Abstract
Excellent agreement was noted in the concentration of major and trace elements in five NIST soil reference materials (NIST SRM 2586, 2587, 2709a, 2710a and 2711a) between measurement results from wavelength dispersive-XRF and ICP-MS from two independent laboratories, and NIST certificate of analysis and literature data. We describe the variability in concentrations of up to forty-nine elements (plus loss on ignition) and provide values for up to twenty-one elements previously uncharacterised by NIST in these soil RMs. The additional characterisation provided in this investigation can be utilised to reduce the measurement bias of custom calibration routines and improve the quality of control checks developed using these NIST RMs.
Keywords: National Institute for Science and Technology, inductively coupled plasma-mass spectrometry, wavelength dispersive X-ray fluorescence, WD-XRF, calibration materials, soil, urban agriculture
Numerous geoscience/urban geochemistry investigations have utilised commercially available NIST SRM soil certified reference materials for calibration or quality control purposes (e.g., Kenna et al. 2011, Murry et al. 2011, Sutton et al. 2012, Weindorf et al. 2012, Fernández et al. 2014, McComb et al. 2014). NIST defines and provides certified, reference and information values for element concentrations presented in certificates of analysis. NIST certified values represent concentrations measured with the smallest measurement uncertainty and where sources of bias have been accounted for (May et al. 2000). Concentrations provided by NIST with larger measurement uncertainty are defined as reference values, whereas reported concentrations where uncertainty has not been evaluated are referred to as information values (May et al. 2000). Reference values or information values for the soil materials NIST SRM 2709, 2710 and 2711, either reported directly or as part of quality control exercises, have been provided previously by numerous investigators using XRF and/or ICP-MS (e.g., Wilson et al. 1994, Cloquet et al. 2005, Makinen et al. 2005, Murry et al. 2011, Weindorf et al. 2012, Gueguen et al. 2013). However, these three soil RMs are no longer commercially available and have been replaced by NIST SRM 2709a, 2710a and 2711a. Along with NIST SRM 2586 and 2587, these five reference materials present a continuum of heavy metal concentrations and are considered representative of soils likely to be encountered in urban agriculture/urban geochemistry studies. However, characterisation of these five soil RMs remains incomplete because very few reference values are available in the literature (Moon et al. 2009, Paul et al. 2009, Hoang et al. 2010, Goix et al. 2011, Milliard et al. 2011, Alvarez-Toral et al. 2013, Claverie et al. 2013, Eriksson et al. 2013, Fernández et al. 2014). The purpose of this study is to further characterise the variability in element concentrations (strictly, the mass-fractions) in the five NIST SRM soil materials and provide reference values for previously uncharacterised elements. This will contribute to reducing the measurement bias of custom calibration routines and improving the quality of control checks developed using these NIST reference materials.
Materials
The commutability of reference materials to anticipated samples is critical in decreasing measurement uncertainty. This study was focussed on soils with heavy metal (primarily Pb) concentrations similar in magnitude to previous urban geochemistry and urban agriculture studies (Finster et al. 2004, Clark et al. 2006, 2008, Huang et al. 2012, Defoe et al. 2014, Hu et al. 2014, McBride et al. 2014, Sharma et al. 2015). Therefore, five commercially available NIST soil reference materials encompassing a continuum in heavy metal concentrations, organic carbon and mineralogy likely to be found in urban soils were selected for characterisation. These originated from (1) a fallow agricultural field in the San Joaquin Valley of California (NIST SRM 2709a); (2) the floodway of Silver Bow Creek in Montana near a Brownfield property (NIST SRM 2710a); (3) an agricultural field located near a former smelting plant in Helena, MT (NIST SRM 2011a); (4) an urban agricultural garden contaminated with lead-based paint (NIST SRM 2587); and (5) urban soils contaminated with lead based paint (NIST SRM 2586).
Experimental procedure
Upon receipt of the NIST materials, each jar was shaken gently by hand for 30 s and aliquots of ca. 5 g were transferred from each jar to separate glass vials, which were then sealed with polyethylene caps. An aliquot of each NIST SRM soil sample was anonymised and submitted under chain of custody to the Wisconsin State Laboratory of Hygiene, Madison, Wisconsin (WSLH; a Wisconsin Department of Natural Resources certified laboratory) for ICP-MS analysis. Concurrently, two aliquots were used to prepare pressed pellets and fused beads for analysis by WD-XRF at the University of Wisconsin-Milwaukee Department of Geosciences XRF laboratory using two separate custom WD-XRF calibration routines. A fourth aliquot was used to determine the mass lost on ignition (LOI).
ICP-MS
NIST SRM soil samples were digested at the WSLH using a standard microwave digestion programme that involved adding 8.0 ml of 16 mol l−1 HNO3 plus 2.0 ml of 12 mol l−1 HCl plus 2.5 ml of HF to 30-mg test portions of each RM. Digestions were measured in triplicate using a Thermo-Finnigan Element 2 magnetic-sector ICP-MS.
WD-XRF (fused bead preparation)
Fused beads of each NIST soil RM were prepared using the protocol described in McHenry (2009) in which 1.000 g of soil was added to 1 g of oxidiser (ammonium nitrate) and 10.000 g of Claisse (Québec, Canada) 50:50 lithium metaborate: lithium tetraborate flux containing 0.5% LiBr as a non-wetting agent. The material was fused at 1050 °C in a Claisse M4 programmable fusion system. Fused beads were measured three times with a Bruker AXS, Inc. Pioneer S4 WDXRF instrument using a custom measurement and calibration procedure based on eleven USGS sedimentary and igneous geological reference materials made in the same manner as samples prepared for this study, as described by McHenry (2009). The USGS geological reference materials used in this calibration routine are AGV-1, BCR-2, BHVO-2, BIR-1, DNC-1, DTS-2b, G-2, GSP-2, RGM-1, SGR-1 and STM-1. The custom routine was refined in the Pioneer S4 software by correcting for peak overlaps, and adjusted for the use of the bromide non-wetting agent. Absorption and enhancement due to matrix effects were corrected in the Pioneer S4 software using fundamental parameters, and calibration materials with concentrations less than the limit of detection were removed from the calibration routine.
The intensities of eighteen major and trace elements in the reference materials were measured under vacuum using Kα1 lines except for Ba and Ce, which were measured using their Lα1 X-ray lines and concentrations determined through the custom fused bead calibration. To measure Na, K, Ca and Fe, the routine was optimised to count fluoresced X-rays for 10 s or until the statistical precision on counting values (determined as 3s based on a Poisson's law) was less than 0.3%. For Al and Si, fluoresced X-rays were counted for fixed times of 10 s and 4 s, respectively. To measure the concentrations of Mg and P, the routine counted fluoresced X-rays for 30 s or until the statistical precision (3s) was less than 0.3% and 1%, respectively. The remaining elements were measured for 10 s or until the statistical precision (3s) was less than 5%. Depending on the element, the routine used a pentaerythrite (PET), lithium fluoride (LIF200) or multi-layer (OVO-55) analyser crystal, and either a flow or scintillation counter. Specific routine details for each element, including generator voltage, tube current, collimator, analyser crystal, detector and peak overlap corrections are provided in online supporting material Table S1.
WD-XRF (pressed pellet preparation)
Pressed pellets of each NIST SRM soil were prepared by adding 10.0 g of material with four GeoQuant (Krupp Polysius Polab ®) wax binder pills (1.25 g total) and combining in a tungsten carbide shatterbox for 30 s. Each prepared sample was placed in an Al sample cup and pressed at 25 t for 60 s in a 40 mm diameter pellet die hydraulic press as described in McHenry et al. (2011). Pressed pellets were measured three times using a Bruker AXS, Inc. Pioneer S4 WD-XRF for major and trace elements utilising a custom measurement and calibration routine developed utilising nine USGS sedimentary and igneous rock reference materials (AGV-2, BCR-2, BHVO-2, DNC-1, DTS-2b, GSP-2, QLO-1, SGR-1 and W-2A) made in the same manner as samples prepared for this study as described in McHenry et al. (2011). The custom calibration routine was refined in the Pioneer S4 software by correcting for peak overlaps, Rh Rayleigh and Compton peaks, and contamination of W and Co from the shatterbox. Data points with concentrations less than the limit of detection were removed from the calibration routine.
The intensities of twenty-two elements in the NIST SRM materials were measured under vacuum using Kα1 lines, except for Ba and Ce, which were measured using Lα1 X-ray wavelengths and concentrations determined through the custom pressed pellet calibration. The routine was optimised to count fluoresced X-rays for 10 s or until the statistical precision (3s) was less than 5%. Depending on the element, the routine used a PET, LIF200 or OVO-55 crystal and either a flow or scintillation counter. Specific routine details for each element, including generator voltage, tube current, collimator, crystal, detector and peak overlap corrections are provided in Table S2 (online supporting information).
Water content and loss on ignition
Test portions, weighing 4 g, of each NIST SRM soil material were dried for 2 hours in an oven at 105 °C to estimate the adsorbed water content of each soil. Each oven-dried NIST SRM soil sample was divided into three 1-g aliquots and, following McHenry (2009), each aliquot was combusted in a muffle furnace at 1050 °C for 15 min and the mean LOI calculated for each RM to estimate the mass of material lost during fused bead preparation.
Quality control of WD-XRF measurements
As noted by Thomsen et al. (2003), the limit of detection (LOD) is considered the smallest concentration of an element that produces a response that can be distinguished from the background. The limit of quantitation (LOQ) is considered the smallest concentration that can be measured with minimal bias and error. The LOD for each WD-XRF measurement was calculated by the Pioneer S4 software and the LOQ of each WD-XRF measurement was estimated by multiplying the LOD by 3.3 as suggested by Thomsen et al. (2003). WD-XRF measurements less than the LOD are omitted from Tables 6–10. WD-XRF measurements greater than the LOD but less than the LOQ are denoted on Tables 6–10 with a “J” data qualifier and are considered information values; likewise the 1s and RSD for these measurements are provided for information purposes only and measurements less than the LOQ are omitted from further evaluation in this data assessment study. In addition, the statistical precision on the intensity measurement for each WD-XRF measurement was calculated by the Pioneer S4 software based on Poisson's law, and if the statistical precision was greater than 12%, WD-XRF measurement results were omitted from Tables 1–10.
Table 6.
Element concentrations in NIST SRM 2586 determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | ± | |
| Li | – | – | – | – | – | – | 24.61 | 1.87 | 8 | 25 | – |
| B | – | – | – | – | – | – | 50.93 | 0.00 | 0 | – | – |
| P | 960.1 | 0.0 | 0 | 1352.9 | 0.0 | 0 | 870.53 | 67.15 | 8 | 1001 | 77 |
| Sc | – | – | – | – | – | – | 26.49 | 0.74 | 3 | 24 | – |
| Ti | 6273.1 | 34.6 | 1 | 6872.5 | 115.5 | 2 | 6492.62 | 335.33 | 5 | 6050 | 660 |
| V | 169.6 | 1.1 | 1 | 205.3 | 18.8 | 9 | 154.76 | 3.80 | 2 | 160 | – |
| Cr | – | – | – | 356.0 | 9.8 | 3 | 301.73 | 11.79 | 4 | 301 | 45 |
| Mn | 1000.0 | 0.0 | 0 | 1033.3 | 57.7 | 6 | 971.20 | 6.33 | 1 | 1000 | 18 |
| Co | 28 J | 3.0 | 11 | – | – | – | 33.63 | 0.71 | 2 | 35 | – |
| Ni | 75.4 | 4.0 | 5 | 80.7 | 1.2 | 1 | 84.39 | 2.27 | 3 | 75 | – |
| Cu | – | – | – | 92.0 | 7.8 | 8 | 82.77 | 2.98 | 4 | 81 | – |
| Zn | 346.3 | 5.8 | 2 | 363.7 | 5.9 | 2 | 302.51 | 46.16 | 15 | 352 | 16 |
| Ga | – | – | – | 20.7 | 0.6 | 3 | – | – | – | 14 | – |
| As | – | – | – | – | – | – | 8.60 | 0.61 | 7 | 8.7 | 1.5 |
| Rb | – | – | – | 61.0 | 1.7 | 3 | 49.01 | 3.76 | 8 | – | – |
| Sr | 98.5 | 2.9 | 3 | 92.0 | 1.7 | 2 | – | – | – | 84.1 | 8 |
| Y | – | – | – | 27.0 | 1.0 | 4 | 23.46 | 1.11 | 5 | 21 | – |
| Zr | 277.9 | 4.6 | 2 | 287.7 | 1.5 | 1 | – | – | – | – | – |
| Nb | – | – | – | – | – | – | 12.74 | 0.33 | 3 | 6 | – |
| Mo | – | – | – | – | – | – | 1.11 | 0.25 | 23 | – | – |
| Ag | – | – | – | – | – | – | 0.55 | 0.09 | 17 | – | – |
| Cd | – | – | – | – | – | – | 2.48 | 0.23 | 9 | 2.71 | 0.54 |
| Sn | – | – | – | – | – | – | 13.29 | 0.05 | 0 | – | – |
| Sb | – | – | – | – | – | – | 3.07 | 0.11 | 3 | – | – |
| Cs | – | – | – | – | – | – | 1.93 | 0.16 | 9 | – | – |
| Ba | 374.4 | 34.8 | 9 | 491.3 | 16.5 | 3 | 411.72 | 15.61 | 4 | 413 | 18 |
| La | – | – | – | – | – | – | 23.52 | 0.40 | 2 | 29.7 | 4.8 |
| Ce | – | – | – | 66.3 | 29.2 | 44 | 51.17 | 2.08 | 4 | 58 | 8 |
| Pr | – | – | – | – | – | – | 6.17 | 0.18 | 3 | 7.3 | – |
| Nd | – | – | – | – | – | – | 24.00 | 0.84 | 4 | 26.4 | 2.9 |
| Sm | – | – | – | – | – | – | 5.01 | 0.27 | 5 | 6.1 | – |
| Eu | – | – | – | – | – | – | 1.23 | 0.03 | 3 | 1.5 | – |
| Dy | – | – | – | – | – | – | 4.36 | 0.21 | 5 | 5.4 | – |
| Ho | – | – | – | – | – | – | 0.88 | 0.02 | 3 | 1.1 | – |
| Yb | – | – | – | – | – | – | 2.44 | 0.09 | 4 | 2.64 | 0.51 |
| Lu | – | – | – | – | – | – | 0.35 | 0.01 | 3 | – | – |
| Ta | – | – | – | – | – | – | 0.85 | 0.00 | 0 | – | – |
| W | – | – | – | – | – | – | 1.24 | 0.28 | 22 | – | – |
| Tl | – | – | – | – | – | – | 0.35 | 0.01 | 2 | – | – |
| Pb | – | – | – | – | – | – | 419.48 | 14.41 | 3 | 432 | 17 |
| Th | – | – | – | – | – | – | 5.80 | 0.05 | 1 | 7 | – |
| U | – | – | – | – | – | – | 1.90 | 0.02 | 1 | – | – |
Element concentrations qualified with a “J” are greater than the limit of detection, but less than the limit of quantitation. Shaded rows represent elements not characterised by NIST.
Table 10.
Element concentrations in NIST SRM 2711a determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | ± | |
| Li | – | – | – | – | – | – | 29.05 | 1.47 | 5 | – | – |
| B | – | – | – | – | – | – | 55.22 | 9.41 | 17 | 50 | – |
| P | 872.8 | 0.0 | 0 | 1352.9 | 0.0 | 0 | 796.05 | 112.82 | 14 | 842 | 11 |
| Sc | – | – | – | – | – | – | 10.60 | 1.47 | 14 | 8.5 | 0.1 |
| Ti | 3196.5 | 34.6 | 1 | 3476.2 | 0.0 | 0 | 3287.54 | 195.65 | 6 | 3170 | 80 |
| V | 85.0 | 3.5 | 4 | 109.0 | 1.7 | 2 | 66.85 | 15.67 | 23 | 80.7 | 5.7 |
| Cr | – | – | – | 84.0 | 5.6 | 7 | 48.24 | 1.68 | 3 | 52.3 | 2.9 |
| Mn | 666.7 | 57.7 | 9 | 719.0 | 10.8 | 2 | 670.44 | 39.41 | 6 | 675 | 18 |
| Co | – | – | – | – | – | – | 10.27 | 1.38 | 13 | 9.89 | 0.18 |
| Ni | 18 J | 5.7 | 31 | 27 J | 1.5 | 6 | 19.50 | 1.60 | 8 | 21.7 | 0.7 |
| Cu | – | – | – | 151.7 | 4.0 | 3 | 144.31 | 20.14 | 14 | 140 | 2 |
| Zn | 401.7 | 5.8 | 1 | 418.3 | 7.6 | 2 | 372.74 | 96.70 | 26 | 414 | 11 |
| Ga | – | – | – | 24.7 | 0.6 | 2 | – | – | – | – | – |
| As | – | – | – | – | – | – | 90.96 | 8.63 | 9 | 107 | 5 |
| Rb | – | – | – | 136.0 | 3.0 | 2 | 121.29 | 12.95 | 11 | 120 | 3 |
| Sr | 232.4 | 2.0 | 1 | 256.0 | 1.7 | 1 | – | – | – | 242 | 10 |
| Y | 29.9 | 0.9 | 3 | 33.0 | 0.0 | 0 | – | – | – | – | – |
| Zr | 318.1 | 2.5 | 1 | 310.3 | 0.6 | 0 | – | – | – | – | – |
| Nb | – | – | – | – | – | – | 20.07 | 1.79 | 9 | – | – |
| Mo | – | – | – | – | – | – | 1.74 | 0.15 | 8 | – | – |
| Ag | – | – | – | – | – | – | 6.17 | 0.94 | 15 | 6 | – |
| Cd | – | – | – | – | – | – | 50.64 | 10.39 | 21 | 54.1 | 0.5 |
| Sn | – | – | – | – | – | – | 4.72 | 0.27 | 6 | – | – |
| Sb | – | – | – | – | – | – | 23.04 | 3.52 | 15 | 23.8 | 1.4 |
| Cs | – | – | – | – | – | – | 6.67 | 0.68 | 10 | 6.7 | 0.2 |
| Ba | 697.7 | 24.6 | 4 | 850.0 | 21.5 | 3 | 760.16 | 77.74 | 10 | 730 | 15 |
| La | – | – | – | – | – | – | 30.53 | 3.17 | 10 | 38 | 1 |
| Ce | – | – | – | 146.33 | 5.13 | 4 | 63.33 | 5.79 | 9 | 70 | – |
| Pr | – | – | – | – | – | – | 7.30 | 0.65 | 9 | – | – |
| Nd | – | – | – | – | – | – | 27.99 | 2.39 | 9 | 29 | 2 |
| Sm | – | – | – | – | – | – | 5.51 | 0.31 | 6 | 5.93 | 0.28 |
| Eu | – | – | – | – | – | – | 1.17 | 0.16 | 14 | 1.1 | 0.2 |
| Dy | – | – | – | – | – | – | 4.74 | 0.39 | 8 | 5 | – |
| Ho | – | – | – | – | – | – | 0.96 | 0.06 | 7 | – | – |
| Yb | – | – | – | – | – | – | 2.95 | 0.27 | 9 | 3 | – |
| Lu | – | – | – | – | – | – | 0.43 | 0.03 | 7 | 0.5 | – |
| Ta | – | – | – | – | – | – | 1.48 | 0.19 | 13 | 1 | – |
| W | – | – | – | – | – | – | 3.07 | 0.04 | 1 | – | – |
| Tl | – | – | – | – | – | – | 2.85 | 0.45 | 16 | 3 | – |
| Pb | – | – | – | – | – | – | 1402.88 | 225.33 | 16 | 1400 | 10 |
| Th | – | – | – | – | – | – | 10.72 | 1.35 | 13 | 15 | 1 |
| U | – | – | – | – | – | – | 2.77 | 0.35 | 13 | 3.01 | 0.12 |
Element concentrations qualified with a “J” are greater than the limit of detection, but less than the limit of quantitation. Shaded rows represent elements not characterised by NIST.
Table 1.
Element concentrations in NIST SRM 2586 determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | ± | |
| Na | 0.50 | 113 | 2 | – | – | – | 0.52 | 63 | 1 | 0.468 | 730 |
| Mg | 1.69 | 0 | 0 | 2.48 | 265 | 1 | 1.67 | 51 | 0.3 | 1.707 | 840 |
| Al | 6.70 | 106 | 0.2 | 7.00 | 2570 | 2 | 6.83 | 2673 | 4 | 6.652 | 760 |
| Si | 28.94 | 546 | 0.2 | 28.72 | 6050 | 1 | – | – | – | 29.150 | 2100 |
| K | 0.99 | 48 | 0.4 | 1.01 | 115 | 1 | 1.03 | 1323 | 13 | 0.976 | 180 |
| Ca | 2.16 | 0 | 0 | 2.79 | 58 | 0.1 | 2.38 | 2695 | 11 | 2.218 | 540 |
| Fe | 5.16 | 162 | 0.3 | 5.96 | 58 | 0.1 | 5.20 | 918 | 2 | 5.161 | 890 |
Due to contamination during sample preparation in the shatterbox, W and Co values cannot be reported for pressed pellet WD-XRF measurements. The flux used to make the fused beads contained 1% LiBr as a non-wetting agent, and due to a large peak overlap between Br and Rb, we are not able to report concentrations of Rb in fused bead WD-XRF pellets.
During the manufacturing process, NIST sieved each soil material through a 200-mesh screen; therefore the maximum particle size should be no more than 75 μm. As WD-XRF X-ray penetration depths for the Mg, Al, Si, P, K, Ca and Ti Kα1 lines are less than 75 μm, it is possible that the concentrations of these elements measured in this study using WD-XRF of pressed pellets are biased to elements concentrated in particles on the surface of the pellet and thus may not be representative of the bulk. Values for these measurands are reported in Tables 1–10 for information purposes only. The penetration depth for Na is only 4.1 μm; therefore these results for WD-XRF measurements of pressed pellets are not reported.
Data reduction
Based on the triplicate measurements of each analyte by ICP-MS and WD-XRF, the mean concentration of each element, associated standard deviation (s), and the relative standard deviation (RSD; expressed as per cent) were calculated for each NIST SRM soil for each measurement technique. Major element concentrations are presented in Tables 1–5 and trace element concentrations are presented in Tables 6–10 along with corresponding NIST certified, information, and reference values and associated uncertainties reported by NIST.
Table 5.
Element concentrations in NIST SRM 2711a determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | ± | |
| Na | 1.24 | 113 | 1 | – | – | – | 1.30 | 1169 | 9 | 1.20 | 100 |
| Mg | 1.02 | 0 | 0 | 1.66 | 173 | 1 | 1.00 | 340 | 3 | 1.07 | 600 |
| Al | 6.73 | 397 | 1 | 6.75 | 2512 | 2 | 6.98 | 4559 | 7 | 6.72 | 600 |
| Si | 30.55 | 742 | 0.2 | 28.78 | 7410 | 1 | – | – | – | 31.40 | 7000 |
| K | 2.53 | 0 | 0 | 2.58 | 115 | 0.4 | 2.15 | 7479 | 35 | 2.53 | 1000 |
| Ca | 2.37 | 0 | 0 | 2.76 | 58 | 0.1 | 2.59 | 2725 | 11 | 2.42 | 600 |
| Fe | 2.89 | 40 | 0.1 | 3.20 | 321 | 1 | 2.72 | 578 | 2 | 2.82 | 400 |
To compare concentrations measured in this study to concentrations reported by NIST and to other values reported in the literature, the relative difference (RD; expressed as a per cent) was calculated following USEPA (2007, 2014) as:
| (1) |
where C1 and C2 are element concentrations in sample 1 and sample 2, respectively. Relative difference is a dimensionless statistical measurement commonly used to evaluate the precision of two measurements of inorganic elements (USEPA 2007, 2014). A RD of 0 indicates that the two measurements are equal, while a larger or smaller RD indicates an increasing difference between the two measurements. A positive RD indicates that C1 > C2; conversely, a negative RD indicates C1 < C2.
For the purpose of this investigation, we assumed that the NIST values are the correct values; therefore, we used RD as a measurement of bias. As recommended in USEPA (2014), we define a RD of ± 20% as the control limit. We acknowledge that many trace elements are difficult to measure; therefore, for our evaluation, we define a RD of ± 40% as the threshold limit. Element concentrations with RD values outside the threshold limit are provided for information purposes only.
The RD for each element for each NIST SRM soil comparing the NIST concentrations (C1) with the WSLH ICP-MS concentrations (C2) is illustrated in Figure 1. The RD for each element for each RM comparing the NIST concentrations (C1) with the fused bead WD-XRF concentrations (C2) is illustrated in Figure 2. The RDs comparing concentrations measured in this study by WSLH using ICP-MS (C2) to concentrations reported in the literature (C1) by Moon et al. (2009) and Paul et al. (2009), Hoang et al. (2010), Goix et al. (2011), Milliard et al. (2011), Alvarez-Toral et al. (2013), Claverie et al. (2013), Eriksson et al. (2013), Fernandez et al. (2014) are shown in Figure 3.
Figure 1.
Relative difference between NIST data and ICP-MS measurements (from WSLH). Positive values indicate NIST values > WSLH measurements. Relative differences outside the presented intervals are provided as text on the figure.
Figure 2.
Relative difference between NIST data and fused bead WD-XRF measurements. Positive values indicate NIST values > fused bead WD-XRF measurements.
Figure 3.
Relative difference between ICP-MS (WSLH) and literature values. Positive values indicate WSLH measurements > literature values.
Results and discussion
Comparison of our measurements to NIST and literature values
Excellent agreement was noted in the major and trace elements between measurements made in this investigation and the NIST certified, reference and information values (Figures 1 and 2). Measurement results from ICP-MS (at WSLH) seem to be uniformly lower compared with NIST values for NIST SRM 2710a, but no other bias is apparent in the WSLH measurements. As illustrated in Figure 1, 85% of WSLH measurements were within the control limit of ± 20% RD compared with NIST values and 99% of measurements were within the threshold limit of ± 40% RD compared with NIST values. In comparing the WD-XRF measurements of fused beads from our laboratory to NIST values, 97% of WD-XRF measurements were within the control limit of ± 20% RD and 100% of measurements were within the threshold limit of ± 40% RD. Elements with RD values outside the threshold limit are present in trace concentrations and are challenging to measure with reasonable precision. Therefore, we have great confidence in the values for the major and minor elements reported in this study.
Element concentrations measured in this study by ICP-MS by WSLH are in close agreement with concentrations reported in the literature (Figure 3). In comparing the WSLH ICP-MS measurements with literature values, 88% of WSLH measurements were within the control limit of ± 20% RD and 99% of measurements were within the threshold limit (± 40% RD). Therefore, we have great confidence in the values for the major and minor elements reported in this study.
For reference, the water contents in NIST SRM 2586, 2587, 2709a, 2710a and 2711a measured in this study were 1.6%, 1.1%, 2.7%, 1.8% and 2.1% m/m, respectively, and the mean LOI concentrations were 8.6%, 6.4%, 6.6%, 7.5% and 6.4% m/m, respectively. The respective standard deviations of the LOI measurements of NIST SRMs 2586, 2587, 2709a, 2710a and 2711a were 0.2%, 0.1%, 0.2%, 0.02% and 0.03% m/m.
Our future goal is to advance the use of portable ED-XRF in measuring concentrations of heavy metals in urban soil in situ. As demonstrated in recent work completed by Perroy et al. (2014) and Weindorf et al. (2012), portable ED-XRF is a promising tool for use in urban agriculture/geochemistry investigations. With the increased information provided in this investigation, the bias in custom calibration routines for portable ED-XRF spectrometers developed with the characterised NIST SRMs will be reduced.
Conclusions
Eighty-five per cent of ICP-MS measurements (made at the Wisconsin State Laboratory of Hygiene, Madison, Wisconsin) and 97% of WD-XRF measurements (made at the Department of Geosciences, University of Wisconsin-Milwaukee) generated in this data assessment exercise when compared with NIST certified, reference and information values fell within a control limit of ± 20% relative difference. This provides confidence in the values for the major and minor elements reported in this study. We have described the variability in concentrations of up to forty-nine elements (plus LOI) and have provided values for up to twenty-one elements previously uncharacterised by NIST in soil reference materials NIST SRM 2709a, 2710a, 2711a, 2586 and 2587. The additional characterisation provided in this investigation will contribute to reducing measurement uncertainty in custom calibration routines and improving the quality of control checks developed utilising these NIST SRMs.
Supplementary Material
Table 2.
Element concentrations in NIST SRM 2587 determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | ± | |
| Na | 1.16 | 0 | 0 | – | – | – | 1.20 | 69 | 1 | 1.13 | 330 |
| Mg | 0.69 | 0 | 0 | 1.33 | 100 | 0.4 | 0.67 | 374 | 6 | 0.67 | 250 |
| Al | 6.07 | 140 | 0.2 | 6.33 | 208 | 0.2 | 6.07 | 3184 | 5 | 5.86 | 1700 |
| Si | 33.06 | 221 | 0.1 | 32.86 | 1966 | 0.3 | – | – | – | 33.13 | 2600 |
| K | 1.62 | 0 | 0 | 1.68 | 58 | 0.3 | 1.60 | 1801 | 11 | 1.58 | 550 |
| Ca | 0.91 | 41 | 0.4 | 1.32 | 0 | 0 | 0.89 | 728 | 8 | 0.93 | 200 |
| Fe | 2.84 | 107 | 0.4 | 3.11 | 100 | 0.2 | 2.79 | 1096 | 4 | 2.81 | 250 |
Table 3.
Element concentrations in NIST SRM 2709a determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | ± | |
| Na | 1.26 | 74 | 1 | – | – | – | 1.29 | 1150 | 9 | 1.22 | 300 |
| Mg | 1.45 | 60 | 0.4 | 2.52 | 208 | 0.4 | 1.41 | 1008 | 7 | 1.46 | 200 |
| Al | 7.44 | 360 | 0.4 | 7.76 | 3177 | 2 | 7.45 | 6528 | 9 | 7.37 | 1600 |
| Si | 29.93 | 1374 | 0.4 | 27.87 | 6372 | 1 | – | – | – | 30.30 | 4000 |
| K | 2.11 | 48 | 0.2 | 2.00 | 100 | 0.4 | 2.08 | 1611 | 8 | 2.11 | 600 |
| Ca | 1.89 | 0 | 0 | 2.52 | 153 | 0.4 | 1.94 | 1233 | 6 | 1.91 | 900 |
| Fe | 3.38 | 214 | 1 | 4.09 | 586 | 1 | 3.34 | 1026 | 3 | 3.36 | 700 |
Table 4.
Element concentrations in NIST SRM 2710a determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | 1s (μg g−1) | RSD | g/100 g | ± | |
| Na | 0.99 | 43 | 0.4 | – | – | – | 0.85 | 872 | 10 | 0.89 | 190 |
| Mg | 0.75 | 35 | 0.4 | 0.87 | 0 | 0 | 0.62 | 500 | 8 | 0.73 | 380 |
| Al | 6.00 | 372 | 1 | 6.31 | 2747 | 2 | 5.43 | 4330 | 8 | 5.95 | 500 |
| Si | 30.31 | 1362 | 0.4 | 28.84 | 6523 | 1 | – | – | – | 31.10 | 4000 |
| K | 2.15 | 0 | 0 | 2.20 | 58 | 0.2 | 1.95 | 883 | 5 | 2.17 | 1300 |
| Ca | 0.93 | 41 | 0.4 | 1.48 | 58 | 0.3 | 0.84 | 734 | 9 | 0.96 | 450 |
| Fe | 4.29 | 331 | 1 | 4.72 | 473 | 1 | 3.83 | 3102 | 8 | 4.32 | 800 |
Table 7.
Element concentrations in NIST SRM 2587 determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | ± | |
| Li | – | – | – | – | – | – | 34.19 | 2.83 | 8 | 32 | – |
| B | – | – | – | – | – | – | 66.84 | 3.32 | 5 | – | – |
| P | 931.0 | 25.2 | 3 | 1352.9 | 0.0 | 0 | 851.06 | 70.98 | 8 | 970 | 100 |
| Sc | – | – | – | – | – | – | 11.76 | 1.07 | 9 | 11 | – |
| Ti | 4235.4 | 34.6 | 1 | 4495.1 | 0.0 | 0 | 4153.97 | 185.30 | 4 | 3920 | 650 |
| V | 96.1 | 6.9 | 7 | 109.0 | 1.7 | 2 | 80.64 | 2.70 | 3 | 78 | – |
| Cr | – | – | – | 99.7 | 4.2 | 4 | 92.67 | 5.02 | 5 | 92 | 11 |
| Mn | 666.7 | 57.7 | 9 | 669.7 | 6.7 | 1 | 655.46 | 28.47 | 4 | 651 | 23 |
| Co | – | – | – | – | – | – | 11.78 | 0.32 | 3 | 14 | – |
| Ni | 43 J | 2.4 | 6 | 37.0 | 2.6 | 7 | 32.28 | 1.95 | 6 | 36 | – |
| Cu | – | – | – | 170.7 | 2.5 | 1 | 160.68 | 3.52 | 2 | 160 | – |
| Zn | 324.7 | 6.4 | 2 | 341.0 | 1.7 | 1 | 309.74 | 34.87 | 11 | 335.8 | 7.6 |
| Ga | – | – | – | 24.0 | 1.0 | 4 | – | – | – | 13 | – |
| As | – | – | – | – | – | – | 13.71 | 1.38 | 10 | 13.7 | 2.3 |
| Rb | – | – | – | 82.7 | 2.5 | 3 | 72.30 | 4.97 | 7 | – | – |
| Sr | 125.6 | 4.5 | 4 | 131.7 | 2.9 | 2 | – | – | – | 126 | 19 |
| Y | – | – | – | 28.0 | 0.0 | 0 | 18.51 | 1.16 | 6 | 15 | – |
| Zr | 296.0 | 4.4 | 1 | 269.0 | 0.0 | 0 | – | – | – | – | – |
| Nb | – | – | – | – | – | – | 11.17 | 0.32 | 3 | 14 | – |
| Mo | – | – | – | – | – | – | 1.64 | 0.20 | 12 | – | – |
| Cd | – | – | – | – | – | – | 1.91 | 0.14 | 7 | 1.92 | 0.23 |
| Sn | – | – | – | – | – | – | 17.10 | 5.73 | 33 | – | – |
| Sb | – | – | – | – | – | – | 2.10 | 0.34 | 16 | – | – |
| Cs | – | – | – | – | – | – | 3.10 | 0.30 | 10 | – | – |
| Ba | 544.3 | 12.7 | 2 | 650.3 | 1.2 | 0 | 566.81 | 25.03 | 4 | 568 | 12 |
| La | – | – | – | – | – | – | 20.77 | 1.42 | 7 | 29 | – |
| Ce | – | – | – | 82.7 | 4.0 | 5 | 44.89 | 2.81 | 6 | 57 | – |
| Pr | – | – | – | – | – | – | 5.09 | 0.27 | 5 | – | – |
| Nd | – | – | – | – | – | – | 19.77 | 1.18 | 6 | 25 | – |
| Sm | – | – | – | – | – | – | 3.95 | 0.19 | 5 | – | – |
| Eu | – | – | – | – | – | – | 1.03 | 0.06 | 6 | – | – |
| Dy | – | – | – | – | – | – | 3.38 | 0.26 | 8 | – | – |
| Ho | – | – | – | – | – | – | 0.68 | 0.04 | 6 | – | – |
| Yb | – | – | – | – | – | – | 2.01 | 0.10 | 5 | 1.6 | – |
| Lu | – | – | – | – | – | – | 0.29 | 0.02 | 7 | – | – |
| Tl | – | – | – | – | – | – | 0.48 | 0.03 | 7 | – | – |
| Pb | – | – | – | – | – | – | 3165.52 | 195.50 | 6 | 3242 | 57 |
| Th | – | – | – | – | – | – | 5.69 | 0.29 | 5 | 7.5 | – |
| U | – | – | – | – | – | – | 2.08 | 0.17 | 8 | – | – |
Element concentrations qualified with a “J” are greater than the limit of detection, but less than the limit of quantitation. Shaded rows represent elements not characterised by NIST.
Table 8.
Element concentrations in NIST SRM 2709a determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (μg g−1) | (1 s) | RSD | (μg g−1) | (1 s) | RSD | (μg g−1) | (1 s) | RSD | (μg g−1) | ± | |
| Li | – | – | – | – | – | – | 51.88 | 0.74 | 1 | – | – |
| B | – | – | – | – | – | – | 73.42 | 2.14 | 3 | 74 | – |
| P | 712.8 | 25.2 | 4 | 1352.9 | 0.0 | 0 | 694.49 | 45.98 | 7 | 688 | 13 |
| Sc | – | – | – | – | – | – | 12.18 | 0.85 | 7 | 11.1 | 0.1 |
| Ti | 3336.3 | 34.6 | 1 | 3895.7 | 0.0 | 0 | 3344.09 | 102.09 | 3 | 3360 | 70 |
| V | 124.7 | 12.3 | 10 | 154.3 | 4.5 | 3 | 105.96 | 4.05 | 4 | 110 | 11 |
| Cr | 114.7 | 9.9 | 9 | 151.0 | 1.7 | 1 | 119.58 | 3.21 | 3 | 130 | 9 |
| Mn | 500 J | 0.0 | 0 | 593.3 | 7.6 | 1 | 522.47 | 4.74 | 1 | 529 | 18 |
| Co | – | – | – | – | – | – | 12.79 | 0.28 | 2 | 12.8 | 0.2 |
| Ni | 87.4 | 7.9 | 9 | 87.3 | 2.1 | 2 | 82.71 | 6.55 | 8 | 85 | 2 |
| Cu | – | – | – | 54.7 | 2.5 | 5 | 34.34 | 2.42 | 7 | 33.9 | 0.5 |
| Zn | 107.2 | 4.2 | 4 | 108.0 | 1.7 | 2 | 86.74 | 7.83 | 9 | 103 | 4 |
| Ga | – | – | – | 22.7 | 0.6 | 3 | – | – | – | – | – |
| As | – | – | – | – | – | – | 11.92 | 3.04 | 25 | 10.5 | 0.3 |
| Rb | – | – | – | 111.3 | 0.6 | 1 | 96.16 | 2.31 | 2 | 99 | 3 |
| Sr | 240.5 | 2.3 | 1 | 270.3 | 2.5 | 1 | – | – | – | 239 | 6 |
| Y | – | – | – | 27.3 | 0.6 | 2 | 15.34 | 0.62 | 4 | – | – |
| Zr | 153.2 | 4.0 | 3 | 170.3 | 1.2 | 1 | – | – | – | 195 | 46 |
| Nb | – | – | – | – | – | – | 8.61 | 0.09 | 1 | – | – |
| Mo | – | – | – | – | – | – | 1.30 | 0.36 | 27 | – | – |
| Ag | – | – | – | – | – | – | 0.31 | 0.08 | 25 | – | – |
| Cd | – | – | – | – | – | – | 0.36 | 0.03 | 8 | 0.371 | 0.002 |
| Sn | – | – | – | – | – | – | 1.87 | 0.78 | 42 | – | – |
| Sb | – | – | – | – | – | – | 1.29 | 0.49 | 38 | 1.55 | 0.06 |
| Cs | – | – | – | – | – | – | 5.14 | 0.21 | 4 | 5 | 0.1 |
| Ba | 936.6 | 5.4 | 1 | 1100.0 | 0.0 | 0 | 972.86 | 16.19 | 2 | 979 | 28 |
| La | – | – | – | – | – | – | 19.89 | 1.10 | 6 | 21.7 | 0.4 |
| Ce | – | – | – | 194.0 | 4.4 | 2 | 40.89 | 1.75 | 4 | 42 | 1 |
| Pr | – | – | – | – | – | – | 4.68 | 0.13 | 3 | – | – |
| Nd | – | – | – | – | – | – | 17.88 | 0.35 | 2 | 17 | – |
| Sm | – | – | – | – | – | – | 3.50 | 0.13 | 4 | 4 | – |
| Eu | – | – | – | – | – | – | 1.02 | 0.06 | 6 | 0.83 | 0.02 |
| Dy | – | – | – | – | – | – | 2.77 | 0.10 | 4 | 3 | – |
| Ho | – | – | – | – | – | – | 0.57 | 0.01 | 2 | – | – |
| Yb | – | – | – | – | – | – | 1.67 | 0.04 | 2 | 2 | – |
| Lu | – | – | – | – | – | – | 0.24 | 0.01 | 5 | 0.3 | – |
| Tl | – | – | – | – | – | – | 0.52 | 0.05 | 10 | 0.58 | 0.01 |
| Pb | – | – | – | – | – | – | 17.26 | 0.77 | 4 | 17.3 | 0.1 |
| Th | – | – | – | – | – | – | 9.28 | 0.28 | 3 | 10.9 | 0.2 |
| U | – | – | – | – | – | – | 3.17 | 0.14 | 4 | 3.15 | 0.05 |
Element concentrations qualified with a “J” are greater than the limit of detection, but less than the limit of quantitation. Shaded rows represent elements not characterised by NIST.
Table 9.
Element concentrations in NIST SRM 2710a determined using three measurement methods
| WD-XRF (FB) | WD-XRF (PP) | ICP-MS | NIST | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | 1s | RSD | (μg g−1) | ± | |
| Li | – | – | – | – | – | – | 24.57 | 0.58 | 2 | – | – |
| B | – | – | – | – | – | – | 16.16 | 0.26 | 2 | 20 | – |
| P | 1047.4 | 0.0 | 0 | 1352.9 | 0.0 | 0 | 841.29 | 135.73 | 16 | 1050 | 40 |
| Sc | – | – | – | – | – | – | 10.03 | 0.80 | 8 | 9.9 | 0.1 |
| Ti | 3056.6 | 59.9 | 2 | 3416.3 | 0.0 | 0 | 2819.15 | 158.77 | 6 | 3110 | 70 |
| V | 97.4 | 14.8 | 15 | 112.3 | 2.5 | 2 | 72.69 | 3.84 | 5 | 82 | 9 |
| Cr | – | – | – | – | – | – | 19.98 | 1.00 | 5 | 23 | 6 |
| Mn | 2066.7 | 57.7 | 3 | 2200.0 | 0.0 | 0 | 1895.26 | 150.89 | 8 | 2140 | 60 |
| Co | – | – | – | – | – | – | 5.04 | 0.33 | 6 | 5.99 | 0.14 |
| Ni | – | – | – | 9 J | 1.5 | 18 | 6.66 | 1.57 | 24 | 8 | 1 |
| Cu | – | – | – | 3100.0 | 0.0 | 0 | 3062.89 | 412.13 | 13 | 3420 | 50 |
| Zn | 3923.2 | 33.3 | 1 | 4100.0 | 0.0 | 0 | 3567.00 | 631.33 | 18 | 4180 | 150 |
| Ga | – | – | – | 38.7 | 1.5 | 4 | – | – | – | – | – |
| As | – | – | – | – | – | – | 1157.05 | 29.31 | 3 | 1540 | 100 |
| Rb | – | – | – | 122.0 | 1.0 | 1 | 102.22 | 9.55 | 9 | 117 | 3 |
| Sr | 240.4 | 2.1 | 1 | 257.3 | 1.5 | 1 | – | – | – | 255 | 7 |
| Y | 27.6 | 1.2 | 4 | 29.0 | 0.0 | 0 | 13.27 | 1.10 | 8 | – | – |
| Zr | 232.9 | 4.9 | 2 | 233.7 | 2.1 | 1 | – | – | – | 200 | – |
| Nb | – | – | – | – | – | – | 11.32 | 0.79 | 7 | – | – |
| Mo | – | – | – | – | – | – | 7.61 | 0.61 | 8 | – | – |
| Ag | – | – | – | – | – | – | 36.11 | 3.21 | 9 | 40 | – |
| Cd | – | – | – | – | – | – | 10.55 | 1.76 | 17 | 12.3 | 0.3 |
| Sn | – | – | – | – | – | – | 8.89 | 1.03 | 12 | – | – |
| Sb | – | – | – | – | – | – | 46.12 | 5.44 | 12 | 52.5 | 1.6 |
| Cs | – | – | – | – | – | – | 7.61 | 0.88 | 12 | 8.25 | 0.11 |
| Ba | 767.3 | 25.4 | 3 | 941.0 | 11.8 | 1 | 724.21 | 54.64 | 8 | 792 | 36 |
| La | – | – | – | – | – | – | 23.92 | 2.77 | 12 | 30.6 | 1.2 |
| Ce | – | – | – | 148.0 | 9.5 | 6 | 47.86 | 4.63 | 10 | 60 | – |
| Pr | – | – | – | – | – | – | 5.22 | 0.45 | 9 | – | – |
| Nd | – | – | – | – | – | – | 19.22 | 1.72 | 9 | 22 | 2 |
| Sm | – | – | – | – | – | – | 3.46 | 0.27 | 8 | 4 | 0.2 |
| Eu | – | – | – | – | – | – | 0.80 | 0.11 | 14 | 0.82 | 0.01 |
| Dy | – | – | – | – | – | – | 2.34 | 0.22 | 9 | 3 | – |
| Ho | – | – | – | – | – | – | 0.48 | 0.04 | 9 | – | – |
| Yb | – | – | – | – | – | – | 1.54 | 0.17 | 11 | 2 | – |
| Lu | – | – | – | – | – | – | 0.23 | 0.02 | 11 | 0.31 | 0.01 |
| Tl | – | – | – | – | – | – | 1.38 | 0.18 | 13 | 1.52 | 0.02 |
| Pb | – | – | – | – | – | – | 4976.80 | 615.47 | 12 | 5520 | 30 |
| Th | – | – | – | – | – | – | 14.16 | 1.75 | 12 | 18.1 | 0.3 |
| U | – | – | – | – | – | – | 8.03 | 0.88 | 11 | 9.11 | 0.3 |
Element concentrations qualified with a “J” are greater than the limit of detection, but less than the limit of quantitation. Shaded rows represent elements not characterised by NIST.
Acknowledgements
This work was supported by the Children's Health Environmental Core Centre at the University of Wisconsin Milwaukee, and funded through National Institute of Environmental Health Sciences Grant Number P30ES004184. The authors would also like to thank Razia Azen and Rebecca Klaper for providing significant comments and suggestions on this manuscript.
References
- Alvarez-Toral A, Fernandez B, Malherbe J, Claverie F, Molloy JL, Pereiro R, Sanz-Medel A. Isotope dilution mass spectrometry for quantitative elemental analysis of powdered samples by radio frequency pulsed glow discharge time of flight mass spectrometry. Talanta. 2013;115:657–664. doi: 10.1016/j.talanta.2013.06.024. [DOI] [PubMed] [Google Scholar]
- Clark HF, Brabander DJ, Erdil RM. Sources, sinks, and exposure pathways of lead in urban garden soil. Journal of Environmental Quality. 2006;35:2066–2074. doi: 10.2134/jeq2005.0464. [DOI] [PubMed] [Google Scholar]
- Clark HF, Hausladen DM, Brabander DJ. Urban gardens: Lead exposure, recontamination mechanisms, and implications for remediation design. Environmental Research. 2008;107:312–319. doi: 10.1016/j.envres.2008.03.003. [DOI] [PubMed] [Google Scholar]
- Claverie F, Malherbe J, Bier N, Molloy JL, Long SE. Putting a spin on LA-ICP-MS analysis combined to isotope dilution. Analytical and Bioanalytical Chemistry. 2013;405:2289–2299. doi: 10.1007/s00216-012-6645-8. [DOI] [PubMed] [Google Scholar]
- Cloquet C, Rouxel O, Carignan J, Libourel G. Natural cadmium isotopic variations in eight geological reference materials (NIST SRM 2711, BCR 176, GSS-1, GXR-1, GXR-2, GSD-12, Nod-P-1, Nod-A-1) and anthropogenic samples measured by MC-ICP-MS. Geostandards and Geoanalytical Research. 2005;29:95–106. [Google Scholar]
- Defoe PP, Hettiarachchi GM, Benedict C, Martin S. Safety of gardening on lead and arsenic contaminated urban brownfields. Journal of Environmental Quality. 2014;4:2064–2078. doi: 10.2134/jeq2014.03.0099. [DOI] [PubMed] [Google Scholar]
- Eriksson SM, Mackey EA, Lindstrom RM, Lamaze GP, Grogan KP, Brady DE. Delayed-neutron activation analysis at NIST. Journal of Radioanalytical and Nuclear Chemistry. 2013;298:1819–1822. [Google Scholar]
- Fernández B, Rodríguez-González P, Ignacio García Alonso J, Malherbe J, García- Fonseca S, Pereiro R, Sanz-Medel A. On-line double isotope dilution laser ablation inductively coupled plasma mass spectrometry for the quantitative analysis of solid materials. Analytica Chimica Acta. 2014;851:64–71. doi: 10.1016/j.aca.2014.08.017. [DOI] [PubMed] [Google Scholar]
- Finster ME, Gray KA, Binns HJ. Lead levels of edibles grown in contaminated residential soils: A field survey. Science of the Total Environment. 2004;320:245–257. doi: 10.1016/j.scitotenv.2003.08.009. [DOI] [PubMed] [Google Scholar]
- Goix S, Point D, Oliva P, Polvé M, Duprey JL, Mazurek H, Guislain L, Huayta C, Barbieri FL, Gardon J. Influence of source distribution and geochemical composition of aerosols on children exposure in the large polymetallic mining region of the Bolivian Altiplano. Science of the Total Environment. 2011;412:170–184. doi: 10.1016/j.scitotenv.2011.09.065. [DOI] [PubMed] [Google Scholar]
- Gueguen B, Rouxel O, Ponzevera E, Bekker A, Fouquet Y. Nickel isotope variations in terrestrial silicate rocks and geological reference materials measured by MC-ICP-MS. Geostandards and Geoanalytical Research. 2013;37:297–317. [Google Scholar]
- Hoang TH, Bang S, Kim K-W, Nguyen MH, Dang DM. Arsenic in groundwater and sediment in the Mekong River delta, Vietnam. Environmental Pollution. 2010;158:2648–2658. doi: 10.1016/j.envpol.2010.05.001. [DOI] [PubMed] [Google Scholar]
- Hu W, Huang B, Weindorf DC, Chen Y. Metals analysis of agricultural soils via portable X-ray fluorescence spectrometry. Bulletin of Environmental Contamination and Toxicology. 2014;92:420–426. doi: 10.1007/s00128-014-1236-3. [DOI] [PubMed] [Google Scholar]
- Huang Z-Y, Chen T, Yu J, Qin D-P, Chen L. Lead contamination and its potential sources in vegetables and soils of Fujian, China. Environmental Geochemistry and Health. 2012;34:55–65. doi: 10.1007/s10653-011-9390-6. [DOI] [PubMed] [Google Scholar]
- Kenna TC, Nitsche FO, Herron MM, Mailloux BJ, Peteet D, Sritrairat S, Sands E, Baumgarten J. Evaluation and calibration of a field portable X-ray fluorescence spectrometer for quantitative analysis of siliciclastic soils and sediments. Journal of Analytical Atomic Spectrometry. 2011;26:395–405. [Google Scholar]
- Makinen E, Korhonen M, Viskari E-L, Haapamaki S, Jarvinen M, Lu L. Comparison of XRF and FAAS methods in analysing CCA contaminated soils. Water, Air and Soil Pollution. 2005;171:95–110. [Google Scholar]
- May W, Parris R, Beck C, Fassett J, Greenberg R, Guenther F, Kramer G, Wise S, Gills T, Colbert J, Gettings R, MacDonald B. Definitions of terms and modes used at NIST for value-assignment of reference materials for chemical measurements. NIST Special Publication; 2000. pp. 260–136. [Google Scholar]
- McBride MB, Shayler HA, Spliethoff HM, Mitchell RG, Marquez-Bravo LG, Ferenz GS, Russell-Anelli JM, Casey L, Bachman S. Concentrations of lead, cadmium and barium in urban garden-grown vegetables: The impact of soil variables. Environmental Pollution. 2014;194:254–261. doi: 10.1016/j.envpol.2014.07.036. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McComb JQ, Rogers C, Han FX, Tchounwou PB. Rapid screening of heavy metals and trace elements in environmental samples using portable X- ray fluorescence spectrometer: A comparative study. Water, Air and Soil Pollution. 2014;225:2169. doi: 10.1007/s11270-014-2169-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McHenry LJ, Chevrier V, Schröder C. Jarosite in a Pleistocene East African saline-alkaline paleolacustrine deposit: Implications for Mars aqueous geochemistry. Journal of Geophysical Research. 2011;116:E04002. [Google Scholar]
- McHenry LJ. Element mobility during zeolitic and argillic alteration of volcanic ash in a closed-basin lacustrine environment: Case study Olduvai Gorge, Tanzania. Chemical Geology. 2009;265:540–552. [Google Scholar]
- Milliard A, Durand-Jézéquel M, Larivière D. Sequential automated fusion/extraction chromatography methodology for the dissolution of uranium in environmental samples for mass spectrometric determination. Analytica Chimica Acta. 2011;684:40–46. doi: 10.1016/j.aca.2010.10.037. [DOI] [PubMed] [Google Scholar]
- Moon JH, Dung HM, Kim SH, Chung YS. Implementation of the k0-NAA method by using k0-IAEA software and the NAA#3 irradiation hole at the HANARO research reactor. Journal of Radioanalytical and Nuclear Chemistry. 2009;280:439–444. [Google Scholar]
- Murray H, Pinchin TA, Macfie SM. Compost application affects metal uptake in plants grown in urban garden soils and potential human health risk. Journal of Soils and Sediments. 2011;11:815–829. [Google Scholar]
- Paul RL, Mackey EA, Zeisler R, Spatz RO, Tomlin BE. Determination of elements in SRM soil 2709a by neutron activation analysis. Journal of Radioanalytical and Nuclear Chemistry. 2009;282:945–950. [Google Scholar]
- Perroy RL, Belby CS, Mertens CJ. Mapping and modeling three dimensional lead contamination in the wetland sediments of a former trap-shooting range. Science of the Total Environment. 2014;487:72–81. doi: 10.1016/j.scitotenv.2014.03.102. [DOI] [PubMed] [Google Scholar]
- Sharma K, Basta NT, Grewal PS. Soil heavy metal contamination in residential neighborhoods in post-industrial cities and its potential human exposure risk. Urban Ecosystems. 2015;18:115–132. [Google Scholar]
- Sutton M, Bibby RK, Eppich GR, Lee S, Lindvall RE, Wilson K, Esser BK. Evaluation of historical beryllium abundance in soils, airborne particulates and facilities at Lawrence Livermore National Laboratory. Science of the Total Environment. 2012;437:373–383. doi: 10.1016/j.scitotenv.2012.08.011. [DOI] [PubMed] [Google Scholar]
- Thomsen V, Schatzlein D, Mercuro D. Limits of detection in spectroscopy. Spectroscopy. 2003;18:112–114. [Google Scholar]
- Wang Z, Becker H. Abundances of sulfur, selenium, tellurium, rhenium and platinum-group elements in eighteen reference materials by isotope dilution sector-field ICP-MS and negative TIMS. Geostandards and Geoanalytical Research. 2013;38:189–209. [Google Scholar]
- Weindorf DC, Zhu Y, Chakraborty S, Bakr N, Huang B. Use of portable X-ray fluorescence spectrometry for environmental quality assessment of peri- urban agriculture. Environmental Monitoring and Assessment. 2012;184:217–227. doi: 10.1007/s10661-011-1961-6. [DOI] [PubMed] [Google Scholar]
- Wilson SA, Briggs PH, Mee JS, Siems DF. Determination of thirty-two major and trace elements in three NIST soil SRMs using ICP-AES and WDXRF. Geostandards Newsletter. 1994;18:85–89. [Google Scholar]
- USEPA . Method 6020a inductively coupled plasma-mass spectrometry. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, SF 846. U.S. Environmental Protection Agency Office of Solid Waste; 2007. pp. 6010A-1–6010A-30. [Google Scholar]
- USEPA National functional guidelines for inorganic superfund data review. 2014 USEPA-540-R-13-001. [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.