Correspondence Comment on “Off-Site Forensic Determination of Airborne Elemental Emissions by Multi-Media Analysis: A Case Study at Two Secondary Lead Smelters” SIR: Kimbrough and Suffet present multimedia data collected around two secondary lead smelters in California and argue that airborne emissions from smelters yield concentrations of lead, arsenic, antimony, and cadmium that are highly correlated and form characteristic ratios (1). In 1994, we performed a similar analysis (2, 3) on data from a secondary lead smelter in Texas and found a similar pattern of concentrations. As part of a study for the United Steelworkers of America, we examined lead, arsenic, and antimony concentrations in soil samples collected near a smelter in West Dallas, TX, to determine if the arsenic and antimony originated from the smelter or were derived from some other source. The smelter has been inoperative since 1984 and is now the RSR Corporation Superfund Site. Soil Data. The first soil data set represented soil samples collected by the U.S. EPA from a large tract of public housing located across the street, north of the smelter. The U.S. EPA divided the tract into 90 equal-area squares and collected soil samples from each area. With approximately 150 data points, we calculated that the mean lead and arsenic concentrations were 468 and 17 mg/kg, respectively. This yields a ratio of 28:1 or, following Kimbrough and Suffet’s convention in which the lead concentration is normalized to 1000, approximately 1000:36. Maximum lead and arsenic concentrations were 2500 and 62 mg/kg, respectively. R2 for 137 soil samples in which both lead and arsenic concentrations were above the detection limit is 0.68. Antimony concentrations were not determined in these samples. According to the U.S. EPA’s risk assessment for the site (4), lead and arsenic were the two primary contaminants of concern. The U.S. EPA’s residential remediation target of approximately 500 mg/kg for lead was exceeded on 27 of the 90 squares; the residential target of 20 mg/kg for arsenic was exceeded on 25 squares. The second soil data set was derived from 64 soil samples that were collected from the public housing area by the U.S. EPA in 1991-1992 but were archived and subsequently reanalyzed in 1994 as part of the remedial investigation (5). The mean concentrations of lead, antimony, and arsenic (300, 2, and 6 mg/kg, respectively) form ratios of approximately 1000:7:20. The following correlations were calculated: R2 for lead vs arsenic ) 0.585; R2 for lead vs antimony ) 0.912; and R2 for arsenic vs antimony ) 0.724. These results are consistent with Kimbrough and Suffet’s finding that the best correlation is between lead and antimony. Air Data. After reading the paper by Kimbrough and Suffet (1), we sought air concentration measurements to
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TABLE 1
Concentration Ratios and R2 at the RSR West Dallas Smelter data set
approx Pb/Sb/As ratioa
soil data set 1 soil data set 2 air monitor 1 air monitor 2
1000:UK:36b (no Sb data) 1000:7:20 1000:UK:43b (no Sb data) 1000:UK:59b (no Sb data)
a Pb concentrations normalized to 1000 mg/kg. or unknown. c Not applicable.
R2 R2 Pb vs Sb Pb vs As NAc 0.91 NA NA b
0.68 0.59 0.87 0.41
UK, not measured
which the soil data could be compared. Ambient air samples were collected weekly at three locations from April 1, 1982, to September 30, 1983, as part of a special monitoring program by the Texas Air Control Board. We found the lead and arsenic measurements in two different documents (6, 7). We examined monthly averages of the two downwind locations for July-December 1982. Location 1, the Boys’ Club at 3004 N. Westmoreland Road, was 0.1 mi north of the smelter stack and adjacent to the public housing area where the soil samples were collected. Location 2, at 3417 Toronto Street, was about 0.1 mi NNW of the smelter property boundary and one block west of location 1. At location 1, the 6-month average ratio of lead to arsenic concentration was 1000:43, and the concentrations of the two metals are highly correlated (R2 ) 0.87). At location 2, the 6-month average ratio was 1000:59, and the correlation is weaker (R2 ) 0.41). Discussion. Table 1 summarizes the concentration ratios and R2 for the soil and air data collected at the RSR West Dallas site. Clearly, there is a high degree of correlation among lead, arsenic, and antimony in these samples. These correlations, the agreement in lead-arsenic ratios between soil and air, and other evidence such as the trend of decreasing concentration with distance from the smelter and the known association of these elements with battery smelting emissions show that the RSR smelter was the source of these elements. The biggest difference between the data sets examined by Kimbrough and Suffet and ourselves is that whereas antimony concentrations were higher than arsenic concentrations at the California smelters, the reverse is true at the Texas smelter. This probably reflects operational differences between the Texas and California smelters which, for example, had different kinds of furnaces, but the specific cause is unclear. Although concentration ratios associated with the RSR smelter are roughly comparable to what was measured around the California smelters, the differences are too large to identify a single industry-wide characteristic ratio. Kimbrough and Suffet rightfully point out that “elemental composition of materials can change through the industrial process. Thus, depending at which point in the process
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emissions are occurring, [their] elemental composition can change”. We would further add that emissions from most secondary lead smelters, particularly the older ones, may have evolved over time in response to both short- and longterm changes in their operations. Thus, when looking at the concentrations of metals in surface soils, which represent a cumulative average of past emissions, the “fingerprint” for each smelter may depend on its operational history. Operational factors controlling the relative concentrations of metals in emissions include the type of furnace (reverbatory, blast, or electric arc), the types of lead and lead alloys produced, air pollution control measures, and slag and dust management practices. Our results support Kimbrough and Suffet’s conclusion that examination of both concentration ratios and correlations among lead, arsenic, and antimony in different media is a dependable means for confirming the presence of airborne emissions from a specific secondary lead smelter. Archived monitoring data can be helpful in reconstructing emission histories, especially after smelters have closed. Our data show that the correspondence in lead to arsenic ratios between air samples and soil samples holds true even though air samples were collected while the smelter was operating and the soil samples were collected many years later after it had closed.
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Literature Cited (1) Kimbrough, D. E.; Suffet, I. H. Environ. Sci. Technol. 1995, 29 (9), 2217-2221. (2) Amter, S. Memorandum to K. Clark, U.S. EPA Region 6, re: Source of Arsenic in Dallas Housing Authority Soils, June 9, 1994. (3) Disposal Safety Incorporated. Comments of Disposal Safety Incorporated on the Remedial Investigations and Human Health Risk Assessments for Operable Units 1 and 2, RSR Corporation Superfund Site. Dec 19, 1994. (4) U.S. EPA Region VI. Baseline Human Health Risk Assessment Report for Operable Unit 2, RSR Corporation Superfund Site, 1994. (5) U.S. EPA Region VI. Remedial Investigation Report for Operable Unit 2, Appendix E, RSR Corporation Superfund Site, 1994. (6) Texas Air Control Board. Letter from L. Butts, Chief of TACB Air Quality Information, to L. Keller, Radian Corporation, dated June 21, 1983, with attached tabulated data. (7) Yancy, M. S. A Case Study of an Environmental Issue: The West Dallas Smelter. M.S. Thesis, University of Texas at Dallas, May 1985.
Steven Amter* and William P. Eckel Disposal Safety Incorporated 1660 L Street NW, Suite 510 Washington, DC 20036 ES9508129
