Trace metal concentrations in genetically dissimilar earthworms: (Aporrectodes longa: Ude, Libyodrillus violaceus: Beddard) from municipal dumpsites in Benin-City, Nigeria

Abstract

The study explored the use of earthworms as sentinels for biomonitoring heavy metal contaminations in the terrestrial environment.  Steady state metal concentrations (Mn, Zn, Fe, Cu, Pb, Cd and cr) were measured in genetically dissimilar earthworms (Aporrectodea longa: Ude, Libyodrillus violaceus: Beddard) and soil samples from contaminated site also located in ancient city of Benin, Nigeria.  Generally metal concentrations in the earthworms were higher than levels in the soil.  Significant interspecific differences occurred in the metal concentrations in the biotaand soil and amongst the study sites (P< 0.05, df16).  The pattern of metal concentrations in earthworms reflected the pattern in the soil. (Mn > Zn > Fe > Cu > Pb > Cd > Cr)  Bioconcentration also depended on the concentration of metal in soil with bioconcentration factor being greater at lower soil concentrations.  L. violaceus appears to be a better sentinel, accumulating more metals than  A. longa in all sites.  Voiding time played vital role as an experimental variable in levels of metals in earthworms, Zn, Cu, Pb, CD, Mn increased as voiding time increa/sed (tissue sequestration) while Fe and cr decreased with increase in voiding time (non-tissue sequestration).  The bioavailability of metals in soil samples were also co-determined by soil texture.  Reduced metal uptake and availability was observed, in soil with high clay content, since metals remained tightly bonded to clay site.