Role of clay content in partitioning, uptake and toxicity of zinc in the earthworm Eisenia fetida

We studied the effect of clay content on the bioavailability of zinc to pre-clitellate earthworm, Eisenia fetida in the laboratory using OECD artificial soil adjusted to 5%, 20%, and 40% clay. Batches of worms were exposed to a wide range of zinc concentrations. Mortality, growth, maturation (% clitellate), cocoon production, and body zinc concentrations were assessed over and after a period of 4 weeks. Total, DTPA, and CaCl2 extractable zinc in the substrates were also determined. The results of the biological responses showed that interaction of clay and zinc had a significant influence on mortality but not on the other biological parameters. None of the three extraction methods showed consistent and significant effect of clay content on zinc partitioning. Although total, DTPA, and CaCl2 extracts of zinc correlated strongly with one another and were in similar relation with the observed biological responses, only the CaCl2 extract revealed a time dependent availability of this metal. It is concluded that clay content had no significant influence on sub-lethal toxicity of zinc to this earthworm over the range of exposure concentrations.