Environ. Sci. Technol. 2008, 42, 1423–1429
Arsenic Transformation and Mobilization from Minerals by the Arsenite Oxidizing Strain WAO E. DANIELLE RHINE,† KATHERYN M. ONESIOS,‡ MICHAEL E. SERFES,§ JOHN R. REINFELDER,‡ AND L . Y . Y O U N G * ,†,‡ Biotechnology Center for Agriculture and the Environment and Department of Environmental Sciences, Cook College, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, and New Jersey Geological Survey, Trenton, New Jersey
Received July 26, 2007. Accepted November 29, 2007.. Revised manuscript received November 28, 2007
Analysis of arsenic concentrations in New Jersey well water from the Newark Basin showed up to 15% of the wells exceed 10 µg L-1, with a maximum of 215 µg L-1. In some geologic settings in the basin, this mobile arsenic could be from the weathering of pyrite (FeS2) found in black shale that contains up to 4% arsenic by weight. We hypothesized that under oxic conditions at circumneutral pH, the microbially mediated oxidation of sulfide in the pyrite lattice would lead to the release of pyrite-bound arsenic. Moreover, the oxidation of aqueous As(III) to As(V) by aerobic microorganisms could further enhance arsenic mobilization from the solid phase. Enrichment cultures under aerobic, As(III)-oxidizing conditions were established under circumneutral pH with weathered black shale from the Newark Basin as the inoculum source. Strain WAO, an autotrophic inorganic-sulfur and As(III)-oxidizer, was isolated and phylogenetically and physiologically characterized. Arsenic mobilization studies from arsenopyrite (FeAsS) mineral, conducted with strain WAO at circumneutral pH, showed microbially enhanced mobilization of arsenic and complete oxidation of released arsenic and sulfur to stoichiometric amounts of arsenate and sulfate. In addition, WAO preferentially colonized pyrite on the surface of arsenic-bearing, black shale thick sections. These findings support the hypothesis that microorganisms can directly mobilize and transform arsenic bound in mineral form at circumneutral pH and suggest that the microbial mobilization of arsenic into groundwater may be important in other arsenic-impacted aquifers.
Introduction With elevated levels of arsenic being detected in groundwater, most notably in parts of Taiwan (1), Bangladesh (2), West Bengal (3), and the United States (4), arsenic has emerged as a serious health concern worldwide. Human exposure to arsenic within the environment is typically through drinking * Corresponding author phone: (732) 932-8165, ext. 312; fax: (732) 932-0312; e-mail:
[email protected]. † Biotechnology Center for Agriculture and the Environment, Rutgers. ‡ Department of Environmental Sciences, Rutgers. § New Jersey Geological Survey. 10.1021/es071859k CCC: $40.75
Published on Web 02/01/2008
2008 American Chemical Society
water, and the US Environmental Protection Agency has recently lowered the maximum contaminant level (MCL) for arsenic in drinking water to 10 µg L-1 (5). Once ingested, arsenic can combine with thiol groups and can substitute for phosphorus, leading to impaired protein function and inhibited oxidative phosphorylation. In humans, exposure to chronic doses of arsenic has been linked to cardiovascular and neurological diseases, jaundice, hyperkeratosis, and cancers of various organs and tissues (6). Arsenic is the 20th most common element found in the earth’s crust and can be found in approximately 250 minerals, with higher concentrations in deposits of iron and sulfur (7). Arsenic-bearing minerals may contain elemental arsenic (As0), arsenides, arsenites [As(III); H3AsO3 and H2AsO3-], or arsenates [As(V); H2AsO4- and HAsO42-]. Pyrite (FeS2) is the most ubiquitous arsenic bearing sulfide mineral, and micronscale spot concentrations have been shown to occur at up to 8.5 and 9.97 mg kg-1 in sedimentary and hydrothermal pyrite, respectively (8, 9). The oxidation of sulfide in pyrite would lead to arsenic mobilization from the mineral to the aqueous phase and an increase in arsenic bioavailability (10). Indeed, this is one proposed mechanism that may have contributed to elevated levels of arsenic in some Bangladesh aquifers (3). The Newark Basin, located primarily in north central New Jersey and Eastern Pennsylvania, is part of the North American Rift Basin system and contains some of the most productive aquifers in the region. The geologic formations of the Newark Basin include the Passaic (mainly cyclical sequences of red mudstone, siltstone, and sandstone with intermittent gray mudstone and black shale) and Lockatong (organic rich black, gray, and red cyclical sequences of argillitic mudstone, siltstone, and shale containing lenses of pyrite and calcite) Formations. Pyrite in black shale and gray mudstone in the Passaic and Lockatong Formations contain up to 4% arsenic by weight and are the most significant and abundant mineral source of arsenic (11). Arsenic concentrations in Newark Basin water supply wells in New Jersey sampled in 1999-2000 ranged from
