Arsenic background concentrations in Florida, USA surface soils: Determination and interpretation

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses i ssues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxon omic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO3-HF, microwave digestion) and graphite furnace atomic absorpt ion spectrophotometry analysis procedure. Values were log-normally distribu ted, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactor y statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n = 267) compared to 7.63 mg As/kg for di sturbed soils (n = 181). Temporal trend of total soil arsenic concentration s from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agricultu re. Soil arsenic background concentrations were generally higher in south F lorida than in north and central Florida, and associated with wet soils. In dividual high arsenic sites were scattered throughout the state, but the mo st highly concentrated of these occurred in the Leon-Lee belt along the Oca la uplift district extending to the southwestern flatwoods district. Extrap olation of the data using a single arsenic value regardless of the taxonomi c and geographical differences in soil arsenic distribution would underesti mate potential arsenic contamination in upland soils. (C) 2001 AEHS.