Background Concentrations of Arsenic in Ohio Soils: Sources and Influencing Factors

Abstract

Arsenic concentrations—representative of natural background conditions in Ohio soils—were compiled from the USGS National Geochemical Survey database, Ohio EPA studies, and private environmental site investigations. The resulting dataset of 2,783 samples collected from 1,116 locations was then correlated with soil data from USDA-NRCS SSURGO, glacial and bedrock geology, and analyses of other metals at these specific locations to identify factors most likely to affect arsenic concentrations in soil. Bedrock geology, particularly Devonian-aged materials and black shales, was found to significantly correlate to arsenic concentrations in soil. However, this correlation is complicated by both glaciation and post-glaciation erosion. Approximately 70% of Ohio’s bedrock is covered in glacial materials, such as till and outwash. As glaciers advanced across Ohio, bedrock materials were eroded and deposited farther south. Arsenic concentrations in Ohio soils tend to be highest where Devonian bedrock materials were deposited by glaciation. Following glacial deposition of materials, arsenic can be eroded or leached from the deposits. Deposits of wind-blown loess and materials deposited by water (as opposed to ice) had lower arsenic concentrations than glacial tills and outwash plains that underwent minimal erosion following glacial deposition.