UC DAVIS (US) — Eating plastic is a threat to marine creatures, but so are the pollutants those plastics have absorbed while floating in the ocean, say researchers.
A new study finds that the most commonly produced plastics also absorbed the most chemicals, and for longer periods of time than previously thought.
Products made from the particular plastic used to make water bottles (polyethylene terephthalate, or PET) might have fewer detrimental chemical impacts than products made from other types of plastic, according to the study, published online in Environmental Science & Technology.
The research, conducted for 12 months at five locations in San Diego Bay, was the first controlled, long-term field experiment measuring the absorption of contaminants by the five most common plastics:
- Polyethylene terephthalate (PET): Recycling symbol #1, like water bottles.
- High-density polyethylene (HDPE): Recycling symbol #2, like detergent bottles.
- Polyvinyl chloride (PVC): Recycling symbol #3, like clear food packaging.
- Low-density polyethylene (LDPE): Recycling symbol #4, like plastic shopping bags.
- Polypropylene (PP): Recycling symbol #5, like yogurt containers, bottle caps.
The researchers deployed pellets of each plastic type in mesh bags tied to a dock at each study site. They retrieved them periodically to measure the plastics’ absorption of persistent organic pollutants.
“Consistently in our study, we found polyethylene [HDPE and LDPE] and polypropylene [PP] absorbed much greater concentrations of contaminants than PET or PVC, and those are the most commonly mass produced and consumed plastics,” says Chelsea Rochman, a doctoral student in ecology at University of California, Davis and San Diego State University. “They are also the most commonly recovered as marine debris.”
In 2007, HDPE, LDPE, and PP accounted for 62 percent of all plastics produced globally, while PVC and PET represented only 19 percent and 7 percent, the study says.
The data imply that products made from HDPE, LDPE, and PP may pose a greater chemical risk to marine animals that ingest plastics than products made from PET and PVC. The study notes that, although PVC did not absorb as many contaminants as did other plastics, vinyl chloride is classified as carcinogenic and toxic.
Rochman expected the pellets would absorb an increasing amount of pollutants for the first several months of the study before reaching equilibrium—the point at which they could not absorb further toxic substances.
However, Rochman found that HDPE and LDPE continued to absorb contaminants throughout the 12 months. The study estimates that, at the Shelter Island study site, it would take 44 months for HDPE and 19 months for LDPE to stop absorbing toxic substances.
“It surprised us that even after a year, some plastics would continue to take up contaminants,” Rochman says. “As the plastic continues to degrade, it’s potentially getting more and more hazardous to organisms as they absorb more and more contaminants.”
The National Science Foundation’s Graduate Research Fellowship Program funded the study, as did the Society of Environmental Toxicology and Chemistry, the San Diego State University Research Foundation, and the Padi Foundation.
Source: UC Davis