At an equal number of sites, the levels of individual contaminants weren't toxic, but the cumulative effect of multiple contaminants could kill the animals. Density of organisms that live in the mud was likely reduced at all contaminated sites. At the worst sites, the sediment was completely devoid of life. More than three-quarters of the samples from the most contaminated sites killed the test animals in the lab. Sediment from sites that were considered moderately contaminated killed the, test organisms more than half the time.
Creatures behave differently in their natural environment than they do in a fish tank.
Similar studies were done in other South Atlantic states as part of the Environmental Assessment and Monitoring Program in Estuaries, a federal effort to evaluate the health of the country's estuaries. No other Southern study turned up as many contaminated sites as North Carolina, Hackney said. The state's most contaminated areas, he said, may well rank among the worst on the East Coast. Chromium, DDT, PCBs, nickel, arsenic and mercury were the major contaminants that the researchers found in the muds. The most contaminated sediments, they noted, came from Albemarle Sound and from the Pamlico and Neuse rivers.