Last year, 150 tons of plastic pellets spilled off the coast of Hong Kong. The BBC reported, “the plastic balls are not toxic on their own, but could absorb toxins that would be lethal to any species that might be tempted to eat them.” According to researchers, this highlights a common misperception regarding small plastic debris in aquatic habitats—the material itself is not considered a hazard to aquatic animals.
In a new study, researchers describe how plastic debris in our oceans introduces toxic chemicals from three different sources.
1. Monomers – The building blocks of plastic polymers are monomers which are linked together during polymerization. However polymerization is never complete leaving some monomers unattached and free to migrate out into whatever the plastic comes in contact—like a sea creature or, in the case of a plastic beverage container – your body.
Examples of harmful monomers are the carcinogen vinyl chloride that makes up polyvinyl chloride (PVC) plastics, or the endocrine disruptor bisphenol-A (BPA) that makes up polycarbonate plastics.
2. Plastic Additives – manufacturers mix in other chemicals to give plastics desired properties. Additives can have toxic properties of their own and they are also free to leach out.
Typical additives include softening agents like phthalates and flame retardants such as polybrominated diphenyl ethers (PBDEs). Adding to the concern is that consumers are often left in the dark as to what’s been added to plastics as manufacturers are not required to disclose additives considered proprietary trade secrets.
3. Pollution magnets – Because plastics are oily substances, they attract other oily chemicals floating about. In one study plastic pellets accumulated toxins at concentrations up to a million times that found in the surrounding seawater—and that was only after six days in the water. Therefore plastics in marine environments become even more toxic as they break down and are ingested by marine life.
The new study compared how readily the five most common mass-produced plastic polymers accumulate hazardous chemicals from local seawater. At intervals of 6 to 12 months, samples were recovered for analysis of two families of persistent toxins: PCBs and PAHs (polycyclic aromatic hydrocarbons – byproducts of burning fossil fuels or forest fires).
What They Found
All five polymers accumulated increasing amounts over time of both PCBs and PAHs. However, three types (HDPE, LDPE and PP) soaked up the pollutants at concentrations higher than the other two (PVC and PET). Concentrations of toxins topped out for PVC and PET at six months, but the other three types continued to rise through 12 months. The researchers believe that the higher levels of toxins on some plastics is due to their being subject to weathering which produces surface pitting, increasing the surface area to which toxins can stick.
Plastic debris in the oceans has a multiplying effect that is potentially more harmful than disposal of plastics on land. Ingestion of marine plastic debris is commonplace at all levels of the food chain, whether passively by filter feeders, like krill and many fish, or actively when mistaken for food by animals as diverse as sea birds, turtles and whales. All such creatures represent entry points into the ocean food web for toxins either manufactured into plastics or accumulated later from seawater.
This study also dispels the notion that developing marine biodegradable plastics will automatically eliminate chemical threats stemming from conventional plastics which are non-biodegradable.
Earth Day Challenge
Today, Earth Day, we are reminded to do our part to help preserve the planet as our health and well-being ultimately depend on it.
One of the single most important things you can do is to limit your use of plastics. By doing so, you’ll help:
- reduce consumption of non-sustainable petroleum products used in plastics manufacturing.
- cut your exposure to numerous toxic compounds such as the carcinogen vinyl chloride and bisphenol-A (BPA).
- keep plastics out of landfills and ocean dumping grounds where they pollute the land, water and ultimately--our food supply.
It’s important to note that most plastics are not safely biodegradeable or recyclable without adding additional toxic load to the environment.
The Environmental Magazine
Environmental Science and Technology