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How Long Does Plastic Persist in the Ocean?

Collin Ward and Christopher Reddy, Marine Chemistry & Geochemistry Department,

Edited by Véronique LaCapra | August 2, 2020

Experiments will provide the first realistic, verifiable estimates of the lifetime of plastic goods in the environment—a critical step towards quantifying the risks associated with plastic pollution

We’ve all seen the headlines: Plastics are polluting the ocean. The numbers are staggering: as many as 8 million tons of plastic end up in the ocean every year. This highly-visible environmental issue has engaged government agencies, industry, non-governmental organizations, and consumers. Exacerbating concerns for ocean life and human health is the perception that plastics last indefinitely in the environment. This assumption helps to drive decision-making, from personal use to national and international policy.

But little is actually known about how long it takes for plastics to break down in the ocean, which makes it difficult to quantify the risks that these plastics may pose to people and marine life. 

Plastics are not all created equal. Each unique formulation is a complex mixture, made up of base-polymers—such as low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET)—plus fillers and additives. Different formulations behave differently in the environment, which means different plastics break down in the ocean at different rates. For example, many plastic additives react chemically to light, leading plastics with additives to degrade more quickly in sunlight.

WHOI chemists Collin Ward and Chris Reddy are engaged in an effort to quantify the environmental lifetimes of a wide range of common plastic goods. These include plastic bags (LDPE), straws (PP), coffee cups and lids (PS), as well as water and soda bottles (PET). The scientists’ two-tiered approach involves small-scale laboratory experiments and large-scale mesocosm experiments, which reproduce ocean conditions in a large container of seawater where temperature, light exposure, and other environmental variables can be controlled and replicated.

These experiments will provide the first realistic, verifiable estimates of the lifetime of plastic goods in the environment—a critical step towards quantifying the risks associated with plastic pollution. Ward and Reddy intend to communicate their findings to legislators, industry leaders, environmental groups, and the public, thus informing policy decisions, manufacturing, consumer choices, and efforts to clean up plastic waste from the ocean.

Colin Ward and Chris Reddy are colleagues in WHOI’s Marine Chemistry & Geochemistry Department and collaborators in WHOI’s Marine Microplastics Initiative.

Ward is a photochemist who studies how light affects chemical, physical, and biological processes in the ocean. His work includes analyzing how sunlight affects oil spills, arctic permafrost, and plastics in the ocean.

Reddy is a chemical oceanographer and a solutions-based leader in the field of marine pollution. His work has ranged from analyzing pesticides and PCBs in coastal sediments to major oil spills such as the Exxon Valdez and Deepwater Horizon. His current focus is on ocean plastics.