What effects are microplastics having on ocean life?

Large amounts of plastics are entering our oceans, with especially high levels found near coastal cities and, most famously, in the Great Pacific garbage patch. But what are the effects of all this plastic on the life that makes up ocean ecosystems? A new review looks at just how scientists are answering this question, from measuring these pollutants to understanding their interactions with biological systems.

While visible plastic scraps floating in ocean waters make compelling headlines and imagery, scientists’ research focus is actually plastic microparticles. In looking at sources, one investigator measured microfibers in sewerage effluent, finding that the variety of polymers he sampled closely matched those used by the garment industry. As a follow-up, he set up laundry machines and found that, for example, washing a fleece jacket once yielded about 1900 microfibers that easily slipped through water treatment and presumably entered oceans. However, measuring or even estimating the total amount of plastics actually present in oceans has proven difficult, in part because the amount absorbed by organisms represents an unknown, but significant, quantity.

Regarding this bioaccumulation, for a long time the main concern was not the plastics themselves, but rather hydrophobic chemicals such as PCBs that microplastics picked up in the water. Generally, scientists believe microplastics passed through digestive tracts. More recently, however, researchers showed in a lab environment that mussels absorbed fluorescently labeled microplastics into their circulatory systems, where they remained for 48 days on average. Another recent study found microplastics in seafood from the supermarket—an average of 90 particles for an order of mussels, 50 particles for an order of oysters.

Is this bioaccumulation harmful and if so, how harmful? This is where more research is needed. Lab studies of lugworms in a microplastics-rich environment showed increased levels of oxidative stress, decreased ability to fight harmful bacteria, and overall increased mortality. However, trying to show cause and effect in the complex ocean environment, which is subject to other changes such as acidification and global warming, has so far proved very challenging. One researcher even suggested that in such a pollution-rich context, microplastics, with their ability to absorb PCBs and other hydrophobic chemicals, might even have a net cleansing rather than harmful effect for organisms. Getting better information on the effects of microplastics is essential in prioritizing our environmental response and protecting our oceans.

Source: PNAS