Metal accumulation by chironomid larvae: the effects of age and body weight on metal body burdens

Age and body weight affected the extent of metal retention in larval chironomids. Elements differed with respect to age- and size-dependent metal uptake. The slopes of the regressions of metal burdens against age and size varied depending on the range in body size considered. Among fourth instar larvae, younger chironomids had higher concentrations of Cd, Mn, Ca, Ni, Fe, and Cu than older instars. When all instars were included, only concentrations of Cd and Ni were greater in young as compared to older larvae. Concentrations of Fe, Mn, Ca, and Ni were greater in larger chironomids than smaller larvae of similar age, but the effect of body weight on metal content was significant only when a wide range in biomass was considered. For the design of biological monitoring programs that use information on tissue residues of contaminants to assess contaminant bioavailability, individuals of different ages and sizes should be collected from each site in order to validate intersite comparisons. The advantages of considering metal burdens in addition to metal concentrations are emphasized.