Multilevel evaluation of nonylphenol toxicity in fourth-instar larvae of Chironomus riparius (Diptera, Chironomidae).

The multilevel biomarker approach, wherein different biological responses ranging from molecular to physiological are evaluated, is essential to determine the general health status of an organism in pollutant biomonitoring programs. Furthermore, it permits extrapolation of the relationship between responses at different levels of biological organization. The aim of this study was to develop, under laboratory conditions, a multilevel biomarker approach for evaluating the toxicological response of nonylphenol (NP) in Chironoms riparius. To investigate the effect of NP on C. riparius, an acute toxicity test was performed measuring 24-h median lethal concentration. Responses on molecular, biochemical, and physiological levels were subsequently investigated on sublethal exposure. To assess molecular-level effects, we investigated DNA damage and the expression of heat shock protein 70 (HSP70) gene, whereas biochemical-level responses were determined by investigation of various enzymes activities. Growth and development were investigated as physiological-level responses. The biomarkers found to be most sensitive to NP treatment were HSP70 gene expression and DNA strand break. After having been studied with lower concentration levels with longer exposure period, these biomarkers could be considered early warning signs of exposure to low concentrations of chemical exposure. Statistically significant correlations were observed between DNA damage and the development descriptor; however, a mechanistic study appears to be necessary to establish causal relationships. This approach could be applied in environmental biomonitoring programs, and the data obtained from this study should constitute an important contribution to knowledge of the toxicology of NP in C. riparius, about which little data is available.