A recent study shows just how long mercury pollutants can persist in the environment and continue to cause problems. The study demonstrates that riverbank and floodplain soils contaminated by a textile manufacturing plant in Waynesboro, Virginia more than half a century ago are the major source of mercury in fish from several Shenandoah Valley rivers.
According to US Geological Survey scientist Jack Eggleston approximately 200 kg of mercury enters the South River every year. However, in order to meet safety standards in fish for human consumption, mercury loads should not exceed about 2 kg pounds per year. Such a tolerance level would require a 99% reduction in contamination asserts hydrologist Eggleston who has authored a report highlighting this serious environmental problem.
Mercury from the textile plant washed into the South River and subsequently contaminated the South Fork Shenandoah River, the Shenandoah River, and the floodplains along the three rivers. The textile plant, operated by DuPont, discharged mercury waste into the river during the period 1929 to 1950. It is difficult to know in retrospect whether those responsible for this action gave any consideration to the long-term environmental impact.
Since 1977, the Commonwealth of Virginia has enforced a fish consumption health advisory on 200 km of river downstream of the textile plant. Safety standards set by the US Environmental Protection Agency state that 0.3 parts per million of mercury in fish are allowable. High concentrations of mercury occur in fish because mercury accumulates throughout the lifetime of an organism. Smaller fish eaten by bigger, predatory fish and so on leads to even greater accumulation up to the point at which people are eating the fish.
During the study, USGS scientists and partners from the Virginia Department of Environmental Quality (VDEQ), and the EPA collected and analysed hundreds of water and sediment samples. They then used computer models to simulate water, sediment and mercury movement in the South River watershed, which revealed how the mercury can still be entering the water 50 years after the plant stopped discharging.
“Now we know why fish continue to have elevated mercury,” says Eggleston. Knowing that contaminated soil is the issue could allow a remediation program to be instigated to extract the toxic metal from the soil.
The South River Science Team working on the project also comprised scientists from government agencies, universities, DuPont itself, and environmental groups who have met regularly over the past decade. DuPont provides financial support for the work.
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