Bioaccumulation of Lead and Cadmium in the Lousiana Heron (Hydranassa tricolor ) and the Cattle Egret (Bubulcus ibis )

Lead and cadmium concentrations in the tissues and stomach contents of several age classes of Louisiana herons (H. tricolor ) and cattle egrets (B. ibis ) from the Galveston Bay region of Texas were measured, and levels of exposure and the rates of accumulation by these species were compared. Statistical analyses showed no differences in the rates and patterns of accumulation of these metals between these species; however, tissue and age class were both significant variables. Lead concentrations were highest in the bone of adult birds, while cadmium was highest in the adult kidney. Although these birds feed in different habitats, analyses of metal content in their food items showed similar rates of exposure. The authors note an important distinction between biomagnification and ontogenetic accumulation in studies which seek to estimate the importance of trophic position on risk of exposure to heavy metals.