Plastic debris picks up ocean toxics

Manufacturers melt tiny pellets of resin and shape them into the foam, toys, and other products of our increasingly plastic-filled environment. However, during pellet manufacture and shipping, some pellets invariably escape into the environment. Tokyo researchers now report that toxic chemicals can glom onto these resins, increasing the pellets’ potential to poison any fish or bird that mistakes them for food.

Over the past 30 years, pellets of plastic resin have become a common contaminant in marine waters, where they frequently end up in the digestive tracts of wildlife. Studies have shown that these pellets often host such toxic chemicals as polychlorinated biphenyls (PCBs), DDE (a breakdown product of DDT), and nonylphenols (commercial wetting agents that are now known to mimic the hormone estrogen).

To pinpoint the contamination source, organic geochemist Hideshige Takada of Tokyo University of Agriculture and Technology and his colleagues collected polypropylene-plastic pellets from four beaches in Japan and measured the amounts of PCBs, DDE, and nonylphenols in them. The quantities varied among the sites but generally correlated with chemical concentrations in sediments and particles in nearby water.

The scientists then floated newly made polypropylene pellets for 6 days in sieves in a seawater canal fed by Tokyo Bay. These pellets started with low or undetectable concentrations of PCBs, DDE, and nonylphenols.

Pellets sampled throughout the period showed no increase in nonylphenol concentrations, but the PCBs and DDE built up steadily, the scientists report in the Jan. 15 Environmental Science & Technology. Since nonylphenols are commonly added to plastics (SN: 7/3/93, p. 12), Takada now suspects they go into the pellets when they’re manufactured. The source for the other pollutants, however, almost certainly was the water.

“The adsorption of PCBs and DDE was not saturated on day 6,” Takada observes. Tests of some long-weathered pellets, Takada told Science News, suggest that the plastic can eventually accumulate concentrations of these pollutants up to 1 million times those in the surrounding seawater.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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