Enrichments of Metals, Including Methylmercury, in Sewage Spills in South Carolina, USA

Abstract

Exposure to microbial pathogens is the primary concern of sanitary sewer overflows; however, sewage spills may also be a significant source of toxic metals, including methylmercury (MeHg). Between November 2015 and January 2017, after Hurricane Joaquin, surface water samples were collected routinely from three creeks in Columbia, SC. Routine sampling coincided with six sewage spills. Total mercury (THg) and MeHg (unfiltered and filtered) and 32 other metals (filtered) were measured. Compared with surface water samples, THg (unfiltered and filtered), MeHg (unfiltered), and 19 other metals were significantly higher in sewage spills (all log-transformed) (two-tailed test, < 0.05 for all, = 38-42). Toxic weighting factors were applied to 18 metals, including THg and MeHg, in samples collected directly from sewage spills ( = 3-4) and a wastewater outfall ( = 5). On average, sewage was 18.2 and 12.0 times more toxic for THg and MeHg, respectively, and 1.75 times more toxic for all 18 metals, compared to treated effluent from the wastewater outfall. Results suggest sewage spills were a source of inorganic Hg, MeHg, and other metals to the receiving waters and may potentially contribute to water quality impairments.