Effect of heavy metal supplementation on local (Allolobophora parva) and exotic (Eisenia fetida) earthworm species: a comparative study.

This study compares the effects of different metal concentration on survival, reproduction and total metal accumulation by two different earthworm species, Allolobophora parva and Eisenia fetida. The substrate was spiked with different heavy metals (Cu, Cr, Pb, Zn & Cd) with concentrations varying from 500-2500 mg/kg. Cu resulted in complete mortality at all doses for both species. The accumulation of heavy metals for Eisenia fetida in 45 days was in order of Cr>Cd>Pb>Zn where as for Allolobophora parva was Cd>Cr>Pb>Zn. Allolobophora parva accumulated significantly higher concentrations of heavy metals was found in Allolobophora parva as compared to Eisenia fetida. The percentage uptake for Cr and Pb ranged from 65-26% and 39-16% for Eisenia fetida while it was 83-30% and 70-24% for Allolobophora parva at 500-2500 mg/kg. Zn uptake was similar for both species. In case of Cd, uptake percentage for Eisenia fetida at 500 and 1000 mg/kg for local species it was 73% and 52%. Zn produced at 100% mortality at both 1500 and 2500 mg/kg, Cd produced was 43% and 44%, whereas 100% mortality at the highest concentration studied (2500 mg/kg). A mortality of 56-64% was observed at a concentration of 500-2500 mg/kg concentration of Cr while 57-68% mortality was found at 500-2500 mg/kg concentration of Pb. Cd had the greatest detrimental effect on cocoon production by Eisenia fetida and Allolobophora parva. Overall, it is concluded that local earthworm species especially the native species Allolobophora parva have tremendous potential to take up heavy metals from contaminated media/soils.