Dredging marine sediments affects garden tomatoes

The dredging and excavation of New Bedford Harbor's contaminated sediments has cleaned up the sediments but has also led to polychlorinated biphenyls from the sediments on garden tomato plants. This issue was studied in the latest issue of Integrated Environmental Assessment and Management.

From World War II to the 1970s, the use of polychlorinated biphenyls (PCBs) in New Bedford, Mass., contributed to severe contamination of the sediments lying beneath the waters of New Bedford Harbor. Fishing and lobstering in the harbour have been restricted since 1979 because of the potential health risk of consuming seafood from the seriously contaminated ecosystem.

The U.S. Environmental Protection Agency began the cleanup process under the Superfund program with the dredging of 11,000 m3 of sediment from the primary contaminated hot spot between April 1994 and September 1995. During dredging, freshly sectioned marine sediments were exposed to the atmosphere and tidal waters, opening up the potential for increased mobility through the environment. Cleanup and dredging continues today.

Near to the harbour are farms and backyard gardens. The resident community enjoys an abundant supply of locally grown produce. In a recent survey, 358 of 531 respondents from the New Bedford area reported consuming local produce.

Researchers found concentrations of PCBs in locally grown tomatoes above expected levels, though below food tolerances and action levels established by the FDA. The PCBs appear to have come from the dredged sediments and have been deposited from the atmosphere.

Although there does not appear to be a human health risk, this example points out the need to conduct risk-risk comparisons of all potential possibilities prior to undertaking remedial action such as dredging.