Bioturbation effects on heavy metals fluxes from sediment treated with activated carbon

Adding activated carbon (AC) to sediment has been proposed as an in situ sediment remediation technique. To date, it is not clear whether this technique is effective in the treatment of heavy metal-contaminated sediment in the presence of bioturbators. In the present study, we compare the ability of granular-activated carbon (GAC) and powder-activated carbon (PAC) to reduce Cu, Zn, and Pb pore water concentrations at environmentally relevant concentrations in the absence and presence of Chironomid larvae. Compared to untreated sediment, PAC and GAC addition in the absence of Chironomid larvae resulted in reductions of free Cu concentrations of 78 and 66 % just below the sediment-water interface after 28 days, respectively. While for Pb and Zn these concentration reductions were only 40 and 38, 19 and 25 %, respectively. The presence of Chironomid larvae in untreated, and GAC sediment generally increased the free heavy metals concentrations in pore water, especially in the deeper layers. In comparison with untreated sediment, the coexistence of AC enhanced the accumulation of heavy metals, especially for PAC. This increased bioaccumulation may decrease the survival of Chironomid larvae. The result indicated that ACs may not be suitable for the remediation of heavy metal-contaminated sediments.