Microplastics lodge in crab gills and guts

Crabs sop up microplastic pollution via their food and gills, researchers have found in a laboratory study. The tiny particles can lodge in the crustaceans’ bodies for weeks. Crabs become the first marine creature known to trap microplastics in their respiratory systems.

Previous studies had looked at how plastics affect marine organisms through their diet but not through what they breathe. “For a marine crustacean to actually uptake microplastics through respiration and then retain them in the gills — that’s groundbreaking,” says environmental marine biologist Phillip Cowie of the University of Glasgow.

Crabs are central players in the marine food web. They consume other seafloor dwellers, including mollusks, while crabmeat often forms meals for large predators like octopuses, otters and humans. Studies have found that many animals’ bodies hang on to plastic particles, but questions remain about where those plastics go once inside a creature and how long they persist in the food chain.  

Microplastics, any plastic particles smaller than 5 millimeters across, are pervasive aquatic pollutants. They can result from the breakdown of larger plastic chunks and also feature in personal care products. “Toothpastes, deodorants, hand cleanser, makeup — most consumer products with a powdery feel have them, and wastewater treatment facilities do not have the means to capture these microplastics,” says marine geochemist Tracy Mincer of the Woods Hole Oceanographic Institution in Massachusetts. “This careful study begins drawing the links between microplastics and the food chain.”

To find out how crabs handle the plastics in their diet, marine ecologist and biochemist Andrew Watts and colleagues at the University of Exeter in England started by feeding mussels fluorescent microplastics. The researchers then fed those mollusks to shore crabs,Carcinus maenas. Normal food passes through a crab’s digestive tract within two days, but the fluorescent microplastics took as many as 14 days to emerge in the crabs’ feces, the researchers report June 27 in Environmental Science & Technology.

To find out whether respiration also filled the crabs with plastic particles, the team fitted shore crabs with masks that flushed high concentrations of microplastic beads over the animals’ gills for 16 hours. Every two days, the researchers changed the water in the crabs’ tanks, putting in fresh seawater and measuring microplastics in the used water. The crabs continued expelling the pollutants even after three weeks.

“The longer that these plastics reside in these organs, the higher the chance that plastics will be transferred up the food chain from crabs onto other animals,” Watts says.

The researchers don’t know why the microplastics stay around so long in the animals’ bodies or whether the pollutants cause internal damage. Dissections revealed microplastic beads embedded in the gills, which harbor a vast network of folds, and Watts suspects that the microplastics somehow get stuck there.“The crabs sport a gill raker, which is like a windshield wiper” for cleaning out muddy debris, Watts says. “However, it doesn’t seem to be clearing the plastics.” Watts’ team has begun investigating how the breathed-in plastic affects the crabs’ physiology. The mask that flows water over the animals’ gills “offers a great way to do that,” Cowie says. 

Editor’s Note: This story was updated July 14, 2014, to correct how often researchers changed the water in the experiment with masks on the crabs, and how long it took the crabs to expel the pollutants in that experiment.