Teratogenic versus mutagenic abnormalities in chironomid larvae exposed to zinc and lead.

Before chironomid mouthpart deformities can be utilized as indicators of aquatic metal pollution with certainty, it must first be established that deformities are teratogenic and not mutagenic. A laboratory experiment was conducted to assess this question using Zn and Pb as causative agents. Parent populations were reared in sediments spiked with zinc (Zn) or lead (Pb) and their resulting offspring (F1 generation) were reared in clean sediments. The proportions of mouthpart deformities in C. tentans larvae were compared via logistic regression, accounting for time of exposure, between parent and offspring populations. Results indicate that 14% of chironomids from Zn-spiked sediment contained deformed menta and/or mandibles. However, the F1-Zn generation displayed a deformity of 1.7%. Larvae reared in Pb-spiked sediments displayed a deformity frequency of 9% and the F1 generations (F1-Pb a and F1-Pb b) had deformity proportion of 7 and 6%, respectively. We concluded that the deformities caused by Zn stress were morphological because the resulting F1 deformity frequencies declined to control levels. However, deformities caused by Pb appear to be genetic since F1 deformity percentages did not differ from the parent deformity frequency. Because larvae reared in Zn- and Pb-spiked sediments were larger than larvae reared in uncontaminated sediments, we could not conclude that Zn and Pb in the sediments stunted the development of C. tentans.