How are Microplastics Affecting Our Oceans?
Microplastics as an Ingestion Threat
The small size of microplastics (<5mm in size) are what make them an environmental hazard. Throughout the world oceans, filter feeding organisms like krill, fish, whales, rays, corals, sponges, crustaceans, and bivalves spend most of their time feeding on small organic particles in the water column. However, these organisms are not usually able to decipher plastic particles from their typical food source and end up consuming them. Microplastics are not easily broken down by marine organisms and often block their digestive tracts leading to mortality. Even if the organism is able to swallow and pass the plastic particle, it is still using precious energy to digest a particle that has no nutritional or caloric value, leading to decreased fitness and energy. Studies have shown that marine species from the size of plankton all the way up to whales are ingesting microplastics in the marine environment (Wright, et al. 2013).
Microplastics As Sponges for Other Ocean Pollutants
Plastics are generally nonpolar and hydrophobic, meaning that they do not interact well with water. Because of this chemical trait, plastic particles act like sponges for Persistent Organic Pollutants (POPs) in the marine environment (Tueten, et al. 2007). POPs like polycyclic aromatic hydrocarbons (PAHs), Dichlorodiphenyltrichloroethane (DDT), and polychlorinated biphenyls (PCBs) are found in higher concentrations on microplastic particles than in the surrounding seawater. In fact, plastic particles can concentrate these toxins up to a million times more than the surrounding water. Although this seems like an ideal trait where toxins are being removed from the water by plastic, it is important to remember that marine organisms are ingesting these plastics and therefore the concentrated chemicals that they carry. Evidence shows that it is possible for the contaminants of these particles to be reabsorbed into the fatty tissue of marine species, many of which provide protein for us as humans (Tueten, et al. 2009).
Microplastics Creating a New home for Microbes
Plastics floating around in the ocean have created an entirely new ecosystem called the "plastisphere" for microbes to inhabit. Leading research from Woods Hole has shown that microbes are using small plastic particles to hitch a ride around the ocean, greatly increasing the potential geographical range of the organisms (Zettler, et al. 2013). Why does this matter? There are harmful bacteria in the ocean that can cause a whole host of diseases and infections that may potentially have a new way to expand their geographical range by attaching to and creating biofilms on microplastic particles. It is once again important to remember that these plastic particles are being ingested by marine organisms around the ocean.
In order to understand the concentration of microplastics in the water column, scientists use several techniques explained here.
- Wright et al. (2013) the physical impacts of microplastics on marine organisms: A review. Environ. Poll. 178, 483-492.
- Teuten et al. (2007) Potential for plastics to transport hydrophobic contaminants. Environ. Sci. Technol. 41, 7759-7764.
- Teuten et al. (2009) Transport and release of chemicals from plastics to the environment and to wildlife. Phil.Trans.R.Soc.. 364, 2027-2045.
- Zettler et al. (2013) Life in the "Plastisphere": Microbial Communities on Plastic Marine Debris. Environ. Sci. Technol. 47, 7137-7146.