Mercury in a municipal solid waste landfill

Abstract

Mercury (Hg) is deposited in landfills via household batteries and a variety of other Hg-containing devices and lamps. Although Hg ranks as number three on the US Environmental Protection Agency's toxic substances list, behind lead and arsenic, it has not been the focus of significant research in landfills. This study investigated the levels of Hg present in a municipal solid waste landfill and a municipal compost material. Mercury concentrations in 106 composite samples obtained from the Alachua County, Florida landfill (USA) ranged from 32.8 to 16,800 μg kg-1, with a geometric mean of 178 μg kg-1 and a 95% confidence interval for the mean of 144 to 221 μg kg-1. The distribution was highly skewed, with over half the samples having concentrations less than 150 μg kg-1; only seven had concentrations exceeding 1000 μg kg-1. Mercury concentrations in compost samples from Palm Beach County, Florida, consisting of a 1:1 mixture of biosolids and yard waste, ranged from 368 to 5320 μg kg-1 with a geometric mean of 924 μg kg-1 and a 95% confidence interval for the mean of 686 to 1244 μg kg-1. Mercury concentrations in the landfill and compost samples were generally above the background levels reported for surface soils in Florida, but were two to three orders of magnitude lower than the clean-up goals currently recommended by the Florida Department of Environmental Protection and US federal regulations governing the land application of sewage sludge. Some municipalities have begun excavating old landfills and using the compostable material as landfill cover. If the Alachua County landfill were reclaimed, the compostable solid waste residue should meet Hg guidelines that are stricter than those currently employed for sewage sludge.