Using earthworms to test the efficiency of remediation of oil-polluted soil in tropical Mexico

This study focuses on the medium-term effects of soil bioremediation on mortality and reproduction rates of Eisenia fetida (laboratory experiment) and of the tropical earthworm Polypheretima elongata (field experiment). We compared soils restored with the two bioremediation technologies landfarming (LF) and compost-bioremediation (BI) with control soils and with soils contaminated with 1% and 2% of petroleum. Control and restored soils both were fertile and showed low hydrocarbon contents. The mortality of E. fetida was not influenced by soil restoration and by contamination with 1% petroleum; it only increased in soils contaminated with 2% petroleum. However, the reproduction rate of E. fetida was significantly lower in the soils restored with LF and in those contaminated with 1% crude oil and significantly higher in the soils restored with BI. P. elongata showed the same reaction as E. fetida. We conclude that it is important to include reproduction or other sub-lethal tests for earthworms when estimating the efficiency of restoration techniques.