Proctor DM, Antonijevic T. Refined health risk assessment for residential exposures to manganese in EAF steel slag. Poster presented at Society of Toxicology Annual Meeting, San Diego, CA, March 2022.
Electric Arc Furnace (EAF) slag is a co-product of steel production and is used primarily for construction purposes, including road base and shoulders, rip-rap, landscape aggregate and for cover of unpaved rural roads. Some applications of EAF slag may result in exposure of residential populations to metals in slag by direct contact and suspended airborne dust. We conducted an extensive EAF slag characterization program measuring concentrations of elements in slag, leaching potential, including bioaccessibility (BA) by EPA Method 1340, and analysis of mineralogy. Based on a screening level assessment, manganese (Mn) in slag was identified as posing the greatest potential for health concern and is being further studied for residential exposure scenarios using refined methods including measures of relative bioavailability (RBA), physiologically-based pharmacokinetic (PBPK) modeling using previously published models, and probabilistic risk assessment (PRA) methods. The levels of Mn in EAF slag are ~3.4%, with ~2.1% in the <150 µm size fraction. BA ranges from 15-62% and is inversely related to total Mn concentration. Because the EPA reference dose for Mn is based on human dietary intake, rather than a measure of toxicity, published PBPK models were used to predict levels of Mn in the brain (i.e., globus pallidus) for children and adults for exposures considered representative of residents exposed to slag. The PBPK model predictions for Mn in the globus pallidus were slightly increased (0.49-0.58 µg/g) for residential exposures compared to diet alone (0.43-0.53 µg/g), and below NOAELs (0.7-0.9 µg/g) reported in the literature from human and primate studies. Incidental slag ingestion exposure was the primary pathway, and inhalation contributed negligibly. Current work includes refining these results using data from an ongoing rat in vivo RBA study.