Microplastics in Karst Groundwaters of Illinois

Worldwide, about one quarter of all drinking water sources are from groundwater in karst aquifers. Carbonate aquifers in northwestern and southwestern Illinois are fractured, creviced, and contain open conduits and caves. Loess, ranging in thickness up to 4 m in northwestern Illinois and up to 10 m in southwestern Illinois, overlie much of the bedrock, and cover-collapse sinkholes are found in both regions. Because of these features and the open nature of the bedrock, the karst aquifers are susceptible to the introduction and rapid transport of both dissolved and particulate pollutants. Previous sampling has indicated that aquifers in both regions are contaminated with chemical and bacterial parameters indicative of human or animal waste, road salt runoff, and N-fertilizers. This project was designed to determine if these karst aquifers were contaminated by microplastics (< 5 mm), a new class of contaminants being detected in many surface waters. In November 2017, eight springs and three shallow wells in Illinois’ Driftless Area in northwestern Illinois and six springs in the Salem Plateau of southwestern Illinois were sampled for microplastics. The Driftless Area sites were also sampled for a suite of pharmaceuticals and personal care products (PPCPs). All but one of the 17 groundwater samples contained microplastics with a maximum concentration of 15.2 pieces per liter. Microplastics can be classified based on shape and other characteristics; all of the microplastics observed in our samples were microfibers. Based on this and previous investigations, the most likely source of microplastics in the karst aquifers is septic effluent, specifically discharge from washing machines. This is the first time we are aware of that microplastics have been detected in groundwater samples.