In recent years, behavior-related endpoints have been proposed as rapid and reliable ecotoxicological tools for risk assessment. In particular, the use of detritivores to test the toxicity of pollutants through feeding is currently becoming a well-known method. Experiments combining feeding with other behavioral endpoints can provide relevant information about direct and indirect toxicological effects of chemicals. We carried out a feeding experiment with the shredder Gammarus pulex in order to detect indirect (through leaf conditioning) and direct effects (through water exposure) of two pollutants at environmentally relevant concentrations: the fungicide prochloraz (6 μg/L) and the antidepressant fluoxetine (100 ng/L). Prochloraz inhibited fungal growth on leaves, but it did not affect either the microbial breakdown rates or the C:N ratio of the leaves. Individuals of G. pulex that were fed with treated leaves presented lower consumption rates, not only those fed with prochloraz-treated leaves, but also those fed with fluoxetine-treated leaves, and those fed with the mixture-treated leaves. Mixed-effects models revealed that the swimming velocity of the amphipods after the experiment was modulated by the exposure to fluoxetine, and also by the exposure to prochloraz. We demonstrate that both the antidepressant and the fungicide may cause significant sublethal effects at low concentrations. The combination of behavioral endpoints together with the application of mixed models provided a useful tool for early detection of the effects of toxicity mixtures in freshwater ecosystems.

We propose that a niche-based experimental approach at population level could be used to solve some uncertainties in traditional approaches in ecotoxicology. We tested this approach in the context of multiple stressors (i.e. chemical and physical) in a selection of six run-of-river reservoirs with different levels of sediment contamination and associated upstream and downstream river sites. A niche-based approach was tested using three functional traits (habitat, food preferences and body size) and discrepancy between the realized and theoretical niches. We first identified three groups of taxa and then recorded differences along the disturbance gradients, such as an increase in competition, a narrowing of spatial and trophic niche breadth (e.g. of Leuctra major and Gammarus pulex), a widening of spatial niche breadth (e.g. of Ephemerella ignita), a greater proportion of small individuals (e.g. of G. pulex) and a decreasing or an increasing (e.g. L. major) discrepancy between realized and theoretical niches.

Over the past decade, microscopic plastic debris, known as microplastics, emerged as a contaminant of concern in marine and freshwater ecosystems. Although regularly detected in aquatic environments, the toxicity of those synthetic particles is not well understood. To address this, we investigated whether the exposure to microplastics adversely affects the amphipod Gammarus pulex, a key freshwater invertebrate.Juvenile (6–9 mm) and adult (12–17 mm) individuals were exposed to irregular, fluorescent polyethylene terephthalate fragments (PET, 10–150 μm; 0.8–4,000 particles mL⁻¹) for 24 h. Results show that body burden after 24 h depends on the dose and age of G. pulex with juveniles ingesting more microplastics than adults. After chronic exposure over 48 d, microplastics did not significantly affect survival, development (molting), metabolism (glycogen, lipid storage) and feeding activity of G. pulex.This demonstrates that even high concentrations of PET particles did not negatively interfere with the analyzed endpoints. These results contradict previous research on marine crustaceans. Differences may result from variations in the exposure regimes (e.g., duration, particle concentrations), plastic characteristics (e.g., type, size, shape, additives) as well as the species-specific morphological, physiological and behavioral traits. As a detritivorous shredder G. pulex is adapted to feed on non-digestible materials and might, therefore, be less sensitive towards exposure to synthetic particles. Accordingly, we argue that the autecology needs to be taken into account and that research should focus on identifying traits that render species susceptible to microplastic exposure.

Organic contaminants such as pharmaceuticals, personal care products (PPCPs) and other emerging contaminants (ECs) are known to persist in the aquatic environment and many are indicated as endocrine, epigenetic, or other toxicants. Typically, the study of PPCPs/ECs in the aquatic environment is limited to their occurrence dissolved in river water. In this study, accumulation and spatial distribution of thirteen PPCPs/ECs were assessed in aquatic sediment (n = 23), periphyton (biofilm, n = 8), plants Callitriche sp. (n = 8) and Potamogeton sp. (n = 7) as well as amphipod crustaceans (Gammarus pulex, n = 10) and aquatic snails (Bithynia tentaculata, n = 9). All samples (n = 65) were collected from the Hogsmill, Blackwater and Bourne Rivers in southern England. Targeted PPCPs/ECs included pharmaceuticals, plasticisers, perfluorinated compounds, illicit drugs and metabolites. Extraction from solid matrices occurred using ultrasonic-assisted extraction followed by an in-house validated method for solid-phase extraction and subsequent liquid-chromatography tandem mass-spectrometry. Field-derived bioconcentration-factors and biota-sediment accumulation-factors were determined for all studied biota. Residues of studied contaminants were found in all sediment and biota. Concentrations of contaminants were generally higher in biota than sediment. Evidence suggests that the studied aquatic plants may effectively degrade bisphenol-A into its main transformation product hydroxyacetophenone, potentially mediated by cytochrome p450 and internalisation of contaminants into the cellular vacuole. A positive association between both hydrophobicity and PFC chain length and contaminant accumulation was observed in this work. Only PFCs, plasticisers and HAP were classified as either ‘bioaccumulative’ or ‘very bioaccumulative’ using BCF criteria established by guidelines of four governments. Contaminants appeared to be differentially bioaccumulative in biota, indicating there may be a need for a species-specific BCF/BSAF classification system. These data form a detailed accounting of PPCP/EC fate and distribution in the aquatic environment highlighting accumulation at lower trophic levels, a potential source for higher organisms.

In reverse osmosis, a frequently used technology in water desalination processes, wastewater (RO concentrate) is generated containing the retained solutes as well as so-called antiscalants (AS), i.e. chemical substances that are commonly applied to prevent membrane-blocking. In this study, a risk assessment of a possible discharge of concentrate into a small stream was conducted. The acute toxicity of two concentrates containing two different ASs and of concentrate without AS to the amphipods Gammarus pulex and Gammarus roeseli was studied. Mortality of gammarids exposed to the concentrate without AS was not different to the control, whereas concentrates including ASs caused mortality rates up to 100% at the highest test concentrations after 168 h. Resulting EC50-values were 36.2–39.4% (v/v) after 96 h and 26.6–58.0% (v/v) after 168 h. These results suggest that the ecotoxicological relevance of antiscalants is greater than currently assumed.

We exposed twelve mesocosm stream channels and four instream channels to one, two, and four pulses of the insecticide lambda-cyhalothrin (0.1 μg L⁻¹) applied at two day intervals, each pulse lasting 90 min. Unexposed controls were included. We monitored macroinvertebrate taxonomic composition in the channels and in deployed leaf packs one day before and 29 days after the first exposure. Further, we measured drift in and out of the channels and leaf litter decomposition. Lambda-cyhalothrin exposures induced significantly increased drift in both experiments especially for Gammarus pulex, Amphinemura standfussi, and Leuctra spp. Macroinvertebrate taxonomic composition increasingly changed with increasing number of lambda-cyhalothrin exposures being most pronounced in the mesocosm channels. Further, leaf decomposition significantly decreased with increasing number of exposures in the mesocosm channels. Our study showed that species with predicted highest sensitivity to lambda-cyhalothrin were primary drivers of significant changes in taxonomic composition lasting for at least one month despite continuous recolonization of exposed channels from upstream parts of the natural stream and from the water inlet in the mesocosm channels. The overall results highlight the importance of sequential exposures to insecticides for understanding the full impact of insecticides on macroinvertebrates at the community level in streams.

The fate of many chemicals in the environment, particularly contaminants of emerging concern (CEC), have been characterised to a limited extent with a major focus on occurrence in water. This study presents the characterisation, distribution and fate of multiple chemicals including pharmaceuticals, recreational drugs and pesticides in surface water, sediment and fauna representing different food web endpoints in a typical UK estuary (River Colne, Essex, UK). A comparison of contaminant occurrence across different benthic macroinvertebrates was made at three sites and included two amphipods (Gammarus pulex &Crangon crangon), a polychaete worm (Hediste diversicolor) and a gastropod (Peringia ulvae). Overall, multiple contaminants were determined in all compartments and ranged from; <LOQ – 386 ng L⁻¹ in surface water (n = 59 compounds), <LOQ – 146 ng g⁻¹ in sediment (n = 39 compounds) and <LOQ – 91 ng g⁻¹ biota (n = 33 compounds). H. diversicolor and P. ulvae (sediment dwellers) showed greater chemical body burden compared with the two swimming amphipod species sampled (up to 2.5 - 4-fold). The most frequently determined compounds in biota (100%, n = 36 samples) included; cocaine, benzyoylecgonine, carbamazepine, sertraline and diuron. Whilst some of the highest concentrations found were in species H. diverscolor and P. ulvae for psychoactive pharmaceuticals including citalopram (91 ng g⁻¹), sertraline (69 ng g⁻¹), haloperidol (66 ng g⁻¹) and the neonicotinoid, imidacloprid (33 ng g⁻¹) Sediment was noted as an important exposure route for these benthic dwelling organisms and will be critical to monitor in future studies. Overall, the analysis of multiple species and compartments demonstrates the importance of including a range of exposure pathways in order to appropriately assess chemical fates and associated risks in the aquatic environment.

The commercial use and spread of silver nanoparticles (AgNPs) in freshwaters have greatly increased over the last decade. Both AgNPs and ionic silver (Ag⁺) released from nanoparticles are toxic to organisms and compromise ecosystem processes such as leaf litter decomposition. Yet little is known about how AgNPs affect multitrophic systems of interacting species. Furthermore, past work has focused on waterborne exposure with scarce attention given to effects mediated by the consumption of contaminated food. We assessed the importance of direct (via water) and indirect (via diet) AgNP exposure to a processing chain comprising leaf litter, fungi, a shredder (Gammarus pulex) and a collector (Habroleptoides confusa) in microcosms. Direct exposure to contaminated water for 15 days impaired microbial leaf decomposition by ∼50% and leaf-associated fungal biomass by ∼10%. Leaf consumption was reduced by ∼20% but only when G. pulex was exposed to silver via contaminated leaves. There was no effect on FPOM production. Ag ⁺ could impose oxidative stress on the shredders and collectors independent of exposure route, as indicated by increased catalase and glutathione S-transferase activities and decreased superoxide dismutase activity. The activity of a neuronal enzyme (cholinesterase) in collectors, but not shredders, also decreased by almost 50% when the animals were indirectly exposed to AgNP. Our results show that AgNPs and Ag⁺ may disrupt detrital processing chains through direct and indirect exposure routes, even at low concentrations. This highlights the importance of AgNP exposure pathways to interconnected stream biota and ecosystem processes for realistic assessments of risks to freshwater ecosystems.

The prevalence of pharmaceuticals and personal care products (PPCPs) in lotic habitats is increasing, with the main source of these contaminants being effluent from waste water treatment works (WwTW). There is still much uncertainty about the impacts of these PPCPs at environmentally relevant concentrations and their potential effects on aquatic ecology. Behaviour is a sensitive endpoint which can help evaluate possible population level effects from changes in physiology. This paper evaluates the effects of WwTW effluent on a range of behaviours in the freshwater invertebrate, Gammarus pulex. Effluent taken from the outflow of two WwTW in southern England was used in the study. Behavioural analyses, namely feeding rate, phototaxis, activity, velocity and precopula pairing, were measured in G. pulex following a period of one and three weeks after exposure to a 50% or 100% effluent and a control. Mortality remained very low throughout the 3 week experiment (0–10%, n = 20) and no significant changes in moulting frequency were observed (p > 0.05). No significant effects on feeding or velocity or phototaxis following 3 weeks of effluent exposures were observed (p > 0.05). However, significant reductions were observed in the overall activity over 3 weeks across which appeared to be exacerbated by exposure to effluents. Interestingly, males exposed for 3 weeks to WwTW effluent re-paired with unexposed females significantly faster (4-6x) than control animals. This result was consistent between the effluents taken from the two WwTW. The implications of these behavioural changes are currently unknown but highlight the need for a varied set of tools to study the behavioural changes in wildlife.

Metals bioaccumulated in aquatic organisms are considered to be a good indicator of bioavailable metal contamination levels in freshwaters. However, bioaccumulation depends on the metal, the species, and the water chemistry that influences metal bioavailability. In the laboratory, a kinetic model was used to describe waterborne Pb bioaccumulated in Gammarus pulex. Uptake and elimination rate constants were successfully determined and the effect of Ca2+ on Pb uptake was integrated into the model. Thereafter, accumulated Pb concentrations in organisms were predicted with the model and compared with those measured in native populations from the Seine watershed (France). The predictions had a good agreement with the bioaccumulation levels observed in native gammarids and particularly when the effect of calcium was considered. To conclude, kinetic parameters experimentally derived for Pb in G. pulex are applicable in environmental conditions. Moreover, the consideration of the water's chemistry is crucial for a reliable interpretation of bioaccumulation.