Plastic contamination in oceans and fresh water has been a growing concern in recent years. Microplastics are especially concerning in that they average around just 5mm in size and can appear as food to fish and other aquatic organisms, including birds, turtles, mammals, and invertebrates.
A new study exploring microplastics in rivers examined samples taken from various rivers and tributaries that feed into the Great Lakes. Under a variety of conditions, including hydrologic, land cover, the contribution of wastewater effluence, and population densities, scientists sampled river sources at least three or four times each in a total of six states.
Ultimately, the study determined that all the rivers flowing into the Great Lakes are full of these tiny bits of plastic.
Plastic particles were present, in varying amounts, every time and in every one of the 107 samples collected. The amounts varied according to where the water was tested, with water sources flowing through urban locations and those with wastewater effluence having the highest concentrations of microplastics.
Rivers and tributaries that ran through forests or rural locations had less plastic content, but still contained enough particles for concern. Concentrations of plastics in fresh water sources were also noted to be the same or higher than those found in oceans and other river sample studies, although there are few studies available for comparison.
Plastics alone contain harmful chemicals, but many of them also contain harmful substance additives like flame retardants, phthalates, antimicrobials, and nonylphenol. These chemical additives are also known to be associated with endocrine disruption and cancer.
Some of the types of plastics found included beads from toothpastes, cleaning products, face and hand soaps or scrubs that often remain in waste water after treatment, which is then introduced into the environment either through water or sludge, finally entering the water supply through run-off.
Other plastic types include lines, fragments, fibers, pellets, film, and foam. Some plastics such as plastic bags, styrofoam, bottles, tires, wrappers, and cigarette butts enter the aquatic environment through physical (mechanical) breakdown or photodegradation.
The study showed that microplastics consisted of 98 percent of the size range, with fibers/lines accounting for the highest occurring particle type at 71 percent. Fragments accounted for the second highest particle type of plastic in each sample, at an average of 17 percent, with foams, films, and fragments being found in higher concentrations from more urban locations, mostly attributed to litter. Pellet/bead particles found in the samples was likely due to industrial sources such as from bead blasting and preproduction pellet spillage.
Scientists note that when aquatic species ingest these tiny particles, it creates physical hazards for the organism. Some of the physical hazards include digestive system obstruction, blocking of feeding systems, reproductive issues, and even death.
Plastic's excellent absorption abilities also introduce another major concern: accumulation of harmful chemicals. Harmful chemicals can be absorbed from the environment - things like polychlorinated biphenyls, organochlorine pesticides, and polycyclic aromatic hydrocarbon. When the plastic is ingested by aquatic species, these harmful chemicals can bioaccumulate in the organisms, and the future impacts of this on humans and ecological systems are still currently unknown.