Evaluation of tire tread particle toxicity to fish using rainbow trout cell lines

Tire and road wear particles (TRWP) resulting from tire abrasion while driving raise concerns due to their potential contribution to aquatic toxicity. Our study aimed to assess cryogenically milled tire tread (CMTT) particle toxicity, used as a proxy for TRWP, and associated chemicals to fish using two Rainbow Trout (Oncorhynchus mykiss) cell lines representing the gill (RTgill-W1) and the intestinal (RTgutGC) epithelium. CMTT toxicity was evaluated through several exposure pathways, including direct contact, leaching, and digestion, while also assessing the impact of particle aging. Following OECD TG249, cell viability was assessed after 24 h acute exposure using a multiple-endpoint assay indicative of cell metabolic activity, membrane integrity and lysosome integrity. In vitro EC50 values for the fish cell lines exceeded river TRWP concentrations (2.02 g/L and 4.65 g/L for RTgill-W1 and RTgutGC cell lines, respectively), and were similar to in vivo LC50 values estimated at 6 g/L. Although toxicity was mainly driven by the leaching of tire-associated chemicals, the presence of the particles contributed to the overall toxicity by inducing a continuous leaching, highlighting the importance of considering combined exposure scenarios. Aging and digestion conditions were also found to mediate CMTT toxicity. Thermooxidation resulted in a decreased chemical leaching and toxicity, while in vitro digestion under mimicked gastrointestinal conditions increased leaching and toxicity. Specific chemicals, especially Zn, 2-mercaptobenzothiazole, 1,3-diphenylguanidine, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) were identified as contributors to the overall toxicity. Although 6PPD-quinone was detected in CMTT digestate, cytotoxicity assays with RTgill-W1 and RTgutGC cell lines showed no toxicity up to 6 mg/L, supporting the notion of a specific mode of action of this chemical. This study provides insights into the toxicological mechanisms induced by tire particles and their associated chemicals and can help in the evaluation of potential risks to aquatic life associated with TRWP.

Environmental DNA metabarcoding for benthic monitoring: A review of sediment sampling and DNA extraction methods

Environmental DNA (eDNA) metabarcoding (parallel sequencing of DNA/RNA for identification of whole communities within a targeted group) is revolutionizing the field of aquatic biomonitoring. To date, most metabarcoding studies aiming to assess the ecological status of aquatic ecosystems have focused on water eDNA and macroinvertebrate bulk samples. However, the eDNA metabarcoding has also been applied to soft sediment samples, mainly for assessing microbial or meiofaunal biota. Compared to classical methodologies based on manual sorting and morphological identification of benthic taxa, eDNA metabarcoding offers potentially important advantages for assessing the environmental quality of sediments. The methods and protocols utilized for sediment eDNA metabarcoding can vary considerably among studies, and standardization efforts are needed to improve their robustness, comparability and use within regulatory frameworks. Here, we review the available information on eDNA metabarcoding applied to sediment samples, with a focus on sampling, preservation, and DNA extraction steps. We discuss challenges specific to sediment eDNA analysis, including the variety of different sources and states of eDNA and its persistence in the sediment. This paper aims to identify good-practice strategies and facilitate method harmonization for routine use of sediment eDNA in future benthic monitoring.

Diversity, Functions and Antibiotic Resistance of Sediment Microbial Communities From Lake Geneva Are Driven by the Spatial Distribution of Anthropogenic Contamination

Lake sediments are natural receptors for a wide range of anthropogenic contaminants including organic matter and toxicants such as trace metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls that accumulate over time. This contamination can impact benthic communities, including microorganisms which play a crucial role in biogeochemical cycling and food-webs. The present survey aimed at exploring whether anthropogenic contamination, at a large lake scale, can influence the diversity, structure and functions of microbial communities associated to surface sediment, as well as their genetic potential for resistance to metals and antibiotics. Changes in the characteristics of these communities were assessed in surface sediments collected in Lake Geneva from eight sampling sites in October 2017 and May 2018. These sampling sites were characterized by a large concentration range of metal and organic compound contamination. Variation between the two sampling periods were very limited for all sampling sites and measured microbial parameters. In contrast, spatial variations were observed, with two sites being distinct from each other, and from the other six sites. Benthic communities from the most contaminated sampling site (Vidy Bay, near the city of Lausanne) were characterized by the lowest bacterial and archaeal diversity, a distinct community composition, the highest abundance of antibiotic resistance genes and functional (respiration, denitrification, methanogenesis, phosphatase, and beta-glucosidase) activity levels. The second sampling site which is highly influenced by inputs from the Rhône River, exhibited low levels of diversity, a distinct community composition, high abundance of antibiotic resistance genes and the highest bacterial abundance. Overall, our results suggest that local anthropogenic contamination, including organic matter and toxicants, is a major driver of the diversity and functioning of sediment-microbial communities in Lake Geneva. This highlights the need to consider benthic microbial communities and a suite of complementary ecotoxicological endpoints for more effective environmental risk assessments of contaminants in lake sediments.

Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic Ecosystems: Current State of Knowledge and Future Challenges

In freshwater environments, microbial assemblages attached to submerged substrates play an essential role in ecosystem processes such as primary production, supported by periphyton, or organic matter decomposition, supported by microbial communities attached to leaf litter or sediments. These microbial assemblages, also called biofilms, are not only involved in nutrients fluxes but also in contaminants dynamics. Biofilms can accumulate metals and organic contaminants transported by the water flow and/or adsorbed onto substrates. Furthermore, due to their high metabolic activity and their role in aquatic food webs, microbial biofilms are also likely to influence contaminant fate in aquatic ecosystems. In this review, we provide (1) a critical overview of the analytical methods currently in use for detecting and quantifying metals and organic micropollutants in microbial biofilms attached to benthic substrata (rocks, sediments, leaf litter); (2) a review of the distribution of those contaminants within aquatic biofilms and the role of these benthic microbial communities in contaminant fate; (3) a set of future challenges concerning the role of biofilms in contaminant accumulation and trophic transfers in the aquatic food web. This literature review highlighted that most knowledge on the interaction between biofilm and contaminants is focused on contaminants dynamics in periphyton while technical limitations are still preventing a thorough estimation of contaminants accumulation in biofilms attached to leaf litter or sediments. In addition, microbial biofilms represent an important food resource in freshwater ecosystems, yet their role in dietary contaminant exposure has been neglected for a long time, and the importance of biofilms in trophic transfer of contaminants is still understudied.

Investigation of the spatial variability of poly- and perfluoroalkyl substance trophic magnification in selected riverine ecosystems

The occurrence at different trophic levels of 17 poly- and perfluoroalkyl substances (PFASs), including perfluoroalkyl acids (PFAAs) and some of their precursors (e.g., perfluoroalkane sulfonamides, 6:2 fluorotelomer sulfonate (6:2 FTSA)), was investigated in riverine freshwater food webs in Southeastern France. Two fish species (Barbus barbus and Squalius cephalus) and various invertebrate taxa were collected in five rivers to assess the spatial variability of trophic magnification factors (TMFs). Particular attention was devoted to sample and data processing to minimize potential biases associated with the TMF determination. Fish were significantly more contaminated than invertebrates (ΣPFAS = 7-1811 vs. 0.9-213 ng g^-1 wet weight (ww)). Those from the Rhône River presented significantly higher levels due to high concentrations of perfluoroundecanoic acid (406 ng g^-1 ww) and perfluorotridecanoic acid (566 ng g^-1 ww) ascribed to an industrial point source. Perfluorooctane sulfonate (PFOS) was dominant at the other sites (concentration range = 3.6-134 ng g^-1 ww). Two linear regression models were compared (i.e., Kendall regression vs. Generalized Linear Mixed-Effect Model, GLMM). Results showed that TMFs calculated using the non-weighted Kendall regression were higher than those obtained using the GLMM approach. GLMM-based TMFs were consistently >1 for C₉-C₁₄ perfluorocarboxylic acids (PFCAs), PFOS and perfluorodecane sulfonate (PFDS), indicating their apparent biomagnification in the investigated food webs. Comparatively, 6:2 FTSA and N-ethylperfluorooctane sulfonamidoacetic acid (N-EtFOSAA) were less often detected and were not significantly biomagnified, probably because of metabolization. TMF estimates were generally consistent across sites although some PFASs (in particular C₉, C₁₀ and C₁₃ PFCAs) displayed higher variability, due to a unique extreme value that may have resulted from the contribution of unattributed precursor biotransformation.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 2: New insights from laboratory and in situ testing with Chironomus riparius Meigen (Diptera, Chironomidae)

Chromium is widely used as a tanning agent and can become a contaminant of concern in aquatic ecosystems receiving discharges from industrial or artisanal tanning activities. In a companion study, we showed that Cr discharged by tanneries was bioavailable to indigenous chironomids with accumulation via sediment ingestion likely to represent the predominant exposure route. However, Cr accumulation by chironomids did not directly reflect the degree of sediment contamination and the potential adverse effects of Cr accumulation on chironomids were not evaluated. In the present study, chironomids were exposed to homogenised, field-collected sediments in the laboratory and to intact sediments in situ using a customized caging system. Chromium concentrations were assessed in sediments, exposed larvae of laboratory-reared Chironomus riparius and overlying waters of in situ cages. Experimental results of Cr bioaccumulation were compared with expected Cr body burden in chironomids calculated using biodynamic modelling. Our data provided strong support to the hypothesis that Cr bioaccumulation in the field is specifically controlled by the deposition of contaminated suspended particulate matter (SPM) containing a pool of Cr readily bioavailable to surface deposit feeders. Considering freshly deposited SPM as an additional route of exposure for surface deposit feeders leads to a good agreement between the modelling and experimental results. Additionally, a Cr body burden of about 77 μg g^-1 d.w. was identified as a tentative threshold above which effects on the growth of C. riparius may appear. While both laboratory and in situ experiments provide evidence for the availability of Cr in aquatic system impacted by tannery wastewaters, standard laboratory exposure conditions may miss additional exposure routes in the field and underestimate possible adverse effects on benthic organisms.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 1: Understanding chromium accumulation by indigenous chironomids

The tanning industry uses large quantities of Cr whose contribution to the contaminant burden of aquatic organisms is not yet fully understood. The present study investigated Cr bioaccumulation by indigenous chironomids in a freshwater ecosystem impacted by tannery effluents. Total Cr content in sediments and in chironomids was determined on several occasions. Chromium distribution among sediments and pore waters, and Cr speciation in overlying and pore waters were studied in detail to understand possible factors controlling Cr bioavailability to chironomids. Total chromium concentration ranged from 69 to over 3000 μg g^-1 dry weight in sediments and from negligible to over 300 μg g^-1 dry weight in chironomids (values corrected for sediment gut content). Filterable (<0.45 μm) Cr concentration in overlying waters and pore waters from the surface sediment layers (upper 2 cm) ranged from 3 to 120 μg L^-1, with Cr(VI) representing 0.5-28% of the total filterable Cr. Chromium profiles in pore waters as determined by diffusive equilibration in thin films (DET) and diffusive gradient in thin films (DGT) were comparable. DGT-labile Cr accounted for <2% of the total Cr measured by DET. Although Cr concentrations in sedimentary and aqueous matrices were not directly proportional to Cr levels measured in chironomids, the available findings suggested that Cr inputs from tanneries were bioavailable to resident chironomids. These observations are of particular importance considering that Cr(III), putatively of limited bioavailability and ecotoxicological concern, is the predominant redox form of Cr in bed sediments impacted by tannery discharges. The companion paper provides further insight into Cr bioavailability and effects in tannery impacted ecosystems using a combination of in situ and laboratory approaches.

Current developments in soil ecotoxicology and the need for strengthening soil ecotoxicology in Europe: results of a stakeholder workshop

BACKGROUND

Soil is one of our most important resources and fulfills many ecological functions such as storage and filtration of water and nutrients, transformation of chemical compounds and nutrients, biomass production, and carbon storage. Such soil functions support ecosystem services provided by soils, which need to be protected to protect soil fertility. However, European soils often contain elevated concentrations of contaminants, putting biodiversity of soil organisms as well as the ecological functions and services at risk. To promote soil ecotoxicology in Switzerland, the Swiss Centre for Applied Ecotoxicology together with the Federal Office for Environment and the Federal Office for Agriculture organized a stakeholder workshop on 7 June 2018 with participants from research, governmental bodies, and associations. One goal of this workshop was to inform participants about currently available risk assessment approaches for soil, the soil risk assessment for plant protection products in Europe, available bioassays and bioindicators, and results of research projects on soil contaminants in Switzerland. Another goal was to discuss the needs for research in soil ecotoxicology in Switzerland and to identify next steps, potential projects, and future collaborations.

RESULTS

The main needs identified during the workshop were the establishment of (bio)indicators to measure soil fertility, functional parameters to determine soil functions, and the preservation of soil biodiversity. Another priority listed was the formation of a working group, which addresses the issue of the development of environmental quality standards for soil. The need for experimental field sites for implementing and testing new approaches or tools for assessing soil quality was also discussed.

CONCLUSION

The next steps planned are two workshops with national and international experts in soil ecotoxicology to develop a soil monitoring concept for Switzerland and to find suitable bioindicators to evaluate soil fertility. Additionally, a literature review will be performed summarizing the current ecotoxicological state of the art with regard to the development of bioindicators in relation to the monitoring of plant protection products in Swiss soil, to evaluate their effects on soil fertility. Furthermore, all attendees agreed on the need for annual meetings or workshops where experts can present scientific results, participants can exchange information, and future projects and collaborations can be developed.

Refining uptake and depuration constants for fluoroalkyl chemicals in Chironomus riparius larvae on the basis of experimental results and modelling

The aims of this study were to determine depuration rates for a range of per- and polyfluoroalkyl substances (PFASs) using Chironomus riparius, and to test a concentration-dependency hypothesis for the long-chain perfluorotridecanoic acid (PFTrDA) for this species. Midge larvae were exposed to field sediments collected downstream of a fluorotelomer plant, and to the same sediment spiked with PFTrDA. Elimination kinetics results indicated complete elimination of all PFASs by chironomids after 42h. These data were used to develop two PFTrDA bioaccumulation models accounting for chironomid growth and for compound concentration dependency or not. There was much better agreement between observed and simulated data under the concentration-dependency hypothesis than under the alternative one (passive diffusion). The PFTrDA uptake rate derived from the concentration-dependency model equaled 0.013 ± 0.008g_ocg_wwh^-1, and the depuration rate 0.032 ± 0.009h^-1.

Field assessment of reproduction-related traits of chironomids using a newly developed emergence platform (E-Board)

Further progress in the development of reliable biomonitoring strategies requires to better link effects in aquatic ecological systems to ambient concentrations of chemical contaminants. Among existing tools, in situ bioassays using caging method represent an interesting way to achieve this challenge. However, elaboration of adapted exposure chambers and suitable operating procedures is still required, particularly to assess ecological relevant traits such as those related to the reproduction. In such context, we developed a new device (Emergence board - E-Board) which allows assessing in rivers the development of the Chironomus riparius species from the early fourth instar larvae to the adult stage. The system acts as a suspended matter trap floating in the subsurface of the water equipped of an emergence trap for catching adults. The system was tested in actual field conditions. Its easy handling allowed obtaining data which demonstrated its applicability for assessing the development of the chironomids. Moreover, by adapting energy-based models (DEB) specifically developed in the laboratory for the species C. riparius, we were able to predict the growth pattern and the emergence of chironomids in real environmental conditions. The E-Board represents thus a promising new in situ tool in perspective of evaluation of the quality of the ecosystems.

Potential exposure routes and accumulation kinetics for poly- and perfluorinated alkyl compounds for a freshwater amphipod: Gammarus spp. (Crustacea)

Gammarids were exposed to sediments from a deposition site located on the Rhône River (France) downstream of a fluoropolymer manufacturing plant. Gammarids accumulated to various extents four long-chain perfluoroalkyl carboxylic acids (PFCAs) from C9 to C13, one sulfonate, perfluorooctane sulfonate (PFOS) and three of its precursors (the perflurooctane sulfonamide (FOSA), the N-methyl perfluorooctane sulfonamidoacetic acid (MeFOSAA), the N-ethyl perfluorooctane sulfonamidoacetic acid (EtFOSAA) and the 6:2 fluorotelomer sulfonic acid (6:2 FTSA). Whatever the compound, the steady state was not achieved after a 3-week exposure; elimination was almost complete after a 3-week depuration period for perfluorononanoic acid (PFNA), PFOS, the three precursors and the 6:2FTSA. However, this was not the case for long-chain PFCAs, whose elimination rates decreased with increasing chain length. PFAS accumulation in gammarids occurred via the trophic and respiratory pathways, in proportions varying with the carbon chain length and the terminal moiety.

On the bioavailability of trace metals in surface sediments: a combined geochemical and biological approach

The bioavailability of metals was estimated in three river sediments (Sensée, Scarpe, and Deûle Rivers) impacted by different levels of Cu, Cd, Pb, and Zn (Northern France). For that, a combination of geochemistry and biological responses (bacteria and chironomids) was used. The results obtained illustrate the complexity of the notion of "bioavailability." Indeed, geochemical indexes suggested a low toxicity, even in surface sediments with high concentrations of total metals and a predicted severe effect levels for the organisms. This was also suggested by the abundance of total bacteria as determined by DAPI counts, with high bacterial cell numbers even in contaminated areas. However, a fraction of metals may be bioavailable as it was shown for chironomid larvae which were able to accumulate an important quantity of metals in surface sediments within just a few days.We concluded that (1) the best approach to estimate bioavailability in the selected sediments is a combination of geochemical and biological approaches and that (2) the sediments in the Deûle and Scarpe Rivers are highly contaminated and may impact bacterial populations but also benthic invertebrates.

Bioaccumulation of perfluoroalkyl compounds in midge (Chironomus riparius) larvae exposed to sediment

Midge larvae (Chironomus riparius) were exposed to sediments from a deposition sampled at a site along the Rhône River (France) downstream of an industrial site releasing various perfluorinated chemicals. This sediment is characterized by high concentrations of perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTrDA) and a low perfluorooctane sulfonate (PFOS) concentration. Concentrations of 23 perfluoroalkyl compounds, including C4-C14 carboxylate acids, C4-C10 sulfonates, and seven precursors, were analyzed in overlying and pore water, sediment, and larvae. Midge larvae accumulated carboxylate acids (C11-C14), PFOS, and two precursors (perfluorooctane sulfonamide: FOSA and 6:2 fluorotelomer sulfonic acid, 6:2 FTSA). These substances accumulated mainly during the fourth instar larvae exponential growth phase. Accumulation of 6:2 FTSA, PFUnA, and PFOS occured via trophic and tegumentary routes. Other compounds mainly accumulated from food. Kinetics followed a partition model, from which uptake and elimination constants were derived.

Characterization of trace element geochemistry in continuous flow-through microcosms: a preliminary step to environmentally meaningful ecotoxicological experiments

The increasing use of freshwater/sediment microcosms in geochemical and ecotoxicological studies requires additional efforts to characterize and understand their functioning and the main parameters that can influence the pollutants' behavior and bioavailability inside the microcosms themselves. In this study, we investigated the geochemical behavior of four elements (Cr(III), Cu, Cd, and Pb) in microcosms containing one type of natural water and sediment. The microcosms were operated under flow-through conditions with continuous metal spiking (2.5-40 μgL(-1) for Cr(III) and Pb; 1.25-20 μgL(-1) for Cu and Cd) over a period of 1 month. During this period, metal concentrations and partitioning between colloidal and truly dissolved phases in the microcosm water columns showed very little variability indicating that the system rapidly reached and maintained a steady state. Metal concentrations in pore waters also showed little variability, while Cd, Cr, and Pb levels in the top layer of sediments increased linearly from day 0 to day 28 (no significant variations in sedimentary Cu levels were observed). These features make this type of microcosms particularly suitable for ecotoxicological studies with zooplanktonic or epibenthic organisms. Characterizing the geochemical properties of microcosms provides critical information for properly interpreting microcosms-based ecotoxicity data and for reducing uncertainty in laboratory-to-field extrapolation.

Chromium(VI) is more toxic than chromium(III) to freshwater algae: a paradigm to revise?

The behavior and toxicity of Cr(III) and Cr(VI) to the green algae Pseudokirchneriella subcapitata and Chlorella kessleri were studied in a standard culture medium (ISO medium) and, for P. subcapitata only, in ultrafiltered natural water enriched with all ISO components (modified ISO medium). In all solutions amended with Cr(III), initial chromium concentrations decreased by 60-90% over 72h (the duration of algal tests) indicating that protocols for testing poorly soluble substances are required to properly evaluate Cr(III) toxicity. After accounting for its behavior in test solutions, chromium(III) was 5-10 times more toxic than Cr(VI) in both media. For P. subcapitata, the average 72h EC50 of Cr(III) in ISO medium was 17.4+/-4.7 microg/L (n=9); lower than corresponding hardness-corrected Continuous Concentration Criteria of the US EPA and well within the range of Cr concentrations found in waters impacted by tannery discharges. These results follow from intrinsic chemical properties of Cr(III) in circumneutral solutions, so that the actual toxicity of Cr(III) to aquatic organisms may be generally underestimated.

Predicting uncertainty in the ecotoxicological assessment of solid waste leachates

Environmental managers need suitable technological methods to use in optimization studies to improve management of hazardous waste. One of the challenges to achieving a reliable hazardous waste classification is the improvement of procedures used forthe ecotoxicological characterization of solid waste leachates. Indeed, this step requires data that meet levels of acceptable quality if scientifically based decisions are to be made. In this study, we illustrate how the variability associated with the successive steps of a procedure used to assess ecotoxicological hazard of solid waste (i.e., primary sampling, laboratory sampling, toxicity measurements) can contribute to the overall variability of the ecotoxicity results. To this end, a municipal solid waste incinerator bottom ash and a slag from a second smelting of lead were studied using a nested experimental design. The results showed that the waste sampling design is of major importance for limiting the final variability of toxicity test parameters. At the opposite, increasing the number of replicates at the toxicity test level has negligible impact on this variability. Our approach could be of great practical interest in ecotoxicological studies not only for ensuring a safe classification for these materials, but also for improving sampling protocols and facilitating less time-consuming and less expensive ecotoxicological evaluations.