Trace element speciation in selected smelter-contaminated soils in Anaconda and Deer Lodge Valley, Montana, USA
Burt, R; Wilson, MA; Keck, TJ; Dougherty, BD; Strom, DE; Lindahl, JA
Long-term copper smelting in the Anaconda and Deer Lodge
Valley area of Montana has resulted in an extensive area of trace element contamination. Aerial
extent of contamination is generally established, but total analysis of soils does not correlate
to relative degree of impact on vegetation growth. Three pedons (Beaverell, Cetrack and Judco)
were analyzed by routine soil characterization methods, aqua regia microwave digestion,
sequential chemical extraction, and X-ray diffraction analysis with the objective of providing a
better understanding of chemical forms and potential reactivity of selected trace elements (Cd,
Co, Cr, Cu, Hg, Mn, Ni, P, Pb). Surface horizons of soils are more acidic than subsoils, with pH
for all horizons ranging from 4.0 to 8.7. Beaverell is the most contaminated in the upper 20 cm
with the sum of total extractable (SUMTE) trace elements by microwave digestion ranging from 1836
to 3605 mg kg(-1), largest H2O-soluble (WS) and exchangeable (EX) fractions (e.g. 1.6 and 9.3%,
respectively), and smallest residual (RES) fraction (e.g. 14.3%). Cetrack has greater SUMTE
elements than Judco, though a lower WS+EX fraction due to the effects of alkaline pH, carbonates
and high P. Oxide (OX), organic matter/sulfide (OM/S), and RES fractions predominate over WS, EX,
and specially-sorbed/carbonate-bound fractions (SS/CAR) for all horizons. Copper, Zn, Ph and Cd
are elevated in surface over subsurface horizons in these latter fractions, indicating these
elements were anthropogenic additions. X-ray data indicate that Pb, Cu, Cr and Cd partially
exists as both OX and sulfide mineral forms. (C) 2002 Elsevier Ltd. All rights reserved.