Proctor D, Mittal L, Vivanco S, Perry C, Blanchette A. Probabilistic health risk assessment for residential exposures to metals in electric arc furnace (EAF) steel slag. Presentation 5.15.P-Th123 to Society of Environmental Toxicology and Chemistry, Pittsburgh PA, November 2022.
EAF slag is a co-product of steel production and is used primarily for construction purposes, including landscape aggregate and cover for unpaved rural roads. Some applications of EAF slag may result in residential exposures by direct contact and inhalation of airborne dust. To evaluate the potential health risks, an EAF slag characterization program was conducted to measure concentrations of metals in slag, leaching potential (including oral bioaccessibility [BA] by EPA Method 1340), and analysis of mineralogy. EAF slag is an alkaline mineral matrix. Comparing metal concentrations in EAF slag to residential Regional Screening Levels, antimony, arsenic (As), hexavalent chromium (CrVI), iron, vanadium, and manganese (Mn) were identified as constituents of interest, although As levels in slag are consistent with naturally occurring As in soil. Using a probabilistic risk assessment (PRA) approach, exposures specific to residential EAF slag applications for driveways/landscape and for residents near unpaved roads were assessed for children and adults. Varying assumptions regarding particulate emissions, time spent at home, and time spent outdoors were considered, with exposure parameters from EPA guidance and measures of EAF slag-specific oral BA. For Mn, measures of relative bioavailability (RBA) from a recently conducted in vivo rat RBA study of EAF slag will be included. The PRA predicted the distribution of dose, and the increased cancer risks and hazard indices (HIs) for the 50th and 90th percentiles of exposure were determined. For the residential roadside scenario, cancer risk and HIs were < 1E-6 and 1, respectively. For the residential driveway/landscape scenario, cancer risks were 2E-6, assuming 100% oral BA for CrVI, and the HI was 1 using EPA’s most conservative Mn reference dose, and BA as an estimate for RBA. To further assess the potential for Mn neurotoxicity, a published physiologically based pharmacokinetic (PBPK) model was used to predict levels of Mn in the brain (i.e., globus pallidus) for children and adults. The PBPK model predictions for Mn in the globus pallidus were slightly increased at the 90th percentile (0.51–0.56 µg/g) compared to diet alone, but were well below NOAELs of 0.7–0.9 µg/g for neurological effects reported from human and primate studies. Overall, using refined risk assessment methods including PBPK modeling, the PRA found that application of EAF slag in residential areas does not pose a health hazard.