Is it justifiable to pool Chironomus species in trace element contamination studies?

Larvae of the insect Chironomus (Chironomidae: Diptera) have great potential for estimating the bioavailability of sedimentary trace elements because they are common in fine sediments and tolerate high concentrations of these contaminants. Their use as biomonitors is limited by the fact that they are difficult to identify as to species, and the species can differ in their trace element concentrations. To determine whether pooling species would compromise their use as trace element biomonitors, we identified species of Chironomus larvae collected from 22 lakes and measured their concentrations of 9 trace elements. We found that the concentrations of arsenic, barium, cobalt, copper, manganese, and nickel did not generally differ between sympatric Chironomus species, which indicates that they could be pooled for analyses of these trace elements. In contrast, we found that cadmium (Cd), selenium (Se), and zinc (Zn) concentrations differed between species living at the same site according to their feeding behavior, that is, Chironomus species feeding on oxic sediments tended to have higher Cd and Zn concentrations, whereas those feeding on deeper anoxic sediments had higher Se concentrations. Because Se and Zn concentrations in sympatric Chironomus species usually differed by only a factor of 2, separating species based on their feeding behavior might not be as crucial as for Cd if larval Se and Zn concentrations vary greatly from site to site. Environ Toxicol Chem 2019;38:145-159. © 2018 SETAC.