Acute and Sub-Lethal Toxic Effects of a Contaminated Dumpsite Soil to the Earthworm, Eisenia fetida (Savigny, 1826)

Aims: Bioassays measure environmentally relevant toxicity. Consequently, increasing attention has focused on incorporating toxicity tests in hazard evaluations of contaminated sites. We evaluated the lethal and sub-lethal effects of contaminated dumpsite soils at various depths using the earthworm Eisenia fetida.
Study Design: Four contaminated dumpsite soils WDA [Waste Dump Area] 1 & 2 representing top soils (0-15cm depth), WDA 3 (15-30cm depth) WDA 4 (75-100cm depth) and field control (CS- control soil) were inoculated with E. fetida (12 worms/500g soil).
Place and Duration of Study: Institute of Applied Ecology, Shenyang, China. March 12-31, 2007.
Methodology: Survival, body weight, and an oxidative stress biomarker (Malondi-aldehyde levels-MDA) of the earthworms were assessed over a seven-to-fourteen day period. Total and bio-available metal and other physico-chemical parameters of the soil were determined using standard procedures. Correlation coefficients and ANOVA were used for data analysis.
Results :Test-soils WDA 1-2 had the highest levels of cadmium: (Mean±SD-28.17±0.01; 24.77±0.003), zinc (1777.98±0.49; 2883.90±1.48); copper (493.08±0.09; 684.57±0.40), and manganese (1345.53±3.46; 1548.03±0.64)mg/kg soil. WDA 3 had the highest levels of lead (356.80±0.18mg/kg). Earthworms showed significant (P =.05) weight reduction in test soils WDA 1-3 from 0.353±0.013g, 0.348±0.035g, 0.348±0.035 to 0.215±0.003g, 0.216±0.019g by day 14; and 0.215±0.030g by day 7 respectively. Mortality in WDA 3 was 100% by day 14. Only earthworms in WDA 4 did not differ significantly in weight from the control. MDA levels showed a general pattern of increased levels by the second day and subsequent declines by the seventh day, suggestive of oxidative stress onset and possible role of anti-oxidant defense mechanisms. Total lead, bio-available cadmium and zinc correlated with growth reduction data on day 7 (-0.919;P=.05), (-0.924) and 14 (-0.995;P=.01) and may partly be responsible for the observed effects. Increased pH in WDA 4 may have through increased metal sorption reduced bio-availability.
Conclusion: These results may explain the absence of earthworms in metal contaminated soils.