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Quoted from “Oceans Awash With Microscopic Plastic“:

‘While most plastics are non-biodegradable, [Richard] Thompson says the action of waves and the elements work to break plastic objects down into fragments tiny enough to be ingested by countless other marine organisms.

‘To test the potential for this to occur, Thompson and his colleagues kept barnacles, lugworms, and detritus-eating amphipods in aquaria with small amounts of microscopic plastics. These invertebrates all ingested the fragments within a few days.

‘Thompson highlights two possible environmental impacts that his team will investigate over the next three years. “One is that these smaller fragments could cause blockages to the feeding apparatus and the digestive tract [of marine invertebrates], just as plastic bags have affected larger animals like turtles,” he said.

‘”The second area we’re exploring is the possibility of chemical transfer from plastics to these organisms.

Many plastics contain toxic chemicals, including biocides (to prevent organisms colonizing their surfaces), colorings, and flexibility-enhancing agents known as plasticizers. These substances could be released if the plastics were eaten.

‘Thompson added: “Another possibility, recently shown by researchers in Japan, is that when plastics are floating in the seas, they will accumulate and absorb toxic chemicals that are present from other sources. These are hydrophobic chemicals that hate to be in water and cling to plastic as an alternative. These chemicals may then be transported to organisms that eat the plastic.”

‘Such toxic chemicals include PCBs (polychlorinated biphenyls) and DDE (dichlorodiphenyldichloroethylene), which are derived from pesticides and other manmade substances. These agents are known endocrine disruptors—chemicals that interfere with the reproductive, developmental, and immune systems of animals.’

-James Owen, “Oceans Awash With Microscopic Plastic“, National Geographic News, 6 May 2004.