Modeling Spatial Patterns in Soil Arsenic to Estimate Natural Baseline Concentrations
- Erik R. Venteris *ac,
- Nicholas T. Bastab,
- Jerry M. Bighamb and
- Ron Reaa
- a Ohio Department of Natural Resources, Division of Geological Survey, 2045 Morse Road, Bldg. C-1, Columbus, OH 43229
c current address: Hydrology, Environmental Sustainability Division, Pacific Northwest National Laboratory 902 Battelle Boulevard P.O. Box 999, MSIN K9-33 Richland, WA 99352
b School of Environment and Natural Resources, The Ohio State Univ., 410C Kottman Hall, 2021 Coffey Rd, Columbus, OH 43210
Arsenic in soil is an important public health concern, but risk-based toxicity regulatory standards derived from laboratory studies should also consider concentrations measured away from obvious contamination (i.e., baseline concentrations that approximate natural background) to avoid unnecessary remediation burdens on society. We used soil and stream sediment samples from the USGS National Geochemical Survey to assess the spatial distribution of As over a 1.16 × 105 km2 area corresponding to the state of Ohio. Samples were collected at 348 soil and 144 stream sites at locations selected to minimize anthropogenic inputs. Total As was measured by sodium peroxide fusion with subsequent dissolution using concentrated HCl and analysis using hydride-generation atomic absorption spectrometry. Arsenic in the soil and streambed samples ranged from 2.0 to 45.6 mg kg−1. Sequential Gaussian simulation was used to map the expected concentration of As and its uncertainty. Five areas of elevated concentration, greater than the median of 10 mg kg−1, were identified, and relationships to geologic parent materials, glacial sedimentation, and soil conditions interpreted. Arsenic concentrations <4 mg kg−1 were rare, >10 mg kg−1 common, and >20 mg kg−1 not unusual for the central and west central portions of Ohio. Concentrations typically exceeded the soil As human generic screening level of 0.39 mg kg−1, a value corresponding to an increase in cancer risk of 1 in 1,000,000 for soil ingestion. Such results call into question the utility of the USEPA and similarly low soil screening levels. The contrast between laboratory screens and concentrations occurring in nature argue for risk assessment on the basis of baseline concentrations.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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