A water-leach procedure for estimating bioaccessibility of elements in soils from transects across the United States and Canada

摘要

An objective of the North American Soil Geochemical Landscapes Project is to provide relevant data concerning bioaccessible concentrations of elements in soil to government and other institutions undertaking environmental studies. A protocol was developed that employs a 1-g soil sample agitated overnight with 40 mL of reverse-osmosis de-ionized water for 20 h, and determination of 63 elements following three steps of centrifugation by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry the following day. Statistical summaries are presented for those 48 elements (Ag, Al, As, B, Ba, Be, Br, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, 1, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Pr, Rb, Re, S, Sb, Si, Sm, Sn, Sr, Tb, Ti, Tl, Tm, U, V, W, Y, Yb, Zn. Zr, and pH) for which <20% of their data were reported as below the detection limit.The resulting data set contains analyses for 161 A-horizon soils collected along two transects,one along the 38th parallel across the USA and the other from northern Manitoba to the USA-Mexico border.The spatial distribution of three selected elements(Ca,Cu,and Pb)along the two transects is discussed in this paper both as absolute amounts liberated by the leach and expressed as a percentage of the total, or near-total, amounts determined for the elements. The Ca data reflect broad trends in soil parent materials, their weathering, and subsequent soil development.Calcium concentrations are generally found to be lower in the older soils of the eastern USA. The Cu data are higher in the eastern half of the USA, correlating with soil organic C,with which it is sequestered. The Pb data exhibit little regional variability due to natural sources, but are influenced by anthropogenic sources. Based on the Pb results, the percentage water-extractable data demonstrate promise as a tool for identifying anthropogenic components. The soil-water partition(distribution)coefficients,K(d)s(L/kg),were determined and their relevance to estimating bioaccessible amounts of elements to soil fauna and flora is discussed. Finally,a possible link between W concentrations in human urine and water-extractable W levels in Nevada soils is discussed. Crown Copyright(C)2009 Published by Elsevier Ltd. All rights reserved.