Nano- and microplastics affect the composition of freshwater benthic communities in the long term.

Given the societal concern about the presence of nano- and microplastics in the environment, our nescience with respect to in situ effects is disturbing. Data on long-term implications under ecologically realistic conditions are particularly important for the risk assessment of nano- and microplastics. Here, we evaluate the long-term (up to 15 months) effects of five concentrations of nano- and microplastics on the natural recolonization of sediments by a macroinvertebrate community. Effects were assessed on the community composition, population sizes and species diversity. Nano- and microplastics adversely affected the abundance of macroinvertebrates after 15 months, which was caused by a reduction in the number of Naididae at the highest concentration (5% plastic per sediment dry weight). For some other taxa, smaller but still significant positive effects were found over time, altogether demonstrating that nano- and microplastics affected the community composition.

Phenotypic plasticity as a clue for invasion success of the submerged aquatic plant Elodea nuttallii.

Two closely related alien submerged aquatic plants were introduced into Europe. The new invader (Elodea nuttallii) gradually displaced E. canadensis even at sites where the latter was well established. The aim of the study was to evaluate the combined effects of environmental factors on several phenotypic characteristics of the two Elodea species, and to relate these phenotypic characteristics to the invasion success of E. nuttallii over E. canadensis. In a factorial design, Elodea plants were grown in aquaria containing five different nitrogen concentrations and incubated at five different light intensities. We used six functional traits (apical shoot RGR), total shoot RGR, relative elongation, root length, lateral spread, branching degree) to measure the environmental response of the species. We calculated plasticity indices to express the phenotypic differences between species. Light and nitrogen jointly triggered the development of phenotypic characteristics that make E. nuttallii a more successful invader in eutrophic waters than E. canadensis. The stronger invader showed a wider range of phenotypic plasticity. The apical elongation was the main difference between the two species, with E. nuttallii being more than two times longer than E. canadensis. E. canadensis formed dense side shoots even under high shade and low nitrogen levels, whereas E. nuttallii required higher light and nitrogen levels. We found that under more eutrophic conditions, E. nuttallii reach the water surface sooner than E. canadensis and through intensive branching outcompetes all other plants including E. canadensis. Our findings support the theory that more successful invaders have wider phenotypic plasticity.

Multiwalled carbon nanotubes at environmentally relevant concentrations affect the composition of benthic communities.

To date, chronic effect studies with manufactured nanomaterials under field conditions are scarce. Here, we report in situ effects of 0, 0.002, 0.02, 0.2, and 2 g/kg multiwalled carbon nanotubes (MWCNTs) in sediment on the benthic community composition after 15 months of exposure. Effects observed after 15 months were compared to those observed after 3 months and to community effects of another carbonaceous material (activated carbon; AC), which was simultaneously tested in a parallel study. Redundancy analysis with variance partitioning revealed a total explained variance of 51.7% of the variation in community composition after 15 months, of which MWCNT dose explained a statistically significant 9.9%. By stepwise excluding the highest MWCNT concentrations in the statistical analyses, MWCNT effects were shown to be statistically significant already at the lowest dose investigated, which can be considered environmentally relevant. We conclude that despite prolonged aging, encapsulation, and burial, MWCNTs can affect the structure of natural benthic communities in the field. This effect was similar to that of AC observed in a parallel experiment, which however was applied at a 50 times higher maximum dose. This suggests that the benthic community was more sensitive to MWCNTs than to the bulk carbon material AC.

Long-term recovery of benthic communities in sediments amended with activated carbon.

Using activated carbon (AC) for sediment remediation may have negative effects on benthic communities. To date, most AC effect studies were short-term and limited to single species laboratory tests. Here, we studied the effects of AC on the recolonization of benthic communities. Sediment from an unpolluted site was amended with increasing levels of AC, placed in trays and randomly embedded in the original site, which acted as a donor system for recolonization of benthic species. After 3 and 15 months, the trays were retrieved and benthic organisms identified. A positive trend with AC was detected for species abundance after 3 months, whereas after 15 months a negative trend with AC was detected for Lumbriculidae and Pisidiidae. On the community level, statistical analyses showed a considerable recovery in terms of species diversity and abundance in 3 months and full recovery of the community after 15 months. This was explained from migration of individuals from the donor system, followed by further migration and reproduction of the species in the next year. AC treatments explained 3% of the variance in the community data. This work suggests that AC community effects are mild as long as AC levels are not too high (1-4%).

Ecotoxicological effects of activated carbon amendments on macroinvertebrates in nonpolluted and polluted sediments.

Amendment of contaminated sediment with activated carbon (AC) is a remediation technique that has demonstrated its ability to reduce aqueous concentrations of hydrophobic organic compounds. The application of AC, however, requires information on possible ecological effects, especially effects on benthic species. Here, we provide data on the effects of AC addition on locomotion, ventilation, sediment avoidance, mortality, and growth of two benthic species, Gammarus pulex and Asellus aquaticus , in clean versus polycyclic aromatic hydrocarbon (PAH) contaminated sediment. Exposure to PAH was quantified using 76 µm polyoxymethylene passive samplers. In clean sediment, AC amendment caused no behavioral effects on both species after 3-5 days exposure, no effect on the survival of A. aquaticus , moderate effect on the survival of G. pulex (LC(50) = 3.1% AC), and no effects on growth. In contrast, no survivors were detected in PAH contaminated sediment without AC. Addition of 1% AC, however, resulted in a substantial reduction of water exposure concentration and increased survival of G. pulex and A. aquaticus by 30 and 100% in 8 days and 5 and 50% after 28 days exposure, respectively. We conclude that AC addition leads to substantial improvement of habitat quality in contaminated sediments and outweighs ecological side effects.

Effects of an anionic surfactant (FFD-6) on the energy and information flow between a primary producer (Scenedesmus obliquus) and a consumer (Daphnia magna).

The effects of a commercially available anionic surfactant solution (FFD-6) on growth and morphology of a common green alga (Scenedesmus obliquus) and on survival and clearance rates of the water flea Daphnia magna were studied. The surfactant-solution elicited a morphological response (formation of colonies) in Scenedesmus at concentrations of 10-100 µl l(-1) that were far below the No Observed Effect Concentration (NOEC) value of 1,000 µl l(-1) for growth inhibition. The NOEC-value of FFD-6 for colony-induction was 3 µl l(-1). Daphnia survival was strongly affected by FFD-6, yielding LC(50-24h) and LC(50-48 h) of 148 and 26 µl l(-1), respectively. In addition, clearance rates of Daphnia feeding on unicellular Scenedesmus were inhibited by FFD-6, yielding a 50% inhibition (EC(50-1.5h)) at 5.2 µl l(-1) with a NOEC of 0.5 µl l(-1). When Daphnia were offered FFD-6-induced food in which eight-celled colonies (43 × 29 µm) were most abundant, clearance rates (~0.14 ml ind.(-1) h(-1)) were only 25% the rates of animals that were offered non-induced unicellular (15 × 5 µm) Scenedesmus (~0.56 ml ind.(-1) h(-1)). As FFD-6 concentrations in the treated food used in the experiments were far below the NOEC for clearance rate inhibition, it is concluded that the feeding rate depression was caused by the altered morphology of the Scenedesmus moving them out of the feeding window of the daphnids. The surfactant evoked a response in Scenedesmus that is similar to the natural chemically induced defensive reaction against grazers and could disrupt the natural information conveyance between these plankton organisms.

Community effects of carbon nanotubes in aquatic sediments.

Aquatic sediments form an important sink for manufactured nanomaterials, like carbon nanotubes (CNT) and fullerenes, thus potentially causing adverse effects to the aquatic environment, especially to benthic organisms. To date, most nanoparticle effect studies used single species tests in the laboratory, which lacks ecological realism. Here, we studied the effects of multiwalled CNT (MWCNT) contaminated sediments on benthic macroinvertebrate communities. Sediment was taken from an unpolluted site, cleaned from invertebrates, mixed with increasing levels of MWCNTs (0, 0.002, 0.02, 0.2 and 2g/kg dry weight), transferred to trays and randomly relocated in the original unpolluted site, which now acted as a donor system for recolonization by benthic species. After three months of exposure, the trays were regained, organic (OC) and residual carbon (RC) were measured, and benthic organisms and aquatic macrophytes were identified. ANOVA revealed a significantly higher number of individuals with increasing MWCNT concentrations. The Shannon index showed no significant effect of MWCNT addition on biodiversity. Multivariate statistics applied to the complete macroinvertebrate dataset, did show effects on the community level. Principal Component Analysis (PCA) showed differences in taxa composition related to MWCNT levels indicating differences in sensitivity of the taxa. Redundancy Analysis (RDA) revealed that MWCNT dose, presence of macrophytes, and spatial distribution explained 38.3% of the total variation in the data set, of which MWCNT dose contributed with 18.9%. Still, the net contribution of MWCNT dose was not statistically significant, indicating that negative community effects are not likely to occur at environmentally relevant future CNT concentrations in aquatic sediments.

Triple domain in situ sorption modeling of organochlorine pesticides, polychlorobiphenyls, polyaromatic hydrocarbons, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans in aquatic sediments.

Here we analyze the potential of black carbon (BC) and oil-inclusive models to explain in situ sorption of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), organochlorine pesticides (OCP), polychlorobiphenyls (PCB), polyaromatic hydrocarbons (PAH), polychlorinated dibenzo-p-dioxins (PCDD), and polychlorinated dibenzofurans (PCDF) to harbor sediments. Such models are important to understand bioavailability and mobility limitations of these chemicals in the aquatic environment. Separate BC- or oil-inclusive models have been described before. However, it is unclear whether oil could dominate in situ sorption in sediments that also contain BC, and whether the relative importance of phases would differ for different compounds. A BC- and oil-inclusive model was evaluated against chemical data and measured sediment characteristics. Parameter uncertainty was assessed using Monte Carlo simulations. Fitted model parameters were consistent with literature data and were satisfactory from a statistical as well as a chemical perspective. Sorption to oil was strong, proportional to octanol-water partitioning (Log K(ow)) and of similar magnitude for OCP, PCB, PCDD, and PCDF. For PAH a single oil sorption coefficient was found. Oil dominated sorption only for PCBs, at oil levels above 50-250 mg oil/kg sediment. BC dominated sorption of most other compounds, especially high molecular PAHs, PCDD, and PCDFs.

Seasonal variation of total and biochemically available concentrations of PAHs in a floodplain lake sediment has no effect on the benthic invertebrate community.

Floodplain areas in the Netherlands are moderately to heavily contaminated with trace metals and organic contaminants. The impact of this sediment pollution on benthic invertebrates is best described with so-called 'bioavailable' concentrations instead of total concentrations. Studies into the effect of contaminants on biota are usually a snapshot in time, with one or two samples in a year. In such studies, effect of seasonal variation cannot be detected. Objective of this study was to investigate the temporal variation of sediment PAH contamination in one floodplain lake, and possible consequences for the benthic invertebrate community. This was done by sampling biota, abiotic variables and sediment contaminants every four weeks during one year. We observed a limited seasonal variation in total and bioavailable concentrations of PAHs. Multivariate analysis revealed that the PAH contamination is not a significant factor for the benthic invertebrate community in this floodplain lake. Bioavailable concentrations of PAHs were low and no effects could be expected based on the measured values. No increase of available PAHs was observed in periods where conditions for degradation were absent (low temperature, anaerobic). These results also indicate that in such floodplain lake systems, with historical pollution, the timing of sampling to assess sediment contamination with organic pollutants is of limited importance. This can be useful for planning sampling in risk assessment studies.

Behavioural responses of Gammarus pulex (Crustacea, Amphipoda) to low concentrations of pharmaceuticals.

The continuous discharge of pharmaceuticals and personal care products into the environment results in a chronic exposure of aquatic organisms to these substances and their metabolites. As concentrations in surface waters are in the ng/L range, and sometimes in the low microg/L range, they are not likely to result in lethal toxicity. However, prolonged exposure to low concentrations of anthropogenic chemicals may lead to sublethal effects, including changes in behaviour. The aim of this study was to assess the effect of three pharmaceuticals, the antidepressant fluoxetine, the analgesic ibuprofen and the anti-epileptic carbamazepine, and one cationic surfactant, cetyltrimethylammonium bromide (CTAB), on the activity of the benthic invertebrate Gammarus pulex (Crustacea: Amphipoda: Gammaridae). We used the multispecies freshwater biomonitor to assess changes in activity of G. pulex in a quantitative manner. Exposure to low concentrations (10-100ng/L) of fluoxetine and ibuprofen resulted in a significant decrease in activity, whereas the activity of G. pulex at higher concentrations (1microg/L-1mg/L) was similar to the control. Response to carbamazepine showed a similar pattern, however, differences were not significant. The tested surfactant CTAB evoked a decrease in activity at increasing concentration. These behavioural effect concentrations were 10(4) to 10(7) times lower than previously reported LOECs and in the range of environmentally occurring concentrations. The potential consequences of this decreased activity for G. pulex population growth and benthic community structure and the exposure to mixtures of pharmaceuticals deserves further attention.

Contaminated sediments and bioassay responses of three macroinvertebrates, the midge larva Chironomus riparius, the water louse Asellus aquaticus and the mayfly nymph Ephoron virgo.

Bioassays are widely used to estimate ecological risks of contaminated sediments. We compared the results of three whole sediment bioassays, using the midge larva Chironomus riparius, the water louse Asellus aquaticus, and the mayfly nymph Ephoron virgo. We used sediments from sixteen locations in the Dutch Rhine-Meuse Delta that differed in level of contamination. Previously developed protocols for each bioassay were followed, which differed in sediment pretreatment, replication, and food availability. The Chironomus bioassay was conducted in situ, whereas the other two were conducted in the laboratory. The measured endpoints, survival and growth, were related to contaminant levels in the sediment and to food quantity in water and sediment. Only the response of A. aquaticus in the bioassay was correlated with sediment contamination. Food availability in overlying water was much more important for C. riparius and E. virgo, thereby masking potential sediment contaminant effects. We conclude that growth of A. aquaticus was depressed by sediment contamination, whereas growth of E. virgo and C. riparius was stimulated by seston food quantity. We discuss that the trophic state of the ecosystem largely affects the ecological risks of contaminated sediments.

Evaluation of bioassays versus contaminant concentrations in explaining the macroinvertebrate community structure in the Rhine-Meuse delta, The Netherlands.

It is often assumed that bioassays are better descriptors of sediment toxicity than toxicant concentrations and that ecological factors are more important than toxicants in structuring macroinvertebrate communities. In the period 1992 to 1995, data were collected in the enclosed Rhine-Meuse delta, The Netherlands, on macroinvertebrates, sediment toxicity, sediment contaminant concentrations, and ecological factors. The effect of various groups of pollutants (polycyclic aromatic hydrocarbons, trace metals, oil, polychlorinated biphenyls) and of ecological variables on the structure of the macroinvertebrate community were quantified. Ecological factors explained 17.3% of the macroinvertebrate variation, while contaminants explained 13.8%. Another 14.7% was explained by the covariation between ecological variables and contaminants. Polycyclic aromatic hydrocarbons explained a larger part of the variation than trace metals. The contributions of oil and polychlorinated biphenyls were small but significant. Elevated contaminant concentrations were significantly associated with differences in the macroinvertebrate food web structure. The response in bioassays (Vibrio fischeri, Daphnia magna, Chironomus riparius) was susceptible to certain contaminants but also to certain ecological factors. There was a weak correlation between in situ species composition and bioassays; 1.9% of in situ macroinvertebrate variation was explained by the bioassay responses. This seems to contradict the validity of using bioassays for a system-oriented risk assessment. Possible reasons for this discrepancy might be the manipulations of the sediment before the test and a higher pollutant tolerance of the in situ macroinvertebrates. Thus, macroinvertebrate field surveys and laboratory bioassays yield different types of information on ecotoxicological effects, and both are recommended in sediment risk assessment procedures.

Effects of benzo(a)pyrene and size of organic matter particles on bioaccumulation and growth of Asellus aquaticus.

The effects of sediment-bound toxicants to aquatic invertebrates may vary due to differences in bioavailability, food quality, or food structure. The equilibrium partitioning theory (EPT) assumes that organic matter content of sediments and not structure of organic matter is relevant for biological effects of polycyclic aromatic hydrocarbons. To test this hypothesis effects of benzo(a)pyrene (B(a)P) and size of sediment organic matter particles on the bioaccumulation and growth of the waterlouse Asellus aquaticus were studied in laboratory microcosms. Sediments and A. aquaticus were both sampled in an unpolluted, spring-fed pond. The sampled sediment was divided into two portions. From one portion the size of the organic matter particles was mechanically reduced. One set of each sediment fraction (fine and coarse) was spiked with B(a)P and incubated for 3 weeks resulting in a concentration of 70 mg B(a)P per kg sediment. Bioassays of 32 days were performed in a 2 x 2 factorial design with four replicas of each treatment. The results showed that the growth of A. aquaticus was mainly influenced by the size of organic matter particles. Growth was significantly less (27%) on finer sediments than on coarser sediments. The increase in length was 9-14% lower in the spiked sediments, but this difference was not significant. The reduced growth of A. aquaticus on finer sediments may be due to a change in the availability and/or quality of food together with a change in feeding behavior. The coarse and fine spiked sediment types did not differ significantly with respect to the sediment water partition coefficient, the organic carbon water partition coefficient, and the bioconcentration factor. In contrast, the biota to sediment accumulation factors were significantly 15% higher in the cosms with coarse sediments than in cosms with fine sediments. However, this difference is too small to conflict with EPT.