Stimulating effects of low lead concentrations on growth and cocoon production of Eisenia fetida (Oligochaeta)
Earthworms form an important component of the soil biota in many soils and are very sensitive to various types of contaminants. Their protection may therefore provide a margin of safety for other fauna once comparative toxicological data are available. The effects of lead on growth, maturation, cocoon viability and cocoon production of the vermicomposting earthworm species Eisenia fetida were studied by exposing worms experimentally to a sublethal concentration of lead (2000 μg. g-1) for a period of 76 days. Growth rate as well as cocoon production were monitored every 14 days and cocoons were incubated to determine their hatching success. Lead content of worms was also analysed. Exposed worms grew noticably better and produced more cocoons than control worms. Cocoon viability was, however, affected detrimentally. It is concluded that, although lead is known to be toxic at higher concentrations, sublethal concentrations close to the predicted EC50 and NOEC-values have a stimulating or hormetic effect on growth and cocoon production.