i
STATISTICAL ANALYSIS OF ARSENIC CONCENTRATIONS IN SUBSURFACE SOILS AT THE UNIVERSITY OF MISSISSIPPI FIELD
STATION
by
David Thomas Webb IV
A thesis submitted to the faculty of The University of Mississippi in partial fulfillment of the requirements of the Sally McDonnell Barksdale Honors College.
Oxford May 2016
Approved by
______________________________
Advisor: Dr. Robert Holt ______________________________
Reader: Dr. Andrew O’Reilly ______________________________
Reader: Dr. Gregory Easson
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© 2016 David Thomas Webb IV ALL RIGHTS RESERVED
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ACKNOWLEDGEMENT
I would like to express my appreciation to my thesis advisor, Dr. Robert Holt, my colleges who aided in the research, the Geology and Geological Engineering Department
of the University of Mississippi, and the Sally McDonnell Barksdale Honors College.
The completion of my research would not have been possible if not for the guidance of Dr. Holt and assistance of my colleges in conducting the large amount of laboratory analysis required for this study, as well as, the gracious contributions of both the Sally
McDonnell Barksdale Honors College and Geology and Geological Engineering Department of the University of Mississippi that funded my research.
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ABSTRACT
The purpose of this investigation is to determine how arsenic concentration varies in soils with respect to soil structures, grain size, soil type, and depth. The investigation was conducted at the University of Mississippi Field Station (UMFS). The UMFS is located in Abbeville, MS and is roughly 700 acres in size. It includes ponds and former agricultural fields, and lies within an internally draining basin.
Seven boreholes were drilled using a direct push geoprobe and sampled. The cores obtained from the borings were then cut at one foot intervals, producing a total of 90 soil samples. Each sample was observed and described in boring logs. Then the samples were split in half, one half was sent for laboratory testing to determine arsenic concentration present in each sample, sieve analysis was conducted on the other half at the University of Mississippi. Each sample was sieved twice. The first time the samples were loosely broken apart in order to maintain natural soil structures, the second time the samples were crushed. In addition, the weight wet and dry weight of each sample was recorded and used to calculate moisture content. Statistical analysis was conducted on the data obtained in order to quantify the relationship of each variable in relation to arsenic concentration.
The analysis revealed that arsenic concentrations decreased with depth, with the highest arsenic concentration found at the surface, and had a weak, positive correlation with moisture content. Arsenic showed the strongest correlation with peds (soil structures
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larger than 1 mm) in uncrushed samples, correlation coefficients ranging from 0.81 to 0.84. In the crushed samples, arsenic showed the strongest correlation to materials less than 0.062 mm, correlation coefficient of 0.78. This relationship is due to the crushing of the peds, which frees clay- and silt-sized particles. The highest arsenic concentrations are found in materials containing peds, within one foot of ground surface in the top soil and at an elevation of 466 to 464 feet which corresponds to the B horizon of the Lexington Silt loam. Our results suggest that natural soil arsenic is concentrated by soil forming processes.
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TABLE OF CONTENTS Page
List of Tables____________________________________________________ vi List of Figures___________________________________________________ vi 1. Introduction __________________________________________________ 1 2. Background __________________________________________________ 4 2.1. University of Mississippi Field Station _________________________ 4 2.2. Regional Geology__________________________________________ 4 2.3. Previous Studies of Arsenic in Soils ___________________________ 5 2.4. Site Geology and Soils _____________________________________ 7 3. Methods ____________________________________________________ 9 3.1. Soil Boring/Sample Collection_______________________________ 9 3.2. Measurement of Arsenic Concentrations _______________________ 10 3.3. Sieve Analysis_____________________________________________ 10 3.4. Statistical Analysis_________________________________________ 11 4. Results _____________________________________________________ 12 4.1. Soil Boring Logs_____________________ ____________________ 12 4.2. Arsenic Concentrations and Distribution________________________ 12 4.3. Relationship between Arsenic, Sieve Fractions, and Moisture Content_ 13 5. Discussion___________ _______________________________________ 14 6. Summary____________________________________________________ 16 7. List of References ___________________________________________ 18 8. Tables _____________________________________________________ 21 9. Figures ____________________________________________________ 24
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10. Appendices _________________________________________________ 41 10.1. Appendix A: Handwritten Sieve Data_____________________ 41 10.2. Appendix B: Sieve Data_______________________________ 70 10.3. Appendix C: Arsenic Concertation Reports________________ 76
LIST OF TABLES Page 1. Mean and Standard Deviation____________ __________________________ 22 2. Correlation Coefficients___________________________________________ 23
LIST OF FIGURES Page
1. Location Map of University of Mississippi Field Station__________________ 25 2. Regional Stratgraphic Column_______________________________________26 3. Geologic Map of UMFS____________________________________________27 4. Soils Map of UMFS_______________________________________________ 28 5. Illustration of Soil Horizons_________________________________________ 29 6. Borehole Map____________________________________________________ 30 7. Soil Boring Log A-1_______________________________________________ 31 8. Soil Boring Log A-2_______________________________________________ 32 9. Soil Boring Log A-3_______________________________________________ 33 10. Soil Boring Logs A-4______________________________________________ 34 11. Soil Boring Logs A-5______________________________________________ 35
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12. Soil Boring Logs A-6_____________________________________________ 36 13. Soil Boring Logs A-7_____________________________________________ 37 14. Image of Sieve Sets_______________________________________________ 38 15. Image of Large Peds______________________________________________39 16. Image of Medium Peds____________________________________________ 40 17. Image of Small Peds______________________________________________ 41 18. Composite Figure________________________________________________ 42
1 1.0 Introduction
Many scientific studies have focused on arsenic concentrations in soils. The strong interest in the subject stems from the relatively high toxicity of arsenic and the substantial quantities in which it has been found in soils. The primary source of arsenic in soils is pesticides and herbicides used on agricultural land (Alloway 1970; Woolson et al.
1971). In areas of North America where these agents have been used, arsenic
concentrations in soils range from 1.8 to 830 ppm, whereas land that has not been treated had concentrations ranging from 0.5 to 14 ppm (Benson, 1953). Arsenic within soils can contaminate plants used as food and aquifers used as sources of drinking water, making it a hazard to human health. In order to minimize potential for harm it is essential that the relationship between arsenic concentrations and soil properties be fully understood.
Previous studies have examined how particular constituents of soil influence arsenic concentrations. Studies have shown that in a lab setting arsenic is readily
absorbed by iron and aluminum oxides, and clays (Goldberg, 1977; Elkhatib et al., 1984, Manning and Goldberg, 1997). These results have been reflected in testing of a variety of soils that displayed a strong correlation between the iron and clay content of soils and arsenic concentration (Pettry and Switzer, 2001). It has also been shown that the presence of organic matter and phosphates can act as desorbants, aiding in the mobilization of arsenic (Grafe et. al., 2001). Although there is a wealth of information on the influence of soil constituents to arsenic concentrations, there is a lack of information on how other characteristic of soils, particularly soil structures, may effect arsenic concentrations.
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Some studies have suggested a potential relationship between soil structures and textures to arsenic concentration (Jiang et al., 2005; Okoye, 2013; Fordham and Norrish, 1983). Soil structures, often referred to as peds, are present in most soils. Peds are soil aggregates that form as a result of natural disruptive forces such as compaction of soil from bioturbation and the shrinking and swelling of clays caused by wetting and drying cycles (Soil Survey Division, 1993). Okoye (2013) evaluated arsenic concentrations in surface soils found at the University of Mississippi Field Station (UMFS) and found a positive correlation (correlation coefficient of 0.56) between arsenic and large soil peds.
Our objective is to extend the work of Okoye (2013) at the UMFS. While Okoye (2013) focused on surface soils and a geostatistical analysis of arsenic and three textural classes (large peds, granular peds, and fine fraction), we evaluate the relationship between arsenic, soil structure, and grain size using soil samples collected from seven soil borings. Soil boring locations were selected to cross existing modern soils and paleosols to reveal potential relationships between arsenic concentrations and soil structure vertically in the soils present at the UMFS. Ninety soil samples were collected and split. One split was analyzed for arsenic concentration. The other split was lightly crushed and sieved to reveal the fraction of peds present in the soils (soil structure); this split was then fully crushed to examine the relationship between arsenic and grain size.
In the following, we first present background information germane to this study, including a description of the UMFS, a discussion of the regional geology, a review of previous studies of arsenic in soils, and an evaluation of geology and soils in the study area. We then discuss the methods used for soil sample collection, measurement of
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arsenic concentrations, sieve analysis, and statistical analysis. Finally, our results are presented and discussed.
4 2.0 Background
2.1 University of Mississippi Field Station (UMFS)
The UMFS is located in Abbeville, MS and is approximately 700 acres in size. A location map of the UMFS is provided in Figure 1. The UMFS encompasses ponds and former agricultural fields, and lies within an internally draining basin. All surface water discharge occurs from a perennial stream. The station was originally a privately owned baitfish farm and was later sold to the University of Mississippi. The Field Station also hosts to the Center for Water and Wetlands Resources (CWWR).
2.2 Regional Geology
In the region encompassing the site, there are two geologic groups present: the Wilcox and the Claiborne. Both groups are Eocene in age. Within the Wilcox Group are the Fearn Springs and Ackerman Formations. The overlying Claiborne group contains the Meridian Sand, and the Tallahatta formations (Figure 2).
The Fearn Springs typically consists of a thin basal unit of sand which may contain lignite, kaolin, and bauxite, and an upper thicker sequence of silts, clays, lignites, and fine sands. In Mississippi the basal sand unit is often not present. In the region the formation is approximately 50 feet (Mellen, 1950).
The Ackerman consists of a basal sand unit and an upper unit comprised of sand, shale, clay, lignite, quartzite, and iron concretions. The basal sand unit is typically white, cross-bedded coarse sands containing lenses of clay. The sands of the upper unit are fine,
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yellow to gray, and often silty. In Mississippi the thickness of the formation ranges from 120 to 20 feet (Turner, 1952).
Overlying the Wilcox is the Meridian Sand. The unit varies in thickness with a minimum of 9 ft. and a maximum of 40 ft. (Merrill et. all, 1985). The formation is nonfossiliferous, cross-bedded, light brown in color, medium to coarse-grained,
moderately to well-sorted, subangular quartz sand that contains minor amounts of mica (Merrill et. al., 1985). The Meridian Sand overlies the Hatchetigbee Formation in the Wilcox Group, with both of the contacts being erosional surfaces.
The Youngest unit present in the area is the Tallahatta is mostly composed of marine silts and clays that have been hardened because of weathering (Wermund, 1965).
Also, traces of fine to coarse-grained sandstone are present in this formation (Szab et al., 1988).
Lafayette County lies within the physiologic region called the North Central Hills.
The topography of the region is characterized by series of moderately sloping hills believed to be series of dissected cuestas. The hills are believed to have formed during the Pleistocene, as an indirect result of a period of glaciation. As glaciation occurred sea level dropped, shifting base level and ultimately increasing the energy of streams leading to a period of down cutting (Keady, 1962).
2.3 Previous Studies of Arsenic in Soils
Arsenic is a naturally occurring element that is found in combination with either inorganic or organic substances to form many different compounds (CDC, 2009).
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Organic arsenic can be found in fish and shell fish. Inorganic arsenic can be found in soils and groundwater. Compounds containing arsenic have been widely used as
pesticides, insecticides, herbicides, soil sterilants, silvicides, and desiccants over the past century (Alloway 1970; Woolson et al. 1971; Pais and Jones 1997). Arsenic
accumulation is a particular concern because of its toxicity in small concentrations, carcinogen classification, and potential to impact surface and ground waters and soil- plant ecological systems (Petry and Switzer, 2001).
In the United States, the highest levels of natural arsenic are found in western states (Delaware Health and Social Services, 2013). The Eastern and Midwestern portions of the United State show relatively high concentrations of inorganic arsenic in soil and groundwater. Mississippi has naturally occurring arsenic concentrations in soil, ranging from 0 to 26 ppm (Association for the Environmental Health of Soils, 1998).
This compares to other parts of the world where natural arsenic concentrations range from 0.1 to 95ppm (Kabata-Pendias and Pendias, 1992).
Parts of the Southern United States, Mississippi, in particular, show concerning concentrations of arsenic in soil. The fertile soils fanning out across the Mississippi River floodplain are up to five times as high in arsenic as other parts of Louisiana, Mississippi, and Arkansas, according to studies done by the United States Geological Survey (Blum, 2014).
Studies have shown that arsenic is readily absorbed by iron and aluminum oxides, and clays (Goldberg, 1977; Elkhatib et al., 1984, Manning and Goldberg, 1997). Manning and Goldberg (1997) found that arsenic mobility in soil primarily depend on the redox potential, soil mineralogy, and pH Goldberg (1977) compared the arsenic absorption
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potential of aluminum oxide, iron oxide, kaolinite, montmorillonite, and illite and found that iron oxides have a significantly higher absorption potential than aluminum or clays.
Other studies, however, suggest that clay can be a large factor in the arsenic absorption, especially when present in larger quantities in surficial soils (Jiang et al., 2005). Petty and Switzer tested 84 soils in Mississippi and found that the highest correlating factor with arsenic concentration is clay content. In some cases, organic matter has been shown to decrease absorption of arsenic in soils (Jiang et al., 2005; Grafe et. al., 2001). Grafe et al.
(2001) noted that the presence of peat, in particular, reduced absorption of arsenic by 27 percent.
In a study conducted by Okoye (2013) at the UMFS, 70 surficial soil samples were collected using a random sampling method. The soil structures were noted and categorized by size into two groups large and granular peds. Both statistical and
geostatistical methods were employed to analyze the data. It was shown that arsenic had a positive correlation with the large peds (correlation coefficient of 0.57), an indeterminate relationship with the granular peds (correlation coefficient of -0.05), and a negative correlation with the fine fraction of the soil (correlation coefficient of -0.58). It was also shown the area of the UMFS which contained the greatest concentration of large peds also displayed the highest arsenic concentrations. This area also displayed the lowest standard deviation, again reaffirming the strength of the correlation (Okoye, 2013).
2.4 Site Geology and Soils
After observing units in the field and collecting samples throughout the study area at the UMFS, three main geologic units were identified within the range of approximately 60 feet. A geologic map (Figure 3) was made to help better illustrate these distinctions.
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The upper unit begins with a light tan to orange, silt loam unit that is approximately eight feet thick. Underlying the silt loam is sand unit with a thickness of 40 feet. The sands are red-brown in color, 95 percent quartz, medium to fine grained, and moderately sorted.
Beneath the sands is a sandy clay layer of undetermined thickness.
In addition, a soils map was created using data obtained from the Lafayette County soil survey (Figure 4). The soils map shows that within the site area the dominant soil type is Lexington silt loam. The silt loam is overlain by a younger, currently
developing, thin soil horizon that drapes the entirety of the study area (Figure 5). The Lexington soil series is primarily composed of gently to moderately sloping, well drained, silty material underlain by loamy material. The silt loam portion of the Lexington series is part of the B horizon and is generally characterized as a red sandy loam with moderate medium subangular blocky structures. The surficial A horizon of the soil was likely removed by erosional forces, which is common in the area (Morris, 1981).
Both the Lexington silt loam and top soil at the site area contain peds. Peds are soil aggregates that form as a result of natural disruptive forces such as compaction of soil from bioturbation and the shrinking and swelling of clays caused by wetting and drying cycles (Soil Survey Division, 1993).
9 3.0 Methods
3.1 Soil Boring/Sample Collection
On November 5th, 2015 McCray Drilling, LLC out of Memphis, Tennessee, drilled eight boreholes (seven for testing and one for backup) using a direct-push
geoprobe. A judgmental sampling approach was used to determine the drilling locations of the boreholes. Two boreholes were drilled on the top of the hill, and five boreholes were oriented in a straight line running downslope. The boreholes were spaced 60 ft.
apart from one another; a map of the borehole locations at the field site is provided (Figure 6). Boreholes one and eight were chosen arbitrarily. Boreholes two through seven were drilled in a straight line down a drainage path. Each well was drilled to a depth of roughly 16 feet in 4 foot intervals. Each interval was called a “run.” The samples were contained in plastic tubes and marked in 1 foot increments with an arrow on the tube to indicate increasing depth. Both ends of the casing were then capped to ensure no loss of soil. Once the transported back to the university, each sample tube was cut into 1 foot intervals, producing a total of 90 samples. The samples were then observed and described in Soil boring logs (Figures 7-13). Then the samples were split, one half was sent
WayPoint Analytical, in Memphis, Tennessee, for arsenic concentration testing, and the other half was used for sieve analysis at the University of Mississippi Geomechanics Lab.
10 3.2 Measurement of Arsenic Concentrations
The samples were sent to Waypoint Analytical in Memphis, Tennessee on November 6th, 2015 where they underwent testing for arsenic concentrations. Waypoint Analytical employed mass spectrometry in order to determine the concentration of arsenic in each sample. The arsenic concentration test result reports can be found in Appendix C.
3.3 Sieve Analysis
Ninety soil samples were used for sieve analysis. The first step in our analysis was to take a wet weight of each sample. The samples were then placed into an oven for 24 hours at 95°F. After being in the oven, a dry sample weight was taken. These weights ranged from 200 to 400 grams. The samples were then placed into a sieve set. The sieves were arranged in an order that would allow for a fining downwards sequence. The
following sieves were used: No. 5, No.7, No .8, No. 18, No. 35, No. 60, No. 120, and No.
230 (Figure 14). The No.5 sieve catches fine pebbles. The No. 7 sieve catches very fine pebbles. The No. 8 sieve catches granules. The No. 18 sieve catches very coarse sand.
The No. 35 sieve catches coarse sand. The No. 60 sieve catches medium sand. The No.
120 sieve catches fine sand. The No. 230 sieve catches very fine sand. At the bottom of the sieves was a pan that catches silts and clays. A gravimetric moisture content was calculated using the sample’s wet and dry weights.
Two sets of sieve analyses were conducted on the samples. The first set was conducted on samples after they had been loosely broken down by hand in order to
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maintain natural soil structure in samples. Each sample was run in the sieve shaker for five minutes. Pictures of small, medium, and large peds are provided. The second set of sieve analysis was performed after the samples were thoroughly crushed. These samples were then placed in the shaker for 15 minutes. The handwritten results of the analysis can be found in Appendix A and a full data sheet tabulating all of the data obtained can be found in Appendix B.
3.4 Statistical Analysis
The four main variables being assessed are grain size fraction, arsenic concentration, moisture content, and depth. In order to understand the relationship between these variables, a variety of statistical analysis methods were employed. The calculations were conducted in Excel using the data analysis tools. In order to define the relative value for each variable, the mean was calculated. The standard deviation was then calculated for each variable to determine the degree of variability within both the crushed and pre-crushed data sets (Table 1). Correlation coefficients were then calculated for each possible combination of variables (Table 2) to determine the degree of
correlation between each variable and if they correlate positively or negatively. These values were then tabulated in matrix form.
12 4.0 Results
4.1 Soil Boring Logs
Three distinct units are found in the soil borings (Figures 7 – 13). The uppermost unit is a light brown to tan, top soil consisting of mostly silt and clay. A light orange to tan silt loam is found beneath the top soil in borings A-1, A-2, A-3, and A-4. This unit appears to have been eroded away in borings A-5, A-6, and A-7. A reddish-brown sand unit underlies the silt loam, where present, and the top soil in down slope borings (A-5, A-6, and A-7).
4.2 Arsenic Concentrations and Distribution
Arsenic concentrations were plotted against depth for each bore location (Figure 18). The figures consistently show a general trend of decreasing arsenic concentrations with increasing depth. Although this is true as an average trend, arsenic concentrations do not steadily decline with depth. The curves for borehole A-1, A-2, A-3, and A-4 display a significant increase in arsenic concentration in the range of 466 to 464 feet in elevation.
The spike in arsenic concentration do not appear in boreholes A-5 and A-6, instead these show a consistently decreasing trend. Borehole A-7 show a sharp spike in arsenic
concentration at an elevation of 442 feet. The maximum value for arsenic concentration is consistently at the highest elevation for each boring. Arsenic concentration values range from 1 to 8.88 mg/kg, and the average value is 3.18 mg/kg.
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4.3 Relationship between Arsenic, Sieve Fractions, and Moisture Content
The mean grain size for both the pre-crushed and crushed samples was 0.5 millimeters, comprising 32.5 percent and 31.9 percent respectively. Sizeable shifts in the mean grainsize percentage occur between the pre-crushed and crushed samples. In particular, for the 4 millimeter grain size the percentage decreases from 15.5 to 0.37 percent, and for the less than 0.62 millimeter grain size the percentage increased from 1.6 to 13.3 percent. From the pre-crushed correlation coefficient table, it can be seen that in the grain size with the highest positive correlation with arsenic concentration is 2.83mm, which is approximately the size of medium peds. In the crushed correlation coefficient table, it can be seen that the grain size that highest positive correlation with arsenic concentration is less than 0.062 millimeters. The highest negative correlation was with a grain size of 0.5 millimeters in both coefficient tables. Moisture content compared to arsenic concentration resulted in a correlation coefficient value of 0.44, which indicates a weak potential correlation. For each boring average grainsize for both pre-crushed and crushed samples and moisture content were plotted against depth. These graphs were paired with the arsenic vs. depth graphs and soil boring logs (Figure 18). Although moisture content only had a weak correlation with arsenic concentration, they trend very similarly with depth.
14 5.0 Discussion
Arsenic showed the strongest correlation with peds (soil structures larger than 1 mm) in uncrushed samples, correlation coefficients ranging from 0.81 to 0.84. In the crushed samples, arsenic showed the strongest correlation to materials less than 0.062 mm, correlation coefficient of 0.78. This relationship is due to the crushing of the peds, which are primarily composed of clay and silt size particles less than 0.062 millimeters in diameter. As has been shown by previous workers (Goldberg, 1977; Elkhatib et al., 1984, Manning and Goldberg, 1997), arsenic concentrations can be higher in clay-rich
materials. In soil profiles, clays are illuviated downward by infiltrating waters. They accumulate around soil peds forming cutans, or clay skins. Our results suggest that the arsenic in UMFS soils is mainly concentrated in soil peds. When the peds are crushed, the arsenic remains in the clay fraction which is liberated from the peds by the crushing process.
At each borehole, the highest arsenic concentrations are found within one foot of ground surface in the top soil, and the second highest arsenic concentrations can be found at an elevation of 466 to 464 feet which corresponds to the B horizon of the Lexington silt loam, both of these are zones where peds are present (Figure 18). Downslope, the Lexington silt loam has been eroded away, exposing sandy soil with lower arsenic concentrations.
It is possible that moisture content has some effect of the concentration of arsenic given their similar distribution and moderate correlation coefficient. However, this relationship could again be related to clay, as some clays readily absorb water. Although
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it is not a definitive conclusion, all of our analysis indicates that arsenic is mainly concentrated within peds.
In order to further validate these findings, the arsenic concentrations of individual peds should be tested along with portions of the top soil not bound in soil structures and the two values compared against one another. This would validate that the high
concentrations are specifically in the peds and not just the top soil. To fully ascertain the mineral composition of the peds X-ray diffraction studies could also be performed. The source of arsenic to the soils should be determined, starting with an analysis of the parent material of the soils. To ensure that there is no cross correlations between other factors, the iron oxide and organic content of the soils should also be tested.
16 6.0 Summary
Our objective is to extend the work of Okoye (2013) at the UMFS. While Okoye (2013) focused on surface soils and a geostatistical analysis of arsenic and three textural classes (large peds, granular peds, and fine fraction), we evaluated the relationship between arsenic, soil structure, and grain size using soil samples collected from seven soil borings. Soil boring locations were selected to cross existing modern soils and paleosols to reveal potential relationships between arsenic concentrations and soil structure vertically in the soils present at the UMFS.
90 samples were collected from seven boreholes drilled at the UMFS. Once collected the samples were split, one half was sent WayPoint Analytical, in Memphis, Tennessee, for arsenic concentration testing, and the other half was used for sieve analysis at the University of Mississippi Geomechanics Lab. Sieve analyses were conducted on two sets samples: 1) loosely crushed samples (to preserve peds) and 2) fully crushed samples.
The borings revealed three main units present at the site. The uppermost unit is a top soil approximately half a foot in thickness. Underlying the top soil is the Lexington silt loam that is eight feet thick. Beneath the silt loam is a sand unit that is approximately 40 feet in thickness. The sands and top soil are present throughout the site, where as the silt loam appears to be eroded along the lower portion of the hill slope.
Arsenic showed the strongest correlation with peds (soil structures larger than 1 mm) in uncrushed samples, correlation coefficients ranging from 0.81 to 0.84. In the crushed samples, arsenic showed the strongest correlation to materials less than 0.062
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mm, correlation coefficient of 0.78. This relationship is due to the crushing of the peds, which frees clay- and silt-sized particles. The highest arsenic concentrations are found in materials containing peds, within one foot of ground surface in the top soil and at an elevation of 466 to 464 feet which corresponds to the B horizon of the Lexington Silt loam. Our results suggest that natural soil arsenic is concentrated by soil forming processes.
18 References Cited
Allaway, W.H., 1970, Agronomic controls over the environmental cycling of trace elements, Adv. in Agron, Geochemistry and the Environment, Vol. 1, p. 17-19.
Baldwin, L., and McCreary H., 1998, Study of state soil arsenic regulations, Association for the Environmental Health of Soils, p. 1-2.
Benson, N.R., 1953, Effect of season, phosphate, and acidity on plant growth in arsenic toxic soils, Soil Science, 76:215- 224, p.1-2.
Blum, D., April 18, 2014, The Trouble with rice, The New York Times, p. 1.
Elkhatib, E.A., and Bennet, O.L., and Wright, R.J., 1984, Arsenite sorption and desorption in soils, Soil Science Society of America Journal, v. 48, p. 3-5
Fordham, A.W., and Norrish, K., 1983, The nature of soil particles particularly those reacting with arsenate in a series of chemically treated samples: Australian Journal of Soil Research, 21 (4), p. 455–477.
Goldberg, S., 2001, Competitive adsorption of arsenate and arsenite on oxides and clay minerals, Soil Science Society of America Journal, v. 662, p. 1-4
Grafe, M., Eick, M.J., and Grossl P.R., 2001, Adsorption of arsenate (V) and arsenite (III) on goethite in the presence and absence of dissolved organic carbon: Soil Science Society of America Journal, 65, p. 1684-1685.
Horton, B. K., and Mackey, G. N., and Milliken, K. L., 2012, Provenance of the
Paleocene– Eocene Wilcox Group, Western Gulf of Mexico Basin: Evidence for
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integrated drainage of the Southern Laramide Rocky Mountains and Cordilleran Arc., p. 22-23.
Jiang W., and Zhang. S., and, Shan X.Q., Feng M., Zhu Y.G., and McLaren R.G., 2005, Adsorption of arsenate on soils. Part 1: Laboratory batch experiments using 16 Chinese soils with different physiochemical properties: Environmental Pollution, 138 (2), pp. 278-284.
Kabata-Pendias, A., and H. Pendias, 1992, Trace Elements in Soils and Plants, Boca Raton, Florida, CRC Press. p. 1
Keady, D. M., 1962, Geologic Study Along Highway 45 from Tennessee Line to Meridian, Mississippi: Mississippi Geological Survey Bulletin 94, p. 19-20 Manning, B. and Goldberg, S., 1997, Arsenic (III) and arsenic(V) adsorption on three
California soils: Soil Science, 162 (1997), p. 886–895.
Mellen, F. F., 1950, Status of Fearn Springs Formation: Mississippi State Geological Survey Bulletin, no. 69, p. 8-9
Merrill, R.K., Sims, J.J., Jr., Gann, D.E., and Liles, K.J., 1985, Newton County geology and mineral resources [Mississippi]: Mississippi Office of Geology Bulletin, no.
126, p.108
Morris, W. M., 1981, Soil Survey of Lafayette County, Mississippi, p. 60-61 Okoye, E. E., 2013, Geostatistical Analysis of Arsenic in Soils at the University of
Mississippi Field Station [B.S. thesis]: Oxford, University of Mississippi, p. 4-30
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Pais, I., and J.B. Jones, Jr., 1997, The Handbook of Trace Elements, Boca Raton, Fla, St Lucie Press, p. 74-76
Petry, D.E. and Switzer, R. E., 2001, Arsenic Concentrations in Selected Soils and Parent Materials in Mississippi: Bulletin 1104, Office of Agricultural Communications, a unit of the Division of Agriculture, Forestry, and Veterinary Medicine at
Mississippi State University. p. 1-4
Soil Survey Division Staff, 1993, Soil survey manual: Soil Conservation Service, U.S.
Department of Agriculture Handbook 18, p. 79-80
Szab, M. W., Osborne, E. W., Copeland, C. W. Jr., Neathery; T. L., 1988, Geologic Map of Alabama: Geological Survey of Alabama Special Map 220, scale 1:250,000.
Turner, J., 1952, Yalobusha County Geology: Mississippi State Geological Survey Bulletin, no. 76, p. 10-13
Wermund, E. G., 1965, Cross-bedding in the Meridian Sand: Sedimentology, Vol. 5, pp 69-79.
Woolson, E.A., J.H. Axley, and P.C. Kearney, 1971, The chemistry and phytotoxicity of arsenic in soils: I. Contaminated Field Soil, Soil Sci, Soc. Amer. Proc. 35:938- 943.
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Tables
22
Crushed Pre-crushed
Table 1. Tables showing values for mean and standard deviation for both data sets.
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Table 2. Tables showing correlation coefficients for both pre-crushed and crushed samples
C rushed
P re -c rus hed
24 Figures
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Figure 1. Map displaying location of the University of Mississippi Field Station (UMFS)(Okoye, 2013).
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Figure 2. Stratigraphic column
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Figure 3. Geologic Map of the University of Mississippi Field Station (UMFS).
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Figure 4. Soils Map of the University of Mississippi Field Station (UMFS).
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(Not to Scale)
Figure 5. Illustration of soil horizons.
Elevation (ft)
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Figure 6. Map displaying borehole locations.
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Figure 7. Soil boring log for borehole A1
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Figure 8. Soil Boring Log for Borehole A2.
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Figure 9. Soil Boring Log for Borehole A3.
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Figure 10. Soil Boring Log for Borehole A4.
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Figure 11. Soil Boring Log for Borehole A5.
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Figure 12. Soil Boring Log for Borehole A6.
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Figure 13. Soil Boring Log for Borehole A6.
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Figure 14. Image of Sieve Set.
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Figure 15. Example of Large Peds.
Figure 16. Example of Medium Peds.
Figure 17. Example of Small Peds.
472 470 468 466 464 462 460 458 456 454 452 450 448 446 444 442 440 438 436 434 432 430 472
470 468 466 464 462 460 458 456 454 452 450 448 446 444 442 440 438 436 434 432 430 470 468
470 468
428 426
428 426
424 424
A-7
454 452 450 448 446
444
445 443 441 439 437 435 433
Elevation (ft) Elevation (ft)
462 460 458 456 454 452 472
470 468 466 464 462 460
471 469 467 465 463 461 459
470 468 466 464 462 460 458 456
467 465 463 461 459 457 455
Elevation (ft) Elevation (ft) Elevation (ft) Elevation (ft) Elevation (ft)
Lithology
Lithology
Lithology
Lithology
Lithology
A-6 A-5
A-4 A-2 A-3
A-1
Lithology
Lithology
Arsenic Concentration
(ppm) Arsenic
Concentration (ppm)
Average Grain Size
(mm)
Arsenic Concentration
(ppm) Arsenic
Concentration (ppm)
Arsenic Concentration
(ppm)
Arsenic Concentration
(ppm)
Arsenic Concentration
(ppm) Average
Grain Size
(mm) Average
Grain Size (mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Elevation (ft)
Elevation (ft)
Moisture Content (%) Average
Grain Size (mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Average Grain Size
(mm)
Average Grain Size
(mm) Moisture
Content (%) Moisture
Content (%) Moisture
Content (%) Moisture
Content (%) Moisture
Content (%) Moisture
Content (%)
Explanation
Top Soil Silt Loam Sand
Precrushed Samples Crushed Samples Borehole Designation
A-1
0 10 30 40 0 10 30 40
0 10 30 40
0 10 30 40
0 10 30 40
0 10 30 40
0 10 30 40
0 5 10
0 5 10
0 5 10
0 5 10
0 5 10
0 5 10
0 5 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
Figure 18. Composite figure
40
41
Appendix A: Handwritten Sieve Data
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
Appendix B: Sieve Data
71
72
73
74
75
76
Appendix C: Arsenic Concentration Report
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
