A collaborative original research study conducted by the University of California Davis Tahoe Environmental Research Center and One Health Institute with funding by the Nevada Division of Environmental Protection and the Tahoe Water Suppliers Association
Due to the ubiquitous and largely unrestricted use of plastics, its frequent unintended release into the environment, and increasing recognition of potentially harmful effects; there is an urgent need to better understand the current levels, environmental fate, as well as the hazards posed to human, wildlife, and ecosystem health in order to appropriately assess risks associated with its presence.
Plastics are composed of synthetic (human-made) polymers typically derived from petroleum oils. These synthetic polymers are made up of repeating identical molecular sub-units (monomers) that are chemically linked together into long chains. The characteristics of a plastic are determined by the particular sub-unit’s chemical properties that can be augmented with additive chemicals (like plasticizers, flame retardants, other polymers, or dyes) that are mixed into the plastic to adjust specific properties including rigidity, flexibility, durability, melting point, color, and clarity.
The term ‘microplastic’ is colloquially used to refer to any small piece of plastic and are generally defined as synthetic polymers measuring between 1 µm and 5 mm in size.
Plastic is refractory to biodegradation, which makes it a resilient and durable material that is useful for many applications. Its chemical resilience means that pieces of plastic often physically break into smaller pieces long before it can chemically degrade. Because chemical degradation tends to occur at a much slower rate than physical break-down into smaller pieces, an accumulation of ever-smaller pieces of plastic (microplastics) may persist in contaminated environments for many decades to centuries or even millennia after being released.
While harmful effects of microplastic exposure have been researched and described, there is currently only a rudimentary understanding of the hazards posed by microplastic pollution. Much remains unknown about how microplastic characteristics and composition may contribute to harmful effects, how environmental fate of microplastics may affect exposure pathways, and at what environmental level harmful effects occur for different environmental matrices.
Although risk to human health from drinking water is considered low at this time, this conclusion assumes drinking water undergoes standard treatment and is based on currently understood health effects. This conclusion may not be appropriate to extrapolate to untreated water sources, other routes of exposure, and wildlife and ecosystem health.