The tiny plastic food impostor!

Did you know you could pollute the ocean just by washing your face? Many facial cleansers now contain plastic microbeads in replacement of more natural exfoliating materials, such as oatmeal, apricot and walnut husks. So where does the microbead go? After being squeezed out of its tube and used, it washes down the drain to the city wastewater system. But because of its small size, it likely escapes any treatment screen, and out it goes to the ocean.

Microbeads float at the surface or are suspended in water. Imagine you’re a plankton feeder, light coloured microbeads sure look like prey. Or imagine you’re a scavenger, like crabs. Microbeads can be accidentally gulped down with normal food. Now imagine you’re a filter feeder, like barnacles. You have less of a choice so anything of the right size could be captured and taken in. Dissections have revealed that, indeed, microplastics are finding way into the gut of many marine animals like barnacles, mussels, and sea cucumbers. Imagine swallowing a plastic bottle cap!

So what will happen biologically when animals are in the presence of microbeads? To find out, I brought two animals of different feeding styles into the lab ― the scavenging green shore crab and the filter feeding barnacle.

Green shore crab - photo by Sarah Ho

Green shore crab – photo by Sarah Ho

I let the crabs live with microbeads at high or low abundance, or with no microbeads at all for two days. Then I gave them a one day all-you-can-eat mussel buffet so I could measure how much food was consumed.

It turns out that crabs exposed to microbeads ate more, but not when microbead abundance was too high. Microbeads may physically and chemically stimulate the senses of crabs, inviting crabs to feed more. But at a higher level of microbead abundance, with the greater probability of ingesting microbeads, they may damage the inner linings of the digestive tract, cause blockages, or trick the crab into feeling full, resulting in less feeding.

Barnacles - photo by Sarah Ho

Barnacles – photo by Sarah Ho

Barnacles were luckier, only having to deal with microbeads for 15 minutes. I placed rocks with barnacles on them in a tank of sea water and a tank of microbead water, the order of which was randomly determined for each rock.

Relatively fewer barnacles fed in microbead water. The interesting thing was, when barnacles were exposed to plain sea water first, beating of their feeding appendages slowed when they were subsequently moved to the microbead tank. But if barnacles were exposed to microbead water first, beating remained slow even when moved to plain sea water. Chemicals released from microbeads may be a warning for barnacles to feed less. But if microbeads were ingested, further feeding may be slowed. There’s a microbead stuck in its stomach!

So next time when you are choosing your facial cleanser, watch out for these microbeads often disguised as “polyethylene” in the list of ingredients. Marine animals are paying the price for this food impostor. And those microbeads might even come back to you in mussels and clams on your dinner plate.

Hear the captain’s message about the plastic soup we are creating, here:

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