Sunday, July 31, 2011

Fish Bones Fight Pollution

To Nullify Lead, Add a Bunch of Fish Bones

Alaskan pollock is usually the faux stand-in for crab meat or the main ingredient in fast-food fish sandwiches. But now the flaky fish is moving into a new realm — as part of the solution to one of the nation’s longest-running toxic waste problems.

Today, there is more lead contamination in America’s cities than any federal or state agency could ever afford to clean up and haul away. So scientists and regulators are trying a new strategy, transforming the dangerous metal into a form the human body cannot absorb, thus vastly reducing the risk of lead poisoning.

The principle is straightforward, said Victor R. Johnson, an engineer with Civil & Environmental Consultants Inc. “The fish bones are full of calcium phosphate,” he said. “As they degrade, the phosphates migrate into the soil.” The lead in the soil, deposited by car exhaust from the decades when gasoline contained lead or from lead-based paint residue, binds with the phosphate and transforms into pyromorphite, a crystalline mineral that will not harm anyone even if consumed.

This alchemy has been practiced in university and commercial laboratories for more than 15 years, and more recently has been employed at acid-mine sites and military bases.

But now it is also coming to residential neighborhoods like South Prescott in Oakland, which this month became the first in the country where fishbone meal is being mixed into the soil for lead control under a project organized by the Environmental Protection Agency.

“It’s fair to say, looking forward, that just about every urban residential area probably has a lead problem and we just can’t afford economically and socially to move that amount of dirt any more,” said Steve Calanog, the E.P.A. official in the San Francisco office that is overseeing the project. “Topsoil is a precious resource, and we don’t have enough topsoil to replace it.”
Lead is a nearly universal contaminant as a result of airborne transport from it's use in leaded gasoline through much of the 20th century. It was phased out of automobile gasoline in the US in the early 1970s; its use continues in aviation gas.  Sediment and soil profiles around the US show a layer of contamination that dates to this period. However, lead is a fairly immobile metal; once bound to sediment, it is largely bound in place until that soil or sediment is moved by erosion, or some extreme chemical event (a good dose of acid will knock it loose).  Most plants cannot take up large much lead from soil, the main route of soil lead to humans is direct ingestion via unwashed residues on food, or actually eating dirt, termed pica.

I do wonder about the use of fish bones as a possible source of phosphate to the soil.  In Maryland, we are being told we are not supposed to added phosphate fertilizers to our soil to prevent runoff to the Chesapeake Bay and it's consequent eutrophication.  Would the use of fish bone based fertilizers for the treatment of lead in soils also lead to runoff of more phosphate?  Is the benefit worth the result?

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