Ecotoxicological evaluation of octachlorostyrene in fourth instar larvae of Chironomus riparius (Diptera, Chironomidae)

The ecotoxicological effects of octachlorostyrene (OCS) on the aquatic larvae of the nonbiting midges Chironomus riparius (Diptera, Chironomidae) were investigated by evaluating their responses in various biological organizations, from the molecular and biochemical to the ecophysiological levels. The results of the 24-h lethality test of OCS on C. riparius suggest that this compound has a low acute toxic potential with respect to this species. The OCS exhibited serious chronic toxicity in C. riparius, however, especially on the species' development (pupation and emergence failure), the sex ratio of the emerged adults (high female to male ratio), and the adults' reproduction (oviposition failure). As the basic premise that changes in the gene expression can be harnessed to diagnose the exposure and effects of environmental chemicals is currently receiving significant attention, the increase in the expression of the heat shock protein and hemoglobin genes suggests that altered molecular-level parameters could be interpreted as early warning biomarkers of chemical stress. The establishment of a causal relationship between molecular and organism or population indicators is important, however, from the ecotoxicological point of view, although it is difficult to perform. The experimental evidence generated in the present study, especially at the molecular and biochemical levels, is not sufficient to demonstrate a plausible mechanistic linkage among responses across biological levels. Had more parameters at the molecular and biochemical levels been investigated, the mechanistic linkage might have been better identified. A mechanistic study appears to be necessary to understand causal relationships between gene expression and higher-level consequences, such as development and reproduction. The results of the present study may constitute an important contribution to knowledge on the ecotoxicology of OCS in aquatic organisms, about which little data is available.