Micro x-ray absorption spectroscopic analysis of arsenic localization and biotransformation in Chironomus riparius Meigen (Diptera: Chironomidae) and Culex tarsalis Coquillett (Culicidae)

The distribution and speciation of arsenic (As) were analyzed in individuals of various life stages of a midge, Chironomus riparius, and the mosquito Culex tarsalis exposed to 1000 μg/l arsenate. X-ray absorption spectroscopy (XAS) revealed that C. riparius larvae accumulate As in their midgut, with inorganic arsenate [As(V)] being the predominant form, followed by arsenite [As(III)] and an As-thiol. Reduced concentrations of As in pupal and adult stages of C. riparius indicate excretion of As between the larval and pupal stages. In adults, As was limited to the thorax, and the predominant form was an As-thiol. In Cx. tarsalis, As was not found in high enough concentrations to determine As speciation, but the element was distributed throughout the larva. In adults, As was concentrated in the thorax and eyes of adults. These results have implications for understanding the biotransformation of As and its movement from aquatic to terrestrial environments. •C. riparius larvae reduced arsenate to arsenite in the midgut.•C. riparius larvae accumulated As in the midgut, with 27% as a transformed As-thiol.•C. riparius adults retained As in the thorax, with 53% as As-thiol.•Larvae of Cx. tarsalis did not have a specific site of As accumulation.•Low concentrations of As in adults suggest reduced terrestrial transfer potential. Arsenic accumulation and biotransformation in aquatic insects is variable, but the location and speciation of As provides insight into the detoxification mechanisms of aquatic Diptera.