Implications of gut purging for tissue residues determined in bioaccumulation testing of sediment with Lumbriculus variegatus

Bioaccumulation test procedures using the oligochaete Lumbriculus variegatus have been developed as a means of evaluating the accumulation of chemicals from freshwater sediments. To avoid including chemicals associated with gut contents as part of the measured tissue residue, a 24-h period of purging in clean water after the uptake phase of the test has been recommended. While purging acts to reduce bias from gut contents, it also has the potential to introduce bias caused by depuration of chemicals from tissues. In this paper, a series of model calculations are used to assess the expected sensitivity of measured residues of nonionic organic chemicals to the presence of sediment in the gut and to varying lengths of purging. If organisms are not purged, the predicted influence of gut contents on measured residue is not large (generally <20%) when a biota-sediment accumulation factor (BSAF) of one is assumed. However, if BSAFs substantially less than one apply, projected errors increase to 30-fold or more. To derive a better estimate of the time required for L. variegatus to clear the gut of sediment, a sediment purging experiment was conducted; results indicate that >98% of sediment had cleared the gut in 6 h (half-life = 0.98 h). Based on these results and model analyses, a much shorter purging period of 6 h, rather than 24 h, is suggested as a reasonable guideline for many test applications.