Fate of Heavy Metal Contaminants in a Former Sewage Treatment Lagoon, Hancock County, Ohio

A Former sewage sludge lagoon, thoroughly mixed and abandoned in 1999, was analyzed to determine the subsequent mobility of heavy metals and their relationship to the dominant plant species at the site. ICP analyses of soils taken with respect to depth relative to the root zone and association with either common ragweed or stinging nettles revealed noticeable differences. In the five years since abandonment, the heavy metals have been stratified due to leaching and plant uptake, with the majority of metals showing higher concentrations at more shallow depths. Although stinging nettles can uptake higher concentrations of heavy metals into their plant parts, the soils do not have an associated reduction in heavy metal content. As the plants die in the fall, the heavy metals are returning to the soil as vegetation decays. Ragweed is less capable of incorporating the heavy metals into its biomass and is found associated with overall higher heavy metal concentrations in the soil around its roots. Thus, some other process is causing the retention of heavy metals in these soils. The lower concentrations in the soils beneath the root zones, which were reported to have been initially identical in composition to the shallower soils, are likely due to leaching.