Microplastic pollution in the effluent-dependent Santa Cruz River

Authors: Kelsey Hollien, Drew Eppehimer, Hamdhani Hamdhani, David Quanrud, Michael Bogan

Year: 2019

Abstract

Microplastics are an emerging contaminant of potential ecological concern in waterbodies across the world. One important point source of microplastic pollution is treated wastewater- after treatment this effluent is often discharged directly into streams. In southern Arizona, USA, effluent discharge supports perennial flow and riparian habitat in the Santa Cruz River but also brings microplastic pollution and its potential ecological challenges. In this project, we quantified microplastic concentrations in the water column, benthic sediment, and in Western Mosquitofish, Gambusia affinis, stomachs at 10 sites along the lower Santa Cruz River in Tucson, Arizona. We also compared microplastic concentrations before and during the monsoon season. We found four types of microplastics in the Santa Cruz River: fibers, fragments, film, and beads. Across all sites, microplastic concentration in the water column was ~33% higher during the monsoon, with the majority of pieces (≥80%) being fibers in both seasons. In benthic sediment, microplastic concentration was nearly twice as high before the monsoon season (340 ± 54 No./Kg) than during the monsoon season (153 ± 21), with fibers and fragments being the most common types of plastic found in sediment. Before the monsoon season, only three of the 200 mosquitofish sampled had ingested microplastics (100% fiber). In contrast, microplastics were found in 20 of 200 fish sampled during the monsoon season (85% fiber, 10% film, 5% fragment). This project provides the first evidence that microplastics are common in the water column and sediment of the Santa Cruz River, and that mosquitofish are more likely to ingest microplastics during the monsoon season. Future studies should assess the long-term impacts of these microplastics on the health and populations of aquatic species.