Activated carbon (AC) is being considered as a sediment amendment to manage contaminants in many aquatic ecosystems. Small-scale (lab) and large-scale (field) research with AC has shown promise in reducing mercury (Hg) bioavailability to the food web. We studied the ability of AC to reduce Hg bioaccumulation in ~100 gallon mesocosm environments with freshwater sediment containing Hg at concentrations only modestly above background levels (100 to 200 ng/g). The mecososms are ecologically and hydraulically complex and are designed to mimic periodic flushing from tidal-like mixing. Conditions are controlled, but complex compared to previous mesocosm studies with single organisms and a static water column or uncontrolled field AC-applications. In mesocosms with AC-amendments, both mercury and dissolved organic carbon, a key binding phase for Hg, was reduced in sediment porewaters during the first two years of the study. Additionally, methyl mercury (MeHg), the bioaccumulative form of mercury, was lower in the mesocosm sediment solid phase, porewater, and surface waters. Biota (zooplankton) in AC-amended mesocosms contained concentrations of MeHg that were less than half of that encountered in control mesocosms. Some ecological differences that likely would not translate to field applications may have been induced by the AC-amendments to mesocosms. Therefore, MeHg reductions in surface waters and biota of mesocosms cannot be translated directly into analogous reductions of surface water MeHg in more complex field conditions. The results from this ecologically complex mesocom study suggest that decreases in MeHg flux from sediment following AC-amendments to sediment could result in decreased bioaccumulation in the food web, even at sites with moderate mercury contamination.

Activated carbon lowers methylmercury release from sediment and bioaccumulation in ecologically complex mesocosms

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