PT12 Metals and Bioaccumulation
Exhibit Hall
8:00 AM - Tuesday
(PT149) Lead toxicity and subcellular compartmentalization 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 lead-contaminated soil can result in high tissue concentrations, but detoxification mechanisms give rise to subcellular compartmentalization with only a fraction of the total body burden actually contributing to toxicity. Therefore, total body metals, as traditionally determined through whole animal tissue analysis, could suggest much higher risk for toxicity than actually may be the case. This work tests the hypothesis that only a fraction of total Pb in exposed earthworms, Eisenia fetida, contributes to toxicity, and that fraction when quantified is relatable to lethality. Earthworms were exposed 14 days in soil spiked with lead, and the LD50 was determined. Surviving animals were collected, and differential centrifugation was used to produce fractions containing metals-rich granules (MRGs), cell debris, cellular organelles, heat-sensitive cytosolic proteins (HSCPs), and metallothioneins (MTs). Statistically significant differences were observed in the HSCP fraction when comparing moderate non-lethal exposures to exposures approaching the LD50. Lead in the HSCP fraction peaked at the exposure level just below the threshold of lethality and declined in higher-level exposures near the LD50, indicating that a critical level had been exceeded as a precursor to lethality. This finding was consistent with the notion that Pb in this fraction would reflect toxicity. In contrast, the MRG fraction, which is the primary fraction associated with detoxification of Pb in earthworms, was not significantly different across the same exposure range. Size exclusion chromatography (used to further evaluate cytosolic fractions) showed no evidence of Pb binding to MTs or heat-sensitive proteins, and it is postulated that Pb detected in these fractions was in an unbound cationic form. These findings 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: lead, earthworms, compartmentalization, detoxification