Lead mining first began in the Big River watershed during the 1700s. Lead was the primary metal mined throughout most of the 1700s and early 1800s and it continued to be mined until the mid-1900s. Barite mining began in the middle part of the watershed in the mid- to late 1800s. Although considerable attention has been given to concentrations of miningrelated trace elements (mostly cadmium, lead, and zinc) in the Big River and its tributaries draining the Old Lead Belt, there is less information regarding concentrations of mining-related trace elements in tributaries draining the Barite District in southeast Missouri, which is downstream from the Old Lead Belt, and the contribution of sediment transported from this district to trace elements in lower reaches of the Big River. The purpose of this report is to present results of an investigation of the distribution of mining-related trace elements in sediments in the middle reach of the Big River downstream from the Old Lead Belt and the Big River tributaries that drain a large part of the Barite District.

In general, concentrations of cadmium and lead in streambed sediment were largest in samples from the Big River and smallest in Barite District tributary samples. Concentrations of zinc were somewhat similar in the Big River and Barite District tributaries; however, higher concentrations were present in upstream Big River site samples, as well as in samples from one site on Maddin Creek and at another site on Old Mines Creek that drains the Barite District. Barium concentrations were considerably larger in samples from Barite District tributaries compared to samples collected on the Big River. Samples collected downstream from the Barite District on the Big River had considerably larger barium concentrations than samples collected upstream from the Barite District.

Flood-plain core samples were collected from 26 cores at 5 transect locations along tributaries in the Barite District. Of the individual 693 bulk (unsieved) samples from these cores analyzed by x-ray fluorescence, the probable effects concentration (PEC) values were exceeded for cadmium (PEC of 4.98 milligrams per kilogram [mg/kg], 218 samples), lead (PEC of 128 mg/kg, 91 samples), nickel (PEC of 48.6 mg/kg, 45 samples), and zinc (PEC of 459 mg/kg, 77 samples). Of the 693 samples, 21 exceeded the U.S. Environmental Protection Agency residential yard cleanup level of 400 mg/kg for lead; 19 of these were samples from a single transect near the mouth of Mineral Fork Creek where its flood plain joins the Big River flood plain.

Shortly after the December 2015 flood on the Big River (the third largest flood along the river since the 1950s), 23 samples of fine sediment deposited from the flood were collected from the Big River flood plain upstream and downstream from the Barite District and several tributaries. Overall, the general pattern of barium, lead, and zinc concentrations in the 2015 flood sediment samples was similar to that observed in the streambed-sediment samples.

Overall concentrations of barium were larger at Big River sites downstream from the Barite District, and cadmium, lead, and zinc concentrations were generally similar or smaller at sites downstream from the Barite District when compared to sites upstream from the Barite District. These data indicate a substantial influx of barium from the Barite District into the Big River but only a minimal influx of cadmium, lead, and zinc.