In many ways, the results of these studies raise more questions than they ask. One of the most important, though, is “What effect do microbeads and other plastic pollutants have on Great Lakes food webs and ecosystems?” Research into this question has only just begun, but years of studies in the oceans provide some insight. Some of these latest findings come from our friends at South Carolina Sea Grant.
From Coastal Heritage:
John Weinstein is studying how grass shrimp (Palaemonetes pugio) respond to a diet of plastic beads. A crustacean about the size of half of a shelled peanut, a grass shrimp consumes microalgae that grow on plant detritus—especially decomposing saltmarsh stems called “wrack”—along estuaries and coasts, but it’s also a predator on a wide variety of small animals.
Because of its abundance, sensitivity, and ecological importance in southeastern U.S. estuaries, the grass shrimp is often used to study the effects of pollution in the field and laboratory.
In Weinstein’s lab, Austin Gray, a graduate student in biology at The Citadel, has been feeding grass shrimp two types of beads: one a bright green and the other one translucent.
The green beads are polyethylene, the type of plastic used in plastic bags, bottles, plastic wrap and other films for food preservation, and many other products. Polyethylene is the most common type of plastic found in marine debris around the world.
The translucent beads are polypropylene, a type of plastic used in bottle caps, candy- or chip-wrappers, and food containers. Polypropylene is the second most common type of plastic found in marine debris.
In a lab dish, Austin Gray deposits translucent 75-micron beads. But a visitor looks in the dish and can’t find a single bead. Under the dissecting microscope, though, dozens of tiny spheres suddenly appear. To put it in perspective, an item at about 40 microns is the width of two spooning human hairs.
Gray fed 16 grass shrimp a diet of brine shrimp mixed in with plastic beads. Each grass shrimp was isolated in water that was changed every other day. Eight animals were fed polyethylene beads and eight were fed polypropylene beads. After six days, all of the 16 shrimp were dead.
Dissecting the animals, Gray found plastic beads in their guts and gills. One individual had 10 tiny beads in its gut and 16 in its gills.
The gut blockages, though, were deadlier. The grass shrimp could still take in water through their partly blocked gills. But they stopped eating with clogged guts—or couldn’t eat—and died.
“In my mind,” says Weinstein, “it’s consistent with starvation. The more particles in guts, the more quickly the grass shrimp die.
Concern about results like these has led Illinois to become the first state to ban the sale of microbeads in personal care products. The law, passed in June, is slated to take full effect in 2019. Similar legislation has also been considered in New York and California.
Click on the link above to read the full article.
***Photo: Collecting plastic samples in southern Lake Michigan in 2013.
