Microplastics in stormwater runoff in a semiarid region, Tijuana, Mexico

Land-based sources are considered the most important source of microplastic pollution to marine environment. Stormwater runoff has been identified as one of the main pollutant contributors to water bodies. Seven sites were sampled to identify and quantify microplastics in stormwater runoff in Tijuana, Mexico. The median microplastic abundance found in the samples was between 66 and 191 particles L^-1, the highest abundance being recorded in an industrial land use site. The estimated annual total microplastic loads were between 8 × 10⁵ and 3 × 10⁶ particles ha^-1. The most abundant microplastic shape and identified polymer type were fibers and polyethylene, respectively. The highest microplastic abundances were observed in events with higher rainfall. The results have shown that stormwater runoff is an important source of microplastic to water bodies.