Exposure to 17α-ethinylestradiol and bisphenol A—effects on larval moulting and mouthpart structure of Chironomus riparius

The effects of the endocrine-disrupting chemicals 17α-ethinylestradiol (EE) and bisphenol A (BPA) on the development of the aquatic life-cycle stages (eggs to pupa) of Chironomus riparius were investigated. The test species was exposed to sublethal concentrations of EE and BPA (10 ng/L–1 mg/L) and effects on larval weight and moulting success were recorded. In addition, three mouthpart structures (mentum, mandibles, and pecten epipharyngis) present on the head capsules of fourth-instar larvae were examined for structural deformities. Moulting was delayed and larval wet weight significantly reduced (P<0.05) at the highest treatment concentration (1 mg/L) of both chemicals. No significant effect on either of these parameters was noted in the remaining treatments. However, deformities in the mouthparts of C. riparius were observed at very low exposure concentrations (10 ng/L), although the incidence of deformities was greater in the chironomids exposed to EE than BPA. Effects were mainly associated with the mentum, with statistically significant differences in median deformity score (Kruskal–Wallis P<0.001) recorded for both chemicals. At similar effect concentrations, an increased percentage of exposed animals had deformities of the pecten epipharyngis; however, little evidence of deformity was noted for the mandibles. At high concentrations, where moulting and wet weight were affected, no incidence of mouthpart deformity was noted. The relevance of these results in relation to the identification of an “endocrine-sensitive” endpoint for invertebrates is discussed.