Article pubs.acs.org/est
Analysis of Heavy Metal Sources in Soil Using Kriging Interpolation on Principal Components Hoehun Ha,*,† James R. Olson,‡ Ling Bian,§,∥ and Peter A. Rogerson*,§,∥,⊥ †
Department of Geography, Central Michigan University, Dow Science, Mount Pleasant, Michigan 48859 United States Departments of Pharmacology and Toxicology and Social and Preventive Medicine, Farber Hall, University at Buffalo, Buffalo, New York 14214 United States § Department of Geography, University at Buffalo, Wilkeson Hall, Buffalo, New York 14261 United States ∥ National Center for Geographic Information and Analysis, University at Buffalo, Buffalo, New York 14261 United States ⊥ Department of Biostatistics, Farber Hall, University at Buffalo, Buffalo, New York 14261 United States ‡
S Supporting Information *
ABSTRACT: Anniston, Alabama has a long history of operation of foundries and other heavy industry. We assessed the extent of heavy metal contamination in soils by determining the concentrations of 11 heavy metals (Pb, As, Cd, Cr, Co, Cu, Mn, Hg, Ni, V, and Zn) based on 2046 soil samples collected from 595 industrial and residential sites. Principal Component Analysis (PCA) was adopted to characterize the distribution of heavy metals in soil in this region. In addition, a geostatistical technique (kriging) was used to create regional distribution maps for the interpolation of nonpoint sources of heavy metal contamination using geographical information system (GIS) techniques. There were significant differences found between sampling zones in the concentrations of heavy metals, with the exception of the levels of Ni. Three main components explaining the heavy metal variability in soils were identified. The results suggest that Pb, Cd, Cu, and Zn were associated with anthropogenic activities, such as the operations of some foundries and major railroads, which released these heavy metals, whereas the presence of Co, Mn, and V were controlled by natural sources, such as soil texture, pedogenesis, and soil hydrology. In general terms, the soil levels of heavy metals analyzed in this study were higher than those reported in previous studies in other industrial and residential communities.
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INTRODUCTION In the 1920s, Anniston was the nation’s largest producer of cast-iron soil pipe and was known as the “Soil Pipe Capital of the World”, with an annual production of about 140 000 tons.1 Various types of chemical contaminants in foundry waste are potentially toxic.2 Heavy metals are such toxic contaminants in the waste since they are components of many alloys widely used for casting. EPA regulated heavy metals include arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), selenium (Se), and Zinc (Zn). Unlike many organics, heavy metals are highly resistant to environmental degradation, and they tend to bioaccumulate.3 Metals are also mobile, in part through changing environmental and climatic conditions, and land use change.4−6 The disposal of foundry waste has been associated with the pollution of soil, with Pb, Cd, Cr, Cu, Ni, V, Zn, and other potentially toxic substances posing possible ecological and human health hazards.7 Communities located near foundries can face higher risks of adverse health effects, such as cancers and other chronic diseases.8−10 In addition to anthropogenic origins, heavy metals associated with nonanthropogenic origins are also contained in soils at a background level. © 2014 American Chemical Society
For the last few decades, the widespread existence of polychlorinated biphenyls (PCBs) and lead in Anniston has gained nationwide attention because of environmental and public health concerns.11−16 The U.S. EPA recently completed an investigation of commercial and residential areas in Anniston and remediated soil in sites with high concentrations of PCBs and lead. As a part of the investigation, soil samples were collected in four different zones with respect to their proximity to foundry operations in Anniston. These data provide an excellent opportunity to gain insights into the current state of heavy metal contamination in Anniston. While previous reports have focused on PCBs that were manufactured in Anniston,14−16 there are no published reports on the potential contamination of this community by lead and other heavy metals. The objectives of this study are (1) to establish a general understanding of the concentrations of 11 heavy metals (Pb, Received: Revised: Accepted: Published: 4999
March 4, 2013 March 11, 2014 April 2, 2014 April 2, 2014 dx.doi.org/10.1021/es405083f | Environ. Sci. Technol. 2014, 48, 4999−5007
Environmental Science & Technology
Article
Figure 1. Sampling zones in the Anniston AL study area designated by the U.S. EPA. Source: EPA24
specific areas of interest are residential neighborhoods near 23 former and currently operating foundries and major railroads in the study area. Soil samples were collected from residential properties in four different zones designated by the U.S. Environmental Protection Agency (EPA), as shown in Figure 1.24 Zone A is defined as the area within 500 m of each former and current Anniston foundry operation (the industrial zone, shown in green). Zone B represents an area that is presumably less polluted (the peripheral zone, shown in yellow). Zone C is the area in the vicinity of the industrial zone (the vicinity of the industrial zone, shown in red). Lastly, Zone D is the area surrounding the Monsanto plant, a former PCB manufacturer in Anniston (Monsanto plant zone, shown in blue).24 A database of soil samples in Anniston was obtained from the EPA that includes measurement of heavy metals at 2046 soil sample locations. Multiple measurements were taken from the upper 3 in. of soil in each location measured in parts per million (ppm or mg/kg). Heavy metal levels were measured by using U.S. EPA method 3050/6010/6020 (ICP/ICP-MS). The latitude and longitude coordinates contained in the database are used to convert the database into a spatial database in order to support the kriging interpolation. To produce a reliable analysis of metal concentrations, the average concentration was computed for each residential property. This process resulted in a total of 595 averaged soil samples: 209 samples in Zone A, 66 samples in Zone B, 270 samples in Zone C, and 50 samples located within Zone D (Figure S1 of the Supporting Information, SI). Data Analysis. Basic descriptive statistics were derived to provide a summary of the concentrations of the 11 heavy metals present in the four zones within the study area. Mann− Whitney and Kruskal−Wallis tests were used to compare the
As, Cd, Cr, Co, Cu, Mn, Hg, Ni, V, and Zn) within four different sampling zones in Anniston, Alabama; (2) to identify patterns of metal contamination in soils from these zones; (3) to identify natural and anthropogenic origins of these heavy metal contaminants; and (4) to interpolate point patterns to the entire study area in order to gain an aerial perspective of the spatial distribution of the contaminants. Principal Component Analysis (PCA) is used to support the first three objectives, while a geostatistical method (kriging) is used to support the fourth objective. Principal Component Analysis (PCA) has been used in many fields of study, including the characterization of polluted sites. The method helps identify the underlying patterns among a large number of contaminants and, based on these patterns, to identify their origin.17,18 Moreover, kriging utilizes the spatial autocorrelation principle to interpolate point samples to areal maps.17−19 The method has been widely adopted in environmental contamination studies19,20 such as producing regional distribution maps of nonpoint sources of heavy metal contamination. GIS has been extensively applied in pollution studies21−23 including those of soil contamination at a regional scale. Together, the results from this study provide a comprehensive geospatial assessment of the lead and other metal contamination in soil in Anniston that may pose a public health concern for this region. Results may help devise spatially informed guidelines for remediation efforts.
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MATERIALS AND METHODS Sampling. The study area is Anniston, Alabama, a community of about 23 000 people located approximately 60 miles east of Birmingham and 90 miles west of Atlanta. The 5000
dx.doi.org/10.1021/es405083f | Environ. Sci. Technol. 2014, 48, 4999−5007
Environmental Science & Technology
Article
Table 1. Heavy Metal Concentrations in Soil Samples, Anniston, Alabamaa,b Lead (Pb) Arsenic (As) Cadmium (Cd) Chromium (Cr) Cobalt (Co) Copper (Cu) Manganese (Mn) Mercury (Hg) Nickel (Ni) Vanadium (V) Zinc (Zn)
Zone A (n = 209)
Zone B (n = 66)
Zone C (n = 270)
Zone D (n = 50)
p
405.59 ± 42.73a (27.50−7715.00) 8.46 ± 0.42a (1.38−74.00) 1.71 ± 0.21a,c (0.05−29.45) 22.80 ± 0.84a (4.85−100.00) 15.96 ± 1.59a (1.71−198.90) 103.37 ± 17.57 (7.75−2429.00) 1544.84 ± 156.62a (176.00−18385.00) 0.40 ± 0.03a (0.05−3.66) 14.26 ± 0.60 (1.35−45.00) 20.34 ± 0.74 (7.60−108.95) 621.18 ± 32.80a (49.33−4055.00)
182.81 ± 22.28b (5.80−830.00) 6.92 ± 0.49b (1.00−24.50) 0.68 ± 0.08b (0.04−3.12) 17.64 ± 1.24b (3.80−64.00) 11.46 ± 1.32a,b (0.61−60.50) 61.66 ± 27.52b (4.80−1839.00) 977.08 ± 93.41a,b (16.85−3600.00) 0.21 ± 0.02b (0.05−0.70) 11.98 ± 1.17 (1.00−48.50) 20.77 ± 1.12a,b (5.20−45.50) 344.71 ± 37.84b (8.65−1300.00)
258.12 ± 16.16c (5.50−1900.00) 7.51 ± 0.46b (0.35−76.00) 1.79 ± 0.36a (0.05−94.00) 25.33 ± 1.22a (4.00−212.50) 10.19 ± 0.93b (1.75−190.00) 112.27 ± 20.70c (2.20−3740.50) 1018.07 ± 50.61b,c (100.00−7600.00) 0.31 ± 0.05b,c (0.04−14.14) 15.45 ± 1.09 (1.40−170.00) 22.07 ± 0.54b,c (8.10−83.75) 537.36 ± 46.35c (11.00−6333.33)
264.61 ± 21.37d (18.50−610.00) 8.34 ± 0.70a (2.95−34.46) 1.78 ± 0.27c (0.04−12.02) 20.36 ± 0.86a (8.87−38.33) 7.27 ± 0.59b (2.60−25.00) 71.30 ± 15.50a,c (7.05−710.00) 860.16 ± 49.67a.,c (210.00−1727.77) 0.42 ± 0.11a,c (0.06−5.44) 12.60 ± 1.25 (2.40−61.25) 21.75 ± 1.04a,c (10.16−44.00) 723.19 ± 267.10c (24.70−14142.50)
