Single Versus Multiple Occupancy-Effect on Toxicity Parameters Measured on Eisenia fetida in Lead Nitrate-Treated Soil

Lead toxicity in contaminated soil was measured by earthworm Eisenia fetida mortality and weight change, comparing containers with ten earthworms to containers with single earthworms. Changes in ammonia content were determined in the soil test, along with Pb uptake by the earthworms and Pb chemical extractability from the soil. Results showed that mortality in the single- and multiple-occupancy soils was similar, and only at a Pb concentration of 1800 mg/kg was there a difference, with mortality greater in the multiple-occupancy soil. No differences were observed in 7-d exposures in terms of weight change, but after 14 d, the reduction in weight of earthworms was significantly greater in the 1800- and 3000-mg/kg multiple-occupancy soil than in the single-occupancy soil. At soil Pb concentrations of 1000, 1800, and 3000 mg/kg, the tissue concentrations of earthworms kept in the multiple-occupancy soil were statistically greater than those in the single-occupancy soil. No differences were noted in the NH sub(3) content of the soils.