MP9 Metals and Bioaccumulation
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(JON-1117-659243) Toxicity and subcellular compartmentalization of lead and tungsten in earthworms exposed to contaminated soil.

Jones, R¹, Inouye, L¹, Bednar, A¹, Boyd, R², ¹ US Army Engineer Research and Development Center, Vicksburg, MS, USA² Analytical Services, Inc., Vicksburg, MS, USA

ABSTRACT- Long-term exposure of terrestrial invertebrates to metals-contaminated soil can result in elevated tissue concentrations, but detoxification mechanisms give rise to subcellular fractions that do not contribute to toxicity. Therefore, total body metals (TBMs) could suggest much higher risk for toxicity than actually may be the case. This work tests the hypothesis that only a fraction of total metal (lead [Pb] or tungsten [W]) in exposed earthworms, Eisenia fetida, contributes to toxicity, and that the toxic fraction (TF) is quantitatively related to adverse effects on survival and reproduction. Earthworms were exposed in soil spiked with lead (as lead(II) nitrate, Pb(NO₃)₂) or tungsten (as sodium tungstate, Na₂WO₄), and the LD₅₀ (14-day exposure) and reproductive effects (28-day exposure) were determined. Differential centrifugation on whole earthworm homogenates from these exposures was used to produce fractions containing metals-rich granules (MRGs), cell debris, cellular organelles, heat-sensitive proteins, and cytosol (with metallothioneins). Concentration-dependent increases in the summed TF (organelles + heat-sensitive proteins + cytosol) were observed in exposures approaching the LD₅₀ for both Pb and W. In 28-day exposures, Pb in the TF also showed a concentration-dependent increase corresponding to statistically significant decreases in reproductive endpoints (cocoon/juvenile counts). In contrast, tungstate completely arrested reproduction at all W exposure concentrations supporting the conclusion that its sublethal toxicity is greater than that of Pb. TBM and TF No Observed Effects Concentrations (NOECs) for both survival and reproduction were measurably lower for W when compared to Pb. These findings were consistent with the notion that Pb or W in the TF would reflect toxicity. These data suggest that fractional body burden analysis may provide valuable information on toxicity of metals in invertebrates as part of bioaccumulation tests, greatly reducing the uncertainty associated with interpretation of metals tissue concentrations in these studies.

Key words: earthworms, lead, tungsten, detoxification