Relationships between metal concentrations and organism size in aquatic insects

SUMMARY. The influence of organism size on whole‐body metal concentrations of eight metals was examined in aquatic insects in field and laboratory studies. Information on the partitioning of metals between adsorbed, absorbed and gut content material was also obtained. For Co, Cr, Fe, Sb and Sc, an exponential decrease in concentration with increasing organism size was observed, indicating surface adsorption as an important mode of metal accumulation. No, or only a slight, concentration‐size relationship was found for K, Mn and Na. This is expected for metals with high absorption efficiencies and a low capacity to be adsorbed. Clearing of the gut of the mayfly Stenonema modestum (Ephemeroptera: Heptageniidae) did not significantly after the concentration size relationship for any of the metals studied. Studies of Cr uptake with Stenacron interpunctatum (Ephemeroptera: Heptageniidae) indicate that the concentration‐size relationship is not affected by variability in the concentration of available Cr. About 52% of the whole‐body burden of Cr in S. interpunctatum was associated with gut material while at least 33% was adsorbed to the organism's exoskeleton and at most 15% was internally absorbed.