Research▼Watch
When sockeye salmon return to their natal lakes to spawn and die, they bring with them PCBs accumulated during a lifetime in the northern Pacific Ocean, according to a study published by Canadian and U.S. researchers in the September 18 issue of Nature. Their decomposing bodies release these persistent industrial pollutants, increasing the PCB content in some Alaskan lake sediments by more than sevenfold. “In the lakes that receive the highest salmon densities, we’re looking at 7 to 10 times the amount [of PCBs] traditionally assigned from atmospheric pathways,” says Jules Blais, a biologist at the University of Ottawa and one of the study’s coauthors. Blais and his colleagues extracted sediment cores from eight lakes during 1995, 1997, 1998, and 2002 for the PCB analysis. They also measured the types and concentrations of PCBs in the muscle tissue of returning sockeye salmon. PCB patterns and concentrations in lake sediments correlated with the density of returning salmon. The salmon themselves do not contain high enough PCB concentrations to warrant consumption advisories, Blais cautions, but the cumulative effect of millions of fish funneling into such small areas could be concentrating these chemicals in the food chain. (Nature 2003, 425, 255–256)
Kitchen drain experiment exonerates triclosan Triclosan (2,4,4-trichloro-2-hydroxydiphenylether), a biocide commonly found in antibacterial products, does not appear to contribute to antibiotic resistance, concludes the first study to assess its impact in a real environmental situation—the kitchen drain. The research was published in the September issue of Applied and Environmental Microbiology. Because of its widespread use, tri© 2003 American Chemical Society
closan occurs in low concentrations in many U.S. streams. In 1998, laboratory researchers identified how triclosan kills bacteria and suggested that lowlevel constant exposure could be fostering drug-resistant bacteria. RHONDA SAUNDERS
PCB transport pathway
A study of a kitchen drain demonstrates triclosan does not contribute to antibiotic resistance.
Peter Gilbert and colleagues from the University of Manchester in the United Kingdom and Procter & Gamble in Cincinnati, Ohio, collected black, slimy biofilms from the kitchen drain of a home that shuns triclosancontaining products. These biofilms were then exposed to a detergent containing triclosan for three months. Bacteria that were naturally resistant to the antibiotics or biocides thrived and expanded. Bacteria that were vulnerable died off. With the exception of E. coli, antimicrobial susceptibility did not increase as a result of exposure to triclosan. But this is not a concern because E. coli is not a target for triclosan because of its well-known low susceptibility to the biocide, according to Gilbert. Several bacterial consortia also appeared to degrade triclosan. The experiment is important, says Gilbert, because it emphasizes the difference between the real world and the laboratory. Bacteria that develop resistance probably pay a fitness cost
and may become less able to compete in the microbe ecosystem within the drain. Procter & Gamble funded the study, but the company does not produce a liquid dishwashing detergent that contains triclosan, according to Gilbert. (Applied Environ. Microbiol. 2003, 69, 5433–5442)
Proteomics and pollution The newest darling of the life sciences community, proteomics, has been used to measure the biological effects of four pollutants on the marine clam Chamaelea gallina. In the August issue of Proteomics, researchers from the University of Córdoba in Spain, the University of Bergen in Norway, and Biosense Laboratories AS in Norway found a total of 99 proteins that changed expression levels when the clams were exposed to varying concentrations of the individual toxicants, which suggests that protein profiles could be a biomarker for environmental pollution. Proteomics is the analysis of all the proteins and their concentrations in a biological fluid. In this case, Juan López-Barea and colleagues exposed C. gallina for seven days to either commercial Aroclor 1254, which contains PCBs; copper(II), which promotes oxidative stress; or toxic tributyltin or arsenic(III) and analyzed the proteins collected from homogenized clams by classic 2-D gel electrophoresis. Depending on the pollutant and its concentration, the clams’ expression of key proteins increased (up-regulated) or decreased (down-regulated). For example, after exposure to as little as 0.1 milligrams of copper per liter, the subsequent analysis found that 15 protein spots on the gel were up-regulated and 3 were down-regulated. For all four toxicants, 99 proteins changed expression, of which 51 were up-regulated, 42 were down-regulated, and the rest varied up or down with changing conditions. (Proteomics 2003, 3, 1535–1543)
DECEMBER 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 431 A
