Assessment of the sediment toxicity in Bulgarian and Turkish rivers using the biomarkers in chironomus riparius Mg. (Diptera: Chironomidae)

Abstract

As a model organism we used Chironomus riparius Mg. - a widely distributed species that can be reared in the laboratory conditions and has excellent salivary gland chromosomes. The study showed that the genome at cytogenetical and biochemical levels is a sensitive biomarker and can serve as early - warning indicators of environmental impact of chemicals. Analysis of trace metals in sediment of Chaya River (Asenovgrad, Bulgaria, 2010) and Derincay River (Turkey, 2010), indicated higher concentrations of trace metals (Pb, Cr, Cu, Cd) in comparison with reference data. The response at cytogenetical level is determined by changes of gene expression of key structures (BRs and NOR) and increased in structural chromosome somatic aberrations. Changes of gene expression are indicated by decreasing the transcriptional activity of BRs and NOR: very often they occurred in the intermediate state of activity or BRs are in collapse. The cells with somatic rearrangements of C. riparius from polluted Derincay and Chaya River were in 16.94% and 36.36% respectively, which were significantly higher than those of the control (Derincay River: G = 125.53, P<0.001; Chaya River: G = 73.81, P<0.001). Somatic index was the highest in the sample from Chaya River - 3.25, following by Derincay River -1.58, while it was 0.13 in the control sample. The response of the C. riparus at biochemical level is characterized by increaseing amount of metallothionein (MT) higher in Chaya River in comparison of Derincay River. Similarly, the other studied enzyme activities, GST and EROD, showed on the average 20% and 24% higher activities respectively, in Derincay than in Chaya. In addition, in accordance with above enzyme activities, the level of AChE inhibition is about 10% higher in Derincay River than in Chaya River. As a result, alterations in these biochemical parameters could be regarded as valid reflections of the increased trace metals in Derincay and Chaya Rivers. It could be concluded that the environmental diagnose quality by multilevel approach (cytogenetical and biochemical) will enable better understanding of the impact of pollutants on organisms and should be successful implemented in environmental monitoring procedures.