ORIGINAL ARTICLE Metal contamination and filtering in soil from an iron (magnetite) mine–smelter complex in the critical Hudson Highlands watershed, New York Sivajini Gilchrist • Alexander E. Gates • Matthew Gorring • Evert Jan Elzinga Received: 1 October 2009 / Accepted: 28 September 2010 / Published online: 29 October 2010 Ó Springer-Verlag 2010 Abstract Organic material in metal contaminated soils around an abandoned magnetite mine–smelter complex in the critical Highlands watershed protects the groundwater and surface water from contamination. Metals in these waters were consistently below local and national water standards. Two groups of soil types cover the area: (1) Group A disturbed metal-rich soils, and (2) Group B undisturbed organic soils. Chromium and nickel were more elevated than other metals with Cr more widespread than Ni. In Group A, Cr correlated strongly with sesquioxides in the lower horizons (Fe 2 O 3 : r = 0.74, p \ 0.025; Al 2 O 3 : r = 0.92, p \ 0.005). In Group B, Cr correlated strongly (r = 0.96, p \ 0.005) with soil organic matter (SOM) in the O-horizons. Ni–Cr (Group A: 52 and 70% in O- and lower horizons, respectively; Group B: *100% in both horizons) and V–Cr correlations (78% only in Group A lower horizons) suggest similar retention mechanisms for these elements. Average soil pH CaCl 2 for both groups ran- ged between 3.65 and 5.91, suggesting that soil acidity is determined by organic acids and solubility of Al 3? releasing H ? ions. SOM and sesquioxides contribute sig- nificantly to creating naturally occurring filtration systems, removing metals, and protecting water quality. High Ca, Fe, and Ti in Group A soils suggest slag and ash were mixed into the soils. Some low-Cr sources include mag- netite, slag, and ash (100, 100 and 200 mg/kg, respec- tively). Constant ZrO 2 :TiO 2 ratios in the lower soils indicate soil formation from breakdown of underlying tailing rocks, contributing Cr to these layers. Keywords Ash  Chromium  Metal contamination  Slag  Soil organic matter Introduction The Highlands Region (Fig. 1a) with over 800,000 acres of forested watershed supplies drinking water to over 15 million people in New York, New Jersey, Pennsylvania, and Connecticut (Porter 2008). The region is increasingly at risk of being overdeveloped and more than 70% of its land is considered environmentally sensitive (Highlands Legislation 2004). Industrialization of the area through extensive iron and related mining operations from 1730 to the early 20th century (Smock 1889; Ransom 1966) left the Highlands environmentally impaired. The Sterling iron- works in southeastern Hudson Highlands, New York, alone was estimated to have produced 1,900,000 tons of iron-ore (Hotz 1953). The regions are still peppered with spoils from the abandoned mines and their operations, even though they have largely recovered through natural atten- uation. Besides iron mining, sulfide mining was also con- ducted. Gilchrist et al. (2009) showed that these mines could pose an environmental threat from acid mine drain- age (AMD) with elevated metals. Volumetrically, spoils from sulfide mines are insignificant compared to those from large-scale iron-mining operations like those in the Sterling magnetite mine area (Fig. 1a, b). The Sterling mine area consisted of 21 iron mines in southern New York, but Lake Mine and Sterling Mine were the principal iron-ore producers (Hotz 1953; Ransom 1966). It is uncommon for smelters to be in the same S. Gilchrist (&)  A. E. Gates  E. J. Elzinga Earth and Environmental Sciences, Rutgers University, Smith Hall 137, 101 Warren Street, Newark, NJ 07102, USA e-mail: sivajini@pegasus.rutgers.edu M. Gorring Department of Earth and Environmental Studies, Montclair State University, 355 Mallory Hall, Montclair, NJ 07043, USA 123 Environ Earth Sci (2011) 63:1029–1041 DOI 10.1007/s12665-010-0779-9