Mercury Content in Water Beetles (Coleoptera: Dytiscidae, Hydrophilidae) of Different Size Classes

The content of mercury in adult water beetles is studied in beaver ponds located in the Polist-Lovat Swamp System (Novgorod oblast). A total of 201 individuals of nine species of the family Dytiscidae and one species of the family Hydrophilidae (size classes II and III) are studied. It is revealed that the mercury content in beetles of size class II differs significantly between species (χ 2 = 32.93, p < 0.01). Maximum concentrations were found in Graphoderus cinereus (0.259 ± 0.091 µg/g dry weight), while minimum concentrations were recorded in Hydrochara caraboides (0.091 ± 0.020 µg/g dry weight). There were no significant differences in the mercury content between the III size class beetles (largest beetles) of the studied species. In beetles of size class II, the concentration of mercury decreases in the body with an increase in the body weight (Kendall rank coefficient τ = –0.31, p < 0.01). The mercury content in the body parts of beetles of the genus Dytiscus increases in order: the elytra and wings-legs-head and thorax-abdomen.