Influence of gut content in immature aquatic insects on assessments of environmental metal contamination

We evaluated the effect of metal associated with the gut content in immature aquatic insects (larvae and nymphs) on spatial and interspecific comparisons of whole-body metal concentrations. Four species, common to cobble-bottom rivers and streams, were collected along an established contamination gradient in the Clark Fork River, and from tributaries of the Clark Fork. Metal concentrations were determined in the gut and its content and in the insect body. Whole-body metal concentrations were higher and more variable as a result of gut content. The positive bias produced by the gut content did not alter interpretations of site contamination in most cases. Interspecific comparisons of metal bioaccumulation also were not greatly affected by the presence of gut content. The influence of gut content was specific for metal, species, and site. Feeding habit, gut size, and metal bioaccumulation in the body affected the relative contribution of the gut and its content to metal concentrations in the whole insect.