Earthworm metallothionein production as biomarker of heavy metal pollution in abattoir soil

The direct response of animals to environmental challenges, such as the production of biomarkers, is a better tool to assess environmental pollution than the conventional methods. In this study, the production of metallothionein (MT) in earthworms (Libyodrilus violaceous, Eudrilus eugeniae and Alma millsoni) was measured as tool for assessing heavy metal pollution in abattoir soil. Earthworm and abattoir soil samples were collected from three abattoir sites (Lafenwa, Gbonogun and Madojutimi) and a control site located beside an undisturbed stream located in Abeokuta, Ogun State, in South-western Nigeria. Heavy metal (Cu, Zn, Pb, Cd, Co, Cr, Ni and Mn) and MT concentrations were measured in the earthworm tissue and abattoir soil using standard methods. The concentrations of Cu, Zn, Pb, Cd and Mn were highest in the tissue of earthworms obtained from Lafenwa abattoir. The Bioaccumulation Factors (BAFs) for all the metals tested for were less than unity, except for Cd which had a BAF > 1. The MT concentrations recorded in the earthworm samples from the Gbonogun and Lafenwa abattoir sites were significantly higher (p ≤ 0.05) than in earthworms from Madojutimi. The lowest MT concentration was recorded in earthworms from the control. Significant (p ≤ 0.05) positive correlations were observed between MT and heavy metal concentrations in all earthworm species indicating that MT concentrations can be used as biomarker of heavy metal pollution in abattoir soils.