|A student holds a rainbow-colored selection of small plastic|
pieces and microplastics picked out of the Occoquan River,
a tributary of the Potomac River. (Whitney Pipkin)
Extremely small bits of plastic are everywhere, and the Chesapeake Bay is no exception. The so-called microplastics, often 5 millimeters or less in size, can be scooped from the surface waters of the Patapsco River and combed from the Bay’s underwater grass beds.They've been looking for effects of microplastics on aquatic biota for years, and not finding enough to get concerned about. My SWAG is that microplastics are not a particularly severe environmental threat. Plastics are generally pretty inert, not digested by organisms that incidentally ingest them, and more a aesthetic concern than an environmental health issue. The one concern that is commonly raised is that certain pollutants, notably toxic organics such are PCBs, pesticides etc, are naturally attracted to the plastic surfaces and may thereby be transferred to organisms after ingesting them. Possible I suppose, but we'd be seeing reports if it had panned out. My guess, again, somewhat educated, is that plastic surfaces cause a net decrease in the relative bioavailability of such toxics.
Microplastics that originated as tiny beads in some face scrubs, soaps and toothpastes are now banned by federal law. But most microplastics begin in much larger pieces: chunks of litter and debris — water bottles, car tires and even plastic piers — that break down into increasingly smaller pieces but don’t biodegrade for hundreds of years. Those plastic bits can leach chemicals or become a carrier of toxins and invasive species they pick up as they float through the water.
Scientists now know that single-celled organisms in the aquatic environment can easily mistake the smallest particles of plastics for food. Those bits then travel up the food chain, eaten by larger and larger fish that are eventually eaten by humans.
The Chesapeake Bay Program, a state-federal partnership that leads the Bay restoration effort, has identified microplastics as a contaminant of mounting concern. But, for all of the headlines and anxiety microplastics have generated, a looming question remains unanswered: What harm are they causing in the Bay?
The Bay Program Scientific and Technical Advisory Committee convened a two-day workshop in late April to begin finding answers. “We might have an idea of the exposure, but on the effect side, we’re not so sure,” said Jerry Diamond, an ecotoxicology and risk management expert with the consulting firm Tetra Tech, at the outset the meeting.
“With a chemical, we can say that this concentration of copper has this effect, so if you have this much in the water it’s not good,” Diamond said. “For microplastics, we don’t have that.”
Research on microplastics and their impact is accelerating around the globe. Scientists know plenty already — though not all applies directly to the Bay or its suite of species. At the workshop, a consensus emerged that more work is needed to measure not just the presence but also the potential harm that microplastics cause when they’re prevalent in the region’s habitats, the bellies of fish and shellfish, and even drinking water.
But they don't want to say that out loud.