River bacteria to help dechlorinate rivers.

River bacteria to help dechlorinate rivers

Some bacteria in river-bed sediments are reportedly able to dechlorinate toxic polychlorinated biphenyls (PCBs), but which bacteria do this and where they live remains unclear. Now, researchers at Carnegie Mellon University, Pittsburgh, US, claim to have performed the first side-by-side comparison of the dechlorinating potential of two different river sediments, but whether this will improve efforts to clear up US waterways remains contentious.

Graduate student Christine Wang and colleagues took sediments from the Grasse and Hudson rivers in New York state and spiked them both with a highly toxic PCB: 2,4,5,- trichlorobiphenyl, also known as BZ-29.

In both cases, BZ-29 was eventually dechlorinated to the considerably less toxic 2-monochlorobiphenyl, BZ-1, but dechlorination in the Hudson sediment was about five times faster. The researchers also spiked the sediment samples with nutrients, ’to compare how different nutrients would effect the dechlorination,’ said Wang.

The researchers found that different nutrients have different effects at different sites. In sediments from the Hudson, adding nitrogen and fatty acids appears to work best at increasing BZ-29 dechlorination, whereas adding phosphate is considerably less successful, and might even work in reverse.

In Grasse sediments, nitrogen, fatty acids and phosphate increased dechlorination, although the rate still didn’t match that measured in untreated Hudson sediments. It took about four months for dechlorination to BZ-1 in nutrient-enhanced Grasse sediments, whereas the process took between seven and eight weeks in Hudson sediments.

Working out which nutrients to add to which rivers will be difficult, but the alternatives are alarming. ’There’s talk about dredging the Hudson River,’ says Wang’s supervisor William Brown. ’If they do it then that material’s going to end up in a landfill someplace. Now, that’s a closed environment where we can’t add as much phosphate or nitrogen or whatever we want to actually speed up or clean up the material once it’s out, and that’s a different situation.’ Draining the river should be considered only as a last resort, says Brown: ’it just moves the problem from one place to another.’

Not everyone agrees. ’It is somewhat ridiculous to say that the problem is being moved elsewhere,’ said Jeffrey Levinton, professor of ecology and evolution at the State University of New York. ’In its present location, the sediment is a major environmental concern and the Hudson river will not have any hope of being a clean river without its removal.’

The Environmental Protection Agency decided in 2003 to dredge a section of the Hudson River into which General Electric is estimated to have discharged almost 600 tonne of PCBs from 1947 to 1977. ’This decision cannot be reversed, as far as I know,’ Levinton told Chemistry World.

PCB production in the US stopped in 1978, but the pollutants continue to pose a serious threat to the environment and human health.

Bea Perks/Philadelphia, US