BOTTOM SEDIMENTS TOXICITY OF TUZLOV RIVER BASIN SMALL RIVERS BY BIOASSAY BATTERY
The Tuzlov river basin is located within the territory of the Eastern Donbass, which currently belongs to environmentally disadvantaged areas of the Rostov region. Ecosystems of small rivers are subjected to multifactor anthropogenic load. The role of bottom sediments is twofold: it contributes to the self-purification of aquatic ecosystems and can be a source of secondary pollution of the water column. Untreated (native) bottom sediments and their aqueous extracts were investigated. Data on the bottom sediments toxicity were obtained by a set of three bioassays. The organism of an ecologically relevant group - benthos - of the chironomid larvae Chironomus plumosus, a representative of planktonic heterotrophs - the rotifer Brachionus calyciflorus, a representative of autotrophs - the higher plant Raphanus sativus (radish) were used as test-objects. The choice of the test-object Raphanus sativus to assess the phytotoxicity of bottom sediments in relation to higher plants is justified by the undemanding of the plant to the nutrient medium, the widespread use in the practice of bioassay and the demand for this crop in the studied region. The bottom sediments toxicity according to the results of bioassay battery differed. The largest number of toxic samples was detected in the bioassay with rotifers (100 %), the smallest was detected in the phytotoxicity bioassay (77 %). Bioassay with Chironomidae (92 %) was similar in sensitivity to the bioassay with rotifers. The bottom sediments of all the studied Tuzlov River Basin small rivers sections were characterized as having an acute toxic effect by the results of three bioassays. Aqueous extracts of bottom sediments were more toxic than native bottom sediments. It confirms the danger of secondary contamination of the water column by bottom sediments for hydrobionts. The bioassay battery including test-objects of different systematic affiliation and trophic level allows to assess the toxicity of native sediments and to identify the potential danger of their aqueous extracts for planktocenoses organisms. Heterotrophic filter feeders (rotifers) were the most sensitive in the bottom sediments toxicity assessment of Tuzlov river basin small rivers.