Soil Weathering as an Engine for Manganese Contamination of Well

Article pubs.acs.org/est

Soil Weathering as an Engine for Manganese Contamination of Well Water Elizabeth C. Gillispie,† Robert E. Austin,† Nelson A. Rivera,†,∥ Rick Bolich,‡ Owen W. Duckworth,† Phil Bradley,§ Aziz Amoozegar,† Dean Hesterberg,† and Matthew L. Polizzotto*,† †

Department of Crop and Soil Sciences, North Carolina State University, 101 Derieux St, Campus Box 7619, Raleigh, North Carolina 26795, United States ‡ North Carolina Department of Environmental Quality − Division of Water Resources, 3800 Barrett Drive, Raleigh, North Carolina 27609, United States § Norh Carolina Geological Survey, 512 North Salisbury Street, Raleigh, North Carolina 27604, United States S Supporting Information *

ABSTRACT: Manganese (Mn) contamination of well water is recognized as an environmental health concern. In the southeastern Piedmont region of the United States, well water Mn concentrations can be >2 orders of magnitude above health limits, but the specific sources and causes of elevated Mn in groundwater are generally unknown. Here, using field, laboratory, spectroscopic, and geospatial analyses, we propose that natural pedogenetic and hydrogeochemical processes couple to export Mn from the near-surface to fracturedbedrock aquifers within the Piedmont. Dissolved Mn concentrations are greatest just below the water table and decrease with depth. Solidphase concentration, chemical extraction, and X-ray absorption spectroscopy data show that secondary Mn oxides accumulate near the water table within the chemically weathering saprolite, whereas less-reactive, primary Mn-bearing minerals dominate Mn speciation within the physically weathered transition zone and bedrock. Mass-balance calculations indicate soil weathering has depleted over 40% of the original solid-phase Mn from the near-surface, and hydrologic gradients provide a driving force for downward delivery of Mn. Overall, we estimate that >1 million people in the southeastern Piedmont consume well water containing Mn at concentrations exceeding recommended standards, and collectively, these results suggest that integrated soil-bedrock-system analyses are needed to predict and manage Mn in drinking-water wells.

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INTRODUCTION

physical processes−including redox transformation, sorption, mineral precipitation/dissolution, and transport−may impact Mn partitioning between aqueous and solid phases,17−23 Prior research on the sources of Mn contamination of groundwater generally has focused on the geological characteristics of aquifers.6−8,24,25 However, near-surface pedogenetic and hydrogeochemical processes, which can play key roles in controlling the distribution and flux of elements that impact groundwater quality,26 have been largely neglected from reports describing Mn well water contamination. The primary objectives of this research were to (1) determine Mn distributions within solid and aqueous phases of the subsurface, (2) elucidate the mechanisms and locations of Mn release to groundwater, and (3) quantify Mn exposure potential from well water across the Piedmont region of the

Manganese (Mn) contamination of well water is increasingly being recognized as a global environmental concern.1−10 For example, across the Piedmont region of the southeastern United States, where approximately 3.9 million people (21% of a population of 18.7 million) rely on private well water,11 chronic Mn exposure through consumption of contaminated well water is now seen as a serious human health threat. In North Carolina (NC), well water Mn concentrations can reach 4 mg/L,12 and recent research indicates that county averages of well water concentrations are positively associated with infant mortality rates,13 conotruncal heart defects,14 neurodevelopmental defects,15 and deaths by cancer.16 To date, few studies of Mn groundwater contamination have attempted to systematically define Mn sources and cycling within the subsurface, information that is crucial for understanding and mitigating the health concerns associated with Mn exposure through well water consumption. The presence of Mn in well water is typically a result of Mn solubilization from natural sources, and numerous biological, chemical, and © XXXX American Chemical Society

Received: April 5, 2016 Revised: August 25, 2016 Accepted: August 28, 2016

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DOI: 10.1021/acs.est.6b01686 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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Environmental Science & Technology

Figure 1. Distributions of NURE well water Mn concentrations in the Piedmont. (a) North Carolina Piedmont soil systems57 overlain by Mn concentrations in well water.12 North Carolina Division of Water Resources (DWR) research stations are indicated with stars. Data are presented in the main portion of this paper for the Morgan Mill DWR site. (b) Combined map of NC Piedmont soil systems with Mn concentrations in well water12 for the Piedmont region of Virginia, North Carolina, South Carolina, and Georgia.

southeastern U.S. We link field, laboratory, spectroscopic, and geospatial analyses to develop an integrated soil-bedrocksystem model for the hydrogeochemical processes governing Mn contamination of well water across the region and demonstrate how active weathering of parent material, secondary mineral dissolution, and groundwater transport combine to deliver Mn from the near-surface to wells. Collectively, our results underscore the need for better integration of soil weathering processes into assessments and predictions of well water quality and human exposure to contaminants.

Carolina Slate Belt, and the Triassic Basin (Figure 1). Although these systems comprise numerous soil series with different compositions, each system generally consists of moderately drained soils with some version of loam texture.27 The Piedmont bedrock is mainly composed of igneous and metamorphic rocks, and therefore contains mostly crystallinerock aquifers, although there is a small section containing a siliciclastic-rock aquifer.28 The transport of groundwater constituents is impacted by groundwater flow through the regolith and fractured bedrock within the Piedmont. The regolith and fractured bedrock groundwater flow system is generally classified into four zones: the unsaturated regolith zone (vadose; includes soil and saprolite), the saturated regolith zone (includes saprolite), the transition zone, and the fractured bedrock (Figure S1).28 The unsaturated regolith zone provides a medium for the recharge to infiltrate to the groundwater system, in which metals and

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MATERIALS AND METHODS Field Area Description. The Piedmont is a physiographic region located between the coastal plain to the east and Appalachian Mountains to the west. The dominant soil systems in this region are Felsic Crystalline, Mixed Felsic and Mafic, B


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(ICP-OES, PerkinElmer model 2000 DV) at the North Carolina State University Environmental and Agricultural Testing Service (EATS) laboratory. Specific protocols for analyses of well water chemistry are found in the Supporting Information. Manganese X-ray Absorption Near-Edge Structure (XANES) Spectroscopy. In order to quantify the percentage of Mn found in primary and secondary mineral phases throughout depth profiles, individual core samples from four of the DWR research stationsLangtree Peninsula, Morgan Mill, NC Zoological Park, and Lake Wheeler (Figure S2) were analyzed by Mn X-ray absorption spectroscopy (XAS). XAS analyses were conducted at ambient temperature on Beamline 11−2 at the Stanford Synchrotron Radiation Lightsource (SSRL), running under dedicated conditions (3 GeV, 500 mA) using an unfocused beam. The data collection and analysis approaches used are discussed by Kelly et al.32 and summarized in the Supporting Information. XANES data were generally collected over three energy ranges of −200 to −50 eV, −50 to 50 eV, and 50 to 300 eV relative to the Mn edge (6539 eV), with smaller step sizes and larger counting times used in the region bracketing the edge (−50 to 50 eV). XANES spectra were averaged, baseline corrected with a linear model, and normalized to an edge step of 1 using the IFEFFIT suite33 of computer programs in the Athena and Artemis software.34 Estimates of proportions of Mn species present in the samples were made using the linear combination fitting (LCF) routine in Athena to determine the combination of scaled XANES spectra from 21 standards that gave the best-fit to sample spectra, following the method of Manceau et al.35 (Supporting Information). Fitting analyses were performed over the range of 6350−6590 eV without an energy shift parameter for the calibrated data. Additionally, the spectrum from a corresponding bedrock sample was used in the fitting of soil, saprolite, and transition-zone samples because pure-mineral standards alone could not accurately account for features in their XANES spectra. The assumption in this approach is that Mn species throughout the profile were weathered from the original species of bedrock, and that the residual quantities of these species are still present. Proportions of XANES spectra for standards that yielded the “best fits” (lowest or near-lowest statistical goodness of fit−see Supporting Information for full explanation of fitting criteria and parameters) to sample spectra when summed were considered as being estimates of average analogous species in the unknown samples.35 The full list of standards used in the analysis is provided in the Supporting Information. Standards used in the final fits of the samples, in addition to the bedrock, were rhodochrosite (Mn2+CO3), birnessite ((Na0.3Ca0.1K0.1) (Mn4+,Mn3+)2O4 · 1.5 H2O), hausmanite (α-Mn2+Mn3+2O4), and groutite (Mn3+O(OH)). The sums of weighting factors on fitting standards were 99−107% (Morgan Mill), 97−107% (Langtree), 92−115% (NC Zoo), and 93−103% (Lake Wheeler), and these were normalized to a sum of 100%. Regional Well-Water Data Sources. Regional well waterquality data were obtained from the United States Geological Survey (USGS) National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) program12 and the NC Department of Health and Human Services (DHHS) Environmental Health Section (EHS) private well database (Figures 1, 2 and S2−S4). As part of the NURE program, 5174 wells were sampled across North Carolina from 1976 to 1978, with an attempt to create study

other constituents may be released from the soil into the percolating water that flows toward groundwater. The saturated regolith zone acts as a reservoir that supplies water to the bedrock.28 The transition zone tends to be more permeable than the other zones, thus creating a potentially high-flow groundwater system, while groundwater only flows through interconnected fractures within the bedrock.28 Recently installed domestic wells in the Piedmont crystalline aquifers tend to be cased through regolith and transition zones and openly screened into the bedrock to yield water from the network of fractures that serve as pipelines between the well and regolith reservoir.28 However, older wells can be cased at varying depths greater than ∼3 m below the surface and often access water in the saturated regolith/saprolite. Sample Collection and Analysis. Geological cores, soil samples, and well water samples were obtained among 10 North Carolina Department of Environmental Quality Division of Water Resources (DWR) research stations (Figure S2).29 Geological cores were originally drilled and extracted during the installation of the well clusters for each research station (between 2001 and 2007). All original geological cores began at surface depth and extended to as deep as 61 m. The cores were collected by wireline diamond drilling, and water was used as the primary circulation/cooling fluid. Core sizes were HQ, or roughly 10 cm in diameter. Core samples were stored in boxes at room temperature across the state by DWR in various warehouses. An average of 12 subsamples for the geological cores from eight of the 10 research stations were retrieved in May and June 2013 for this study. Samples were chosen from the geological cores to obtain a representation of the unsaturated regolith, saturated regolith, transition zone, bedrock, and any transition between those zones. Samples were placed into storage bags and stored in the dark at room temperature for laboratory experiments. To minimize analysis of any chemical artifacts that may have been derived from core collection or storage, prior to analysis or experimentation, “fresh” samples were obtained from the interior of the ∼10 cm-diameter cores. Specific protocols for measurement of (1) total solid-phase Mn (and Ti) concentrations by neutron activation analysis, (2) strongacid-digestion Mn concentrations in solid phases,30 and (3) chemical fractionation of solid-phase Mn by sequential extraction31 are provided in the Supporting Information. Wells in nine of the ten DWR study sites were sampled for Mn concentrations once in the summer and once in the winter of 2014 following a well water sampling protocol by the NC Department of Environmental Quality DWR.29 Water levels were measured in each well at the site before sampling. Prior to sampling, three well volumes of water were purged from shallow and intermediate wells and 1−1.5 well volumes of water were purged from deep wells using a SS Geosub 12 V DC Sampling pump and controller (Geotech Environmental Equipment, Inc.), Monsoon Purging pump (ProActive Pumps), submersible down-well pump (Grundfos), or a peristaltic pump (Pine Environmental Services, Inc.) depending on location and well depth. Water samples were filtered using in-line 0.45 μm filters (Dispos-a-filters, Geotech Environmental, Inc.) into 30 mL HDPE bottles, acidified using concentrated nitric acid, then stored on ice until permanently stored at 4 °C. All pumps were decontaminated after each use by rinsing inside and out with soapy water and then deionized water according to the DWR protocol.29 Samples were analyzed for Mn by inductively coupled plasma-optical emission spectrometry C


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of Mn concentrations in groundwater. The DHHS data set contains data from 8926 private drinking wells, analyzed with single measurements, across all 100 counties of NC that were constructed, repaired, or abandoned on or after July 2008.36 Well depths are not contained in the DHHS data set. Data were clipped to the Piedmont physiographic region and geocoded using the Google geocoding service. Spatial Analyses. The estimate of people possibly affected by Mn in well water was calculated based on the NURE data set12 and the U.S. Census county-level estimates of population and household well use.11 The estimate was calculated as population impacted Figure 2. Manganese concentrations from NURE well data12 plotted against corresponding bottom-of-well depths. Wells with a reported depth of zero were eliminated from the data. Data shown include 1283 wells from the ∼43 000 km2 North Carolina Piedmont region. The dashed blue line at 0.05 mg/L represents the NC drinking water standard and U.S. Environmental Protection Agency SMCL.

=

∑ (TP × %WW) × TFthreshold conc × AP

(1)

Where TP is the total county population; %WW is the percent of the county population using well water; TF is the fraction of county wells above a given Mn concentration (0.05, 0.1, 0.2, 0.3, 0.4, 0.5 mg/L); and AP is the percent of the county land area within the Piedmont region. The NURE data were joined to the county-level population estimates using a geographic information system. This method assumes a uniform population density within a county and that the NURE samples collected are representative of the county and spatially unbiased.

areas on a 1° × 2° quadrangle basis.12 Well water consisted of private, semiprivate, and public water supplies. Water samples, reported without replication, were analyzed for a wide range of inorganic species like sodium and chloride, as well as other parameters such as bottom-of-well depth and pH.12 The NURE data for North Carolina were spatially projected using the longitude and latitude coordinates associated with each well and then clipped to the Piedmont physiographic region. In addition to the NURE data, the NC DHHS EHS provided a data set of Mn concentrations in well water from 2008 to 2011 that was also included in this study for further evaluation

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RESULTS AND DISCUSSION Manganese Depth Profiles in Aqueous and Solid Phases. The highest well water Mn concentrations are generally found in shallow wells across the NC Piedmont

Figure 3. Depth profiles from the NC Division of Water Resources (DWR) Morgan Mill research site. (a) Chemically weathering soil and saprolite overlie the physically weathering transition zone and bedrock. (b) Sequential extractions of soil and saprolite ( 0 represents Mn accumulation within the weathering profile whereas τMn,Ti < 0 represents Mn depletion, relative to bedrock abundances (see Supporting Information). (a) The tau plot for total solid-phase Mn is suggestive of a “depletion-enrichment” profile. (b) The tau plot for Mn within parent-material phases, calculated from total Mn and XANES fit data, suggests an elemental weathering “depletion” profile.25 E


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Environmental Science & Technology weathering “depletion” profile (Figure 4b).26 Concentrations of Mn oxides increased to the water table but decreased below it within the saprolite (Figure 3b,c). Taken together, these solidphase Mn profiles are consistent with primary mineral dissolution during weathering of bedrock into soil via saprolite, leaching of Mn, and precipitation/accumulation of secondary Mn oxides. Elevated aqueous concentrations of Mn in wells screened just below the zone of maximum solid-phase Mn concentration (Figure 3d) suggest the reductive dissolution of Mn from more labile secondary Mn oxides. Consistent with sediment diagenesis and other redox-driven hydrogeological settings, reductive dissolution of Mn oxides likely depends on the availability of organic carbon and alternate electron acceptors for microbial metabolism17,23,39,40 and is influenced by the system hydrology. Hydrologic Controls on Mn Release and Downward Transport. Hydrologic features superimposed on weathering patterns create conditions that mobilize Mn to groundwater. Chemical weathering of parent materials near the land surface increases the availability of Mn for mobilization to groundwater, and secondary Mn(III,IV) oxides formed under oxic conditions are susceptible to microbial reductive dissolution under anoxic conditions. The location of the water table within the saprolite thus creates a geochemical gradient promoting reduction of Mn(III,IV). Across the ten sampled DWR stations in the NC Piedmont, the measured water table was roughly proximate to the maximum peak of strong-acid-digestible solidphase Mn concentrations (Figure S5), and natural or pumpinginduced fluctuations in the water table can induce sharp gradients that stimulate repeated precipitation and reductive dissolution of the Mn oxides that dominate these Mn peaks (Figure 3; Figure S7).41,42 Groundwater was devoid of dissolved oxygen, with a redox potential generally below the potential of Mn(III,IV) reduction (Table S1), so when soil and saprolite containing Mn oxides are saturated, conditions would be favorable for reductive release of Mn(II) into solution. Accordingly, the highest well water Mn concentrations were typically found in shallow wells (Figure 2), screened just below the water table and zone of secondary Mn(III/IV) oxide accumulation (Figure 3; Figure S5). Once into solution, Mn(II) (predicted to be present as Mn2+, its hydrolysis species, or in complexes with inorganic and organic ligands23), may be retained by adsorption to mineral surfaces and organic matter, but it is relatively soluble, especially as compared to Mn(III,IV) species. Furthermore, Mn(II) oxidation, which is commonly microbially mediated,43 is negligible in the absence of dissolved oxygen at typical environmental pH conditions,23 and thus Mn(II) may be transported with natural flow patterns to wells. The unsaturated regolith zone (soil + saprolite) provides a medium for the recharge water to infiltrate to the groundwater system, and the saturated regolith zone (saprolite) acts as a reservoir that supplies water to the bedrock through fractures (Figure S1).28,44,45 Prediction of specific water flowpaths from the surface into the groundwater and to drinking-water wells is complex and requires hydrological modeling supported by extensive field data that are difficult to obtain. Generally, however, despite a large network of private and public water wells, groundwater in the Piedmont region is being recharged when there is no drought, and net groundwater recharge from the surface through the vadose zone and into groundwater is downward, with mean recharge rates of ∼16 cm/yr across the region.28,44−48 In addition, surface-applied chemicals, such as

nitrate and pesticides, have been observed in well water throughout Piedmont aquifers,28 thus highlighting the interrelationship among groundwater recharge, water chemistry, and groundwater quality. Domestic wells may be screened over tens of meters to access water from bedrock fractures (Figure 3; Figure S5), and downward delivery of Mn, at least to the upper depths of well screens, could lead to high Mn concentrations in wells even if diluted with low-Mn water from regional horizontal groundwater flow to deeper screening depths or alternate recharge sources. Manganese Depletion and Fluxes from the NearSurface. At the Morgan Mill research site, repartitioning of Mn in the near-surface has resulted in a net loss of Mn. Over 40% of the initial total Mn has been depleted from the soil and saprolite during pedogenesis, based on the total solid-phase Mn profile in Figure 3d (which includes Mn in primary and secondary mineral phases), assuming an initial soil/saprolite parent-material Mn content equivalent to that in bedrock and bulk densities and material compaction as defined previously for the Piedmont.49 Given an annual vertical recharge rate of 16 cm/yr,44,48 a soil/saprolite thickness of 15 m,45 a porosity of 0.3 m3/m3,45 and the solid-phase density of quartz (∼2.7 g/cm3), only 1.1 × 10−3 mg Mn/kg soil or saprolite would need to be released per year to maintain Mn concentrations of 0.2 mg/L in groundwater (roughly the maximum concentration observed at our Morgan Mill site and equal to four times the EPA SMCL). Total, strong-acid-digestible, and Mn(III,IV)-oxide solid-phase Mn concentrations reached ∼4000 mg/kg in Piedmont saprolite (Figure 3; Figure S5; Figure S7), thereby providing a large natural reservoir for feeding Mn into groundwater, particularly following reductive dissolution of secondary Mn(III,IV) oxides. Although Mn losses from the regolith may have also occurred due to erosion and efflux to rivers,50 current depth profiles and hydrological and geochemical gradients suggest that Mn delivery to groundwater is an important process governing the ultimate fate of Mn depleted from the near-surface during pedogenesis. Soil weathering and redox partitioning couple to increase the availability and mobilization of Mn to groundwater. The spatial variability in well water Mn concentrations observed at the field-site and regional scales (Figure 1) may reflect variability in bedrock parent material, weathering rates, the form of secondary mineral phases, local hydrology, and/or Mn contributions from deep sources. Although solid-phase Mn concentrations are sufficientby up to 6 orders of magnitudeto provide elevated well water Mn concentrations across the Piedmont, the deep weathering profiles within the Felsic Crystalline series trap Mn in solid-phase Mn(III,IV) oxides to deeper depths within the chemically weathering regolith, as evidenced at the Langtree site (Figures S5−S7). In contrast, the intersection of the water table within the chemically weathering zones of the Carolina Slate Belt (Morgan Mill, NC Zoological Park, Lake Wheeler sites) (Figure 3; Figure S5) may promote enhanced downward delivery of dissolved Mn below the regolith. Importantly, the presence of near-surface sources of Mn to groundwater in the Piedmont does not preclude additional sources of Mn from deeper within profiles. The magmatic-arc and low-grade metamorphic rocks of the Carolina Slate Belt are likely contributors to Mn subsurface cycling,51 and some of the heterogeneity of Mn within underlying parent material across the NC Piedmont is likely due to the volcanic nature of the region and the diverse and complex geology.52 Additionally, F


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Environmental Science & Technology topographic-induced groundwater flow patterns may also impact Mn transport and accumulation within oxygenated discharge zones,24 complicating observed weathering and depletion profiles. Detailed site-based hydrogeochemical assessments are needed for improved predictions of the dominant controls on Mn distributions, the concentrations of Mn in well water, and the resulting risks for human exposure. Spatial Distributions and Exposure to Mn in Piedmont Well Water. The distribution of Mn in groundwater is spatially heterogeneous across the southeastern Piedmont (Figure 1; Figure S3). Based on our spatial analysis of well water use and Mn concentrations, we estimate that over 387 000 of the ∼1.5 million people who rely on private wells in the NC Piedmont are currently using well water with Mn concentrations that exceed 0.05 mg/L, the NC drinking-water standard and U.S. Environmental Protection Agency secondary maximum contaminant level (SMCL). Across the entire southeastern U.S. Piedmont, where ∼3.9 million people rely on private wells, roughly one-million people consume well water above the SMCL (Table 1). The SMCL is based on water

mineral phases, oxidative accumulation and reductive dissolution of secondary Mn(III,IV) oxides within saprolite, and hydrologically driven downward transport of dissolved Mn to bedrock aquifers. Although mineral dissolution at depth may also contribute Mn to groundwater, observed hydrological gradients and geochemical profiles of Mn in solid and aqueous phases suggest that near-surface processes act as important drivers on well water quality. This study represents the first attempt to systematically identify how soil weathering processes supply high Mn concentrations to groundwater. Although there has been considerable work quantifying how soil weathering drives solute fluxes and secondary mineral formation in the Critical Zone,26,53−56 most focus has been on major minerals and elements of high abundance. Few models exist for field-scale cycling of redox-active trace/minor elements like Mn due to challenges associated with determining host mineral phases and deconvolving the numerous overlapping processes that drive the elemental distributions. Our findings indicate that integrated studies that account for the processes spanning the dynamic soil-bedrock continuum are essential for predicting and managing elevated concentrations of Mn, and other contaminants, in well water. Finally, from a practical viewpoint, Mn concentrations in well water extracted from Piedmont aquifers could be minimized through deeper casing of bedrock wells and water planning based on physiographic features rather than political boundaries, the units over which many health assessments are currently based. Moreover, groundwater management plans that modify hydrologic and geochemical conditions, for instance by lowering water tables through overpumping, should be carefully evaluated because they have the potential to impact the extent and location/depth of Mn mobilization to groundwater.

Table 1. Estimated Number of People Using Well Water with Mn Concentrations Greater than Given Thresholds in the North Carolina and Southeastern Piedmont (VA, NC, SC, and GA) Mn (mg/L)

people impacted in NC Piedmont

people impacted throughout southeastern Piedmont (VA,NC,SC,GA)

≥0.05a ≥0.1b ≥0.2 ≥0.3c ≥0.4 ≥0.5

387 566 244 423 98 198 58 375 22 943 2878

1 008 445 536 911 188 788 106 071 45 404 9183

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a

NC drinking water standard and US Environmental Protection Agency Secondary Maximum Contaminant Level (SMCL). bDemonstrated threshold for health effects,14,15 cU.S. Environmental Protection Agency drinking-water human health benchmark.58

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.6b01686. Associated content in support of the main manuscript includes additional methods, nine figures, and two data tables (PDF)

aesthetics and is not a health-based standard, but adverse health effects have been observed in people routinely consuming well water with Mn concentrations as low as 0.1 mg/L,14,15 a level to which over 240 000 people in NC and over 535 000 people in the southeastern Piedmont are likely exposed (Table 1). Although Mn in well water has been correlated to a range of health issues in NC,13−16 the spatial heterogeneity of Mn in groundwater has made it difficult to predict specific locations where people are at risk for exposure. Concentrations above 0.05 mg/L are widespread and are observed in all major mapped geological formations and soil systems (Figure 1; Figure S3; Figure S4), but over 60% of wells with concentrations above 0.15 mg/L are clustered within two areas that run parallel to the orientation of the major geologic and soil systems within the state and that make up less than 30% of the Piedmont region. Overall, the greatest average Mn well water concentration (0.11 ± 0.21 mg/L) is found within the Carolina Slate Belt and the lowest average (0.03 ± 0.06 mg/L) is found within the Felsic Crystalline system (Figure S4). Environmental Implications. Across the southeastern Piedmont, Mn concentrations in groundwater are modulated by a complex sequence of natural processes, including chemical weathering of parent material that depletes Mn-bearing primary

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AUTHOR INFORMATION

Corresponding Author

*Phone: (919) 515-2040; fax: (919) 515-2167; e-mail: matt_ [email protected]. Present Address ∥

(N.A.R.) Department of Civil and Environmental Engineering, Duke University, Box 90287, 121 Hudson Hall, Durham, North Carolina 27708, United States. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the Water Resources Research Institute of the University of North Carolina, project 13-05-W. We thank the North Carolina regional hydrologists Joju Abraham and Shuying Wang from the Department of Environmental Quality Division of Water Resources as well as Wilson Mize from NC Department of Health and Human Services for reaching out to us to educate well contractors and health specialists on our research and Mn cycling in North G


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(16) Spangler, J.; Reid, J. Environmental Manganese and Cancer Mortality Rates by County in North Carolina: An Ecological Study. Biol. Trace Elem. Res. 2010, 133 (2), 128−135. (17) Massmann, G.; Nogeitzig, A.; Taute, T.; Pekdeger, A. Seasonal and spatial distribution of redox zones during lake bank filtration in Berlin, Germany. Environ. Geol. 2008, 54 (1), 53−65. (18) Bourg, A. C.; Bertin, C. Seasonal and spatial trends in manganese solubility in an alluvial aquifer. Environ. Sci. Technol. 1994, 28 (5), 868−876. (19) Bricker, O. Some Stability relations in the system Mn-O2-H2O at 25 degrees and 1 atm total pressure. Am. Mineral. 1965, 50, 1296. (20) Burdige, D. J.; Dhakar, S. P.; Nealson, K. H. Effects of manganese oxide mineralogy on microbial and chemical manganese reduction. Geomicrobiol. J. 1992, 10 (1), 27−48. (21) Gounot, A.-M. Microbial oxidation and reduction of manganese: consequences in groundwater and applications. FEMS Microbiol. Rev. 1994, 14, 339−350. (22) Martin, S. T., Precipitation and dissolution of iron and manganese oxides. In Environmental Catalysis; Grassian, V. H., Ed.; CRC Press, 2005; pp 61−81. (23) Morgan, J. J. Manganese in natural waters and earth’s crust: Its availability to organisms. Metal Ions in Biological Systems 2000, 37, 1− 34. (24) Kiracofe, Z. A.; Henika, W.; Schreiber, M. Assessing the geologic sources of manganese in the Roanoke River watershed, Virginia. Environmental & Engineering Geoscience 2016, 1078-7275.EEG-1740. (25) Fisher, R. S. a.; D, B., Groundwater Quality in Kentucky: Manganese. Geological Survey, ser. 12, Information Circular 14 2007. (26) Brantley, S. L.; Lebedeva, M. Learning to Read the Chemistry of Regolith to Understand the Critical Zone. Annu. Rev. Earth Planet. Sci. 2011, 39 (1), 387−416. (27) Daniels, R. B., Buol, S. W., Kleiss, H. J., Ditzler, C. A., Soil Systems in North Carolina. Technical Bulletin 314 1999. (28) Lindsey, B. D.; Falls, W. F.; Ferrari, M. J.; Zimmerman, T. M.; Harned, D. A.; Sadorf, E. M.; Chapman, M. J. Factors affecting occurrence and distribution of selected contaminants in ground water from selected areas in the Piedmont Aquifer System, Eastern United States, 1993−2003. U.S. Geological Survey Scientific Investigations Report 2006−5104 2006, 40. (29) NCDENR and USGS (North Carolina Department of Environmental and Natural Resources, United States Geological Service), Standard operating procedures for groundwater research stations. North Carolina Piedmont and Mountains Groundwater Resource Evaluation Program, 2008. (30) USEPA (U.S. Environmental Protection Agency), Method 3050B: Acid digestion of sediments, sludges, and soils, 2nd Ed., U.S. Environmental Agency, Washington, DC, 1996. (31) McDaniel, P. A.; Buol, S. W. Manganese Distributions in Acid Soils of the North Carolina Piedmont. Soil Science Society of America Journal 1991, 55 (1), 152−158. (32) Kelly, S.; Hesterberg, D.; Ravel, B. Analysis of soils and minerals using X-ray absorption spectroscopy. Methods of soil analysis. Part 5 2008, 387−463. (33) Newville, M. IFEFFIT: interactive XAFS analysis and FEFF fitting. J. Synchrotron Radiat. 2001, 8 (2), 322−324. (34) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12 (4), 537−541. (35) Manceau, A.; Marcus, M. A.; Grangeon, S. Determination of Mn valence states in mixed-valent manganates by XANES spectroscopy. Am. Mineral. 2012, 97 (5−6), 816−827. (36) Permitting, Inspection, and Testing of Private Drinking Water Wells; General Assembly of North Carolina, 2015; Vol. H.B. 2873. (37) Buol, S. W.; Weed, S. B. Weathering of soils Saprolite-soil transformations in the Piedmont and Mountains of North Carolina. Geoderma 1991, 51 (1), 15−28. (38) Peltier, E.; Dahl, A. L.; Gaillard, J.-F. Metal speciation in anoxic sediments: When sulfides can be construed as oxides. Environ. Sci. Technol. 2005, 39 (1), 311−316.

Carolina. We thank Peggy O’Day and Cara Santelli for providing Mn mineral standards, and we also thank Kim Hutchison, Audrey Matteson, Allison Sams, Christine Knight, and Corey Connell for field and laboratory support. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.

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REFERENCES

(1) Woolf, A.; Wright, R.; Amarasiriwardena, C.; Bellinger, D. A child with chronic manganese exposure from drinking water. Environ. Health Perspect. 2002, 110 (6), 613. (2) Bouchard, M. F.; Sauvé, S.; Barbeau, B.; Legrand, M.; Brodeur, M.-È.; Bouffard, T.; Limoges, E.; Bellinger, D. C.; Mergler, D. Intellectual impairment in school-age children exposed to manganese from drinking water. Environ. Health Perspect. 2010, 119 (1), 138−143. (3) Wasserman, G. A.; Liu, X.; Parvez, F.; Ahsan, H.; Levy, D.; Factor-Litvak, P.; Kline, J.; van Geen, A.; Slavkovich, V.; Lolacono, N. J. Water manganese exposure and children’s intellectual function in Araihazar, Bangladesh. Environ. Health Perspect. 2006, 144 (1), 124− 129. (4) He, P.; Liu, D.; Zhang, G. [Effects of high-level-manganese sewage irrigation on children’s neurobehavior]. Zhonghua yu fang yi xue za zhi [Chinese journal of preventive medicine] 1994, 28 (4), 216− 218. (5) Zhang, G.; Liu, D.; He, P. [Effects of manganese on learning abilities in school children]. Zhonghua yu fang yi xue za zhi [Chinese journal of preventive medicine] 1995, 29 (3), 156−158. (6) Homoncik, S. C.; MacDonald, A. M.; Heal, K. V.; Ó Dochartaigh, B. É .; Ngwenya, B. T. Manganese concentrations in Scottish groundwater. Sci. Total Environ. 2010, 408 (12), 2467−2473. (7) Groschen, G. E.; Arnold, T. L.; Morrow, W. S.; Warner, K. L. Occurrence and Distribution of Iron, Manganese, and Selected Trace Elements in Ground Water in the Glacial Aquifer System of the Northern United States. Urbana 2009, 51, 61801−2347. (8) Flanagan, S. M.; Belaval, M.; Avotte, J. D. Arsenic, irong, lead, manganese, and uranium concentrations in private bedrock wells in southeastern New Hampshire, 2012−2013. U.S. Geological Survey Fact Sheet 2014−3042 2014, 6. (9) Buschmann, J.; Berg, M.; Stengel, C.; Sampson, M. L. Arsenic and Manganese Contamination of Drinking Water Resources in Cambodia: Coincidence of Risk Areas with Low Relief Topography. Environ. Sci. Technol. 2007, 41 (7), 2146−2152. (10) Hug, S. J.; Gaertner, D.; Roberts, L. C.; Schirmer, M.; Ruettimann, T.; Rosenberg, T. M.; Badruzzaman, A. B. M.; Ashraf Ali, M. Avoiding high concentrations of arsenic, manganese and salinity in deep tubewells in Munshiganj District, Bangladesh. Appl. Geochem. 2011, 26 (7), 1077−1085. (11) State and County QuickFacts; United States Census Bureau, 2014 (12) Smith, S. M. National Geochemical Database-Reformatted Data from the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) Program. U.S. Geological Survey Open-File Report 97−492 Version 2006, 1, 41. (13) Spangler, A. H.; Spangler, J. G. Groundwater manganese and infant mortality rate by county in North Carolina: an ecological analysis. EcoHealth 2009, 6 (4), 596−600. (14) Sanders, A. P.; Desrosiers, T. A.; Warren, J. L.; Herring, A. H.; Enright, D.; Olshan, A. F.; Meyer, R. E.; Fry, R. C. Association between arsenic, cadmium, manganese, and lead levels in private wells and birth defects prevalence in North Carolina: a semi-ecologic study. BMC Public Health 2014, 14 (1), 1−12. (15) Langley, R. L.; Kao, Y.; Mort, r.; Bateman, A.; Simpson, B. D.; Reich, B. J. Adverse neurodevelopmental effects and hearing loss in children associated with manganese in well water, North Carolina, USA. J. Environ. Occup Sci. 2015, 4 (2), 62−69. H


Article

Environmental Science & Technology (39) Van Cappellen, P.; Wang, Y. Cycling of iron and manganese in surface sediments; a general theory for the coupled transport and reaction of carbon, oxygen, nitrogen, sulfur, iron, and manganese. Am. J. Sci. 1996, 296 (3), 197−243. (40) Nealson, K. H.; Saffarini, D. Iron and manganese in anaerobic respiration: environmental significance, physiology, and regulation. Annu. Rev. Microbiol. 1994, 48 (1), 311−343. (41) Massmann, G.; Sültenfuß, J. Identification of processes affecting excess air formation during natural bank filtration and managed aquifer recharge. J. Hydrol. 2008, 359 (3), 235−246. (42) Farnsworth, C. E.; Voegelin, A.; Hering, J. G. Manganese oxidation induced by water table fluctuations in a sand column. Environ. Sci. Technol. 2011, 46 (1), 277−284. (43) Tebo, B. M.; Johnson, H. A.; McCarthy, J. K.; Templeton, A. S. Geomicrobiology of manganese (II) oxidation. Trends Microbiol. 2005, 13 (9), 421−428. (44) Heath, R. C. Groundwater recharge in North Carolina, U.S. Geological Survey Water Resources Investigations Report 97−4140, 1994; Prepared for the Groundwater Section, 575 Environment, Health, and Natural Resources March 1994. (45) Heath, R. C. Basic elements of ground-water hydrology with reference to conditions in North Carolina. U.S. Geological Survey Water-Resources Investigations Open-File Report 1980, 80−44, 86. (46) Daniel, III, C. Ground-Water Recharge to the Regolith-Fractured Crystalline Rock Aquifer System; Orange County, 1996. (47) Daniel, C. C.; Smith, D. G.; Eimers, J. L. Hydrogeology and simulation of ground-water flow in the thick regolith-fractured crystalline rock aquifer system of Indian Creek Basin, North Carolina. US Geological Survey Water-Supply Paper 1997, 2341C, C1−C137. (48) Daniel, C. C.; Harned, D. Ground-Water Recharge to and Storage in the Regolith-Fractured Crystalline Rock Aquifer System, Guilford County; US Department of the Interior, US Geological Survey, 1998. (49) Pavich, M. J. Processes and rates of saprolite production and erosion on a foliated granitic rock of the Virginia Piedmont. Rates of Chemical Weathering of Rocks and Minerals 1986, 2, 551−590. (50) Herndon, E. M.; Brantley, S. L. Movement of manganese contamination through the Critical Zone. Appl. Geochem. 2011, 26 (Supplement), S40−S43. (51) Harden, S. L.; Chapman, M. J.; Harned, D. A. Characterization of Groundwater Quality Based on Regional Geologic Setting in the Piedmont and Blue Ridge Physiographic Provinces, North Carolina 2009, 2009− 5149. (52) North Carolina Geological Survey, Geological Map of North Carolina: Raleigh, North Carolina. In North Carolina Department of Natural Resources and Community Development, G. S., Ed. 1985. (53) Buss, H.; Bruns, M.; Schultz, M.; Moore, J.; Mathur, C.; Brantley, S. The coupling of biological iron cycling and mineral weathering during saprolite formation, Luquillo Mountains, Puerto Rico. Geobiology 2005, 3 (4), 247−260. (54) Maher, K.; Steefel, C. I.; White, A. F.; Stonestrom, D. A. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California. Geochim. Cosmochim. Acta 2009, 73 (10), 2804−2831. (55) White, A. F. Determining mineral weathering rates based on solid and solute weathering gradients and velocities: application to biotite weathering in saprolites. Chem. Geol. 2002, 190 (1), 69−89. (56) White, A. F.; Bullen, T. D.; Schulz, M. S.; Blum, A. E.; Huntington, T. G.; Peters, N. E. Differential rates of feldspar weathering in granitic regoliths. Geochim. Cosmochim. Acta 2001, 65 (6), 847−869. (57) SSURGO Database for North Carolina. http://websoilsurvey.sc. egov.usda.gov/App/HomePage.htm. (58) USEPA (U.S. Environmental Protection Agency), Drinking water health advisory for manganese; 2004.

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Soil Weathering as an Engine for Manganese Contamination of Well

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