Effects of Agricultural and Urban Land on Microplastic Concentrations in Rivers

Microplastics are a harmful pollutant found in most ecosystems due to the breakdown of plastic products (e.g. clothes and tires). While plastics can be used to create a wide range of goods, exposure to them can cause significant health problems in all living beings. Because of this, it is important to understand how microplastic concentrations vary in each ecosystem type, especially freshwater systems. Microplastics in freshwater systems have not been studied to a similar extent as marine ecosystems. It is important to establish their properties in freshwater environments because rivers are the main pathway for microplastics to enter the ocean. In addition, rivers are impacted by agricultural and urban activities that could change the amount and types of microplastics found in each system. To address this, we sampled 12 rivers in Monterey and Santa Cruz counties with agricultural or urban dominant watersheds during the dry and wet seasons. We determined each rivers’ microplastic concentrations and the polymer types of 33 samples to identify how they vary between seasons and watersheds with different land uses. We found relatively similar microplastic concentrations (p > 0.05; mean = 0.60 MPs/L) over the dry and wet seasons in agricultural and urban sites. We also identified that polyolefins occur more than any other polymer in both site types. We think these results can be used to support the objectives of the Statewide Microplastics Strategy to better manage microplastics in rivers.