When you think of plastic pollution, you might imagine ocean “garbage patches” swirling with millions of plastic bottles and shopping bags.
Microplastics — small plastic fragments less than 5 mm in diameter, a little less than one-third the size of a dime — have become everywhere in the environment. They form when more oversized plastic items like water bottles, grocery bags, and food wrappers are exposed to the elements, chipping into smaller and smaller pieces as they degrade. Smaller plastic fragments can get down into a tiny fraction of the width of a human hair.
These plastic particles do many of the same bad things that more oversized plastic items do: mar the land and sea and leach toxic chemicals into the food chain. But scientists are increasingly worried about their potential impact on the global climate system. Microplastics release potent greenhouse gases as they break down and may be inhibiting one of the world’s most important carbon sinks, preventing planet-warming carbon molecules from being locked away in the seafloor.
Perhaps most concerning to scientists is the way microplastics may be affecting that final stage, the sinking of zooplankton poop to the bottom of the seafloor. Once consumed, microplastics get incorporated into zooplankton poop and can cause fecal pellets to descend more slowly.
There are other worries too, about the way microplastics can affect phytoplankton and zooplankton health — potentially compounding the stresses already posed by rising carbon dioxide concentrations, which are making the oceans warmer and more acidic, and are contributing to the expansion of oxygen-depleted “dead zones.” High concentrations of microplastics in water are toxic to phytoplankton, and lab experiments have shown they can cause up to a 45 percent reduction in some species’ growth.