Implications of Genome Alterations in Chironomus bernensis Klȍtzli (Diptera) for Assessment of Trace Metal Pollution in Two Bulgarian Rivers

Abstract

AbstractThis study assesses the effect of sediment contaminants as indicated by the measurement of trace metal levels in two large Bulgarian rivers (river Maritsa and a tributary and the river Chaya) on the genome of the abundant chironomid species Chironomus bernensis Klȍtzli. Six trace metals: Cd, Cr, Cu, Mn, Pb and Zn were analysed in the sediments plus the overlying water. The polytene chromosomes of C. bernensis were very sensitive to the pollutants on the basis of numerous somatic chromosome alterations. Two biomarkers based on the degree of somatic structural chromosome alterations—the somatic and cytogenetic indices were applied. Both indices are a sensitive and reproducible approach for assessing the genotoxic effect of contaminants in the sediments. The somatic index from the differentially contaminated sites varied from 1.93 to 2.61, indicating the sensitivity of the C. bernensis genome to anthropogenic stress. The cytogenetic index revealed a high level of pollution in the rivers with a score between 0.27 and 0.37 (<0.5 indicates ‘highly polluted’). The genome of C. bernensis responded to the trace metal pollution by the appearance of a ‘B’ chromosome in between 4.4% and 7.1% of the individuals and detected for the first time in this species. Pollution also induced a heterozygous state in one of the Nucleolar Organizers in up to 3% of the sampled populations.The sensitivity of the C. bernensis genome shows that this species is a good candidate for detecting the presence of genotoxic compounds in freshwater and assessing their genotoxic effects. Copyright © 2015 John Wiley & Sons, Ltd.