FLUCTUATIONS OF MICROPLASTIC CONCENTRATIONS IN GROUNDWATER AND A RURAL CREEK RELATING TO SEASONAL FARMING PRACTICES

Microplastic (MP) pollution has emerged as a growing concern to human and ecological health. Introduction of MPs comes from the degradation of plastics produced for agricultural, industrial, commercial, and personal use. There is significant research on MPs in surface and groundwater and MPs in agricultural soils, but there is little research relating the two. Seasonal farming practices introduce new sources of MPs through chemicals, plastic mulch/mesh, and wastewater sludge and effluent while loosening and disrupting the soils, creating pathways for MP migration. We hypothesize that MP concentrations in surface and groundwater increase during the seasonal use of fertilizers, pesticides, mulch, and wastewater irrigation in farming.

We chose six sampling sites along Kilbuck Creek, a 28 mile-long creek flowing almost exclusively through agricultural land in northern Illinois; one site has visible tile drainage emptying into the creek. We also sample a groundwater observation well located near the creek. Sampling is done bi-monthly and following rainfall totaling more than 20 mm, for the period of one year to include the four seasons of farming: dormancy, tilling/planting, growing, and harvesting. We pump 20 L of water through three filter screens, sized 400 μm, 250 μm, and 125 μm. In the laboratory, we digest organic material, put samples through density separation, and then filtered onto gridded cellulose filters where MPs are counted using a stereomicroscope. Preliminary visual analysis of samples showed an increase in MPs and organic material from dormancy to tilling/planting season.

MP migration from farming practices threatens groundwater and rural surface water with not only MPs, but any farming chemicals that adsorb onto the MPs. In rural areas, drinking water is primarily sourced from groundwater and is not subject to municipal treatment plants. Rivers can be contaminated by runoff from farming and the addition of adsorption onto MPs that migrate through the soil into water could increase this contamination, threatening human health as well as wildlife and plant health. Many of these sources in farming are avoidable with alternatives available.