Uranium Bioaccumulation Dynamics in the Mayfly Neocloeon triangulifer and Application to Site-Specific Prediction.

Little is known about the underlying mechanisms governing the bioaccumulation of uranium (U) in aquatic insects. We experimentally parameterized conditional rate constants for aqueous U uptake, dietary U uptake, and U elimination for the aquatic baetid mayfly Neocloeon triangulifer. Results showed that this species accumulates U from both the surrounding water and diet, with waterborne uptake prevailing. Elevated dietary U concentrations decreased feeding rates, presumably by altering food palatability or impairing the mayfly's digestive processes, or both. Nearly 90% of the accumulated U was eliminated within 24 h after the waterborne exposure ceased, reflecting the desorption of weakly bound U from the insect's integument. To examine whether the experimentally derived rate constants for N. triangulifer could be generalized to baetid mayflies, mayfly U concentrations were predicted using the water chemistry and U measured in periphyton from springs in Grand Canyon (United States) and were compared to U concentrations in spring-dwelling mayflies. Predicted and observed mayfly U concentrations were in good agreement. Under the modeled site-specific conditions, waterborne U uptake accounted for 52-93% of the bioaccumulated U. U accumulation was limited in these wild populations due to a combination of factors including low concentrations of bioavailable dissolved U species, slow U uptake rates from food, and fast U elimination.

Severing Ties: Different Responses of Larval and Adult Aquatic Insects to Atrazine and Selenium.

Aquatic insects link aquatic and terrestrial ecosystems through their metamorphosis and subsequent transition from water to land. Chemical stressors in freshwater, such as agricultural contaminants, can potentially disrupt insect life cycles and reduce the number of insects emerging as terrestrial adults, thereby damaging or severing this linkage. Atrazine and selenium, though frequently detected in waterways and often co-occurring, have not been previously studied together in controlled experiments. We conducted a six-week mesocosm experiment to measure the responses of larval and emerging aquatic insects to treatments of atrazine (15 µg/L), selenium (10 µg/L), and a direct combination of the two. Peak adult insect abundance was reduced in all treatments by 35% to 45% relative to the control. Further, cumulative adult emergence in the combined treatment was 33% lower than in the control. However, no reductions in primary production were observed with treatments, and consistent reductions in benthic insect abundance relative to the control were not observed until the end of the experiment, when overall abundance was low. Results suggest that adult insects are more sensitive than larval insects to atrazine and selenium and that the impacts of these contaminants are stronger on the terrestrial than the aquatic ecosystem.