National Geographic : 2018 Jun
IN A LABORATORY AT Columbia University’s Lamont-Doherty Earth Observatory, in Palisades, New York, Debra Lee Magadini positions a slide under a microscope and flicks on an ultraviolet light. Scrutinizing the liquefied digestive tract of a shrimp she bought at a fish market, she makes a tsk-ing sound. After examining every millimeter of the slide, she blurts, “This shrimp is fiber city!” Inside its gut, seven squiggles of plastic, dyed with Nile red stain, fluoresce. All over the world, researchers like Magadini are staring through microscopes at tiny pieces of plastic—fibers, fragments, or microbeads—that have made their way into marine and freshwater species, both wild caught and farmed. Scientists have found microplastics in 114 aquatic species, and more than half of those end up on our dinner plates. Now they are trying to determine what that means for human health. So far science lacks evidence that micro- plastics—pieces smaller than one-fifth of an inch—are affecting fish at the population level. Our food supply doesn’t seem to be under threat—at least as far as we know. But enough research has been done now to show that the fish and shellfish we enjoy are suffering from the omnipresence of this plastic. Every year five million to 14 million tons flow into our oceans from coastal areas. Sunlight, wind, waves, and heat break down that material into smaller bits that look—to plankton, bivalves, fish, and even whales—a lot like food. Experiments show that microplastics damage aquatic creatures, as well as turtles and birds: They block digestive tracts, diminish the urge to eat, and alter feeding behavior, all of which reduce growth and reproductive output. Their stomachs stuffed with plastic, some species starve and die. In addition to mechanical effects, microplastics have chemical impacts, because free-floating pollutants that wash off the land and into our seas—such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and heavy metals—tend to adhere to their surfaces. Chelsea Rochman, a professor of ecology at the University of Toronto, soaked ground-up poly- ethylene, which is used to make some types of plastic bags, in San Diego Bay for three months. She then offered this contaminated plastic, along with a laboratory diet, to Japanese medakas, small fish commonly used for research, for two months. The fish that had ingested the treated MARTIN OGONOWSKI AND CHRISTOPH SCHÜR, DEPARTMENT OF ENVIRONMENTAL SCIENCE AND ANALYTICAL CHEMISTRY (ACES), STOCKHOLM UNIVERSITY Microplastics ingested by a water flea that’s three millimeters long glow green. In a lab, fleas were exposed to round beads and irregularly shaped fragments in amounts higher than in nature. The irregular pieces pose a greater threat because they can clump and get stuck in the gut.