Freshwater ecosystems are increasingly affected by anthropogenic stressors, necessitating the assessment of sensitive biomarkers of sublethal impact. This study assessed the seasonal variability of oxidative stress parameters in the amphipod Gammarus lacustris from three tributaries of Lake Sevan (Armenia)—the Gavaraget, Karchagbyur, and Argichi Rivers—with contrasting hydrophysical and hydrochemical conditions. During 2022–2024, lipid peroxidation (MDA), antioxidant enzymes (CAT, SOD, GR, and GST), and glutathione (GSH) were measured in specimens collected in May, July, and October and related to temperature, dissolved oxygen, nutrients, major ions, and trace elements. Biomarker levels generally increased from spring to summer and declined in autumn, following temperature and photoperiod patterns. Statistically significant seasonal dynamics were most consistent in the Karchaghbyur River, while, in the Gavaraget and Argichi Rivers, they varied by biomarker and year. Amphipods from the Gavaraget River exhibited consistently elevated levels of oxidative stress biomarkers, consistent with elevated nutrient concentrations and stronger anthropogenic impacts. A short-term increase in all biomarkers in the Argichi River in 2023 indicated episodic acute stress. Overall, the response of oxidative stress biomarkers in G. lacustris reflected both the natural seasonal variability and spatial differences in environmental pressure, confirming their potential as a tool for monitoring Lake Sevan’s tributaries.

A biodiagnostic assessment was performed for the Uva River, which is affected by dairy plant wastewater. Macrozoobenthos indicators were used for bioindication. In total, 129 species and higher‑rank taxa of macrozoobenthos were recorded. In the reach downstream of the wastewater discharge, a sharp decline in taxonomic richness was accompanied by lower values of the Shannon index, Pielou evenness, the EPT index, TBI, and BMWP. Concurrently, the proportion of oligochaetes in the community increased, as reflected by the Goodnight–Whitley index, while macrozoobenthos abundance (up to 40 500 specimens/m²) and biomass (up to 155 g/m²) increased substantially. The saprobity index ranged from 1.7 to 7.0. The upper reaches corresponded to a β-mesosaprobic zone; in the middle reaches, the saprobity index ranged from 1.89 to 7.0, corresponding to β-mesosaprobic, α-mesosaprobic, and polysaprobic zones. In the lower reaches, the saprobity index again corresponded to the β-mesosaprobic zone. Biotesting of aqueous extracts of bottom sediments using luminescent bacteria with the Ecolum test system revealed acute toxicity at two stations downstream of the wastewater discharge. An approximately 25-km ecological disaster zone was identified downstream of the dairy plant wastewater discharge in the urban-type settlement of Uva.

Anthropogenic pollution of the aquatic environment with microplastics is one of the most urgent but least studied problems of modern ecotoxicology. The review, based on recent literature data, provides an analysis of studies in the field of absorption, bioaccumulation, and biological effects of microplastic exposure in freshwater bivalve molluscs (Bivalvia). A total of 22 studies have been conducted so far, which were performed on representatives of three families: Cyrenidae (45), Unionidae (25) and Dreissenidae (30%). The conducted studies are represented by field observations (43.5), field (8.7) and laboratory (47.8%) experiments. It has been shown that freshwater bivalves, as active filters, are able to absorb and accumulate in soft tissues (gills, hepatopancreas) microplastic particles from both water and bottom sediments, perceiving them as food objects. Bioaccumulation of microplastics in molluscs leads to functional and structural disorders in the body. The joint action of microplastics and other pollutants (cadmium, polychlorinated biphenyls, pharmacological drugs) can cause both synergistic and antagonistic effects in the biological responses of molluscs. Based on the conducted studies, it is suggested to use bivalve molluscs as organisms-bioindicators of freshwater pollution with microplastics.