Rapid Method for Estimation of Mean Sulfur Dioxide Pollution Using Lead Candles and Atomic Absorption Spectrophotometry Gary D. Carlson’ and Wayne E. Black2 Division of Laboratories, St. Louis County Health Department, 801 South Brentwood Boulevard, Clayton, Mo. 631 05 An atomic absorption spectrophotometric method is described for the rapid analysis of lead dioxide candles exposed to ambient air containing sulfurous pollutants. The sulfur-bearing material is stripped from the candle, and lead sulfate is dissolved by stirring in a 30% ammonium acetate solution. The slurry is allowed to settle for a short period of time, and a small portion is centrifuged to remove any lead dioxide particles. The clear supernatant is then analyzed for lead by atomic absorption. Results are compared with the gravimetric method on duplicate field candles to illustrate the close agreement between the methods. Nitrogen dioxide and nitric oxide gases do not interfere when present in concentrations of 1 ppm or less. Only seven man-hours are required for the analyses of 25 candles. This method should be readily applicable to other types of lead dioxide samplers, such as sulfation plates. ~
The usefulness of the lead dioxide candle as an economical device for estimating mean concentration of sulf u r dioxide pollution is well known. However, the tedious and time-consuming gravimetric analyses of exposed candles have been a major disadvantage of this technique. Several developments and modifications have been made during the last decade in efforts to shorten the analytical procedure. Kanno (1959) used a colorimetric method which facilitated shortened exposure periods, while Bowden (1964) employed acidimetry after conversion of lead sulfate to sulfuric acid by ion exchange. Rayner (1966) titrated sulfate using barium perchlorate as a titrant. Huey (1967) employed a turbidimetric procedure, while Vijan (1969) proposed a high temperature combustion method in which liberated sulfur dioxide was titrated using potassium iodate as a titrant. This paper proposes a precise and accurate atomic absorption spectrophotometric method which is rapid and convenient. The method is based upon the fact t h a t lead sulfate is significantly more soluble than lead dioxide in ammonium acetate solution. The exposed lead dioxidecoated gauze is stirred with ammonium acetate solution which is then analyzed for lead using atomic absorption. Nitric oxide and nitrogen dioxide a t concentration levels observed in ambient air do not interfere.
Experimental A Jarrell-Ash Model 82-546 atomic absorption spectrophotometer equipped with a laminar flow burner was used. Reagents used were a 300 g/1 (30%) solution of a m monium acetate, a 60 g/l (6%) solution of ammonium acetate, and a 4.7-5.0% solution of stock resin P3-100. Stock resin P3-100 binder was obtained as a 50% solution from the Industrial Products Group, A. E. Staley Manufacturing Co., Decatur, Ill. 62525. A stock solution of lead sulfate (10.00 mg/ml) was prepared by dissolving 1.000 gram of lead sulfate in 20 ml of 30% ammonium acetate solution and diluting to 100 ml Present address. Director Air Program, Browand County Pollution Control Board, 300 SW 14th St., Fort Lauderdale, Fla. To whom correspondence should be addressed. 1040
Environmental S c i e n c e & Technology
using deionized water. Working standards ranging between 0-1.OOO mg/ml of lead sulfate were prepared by diluting appropriate volumes of stock lead sulfate solution with 6% ammonium acetate solution. All chemicals used were reagent grade. Lead dioxide powder (99.2% purity) was supplied by Apache Chemicals, Rockford, Ill. 61105. Procedure. Prepare the lead candle for exposure according to the ASTM (1966) gravimetric method substituting a 4.7-5.070 solution of P3-100 resin binder for the 2-3% gum tragacanth. The lead dioxide used should be of high purity and provide a low background level of lead when treated according to the procedure. Using about 100 ml of a measured 200-ml volume of 30% ammonium acetate solution in a 400-ml beaker, soak the coated gauze and strip it from the cylindrical form. Police and rinse the outside surface of the cylinder with the remaining 100 ml of solution. Using a magnetic stirrer, stir for 15 min with an asbestos plate placed between the beaker and stirrer motor to retard heat transfer. Allow the solids to settle for 2 or 3 min and decant about 10 ml of the top liquid into a 15-ml centrifuge tube. Spin a t 2500-3000 rpm until supernatant is clear (about 1 min). Pipet 5 ml of the supernat a n t into a 25-ml volumetric flask and dilute to the mark with deionized water. The concentration of the resulting solution is about 6% ammonium acetate. Using conventional atomic absorption techniques, determine lead as compared to lead sulfate standards. An unexposed candle is used as a blank.
Calculation. Milligrams S03/100 sq. cm. per day = [ ( S - B ) 264/D].[lOO/A] where S = mg/ml PbS04 in sample solution B = mg/ml PbS04 in blank solution D = number of days of exposure A = area of exposed coated surface in square centimeters
Results and Discussion Initially, when lead candles were prepared with gum tragacanth binder and analyzed by the proposed atomic absorption procedure, very high background levels of lead were observed. This could not be attributed to the lead dioxide used, since only 4 mg of lead was present in the decantate when 8 grams of lead dioxide were analyzed according to the procedure. However, when gum tragacanth and lead dioxide were mixed prior to analysis, the quantity of lead observed in the decantate increased markedly. Since various forms of lead oxide are soluble under conditions of this procedure, it was thought t h a t free hydroxyl groups present in the structure of gum tragacanth might be participating in an oxidation-reduction reaction in which lead dioxide is reduced to a more soluble form(s). This hypothesis was examined in an empirical manner by mixing 8 grams of lead dioxide with about 0.1 gram of glyceol and treating the mixture according t o the proposed procedure. The significant amounts of lead found in the decantate indicated t h a t the reduction of lead dioxide t o a more soluble form by free hydroxyl groups is a very probable phenomenon.
It was therefore clear t h a t a nonreducing binder was required to replace t h e gum tragacanth. Such a material, Experimental Resin P3-100, was obtained from the A. E. Staley Manufacturing Co. Several studies were then conducted t o determine if P3-100 had suitable physical and chemical properties to serve as a binding material. Table I shows the results obtained from the analysis of unexposed candles prepared with gum tragacanth and experimental resin P3-100. As shown, the reaction between gum tragacanth and lead dioxide is time-dependent and significantly high background levels of lead are to be expected even after a 16-day period. Candles prepared using P3-100 resin yielded negligible background levels of lead. To determine if lead candles prepared with P3-100 resin would react with sulfur dioxide a t a rate comparable to candles prepared using gum tragacanth, both types of candle were exposed under identical conditions for the same period of time. After exposure, both types were analyzed using the gravimetric technique. As shown in Table 11, the results observed were in excellent agreement. ,4 recovery study was performed by mixing various amounts of reagent-grade lead sulfate to simulated candles prepared by mixing 8 grams of lead dioxide. 100 cm2 of cottom gauze, and about 3 ml of 4.7% P3-100 resin solution in a 400-ml beaker. The beakers were covered with polyethylene sheets and allowed to remain for four days before analysis by the atomic absorption method. Table 111 shows the observed results of the recovery study. Another study was conducted to determine if nitric oxide and nitrogen dioxide might interfere by forming soluble lead nitrate under ambient air conditions. Several lead candles were placed in a large, air-tight glass jar having an inlet and an outlet valve fitted into the lid. Known concentrations of gases were then introduced into the jar using a permeation tube for nitrogen dioxide and previously calibrated tank of nitric oxide. The gas was allowed to flow into t h e jar until it was estimated that the jar was completely flushed. This process was repeated daily for one month using 1 ppm in air of nitric oxide and nitrogen dioxide. The candles were then removed from t h e jar and analyzed by atomic absorption. The observed results were nearly identical to those obtained from the analysis of blank, unexposed candles, showing that nitric oxide and nitrogen dioxide do not interfere when present a t concentrations of a t least 1 ppm. To obtain comparative d a t a between the gravimetric and atomic absorption methods, two candles were exposed under identical conditions in the field a t each of three sites for various lengths of time and during various seasons of t h e year. One candle was prepared with gum tragacanth and analyzed gravimetrically, while the other was prepared with the P3-100 resin and analyzed by the procedure presented here. As shown in Table IV, the observed results from both methods compared favorably. In general, substances which will reduce lead to a lower valence state would interfere and appear as sulfate in this procedure. However, the d a t a shown in Table IV, which compares the gravimetric procedure with the atomic absorption procedure, indicate t h a t such substances are not normally present in t h e ambient air in sufficient concentration to' cause any measurable interference. It was shown also that exposure of lead candles u p to 1 ppm of oxides of nitrogen for a period of one month had no measurable effect. All the stations (sampling sites) used in this study were located in the urban area of metropolitan St. Louis. Stations 1 and 3 were situated near a source of high industrial pollution while station 2 was located in a residential-light business area near a heavily traveled expressway.
Table I . Effect of Binding Material on Background Level of Lead Age of U n exposed candle, days 2 5 8 16 30 31 31
Binder
G u m tragacanth
Experimental P3-100
Lead found,
mg 21 36 46 59 2 3 2
Table I . Results from Duplicate Lead Dioxide Candles Prepared with Different Binders (Gravimetric technique) SO3 m g per 100 crn2 d a y
Month
January February June July
August September
Gum tragacanth 3 57 4 43 4 99 2 03 0 27 0 72 0 27 0 54 0 20
Station 1 3 3 1 2 1 2 1 2
P3 100
3 4 5 2 0 0
66 38 02 06 23 60 0 31 0 55 0 32
Table I I I . Recovery of Lead Sulfate in Simulated Lead Dioxide Candles PbSOL, m g
Added
Found
% Recovery
15.0 30.0
14.9 30.0 58.0 95.1 303.4 493.3 660.5
99.3 100.0 96.7 95.1 101.1 98.6 94.4
60.0 100.0 300.0 500.0 700.0
A v . 97.9
Table I V . Results from Duplicate Exposed Lead Dioxide Candles Analyzed by Two Methods SO3 mg per 100 c m 2 day
Month
January February June July
August
September
Weeks
Gravi-
Atomic
Station 1 2 3 2 3
exposed 4 1 4 4 4
metric
absorption
1
4
2 2 1 2 2 1 2 2 1 2 2
4 1 4 4 1 4 4 2 4
3 57 0 26 4 43 0 53 4 99 2 03 0 27 0 46 0 72 0 27 0 35 0 54 0 35 0 28 0 07 0 32 o 28
3 62 0 26 4 40 0 55 5 01 2 15 0 22 0 33 0 67 0 20 0 28 0 58 0 27 0 27 110 0 27 0 29
4
2
Volume 7, Number 11, November 1973
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T h e atomic absorption method has been used for over a year in this laboratory t o analyze both urban a n d rural lead candles. This method provides a rapid a n d economical approach for t h e laboratory analysis of lead candles used to evaluate atmospheric sulfation in monitoring and surveillance programs. Approximately 25 lead candles can be analyzed in one man-day using t h e atomic absorption procedure compared t o a week or more using t h e gravimetric procedure. T h e atomic absorption method should be applicable to other types of lead dioxide samplers such as sulfation plates. Acknowledgment The authors t h a n k C. S. Nevin of t h e A. E. Staley Manufacturing Co. for his consultation a n d initial s a m ples of P3-100 resin. Thanks are also given to Jacqueline Dohm and Lois Fox for sample preparation and handling
during many of t h e analyses. Special thanks are extended to Robert Jorgen for his contribution t o this study. Literature Cited Am. SOC.Testing Materials, ASTM Standards Industrial Water, Atmospheric Analysis, p 813, 1966. Bowden, S. R., Int. J. Air Water Pollut., 8, 101 (1964). Huey, N . A., “The Lead Dioxide Estimation of Sulfur Dioxide Pollution.” 60th Annual Meeting APCA. Cleveland. Ohio. Paper No: 67-198, 1967. Kanno. S., Int. J . Air Pollut., 1, 231 (1959) Rayner, A. C., J . Air Pollut. Contr. Assn., 16,418 (1966) Vijan, P. N., Enuiron. Sci. Technol., 3,931 (1969). Y
Received for recieu February 8, 1973. Accepted July 20, 1973. Presented a t the 8 t h M i d u s t Regional Meeting of the American Chemical Society, Nocember 8-10, 1972. The use of brand names for specific chemicals or equipment and names of their suppliers does not constitute an endorsement by the Health Department or S t . Louis County.
Levels of Copper, Nickel, Rubidium, and Strontium in Institutional Total Diets Gopala K. Murthy,’ Ulysses S. Rhea, and James T. Peeler Food and Drug Administration, U.S. DeDartment of Health. Education, and Welfare, Cincinnati, Ohio 45226
The average trace element content in the diets of institutionalized children, aged 9 to 12, from 28 U.S. cities, expressed as mg/kg of food, varied as: copper, 0.4380.873; nickel. 0.140-0.321; rubidium, 0.601-2.338; and strontium, 0.319-0.957. Similarly. the consumption of food varied from 1.18-2.55 kg/day and t h e milk content of diet varied from 9.5-63.870. Minerals from drinking water were not included in the study. Statistical analyses of the data ( m g / d a y ) showed significant seasonal a n d geographical variations. hlonthly averages for all elements showed that copper was slightly higher during summer, rubidium and strontium tended to peak during spring and autumn. and no trend could be ascribed to nickel. The low and high levels of trace elements observed in different geographical areas are briefly discussed. In a previous paper (Murthy et al., 1971). we reported the levels of antimony. cadmium, chromium, cobalt, manganese. and zinc in institutional total diets. The present paper is concerned with the levels of copper ( C u i . nickel ( X i ) , rubidium ( R b ) . and strontium ( S r ) in the same samples. Most of the available d a t a on trace elements (Cu, Xi. Rb. and S r ) in foods pertain to individual components of the diet (El-Gindy. 1959; Golvkin and Kraynova. 1969; Gormican. 1970; Il’vitskii a n d Asmaeva, 1969; Kleinbaum. 1962; Leshchenko et al., 1972; Los and Pjatnickaja, 1962; Malina a n d Klyachko, 1969; Murthy e t al., 1967; Schlettwein-Gsell and Mommsen-Straub, 1971a,b; Schroeder et al., 1962; Schroeder et al., 1966; Tsvetkova, 1969; Jaulmes and Hamelle. 1971; and Stephanov et al., 1970) with very little d a t a on total diets. Kent and McCance (1941) studied ingestion by humans of Ni from ordinarv diets. Harrison et al. (1960) deter1
To whom corre?pondence should be addressed.
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Environmental Science & Technology
mined the S r balance in children maintained on normal diets and reported S r intake over a 12- to 18-day period. Similarly, Bryant et al. (1958) analyzed various foods in different regions of England and Wales and reported the average dietary intake of Sr. Yamagata (1962) determined R b intake by analyzing the diets of urban and rural adults and children in J a p a n . Feldman and Jones (1964) determined several trace elements by spectrographic analyses of institutional diets from 10 cities in t h e Ynited States. Zook a n d Lehmann (1965) analyzed total diets prepared from basket foods and computed the intake of certain trace elements by children receiving 4200 calories per day. Tipton et al. (1966) reported d a t a on diets and excreta of two human subjects maintained on a normal diet for a 30-day period. Tipton et al. (1969) reported d a t a on diets and patterns of elemental excretion in long-term balance studies. Engle et al. (1967) determined ingestion of certain trace elements by preadolescent girls maintained on measured amounts of diets. Soman et al. (1969) determined total intake of certain trace elements from diets of different ethnic groups in India. Rehnberg et al. (1969) determined Sr in the institutional total diets and milk collected from southeastern Cnited States. Murphy et al. (1971) analyzed type A school lunches for certain trace elements. White (1969) analyzed forty-eight 24-hr weighed samples of diets of high school girls and college women for various trace elements. Meranger and S m i t h (1972) analyzed various components of the Canadian diet and estimated daily intake of several trace elements. No systematic analyses of diets have been made for extended periods, however. to determine variations attributable to geographic location and season. E x p erim e n t a 1
M a t e r i a l s . Samples used in this study. including description and method of collection. have been described previously ( l l u r t h y et al. (1971)). The samples were homogenized by a n electric blender in a stainless steel con-
