Towards simple tools to assess functional effects of contaminants on natural microbial and invertebrate sediment communities

The use of copper as plant protection product contributes to environmental contamination and resulting impacts on terrestrial and aquatic biodiversity and ecosystem functions

Copper-based plant protection products (PPPs) are widely used in both conventional and organic farming, and to a lesser extent for non-agricultural maintenance of gardens, greenspaces, and infrastructures. The use of copper PPPs adds to environmental contamination by this trace element. This paper aims to review the contribution of these PPPs to the contamination of soils and waters by copper in the context of France (which can be extrapolated to most of the European countries), and the resulting impacts on terrestrial and aquatic biodiversity, as well as on ecosystem functions. It was produced in the framework of a collective scientific assessment on the impacts of PPPs on biodiversity and ecosystem services in France. Current science shows that copper, which persists in soils, can partially transfer to adjacent aquatic environments (surface water and sediment) and ultimately to the marine environment. This widespread contamination impacts biodiversity and ecosystem functions, chiefly through its effects on phototrophic and heterotrophic microbial communities, and terrestrial and aquatic invertebrates. Its effects on other biological groups and biotic interactions remain relatively under-documented.

Cd indirectly affects the structure and function of plankton ecosystems by affecting trophic interactions at environmental concentrations

The toxic effects of potentially toxic elements have been observed at low concentrations; however, many studies have focused on single-species toxicity testing. Consequently, it is imperative to quantify toxicity at the community level at environmental concentrations. A microcosm approach was employed in conjunction with the Lotka-Volterra model to ascertain the impact of environmentally relevant concentrations of cadmium (Cd) on plankton abundance, community function, and stability. The results demonstrated that Cd led to a reduction in the abundance of Daphnia magna, yet unexpectedly resulted in an increase in the abundance of Brachionus calyciflorus and Paramecium caudatum. Additionally, Cd was observed to impede primary productivity, metabolic capacity and the stability of the planktonic community. Further model analyses revealed that the environmental concentration of Cd directly reduced intrinsic growth rates and intraspecific interactions. In particular, we found that the predation effects of Daphnia magna on Brachionus calyciflorus were significantly weakened. The findings of this study offer quantitative evidence that Cd exposure exerts an indirect influence on the structure and functioning of plankton ecosystems, mediated by alterations in trophic interactions. The findings indicate that the impact of environmental concentrations of potentially toxic elements may be underestimated in single-species experiments.

Unlocking secrets of microbial ecotoxicology: recent achievements and future challenges

Environmental pollution is one of the main challenges faced by humanity. By their ubiquity and vast range of metabolic capabilities, microorganisms are affected by pollution with consequences on their host organisms and on the functioning of their environment. They also play key roles in the fate of pollutants through the degradation, transformation, and transfer of organic or inorganic compounds. Thus, they are crucial for the development of nature-based solutions to reduce pollution and of bio-based solutions for environmental risk assessment of chemicals. At the intersection between microbial ecology, toxicology, and biogeochemistry, microbial ecotoxicology is a fast-expanding research area aiming to decipher the interactions between pollutants and microorganisms. This perspective paper gives an overview of the main research challenges identified by the Ecotoxicomic network within the emerging One Health framework and in the light of ongoing interest in biological approaches to environmental remediation and of the current state of the art in microbial ecology. We highlight prevailing knowledge gaps and pitfalls in exploring complex interactions among microorganisms and their environment in the context of chemical pollution and pinpoint areas of research where future efforts are needed.

Combined Chemical and Ecotoxicological Measurements for River Sediment Management in an On-Land Deposit Scenario

Sediment management along engineered river systems includes dredging operations and sediment deposition in the sea (capping) or on land. Thus, determining the ecotoxicological risk gradient associated with river sediments is critical. In this study, we investigated sediment samples along the Rhône River (France) and conducted environmental risk assessment tests with the idea to evaluate them in the future for deposit on soil. Based on an on-land deposit scenario, the capacity of the sediment samples from four sites (LDB, BER, GEC, and TRS) to support vegetation was evaluated by characterising the physical and chemical parameters (pH, conductivity, total organic carbon, grain size, C/N, potassium, nitrogen, and selected pollutants), including polychlorinated biphenyls (PCBs) and metal trace elements. All tested sediments were contaminated by metallic elements and PCBs as follows: LDB > GEC > TRS > BER, but only LDB had levels higher than the French regulatory threshold S1. Sediment ecotoxicity was then assessed using acute (plant germination and earthworm avoidance) and chronic (ostracod test and earthworm reproduction) bioassays. Two of the tested plant species, Lolium perenne (ray grass) and Cucurbita pepo (zucchini), were highly sensitive to sediment phytotoxicity. Acute tests also showed significant inhibition of germination and root growth, with avoidance by Eisenia fetida at the least contaminated sites (TRS and BER). Chronic bioassays revealed that LDB and TRS sediment were significantly toxic to E. fetida and Heterocypris incongruens (Ostracoda), and GEC sediment was toxic for the latter organism. In this on-land and spatialised deposit scenario, river sediment from the LDB site (Lake Bourget marina) presented the highest potential toxicity and required the greatest attention. However, low contamination levels can also lead to potential toxicity (as demonstrated for GEC and TRS site), underlining the importance of a multiple test approach for this scenario.

Synthetic periphyton as a model system to understand species dynamics in complex microbial freshwater communities

Phototrophic biofilms, also known as periphyton, are microbial freshwater communities that drive crucial ecological processes in streams and lakes. Gaining a deep mechanistic understanding of the biological processes occurring in natural periphyton remains challenging due to the high complexity and variability of such communities. To address this challenge, we rationally developed a workflow to construct a synthetic community by co-culturing 26 phototrophic species (i.e., diatoms, green algae, and cyanobacteria) that were inoculated in a successional sequence to create a periphytic biofilm on glass slides. We show that this community is diverse, stable, and highly reproducible in terms of microbial composition, function, and 3D spatial structure of the biofilm. We also demonstrate the ability to monitor microbial dynamics at the single species level during periphyton development and how their abundances are impacted by stressors such as increased temperature and a herbicide, singly and in combination. Overall, such a synthetic periphyton, grown under controlled conditions, can be used as a model system for theory testing through targeted manipulation.

Physicochemical and biological status of Aghlagan river, Iran: effects of seasonal changes and point source pollution

Although the macroinvertebrates have been widely used as bio-indicator for river water quality assessment in developed countries, its application is new in Iran and data on the health status of the most ecologically important rivers in Iran is scarce. The present study aimed at monitoring and assessing the ecological quality of Aghlagan river, northwest of Iran, using integrated physicochemical-biological approaches. A total of 14,423 samplings were carried out from the headwater to downstream sites at four stations (S1, 2, 3, 4) by a Surber sampler (30 cm × 30 cm) from June 2018 to April 2019. The results obtained from macroinvertebrate biotic index revealed that the genera of Gammarus (Amphipoda) and Baetis (Ephemeroptera) were the most abundant in all seasons. The PAST software was applied to analyze the diversity indices (Shannon-Weiner diversity, Evenness, and Simpson indices). Based on the cluster analysis, S3 established the least similarity to other stations. The average frequency of each macroinvertebrate species was determined by one-factor analysis of similarities (ANOSIM). In accordance with canonical correspondence analysis (CCA), temperature and phosphate were found as the dominant factors effecting the macroinvertebrate assemblage and distribution. Moreover, the results obtained from the biological indices concluded very good quality of S4 by Helsinhoff and EPT indices and fair quality using BMWP index. The data on the macrobenthos assemblage and dynamics in the Aghlagan river across a hydraulic gradient provided useful information on water management efforts that assist us to find sustainable solutions for the enhanced quality of the river by balancing environmental and human values.

Changes in sediment microbial diversity following chronic copper-exposure induce community copper-tolerance without increasing sensitivity to arsenic

Sediment microbial communities were exposed for 21 days to an environmental concentration of copper to assess Cu-induced composition changes and resulting effects on microbial sensitivity to acute Cu and As toxicity. Chronic Cu exposure reduced the diversity of the bacterial and archaeal communities from Day 0 to Day 21. The pollution-induced community tolerance concept (PICT) predicts that loss of the most sensitive taxa and gain of more tolerant ones should increase the capacity of Cu-exposed communities to tolerate acute Cu toxicity. Although diversity loss and functional costs of adaptation could have increased their sensitivity to subsequent toxic stress, no increased sensitivity to As was observed. PICT responses varied according to heterotrophic activity, selected as the functional endpoint for toxicity testing, with different results for Cu and As. This suggests that induced tolerance to Cu and As was supported by different species with different metabolic capacities. Ecological risk assessment of contaminants would gain accuracy from further research on the relative contribution of tolerance acquisition and co-tolerance processes on the functional response of microbial communities.