Comparisons Between Laboratory Sediment Toxicity Test Results and Assessment of Benthic Community Changes for a Lake with Mild Metal Contamination

Do sediment-bound nickel and lead affect chironomids life-history? Toxicity assessment under environmentally relevant conditions

Metal pollution in aquatic ecosystems translates into increased concentrations of sediment-bound metals, representing a risk for benthic species. This risk might be enhanced in soft and moderately hard waters, world widely distributed, due to the protective role of hardness against metal toxicity. As lead (Pb) and nickel (Ni) are amongst the more abundant metals in aquatic systems, and since their combined effects to benthic species have been overlooked, in this study we aimed to investigate the life-cycle toxicity of Pb and Ni (using spiked sediment) to the benthic species Chironomus riparius, considering both single and mixture exposures, in moderately hard water. Environmentally relevant concentrations of each metal were used (25 and 75 mg kg^-1, based on a scenario of pollution by runoff waters from burnt forests), following a full factorial design. Effects of the mixture with the highest metal concentrations (Pb 75 mg kg^-1 dw + Ni 75 mg kg^-1 dw) were also assessed in the second generation. In the first generation, exposure to Pb increased emergence and the weight of males, and decreased time to emergence of both males and females. Conversely, exposure to Ni delayed female emergence and decreased the weight of imagoes. Summarizing, Pb affected more endpoints but showed an apparent positive effect, whereas Ni affected less endpoints but exhibited adverse effects. Reproduction was not affected by these metals. In the second generation, the mixture Pb 75 mg kg^-1 + Ni 75 mg kg^-1 dw delayed emergence and reduced the emerged female fraction and their weight. These results highlight that Pb and Ni can alter the structure of C. riparius populations at environmentally relevant concentrations, which signals potential repercussions in the dynamics and functioning of freshwater ecosystems under these contamination scenarios. The findings of the present study are relevant not only for metal-polluted environments, in general, but also for fire-affected ecosystems.

Bioconcentration of Organotin Cations during Molting Inhibits Heterocypris incongruens Growth

The densely populated North Sea region encompasses catchments of rivers such as Scheldt and Meuse. Herein, agricultural, industrial, and household chemicals are emitted, transported by water, and deposited in sediments, posing ecological risks. Though sediment monitoring is often costly and time-intensive, modeling its toxicity to biota has received little attention. Due to high complexity of interacting variables that induce overall toxicity, monitoring data only sporadically validates current models. Via a range of concepts, we related bio-physicochemical constituents of sediment in Flanders to results from toxicity bioassays performed on the ostracod Heterocypris incongruens. Depending on the water body, we explain up to 90% of the variance in H. incongruens growth. Though variable across Flanders' main water bodies, organotin cations and ammonia dominate the observed toxicity according to toxic unit (TU) assessments. Approximately 10% relates to testing conditions/setups, species variabilities, incoherently documented pollutant concentrations, and/or bio-physicochemical sediment properties. We elucidated the influence of organotin cations and ammonia relative to other metal(oxides) and biocides. Surprisingly, the tributylin cation appeared ∼1000 times more toxic to H. incongruens as compared to "single-substance" bioassays for similar species. We inferred indirect mixture effects between organotin, ammonia, and phosphate. Via chemical speciation calculations, we observed strong physicochemical and biological interactions between phosphate and organotin cations. These interactions enhance bioconcentration and explain the elevated toxicity of organotin cations. Our study aids water managers and policy makers to interpret monitoring data on a mechanistic basis. As sampled sediments differ, future modeling requires more emphasis on characterizing and parametrizing the interactions between bioassay constituents. We envision that this will aid in bridging the gap between testing in the laboratory and field observations.