Gut Content Weight and Clearance Rate for Three Species of Freshwater Invertebrates

There is concern for potential error in the accurate estimation of chemical bioaccumulation in benthic organisms due to chemicals associated with gut contents (sediments). In this study the benthic macroinvertebrates Hexagenia limbata, Chironomus tentans, and Lumbriculus variegatus were exposed to five sediments from the Lower Fox River/Green Bay area of Wisconsin to determine the percentage of their weight due to gut contents and the rate at which guts were emptied when the animals were held in clean water. Upon removal from the test sediments, inorganic gut contents in H. limbata, C. tentans, and L. variegatus represented approximately 9, 10, and 10% of their whole body dry weights, respectively. Depuration rates were relatively rapid, with mayflies, midges, and oligochaetes losing approximately 75, 90, and 100% of their gut contents during the first 12 h of depuration. This suggests that a 12–24-h holding period in clean water at the conclusion of sediment bioaccumulation tests with the three species should be sufficient to eliminate potential bias in tissue residue concentrations due to gut contents.