TY - JOUR
T1 - Arsenic and iron speciation and mobilization during phytostabilization of pyritic mine tailings
AU - Hammond, Corin M.
AU - Root, Robert A.
AU - Maier, Raina M.
AU - Chorover, Jon
N1 - Funding Information:
This research was supported by the National Institute of Environmental Health Sciences (NIEHS) Superfund Research Program Grant 2 P42 ES04940. Portions of this research were carried out at Stanford Synchrotron Radiation Lightsource, a National User Facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. We thank Steven Schuchardt, president of North American Industries, for providing access to the IKMHSS site and help with irrigation and weather station. Special thanks to Scott White for extensive work in establishing and maintaining the field site and greenhouse study and for supervising all field sampling efforts; to Juliana Gil-Loaiza who contributed invaluable assistance in organizing field sampling; and to William Scott, Mon Bejar, and Christopher Schicker for significant assistance with tailings sample processing. We thank the Environmental Microbiology, Environmental Biogeochemistry, and Contaminant Transport Labs at the University of Arizona for help during field preparation and sampling from 2010 to 2013. We thank Mary Kay Amistadi, Kelsie Lasharr, Shawn Pedron, and Rachel Burnett for ICP-MS analyses of tailings elemental content performed at the Arizona Laboratory for Emerging Contaminants (ALEC) at the University of Arizona. The views of authors do not necessarily represent those of the NIEHS, NIH.
Funding Information:
This research was supported by the National Institute of Environmental Health Sciences (NIEHS) Superfund Research Program Grant 2 P42 ES04940 . Portions of this research were carried out at Stanford Synchrotron Radiation Lightsource, a National User Facility operated by Stanford University on behalf of the U.S. Department of Energy , Office of Basic Energy Sciences . We thank Steven Schuchardt, president of North American Industries, for providing access to the IKMHSS site and help with irrigation and weather station. Special thanks to Scott White for extensive work in establishing and maintaining the field site and greenhouse study and for supervising all field sampling efforts; to Juliana Gil-Loaiza who contributed invaluable assistance in organizing field sampling; and to William Scott, Mon Bejar, and Christopher Schicker for significant assistance with tailings sample processing. We thank the Environmental Microbiology, Environmental Biogeochemistry, and Contaminant Transport Labs at the University of Arizona for help during field preparation and sampling from 2010 to 2013. We thank Mary Kay Amistadi, Kelsie Lasharr, Shawn Pedron, and Rachel Burnett for ICP -MS analyses of tailings elemental content performed at the Arizona Laboratory for Emerging Contaminants (ALEC) at the University of Arizona . The views of authors do not necessarily represent those of the NIEHS , NIH .
Publisher Copyright:
© 2020 Elsevier Ltd
PY - 2020/10/1
Y1 - 2020/10/1
N2 - Particulate and dissolved metal(loid) release from mine tailings is of concern in (semi-)arid environments where tailings can remain barren of vegetation for decades and, therefore, become highly susceptible to dispersion by wind and water. Erosive weathering of metalliferous tailings can lead to arsenic contamination of adjacent ecosystems and increased risk to public health. Management via phytostabilization with the establishment of a vegetative cap using organic amendments to enhance plant growth has been employed to reduce both physical erosion and leaching. However, prior research suggests that addition of organic matter into the oxic weathering zone of sulfide tailings has the potential to promote the mobilization of arsenate. Therefore, the objective of the current work was to assess the impacts of phytostabilization on the molecular-scale mechanisms controlling arsenic speciation and lability. These impacts, which remain poorly understood, limit our ability to mitigate environmental and human health risks. Here we report on subsurface biogeochemical transformations of arsenic and iron from a three-year phytostabilization field study conducted at a Superfund site in Arizona, USA. Legacy pyritic tailings at this site contain up to 3 g kg−1 arsenic originating from arsenopyrite that has undergone oxidation to form arsenate-ferrihydrite complexes in the top 1 m. Tailings were amended in the top 20 cm with 100, 150, or 200 g kg−1 (300–600 t ha−1) of composted organic matter and seeded with native halotolerant plant species. Treatments and an unamended control received irrigation of 360 ± 30 mm y−1 in addition to 250 ± 160 mm y−1 of precipitation. Cores to 1 m depth were collected annually for three years and sectioned into 20 cm increments for analysis by synchrotron iron and arsenic X-ray absorption spectroscopy (XAS) coupled with quantitative wet chemical and mass balance methods. Results revealed that >80% of arsenic exists in ammonium oxalate-extractable and non-extractable phases, including dominantly ferrihydrite and jarosite. Arsenic release during arsenopyrite oxidation resulted in both downward translocation and As(V) attenuation by stable Fe(III)(oxyhydr)oxide and Fe(III) (hydroxy)sulfate minerals over time, highlighting the need for sampling at multiple depths and time points for accurate interpretation of arsenic speciation, lability, and translocation in weathering profiles. Less than 1% of total arsenic was highly-labile, i.e. water-extractable, from all treatments, depths, and years, and more than 99% of arsenate released by arsenopyrite weathering was attenuated by association with secondary minerals. Although downward translocation of both arsenic and iron was detected during phytostabilization by temporal enrichment analysis, a similar trend was measured for the uncomposted control, indicating that organic amendment associated with phytostabilization practices did not significantly increase arsenic mobilization over non-amended controls.
AB - Particulate and dissolved metal(loid) release from mine tailings is of concern in (semi-)arid environments where tailings can remain barren of vegetation for decades and, therefore, become highly susceptible to dispersion by wind and water. Erosive weathering of metalliferous tailings can lead to arsenic contamination of adjacent ecosystems and increased risk to public health. Management via phytostabilization with the establishment of a vegetative cap using organic amendments to enhance plant growth has been employed to reduce both physical erosion and leaching. However, prior research suggests that addition of organic matter into the oxic weathering zone of sulfide tailings has the potential to promote the mobilization of arsenate. Therefore, the objective of the current work was to assess the impacts of phytostabilization on the molecular-scale mechanisms controlling arsenic speciation and lability. These impacts, which remain poorly understood, limit our ability to mitigate environmental and human health risks. Here we report on subsurface biogeochemical transformations of arsenic and iron from a three-year phytostabilization field study conducted at a Superfund site in Arizona, USA. Legacy pyritic tailings at this site contain up to 3 g kg−1 arsenic originating from arsenopyrite that has undergone oxidation to form arsenate-ferrihydrite complexes in the top 1 m. Tailings were amended in the top 20 cm with 100, 150, or 200 g kg−1 (300–600 t ha−1) of composted organic matter and seeded with native halotolerant plant species. Treatments and an unamended control received irrigation of 360 ± 30 mm y−1 in addition to 250 ± 160 mm y−1 of precipitation. Cores to 1 m depth were collected annually for three years and sectioned into 20 cm increments for analysis by synchrotron iron and arsenic X-ray absorption spectroscopy (XAS) coupled with quantitative wet chemical and mass balance methods. Results revealed that >80% of arsenic exists in ammonium oxalate-extractable and non-extractable phases, including dominantly ferrihydrite and jarosite. Arsenic release during arsenopyrite oxidation resulted in both downward translocation and As(V) attenuation by stable Fe(III)(oxyhydr)oxide and Fe(III) (hydroxy)sulfate minerals over time, highlighting the need for sampling at multiple depths and time points for accurate interpretation of arsenic speciation, lability, and translocation in weathering profiles. Less than 1% of total arsenic was highly-labile, i.e. water-extractable, from all treatments, depths, and years, and more than 99% of arsenate released by arsenopyrite weathering was attenuated by association with secondary minerals. Although downward translocation of both arsenic and iron was detected during phytostabilization by temporal enrichment analysis, a similar trend was measured for the uncomposted control, indicating that organic amendment associated with phytostabilization practices did not significantly increase arsenic mobilization over non-amended controls.
KW - Arsenic speciation
KW - Depth profile
KW - Ferrihydrite
KW - Field-scale
KW - Iron (oxy)hydroxides
KW - Jarosite
KW - Phytostabilization
KW - XAS
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U2 - 10.1016/j.gca.2020.07.001
DO - 10.1016/j.gca.2020.07.001
M3 - Article
AN - SCOPUS:85089236472
SN - 0016-7037
VL - 286
SP - 306
EP - 323
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
ER -