Cytogenetic index and functional genome alterations in Chironomus piger Strenzke (Diptera, Chironomidae) in the assessment of sediment pollution: A case study of Bulgarian and UK rivers

• Genotoxicity of trace-metal contaminated river sediments was examined.
• Somatic damages of Chironomus piger polytene chromosomes were used as biomarkers.
• Chromosome alterations were marked by changes in somatic and cytogenetic indices.
• C. piger is a good candidate for the ecotoxicological monitoring in running waters.

The genotoxicity of trace metals in the sediments from a number of polluted sites on UK and Bulgarian rivers to Chironomus piger was assessed by an examination of genome instability as demonstrated by structural and functional changes to the salivary glands chromosomes. Based on the metal assays, the sediments were characterized to range from ‘extremely’ to ‘strongly contaminated’. The cytogenetic index calculated on the basis of somatic structural chromosome alterations in the polytene chromosomes indicates a high level of pollution (0.07–0.06 in Bulgarian and 0.10–0.13 in UK stations). Exposure of C. piger to contaminated sediments resulted in a high level of chromosome damage as indicated by a somatic index of between 1.96 and 4.0. The transcription mechanism of the Balbiani rings and nucleolar organizer was damaged as their activity was either partially or completely suppressed. We have demonstrated that the C. piger genome is a sensitive sublethal indicator of sediment contamination, and is a highly suitable candidate for ecotoxicological monitoring of running waters.