Voyager: Are there specific chemicals in marine plastic debris that pose more of a threat than others?

Plastic in the environment contains chemicals from two sources.

The first source is chemical compounds that are added to the outside structure of the plastic in order to make the structure of plastics more durable. These compounds don’t have a strong chemical bond to the plastic and as a result can leach out into the environment. They have been found in the tissues of some marine organisms and in ocean water and sediment at concentrations high enough to cause toxic effects. Some types of these compounds are what scientists call estrogen mimickers — they can harm the reproductive system of an organism — which can negatively affect a population by decreasing its mating success.

Pollutants such as pesticides and flame-retardants are referred to as POPs, or persistent organic pollutants, and are the second source of chemicals associated with marine plastic debris. These pollutants are attracted to the surfaces of plastics because they are hydrophobic,  meaning they don’t mix with water. Once introduced into the water, they quickly attach to a surface and as a consequence,  debris is found to contain very high concentrations of these pollutants. If an organism eats plastic with these pollutants (there is evidence that many marine species do mistake plastic for food), the pollutants can transfer from the plastic to the animal and continue further up the food chain. This makes plastic a toxic meal to marine creatures since many of these POPs are known to cause cancer, reproductive harm, and can disrupt the nervous system.

When we speak of pollutants, the answer is often “the dose makes the poison.” This means that the answer to which chemical poses more of a threat is a question of quantity. The chemicals of highest concentration in the environment are likely the ones causing the most adverse affects.

-- Chelsea Rochman, graduate student researcher, San Diego State University and UC Davis

To learn more about the Pacific Ocean Garbage Patch read our story, “Inside the Plastic Vortex.”