Heavy Metal Studies with Oligochaetes

Current studies suggest that oligochaetes, initially considered by many authors to be intolerant to heavy metals, are among the most tolerant benthic invertebrates. Heavy metal studies with oligochaetes have concentrated almost exclusively on tubificids, in particular Limnodrilus hoffmeisteri Claparede and Tubifex tubifex (Muller), and the literature on this subject is reviewed. In a recent study on metal levels in sediments and tubificids in the Fraser River, B.C. conducted over a year with monthly sampling for nine metals (Cu, Zn, Pb, Fe, Mn, Ni, Co, Cd and Hg), there was no seasonal variability in tissue metal levels. Tissue metal levels can only be determined accurately if preservatives are not used and a correction is made for gut sediment metal levels. Accumulation rates of metals by tubificids in the Fraser River and in other areas are variable and may reflect local differences in biologically available metal levels; the actual route of accumulation (e.g. from sediment, bacteria or interstitial water) has not been determined.