding organisms. Effects of sediment-associated HHCB on growth, feeding rate, survival and reproduction in the gastropod Potamopyrgus antipodarum were measured in the laboratory. Snails were exposed to six nominal HHCB concentrations: 0, 0.1, 1, 10, 30 and 100microg g(-1) dry weight (dw) sediment. Adult survival and growth were not affected by HHCB. However, juvenile growth and survival, reproduction, time to first reproduction and adult feeding rate were more sensitive endpoints and declined with increasing HHCB concentration. Individual-level endpoints for P. antipodarum were integrated into a population model to investigate the effects of HHCB on population growth rate. Under otherwise favorable laboratory conditions, population growth rate was slightly (by ca. 2%), but not significantly, reduced with increasing HHCB exposure concentration. Model simulations were performed to explore the consequences of HHCB exposure under more ecologically realistic conditions (i.e., survival and reproduction of unexposed snails were markedly reduced relative to the laboratory). The results suggest that despite detectable effects of HHCB on individual-level endpoints measured in the laboratory, impacts on population dynamics of this deposit feeder are not likely to occur at environmentally relevant exposure concentrations.

Response of sediment bacterial community to triclosan in subtropical freshwater benthic microcosms.

The response of sediment bacterial communities in subtropical freshwater benthic microcosms to sediment-associated triclosan (TCS; 28 d exposure) was analysed using Illumina high-throughput sequencing. This study highlights the interactive effects of TCS and the presence of benthic macroinvertebrates (Limnodrilus hoffmeisteri and Viviparidae bellamya) on sediment bacterial communities. Our results show that TCS alone significantly altered the taxonomic composition and decreased alpha diversity of sediment bacterial communities at concentrations ≥80 µg TCS/g dry weight (dw) sediment (sed). Regarding dominant phyla, TCS significantly reduced the relative abundance of Bacteroidetes and Firmicutes at these concentrations, whereas the relative abundance of Chloroflexi and Cyanobacteria increased. In the presence of benthic macroinvertebrates, the sediment bacterial community was affected by 8 µg TCS/g dw sed as well. However, the presence of benthic macroinvertebrates did not cause measurable changes to bacterial community in unspiked (i.e., control) sediment. These results indicate that TCS alone would not alter the sediment bacterial community at environmentally relevant concentrations (up till 8 µg/g dw sed), but may have an effect in combination with the presence of benthic macroinvertebrates. Therefore, we recommend to include benthic macroinvertebrates when assessing the response of sediment bacterial communities during exposure to environmental stress such as organic contaminants.

Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms.

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.