Biotransformation and sequestration of arsenic in aquatic Diptera

While the affects of arsenic (As) on mammals have been widely documented, relatively little attention has been allotted to how insects are affected by and respond to As exposure. The aquatic dipterans Chironomus riparius (Chironomidae) and Culex tarsalis (Culicidae) are tolerant to chronic As exposure at environmentally relevant concentrations, but the means by which they are able to withstand exposures has not been examined. As a first step in assessing detoxification mechanisms, larvae of C. riparius and Cx. tarsalis were reared in water containing 0 or 1000 μg As(V)/l, and whole specimens were analyzed using X-ray Atomic Spectroscopy analysis to map the distribution and speciation of As in the samples. Individuals were sacrificed at different life stages for the XAS analysis. Whole body imaging revealed that the majority of As appears in the midgut of fourth instar larvae of C. riparius, with 43.4%, 29.2%, and 27.4% of total As represented as As(V), As(III), and As(III)-glutathione, respectively. Adults had 23.7%, 23.0%, and 53.3% of total As as As(V), As(III), and As(III)-glutathione, respectively, present in the abdomen and thoracic exoskeleton. Culex tarsalis did not have the same quantifiable degree of differentiation in larvae or adults, and As appeared to be present throughout the exoskeleton of both life stages. These results provide valuable information regarding detoxification pathways of As in aquatic dipterans. Potential mechanisms by which C. riparius and Cx. tarsalis detoxify As are discussed.