Journal of Environmental Quality 32:736-738 (2003)
© 2003 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
SHORT COMMUNICATION
Antimony Impurity in Lead Arsenate Insecticide Enhances the Antimony Content of Old Orchard Soils
Sandra E. Wagnera,
Frank J. Peryea*,b and
Royston A. Filbyc
a Los Alamos National Laboratory, Los Alamos, NM 87545
b Tree Fruit Research and Extension Center, Washington State Univ., Wenatchee, WA 98801
c Dep. of Chemistry, Washington State Univ., Pullman, WA 99164
* Corresponding author (fjperyea{at}wsu.edu)
Received for publication July 1, 2002.
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ABSTRACT
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Lead arsenate was a commonly used insecticide during the first half of the 20th century, particularly in deciduous tree fruit orchards. Antimony is cotransported with As during the ore refining process and could occur as an impurity in commercial lead arsenate products. The total concentrations of As and Sb in eight soil samples collected from eight orchards located throughout central Washington State were analyzed by neutron activation analysis. Total soil Sb concentrations ranged between 0.4 and 1.5 mg kg-1, while total soil As concentration ranged from 1 to 170 mg kg-1. Total soil Sb and As concentrations were positively related. Total Pb and As concentrations in four of the soils were substantially higher than natural background, while the Sb to As concentration ratios in these soils were consistent with values measured in three lead arsenate insecticide products. These results confirm that Sb impurity is present in lead arsenate insecticide and has contributed to Sb enrichment of soils on which lead arsenate–treated plants were grown. Although higher than in uncontaminated soils from the same region, the Sb concentrations in the affected soils fall within the normal range observed worldwide and are substantially lower than values associated with impaired human or environmental health.
Abbreviations: NAA, neutron activation analysis
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INTRODUCTION
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ACID LEAD ARSENATE (PbHAsO4) was a commonly used insecticide during the first half of the 20th century, particularly in deciduous tree fruit orchards, until it was largely displaced by DDT (dichlorodiphenyltrichloroethane) in about 1947 (Peryea, 1998). Lead arsenate use on agricultural crops was banned in the United States in 1988 (USEPA, 1988). Application of lead arsenate at high frequencies and rates has resulted in substantial accumulation of lead (Pb) and arsenic (As) in topsoil. Much of the As used to formulate lead arsenate was derived from processing of high-As copper ore (Loebenstein, 1994). Copper ores also frequently contain antimony (Sb) as an impurity. Because it has physicochemical properties similar to As, Sb is transported in conjunction with As during the processes of ore smelting, trapping of gaseous and particulate As compounds, and subsequent formulation of As-containing products (Crecelius et al., 1974). As a result, it is possible that lead arsenate insecticide products may have contained appreciable amounts of Sb as an impurity. Contamination of soils with lead arsenate residues therefore implies the possible presence of simultaneous contamination with Sb.
Although the biogeochemical behavior of Sb is poorly studied, there is some evidence that it is similar to As and P (Adriano, 2001). Excessive exposure to Sb through ingestion and inhalation is known to cause deleterious health effects in humans and other mammals (Elinder and Friberg, 1986), although it appears that few if any health studies have examined exposure to Sb associated with soil. Antimony is used in the treatment of parasitic diseases and infections; however, health effects associated with long-term exposure to low levels are not well-established (Agency for Toxic Substances and Disease Registry, 1992).
The purpose of the current study was to determine if past use of lead arsenate insecticide sprays resulted in increased Sb concentrations in affected soils, and the magnitude of possible soil Sb enrichment.
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Materials and Methods
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Topsoil samples (0- to 20-cm depth) were collected from eight orchards spanning central Washington from the Canadian to the Oregon border. The samples were air-dried and gently crushed to pass a 2-mm plastic sieve. Soil texture was measured with a micropipette method (Miller and Miller, 1987) and pH in 1:1 soil and distilled water. Total soil Pb concentration was estimated with concentrated HCl extraction (Veneman et al., 1982) and assay by flame atomic absorption spectrophotometry. Available soil P concentration was measured by 0.5 M NaHCO3 (pH 8.5) extraction and assayed colorimetrically by the modified ascorbic acid method (Kuo, 1996) after eliminating AsO4 interference (USEPA, 1983, p. 365.3-1 to 365.3-4).
Total As and total Sb in the samples were determined by neutron activation analysis (NAA) at the Washington State University Nuclear Radiation Center, Pullman, WA. Arsenic was measured by irradiating 50-mg subsamples of each soil for 4 h at a neutron flux of 6.53 x 1012 cm-2 s-1. The irradiated samples were allowed to decay for 5 d, after which 
-ray emission from the 76As isotope was counted with a Ge(Li) detector and an acquisition time of 4000 s. Antimony was determined with the same procedures except that 100-mg soil subsamples were used and -ray activity of the 124Sb isotope was measured with an acquisition time of 40 000 s. The procedure for As was validated with three standard reference materials: SRM 1571, Orchard Leaves; SRM 1633, Coal Fly Ash; and SRM 1632a, Bituminous Coal. All analyses were conducted in duplicate and the results are expressed on an oven-dry soil basis.
In addition to the soil samples, samples from three commercially marketed lead arsenate pesticides were analyzed for total As and total Sb by NAA.
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Results and Discussion
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The soils ranged in texture from sand to silt loam, and in pH from acid to alkaline (Table 1). Total soil Pb ranged from <1 to 555 mg kg-1, and As from 2.8 to 168 mg kg-1. Peryea and Creger (1994) found natural background Pb concentration to be <13.5 mg kg-1 and As to be about 5 mg kg-1 in central Washington orchard soils. These values are consistent with a study reporting natural background Pb and As concentrations of 11.0 and 5.1 mg kg-1, respectively, for soils collected from undisturbed or undeveloped sites of unknown land use history in central Washington (San Juan, 1994). Concentrations of both Pb and As in four of the soils in the current study were higher than the anticipated background, indicating probable contamination from historical applications of lead arsenate insecticide. High concentrations of available soil P in most of the soils may reflect past use of P-containing fertilizers, although it is possible that the presence of high concentrations of soil As enhances the relative extractability of soil P, because the two elements competitively react with the same sorption sites on soil particles (Woolson et al., 1972; Smith et al., 2002).
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Table 1. Selected properties of orchard soils used in the current study, arranged north-to-south within central Washington.
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Total As and Sb concentrations in the three commercial lead arsenate products were: 20.0% As, 3207 mg kg-1 Sb (Product 1); 20.2% As, 742 mg kg-1 Sb (Product 2); and 20.7% As, 705 mg kg-1 Sb (Product 3). These results confirm the presence of substantial amounts of Sb as a contaminant in lead arsenate insecticide.
Total soil Pb was linearly related to total soil As (HCl-Pb = 6.999 + 3.0470NAA-As; r2 = 0.876, significant at the 0.01 probability level). The Pb to As concentration ratio in the four contaminated soils averaged 3.49 ± 0.98 (mean ± SD, mg kg-1 basis), higher than the value of 2.77 for pure PbHAsO4. The enrichment of topsoil Pb relative to As is consistent with loss of As due to differential leaching rates of the two elements (Peryea and Creger, 1994). Available soil P was unrelated to total soil As (NaHCO3–P = 15.497 + 0.0854NAA-As; r2 = 0.219).
Total soil Sb and As concentrations were positively related, suggesting that lead arsenate application contributed to Sb enrichment in the soil (Fig. 1)
. Antimony concentrations in the apparently uncontaminated orchard soils of the current study fell between 0.41 and 0.71 mg kg-1. In the contaminated soils, Sb concentrations were between 0.48 and 1.46 mg kg-1. These values are not unusually high. Concentrations of Sb in surficial soils of the United States have a geometric mean of 0.48 mg kg-1, with a range of <1 to 8.8 mg kg-1 (Shacklette and Boerngen, 1984). Similar mean and range values are reported for soils worldwide (Reimann and de Caritat, 1998; Adriano, 2001). The Sb to As ratios in the four soils with elevated Pb and As concentrations were consistent with the values determined for the three lead arsenate insecticide products (Fig. 2)
, further suggesting that the source of Sb and As contamination is the pesticide.
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Fig. 1. Relationship of Sb and As concentrations in orchard topsoils. NAA, neutron activation analysis.
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The magnitude of the enhanced Sb concentrations in the lead arsenate–contaminated soils appears to be too low to raise concerns about human or environmental health. Elinder and Friberg (1986), referring to pure chemical compounds, stated that As is much more toxic than Sb. Human health–based cleanup standards for residential soils in the USA are substantially higher than those observed in the study soils; for example, 31 mg kg-1 in Arizona (Arizona Administrative Code, 1997) and 14 mg kg-1 in New Jersey (New Jersey Administrative Code, 1992). A hazard assessment model using data for smelter-contaminated soils in Washington State suggested that exposure to soil containing a Sb concentration of 30.5 mg kg-1 did not create a significant human health risk (Glass, 1992). Bioavailability of soil Sb and Sb mobility within the animal food chain appear to be very low (Ainsworth et al., 1990a,b; Hammel et al., 2000). Efroymson et al. (1997) concluded that no primary reference data exist describing toxicity of soil Sb to plants, and adopted a value of 5 mg kg-1 based on weakly supported evidence. Eikmann and Kloke (1993) reported that soil Sb concentrations up to 5 mg kg-1 were acceptable for agricultural food crop production. In contrast, Hammel et al. (2000) found that the Sb content of food plants grown on minespoil-affected soils containing up to 500 mg kg-1 was too low to create a hazard to human health. Crommentuijn et al. (1997) concluded that 3.5 mg kg-1 is the maximum permissible soil Sb concentration to preclude detrimental effects on environmental quality. The available information suggests that the maximum Sb concentration observed in the lead arsenate–contaminated soils is lower than prevailing human and environmental health protection standards.
The results of this study confirm that Sb was an impurity in lead arsenate insecticides. The amount of Sb applied in the historical lead arsenate sprays was sufficient to enhance the Sb content of affected soils; however, the resulting Sb concentrations in the lead arsenate–affected soils are too low to have an appreciable effect on human or environmental health.
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NOTES
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Release of information presented in this paper was approved by Los Alamos National Laboratory, Security Release Number LA-UR-02-3364.
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