Contribution of Gut Contents to the Concentration and Body Burden of Elements in Tipula spp. from a Spring-Fed Stream

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Abstract
Larvae of Tipula spp., a detritus-feeding aquatic insect collected from an unpolluted spring-fed stream, were analyzed for 30 elements before and after gut evacuation to determine the contribution of gut contents to whole-body concentrations. Cr and Al concentrations were inversely related to body size, suggesting surface contamination. All elements analyzed except Na, Cr, Hg, Zn and Se were significantly lower (P < 0.01) in concentration after gut evacuation (18% decrease for K to .apprx. 70% for V, Mn, Hf, and some of the rare earths). Ratios of variances of mean concentrations in organisms with guts filled to those with guts evacuated indicated that gut contamination was a major source of variation in measured whole-body concentrations of many elements. Calculated percentage of element body burden associated with gut contents ranged from < 1% for Na to 89% for Zr, with a mean for all elements analyzed of 57 .+-. 8% (.+-. 2 SE). Calculated trophic transfer factors (TTF = element concentration in larvae with guts evacuated/concentration in leaf detritus) for elements obtained primarily through the food chain were significantly > 1 only for Zn; TTF for all other elements were .ltoreq. 1.

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