Cadmium sources and exchange rates for Chaoborus larvae in nature
Limnol. Oceanogr., 44(7), 1999, 1763-1771 | DOI: 10.4319/lo.1922.214.171.1243
ABSTRACT: Although freshwater insects are known to accumulate trace metals in the laboratory from both water and food, the relative importance of metal sources for these animals, as well as the rate at which they take up and eliminate their metal, has not been measured in nature. We describe a novel in situ approach that allowed us to determine that trophic transfer is the main source of cadmium for larvae of a common lake-dwelling animal, the phantom midge Chaoborus punctipennis. We transferred C. punctipennis larvae from a low-cadmium to a high-cadmium lake, where they were exposed in 64- mm-mesh mesocosms to the prevailing high-Cd concentrations in water and to various quantities of prey collected from the Cd-rich lake. Our experimental design ensured exposure of C. punctipennis larvae to realistic Cd concentrations in water and in a natural mixture of prey types. Our results indicate that larvae take up their Cd mainly from prey. Thus models of metal dynamics and effects on these invertebrates are likely to be more realistic if they include food as a metal source. Using the same mesh mesocosm design, we also determined that C. punctipennis larvae transferred from a high-Cd to a low-Cd lake lost their Cd slowly. Combining our information on Cd uptake and loss from C. punctipennis allowed us to model Cd exchange between this insect and its surroundings.