Environmentally Relevant Chemical Mixtures of Concern in Waters of U.S. Tributaries to the Great Lakes

The North American Great Lakes are a vital natural resource that provide fish and wildlife habitat, as well as drinking water and waste assimilation services for millions of people. Tributaries to the Great Lakes receive chemical inputs from various point and non-point sources, and thus are expected to have complex mixtures of chemicals. However, our understanding of the co-occurrence of specific chemicals in complex mixtures is limited. To better understand the occurrence of specific chemical mixtures in the U.S. Great Lakes basin, surface water from 24 U.S. tributaries to the Laurentian Great Lakes was collected and analyzed for diverse suites of organic chemicals, primarily focused on chemicals of concern (e.g. pharmaceuticals, personal care products, fragrances, etc.). A total of 181 samples and 21 chemical classes were assessed for mixture compositions. Basin wide, 1,664 mixtures occurred in at least 25% of sites. The most complex mixtures identified were comprised of nine chemical classes and occurred in 58% of sampled tributaries. Pharmaceuticals typically occurred in complex mixtures, reflecting pharmaceutical-use patterns and wastewater facility outfall influences. Fewer mixtures were identified at lake or lake-influenced sites than at riverine sites. As mixture complexity increased, the probability of a specific mixture occurring more often than by chance greatly increased, highlighting the importance of understanding source contributions to the environment. This empirically-based analysis of mixture composition and occurrence may be used to focus future sampling efforts or mixture toxicity assessments. This article is protected by copyright. All rights reserved.