Determination of Selenium in Solid Waste Henry Johnson Bureau of Solid Waste Management, US.Department of Health, Education, and Welfare, Cincinnati, Ohio 45213
Selenium was determined to be present in solid waste and related materials. Quantitative measurements were made by spectrophotofluorescence with 2,3-diaminonaphthalene as the reagent. Data are reported on various types of paper, municipal solid waste, incinerator stack emissions, incinerator quench waters, incinerator residue, and compost samples. Most emphasis was placed on emission of selenium into the environment as a result of incinerating solid waste. The highest concentration observed was 14.5 gg. per gram of particulate matter collected in a stack emission sample. Maximum values of 0.014 mg. per liter and 0.023 mg. per liter were observed for an incinerator residue quench water and an incinerator fly ash quench water sample, respectively.
S
ince approximately 70% of the almost 1 billion pounds of solid waste collected per day in the United States is paper (U.S. Department of Health, Education, and Welfare, 1967) and since selenium is known to be present in almost all conceivable types of paper (West, 1968), regardless of the source, the possibility of environmental exposure to selenium is ever increasing through solid waste handling, processing, and disposal. Although trace amounts of selenium have been shown to be nutritionally beneficial in some animal diets (Schwartz and Foltz, 1957), exposure to higher concentrations produces toxic effects (Cerwenka and Cooper, 1961), and there are implications that selenium is a carcinogen (Chem. Eng. News, 1967). It is therefore of great importance to determine the extent to which solid waste handling, processing, and disposal are contributing selenium to the environment. This report contains the results of the analysis of municipal solid waste (such as garbage and trash), incinerator residue, stack particulate emission, fly ash quench water, residue quench water, finished compost, and various kinds of paper commonly found in municipal refuse. Experimental Apparatus. A Farrand Mark I spectrofluorometer with 10-mm. slits and with an RCA IP21 phototube was used. The readings were corrected for fluctuations in the source intensity with a 1 pg. per ml. standard solution of quinine in 0.1N HzS04.A Wiley mill fitted with a 10-mesh screen or a Williams patent hammermill and double-cone homogenizer were used on refuse, compost, and paper samples before pelletizing and ashing in a Parr bomb calorimeter. A Beckmanzeromatic was used to monitor pH adjustments. Reagents. Analytical grade reagents included HC1, NaOH, H N 0 3 , 72 % HC104, ethylene chloride, carbon tetrachloride, cyclohexane, NaF, Na2CzO4,and EDTA (disodium salt). Two white-labeled chemicals, 2,3-diaminonaphthalene (DAN) 850 Environmental Science & Technology
(Aldrich Chemical Co.) and toluene-3,4-dithiol zinc salt (Eastman Organic Chemicals), were used as received. Sample Preparation. Most samples of municipal solid waste, compost, and paper were ground in a Wiley mill, but some of the municipal solid waste samples were run through a hammermill and a double-cone homogenizer (Table I). After grinding, the material was dried at 100" C. overnight, and 1-g. samples were pelletized and ashed in a Parr bomb (Dye, Bretthauer, et al., 1963) using 10 to 15 ml. of water as an absorbing solution under 30 atmospheres of oxygen pressure. The bomb was tap cooled for 10 min., and excess oxygen was released over a 2-min. period. The bomb contents and washings were filtered through Whatman no. 12 filter paper, and the volume was adjusted to 25 ml. Glass fiber Millipore filters containing particulates collected by isokinetic stack sampling were placed in a 100-ml. beaker, to which was added 15 ml. of a 10 to 1 "03 and HClOl acid mixture. The mixture was heated cautiously to remove oxides of nitrogen. After 25 ml. of water had been added, the solution was brought to a boil, allowed to cool, and passed through a sintered glass filter, The volume was then adjusted to 50 ml. One-gram samples of incinerator residue were extracted in the same manner. Residue quench water and fly ash quench water samples were filtered through Whatman no. 12 filter paper and stored until analyzed. Procedure. The DAN analytical procedure (Watkinson, 1966) was preceded by isolation of selenium with toluene3,4-dithiol (Watkinson, 1960) and included the use of EDTA, sodium fluoride, and sodium oxalate masking agents (Lott, Cukor, et al., 1963). A 25-ml. sample, or aliquot containing not less than 0.01 pg. of selenium, was placed in a 125-ml. separatory funnel. The volume was adjusted to 35 ml. with water and 50 ml. of concentrated HCl was added. To this was added 4 ml. of a freshly prepared 1% zinc dithiol suspension (Clark, 1957) in ethanol, The solution was mixed and allowed to stand 15 min. The solution was extracted with 5- and 10-ml. portions of an ethylene chloride and carbon tetrachloride mixture (1 to I), and the organic phases were combined in a stoppered test tube. After the addition of 1 ml. of 72% HC104and 10 drops of concentrated H N 0 3 ,the tube was placed in a boiling water bath to remove the organic solvent. The tube was then cautiously heated with a burner until HClOl fumes evolved. One milliliter of water was added, the tube was reheated until HClO, fumes were emitted, then 10 ml. of water was added. The pH was adjusted to 2 with NaOH, and 0.5 ml. each of 0.1M aqueous solutions of EDTA, NaF, and Na2C204 were added. The pH was readjusted to 2 with HC1, and 5 ml. of freshly prepared DAN (0.1 in 0.1N HCl) was added. The tube was placed in a 50" C. water bath for 20 min. and then tap cooled. Contents of the tube were transferred to a 125-ml. separatory funnel containing 10 ml. of cyclohexane. The solution was extracted and the organic phase collected
in a centrifuge tube. The tube was centrifuged at 2000 r.p.m.
for 2 min. and then read in the spectrophotofluorometer, exciting at 370 mp and emitting at 517 mp. All runs included a 1-pg. standard of selenium prepared with Na2Se03.
Results and Discussion The investigation of selenium emission from solid waste processing was based primarily on incineration. Data were compiled on the selenium content of the types of paper commonly found in solid waste, and the levels of selenium found in these materials give an indication of the potential selenium emission that may result from incineration (Table I). Since selenium is not uniformly distributed in paper (West, 1968), the average and the range of selenium residue are given for several determinations. Variation seen in the amount of selenium residue in municipal solid waste samples is also caused by the nonhomogeneity of the samples. In an attempt to create a homogeneous sample, 2280 pounds of municipal solid waste were ground in a large hammermill. Of this amount, 175 pounds was placed in a double-cone homogenizer and 1-g. samples were subsequently analyzed (Table I). Municipal solid waste 2 (Table I) was treated in the same manner, but only 366 pounds was ground in the hammermill, and the entire amount was blended in the double-cone homogenizer. The selenium concentration of 1-g. samples from municipal solid waste 2 was somewhat lower than that in the samples from municipal solid waste 1, but both types showed higher concentrations than municipal solid waste 3 (Table I) and the municipal solid waste grab samples of several pounds ground in a Wiley mill (Table 11). Overall, municipal solid waste samples of similar size were comparable in concentration regardless of sample source and grinding method. Further information was obtained from analyzing a synthetic solid waste sample made in the laboratory by mixing paper, food, and grass and leaves in a 60:20:20ratio by weight. Though all of the various types of
materials found in municipal solid waste were not present in the synthetic sample, the results obtained were within the range of results found for municipal solid waste, which probably indicates that food, garden, and especially paper waste are the major contributors of selenium in solid waste. The data on fly ash quench water, residue, residue quench water, and stack samples from two different incinerators (Table I) give an indication of the amount of selenium emitted into the environment as a result of incinerating solid waste. As might be expected, because of selenium’s volatility, the highest concentrations of the element were seen in the stack gases and fly ash quench water. Smaller amounts were found in the residue and residue quench water. The two stack emission samples from Incinerator I1 showed quite different selenium concentrations based on the weight of selenium per weight of particulate collected; but this difference was the result of having an electrostatic precipitator upstream from the sampling point in one case and downstream from the sampling point in the other. The concentrations of selenium based on the volume of gas sampled were almost identical in both cases. Thus, the electrostatic precipitator had little effect on removal of selenium and its compounds from the emission gases. Further data on selenium emission by incineration were obtained in a three-day study of one incinerator. Concentrations of selenium found in the various samples were determined (Table 11), and by hand sorting 200 pounds of refuse, the general composition of the incoming solid waste to be burned during the three days was established (Table 111). Although the sorting was done by another group more interested in the operation of the incinerator from an engineering standpoint, the information on municipal solid waste composition is very useful in interpreting and even predicting chemical data. The highest concentrations of selenium were found in the stack emissions. The relative decrease of selenium seen in the fly ash quench water along with an increase in the residue
Table I. Determination of Selenium in Solid Waste and Solid Waste-Related Materials No. of samples
Av.
Newspaper Cardboard Laboratory tissue
8 8 4
8.6 2.8 7.1
2.3-18.3 1.6-5.1 1.6-19.5
Municipal solid waste 1. Municipal solid waste 2. Municipal solid waste 3 6 Synthetic refuse
2 4 3 3
4.41 1.08 0.49 4.5
4.08-4.74 0.92-1.30 0.29-0.59 3.07-5.9
Incinerator Incinerator Incinerator Incinerator Incinerator Incinerator
1 1 1 1 1 1
0.7g 14.9
3 3
0.76 0.43
hfaterial
ICfly ash quench water
I residue quench water I residue I tap water 11. stack emission/ I1 stack emissionh
Finished compost A Finished compost B 5
/.tg./g. d.wt.
Range
mg./liter
Stack emission __ lb. &/ton /.tg.lM3 refuse
8.82 2.16 9.80
x x x
3.65 3.76
x x
10-3 10-3 10-4
0.023 0.003 0.003 d
0.23 0.24 0.54-0.91 0.38-0.52
Ground in hammermill and blended in double-cone homogenizer.
* Ground in Wiley mill.
Reciprocating grate, continuous feed 300-ton-per-day capacity, two furnaces operating. None detected. Conical burner, continuous feeding with screw conveyor, 0.595 ton per hour burned, f Inlet of electrostatic precipitator. p Micrograms of selenium per gram of particulate collected. Outlet of electrostatic precipitator. e
Volume 4, Number 10,October 1970 851
Table 11. Three-Day Incinerator. Study for the Determination of Selenium NO. of d g . d.wt. Stack emission Material samples Av. Range mg./liter 1g./M3 lb. Se/ton refuse Av. Range Av. Range 1st Day municipal solid waste 3 0.55 0.42-0.69 Residue 1 0.10 b Residue quench water 1 Fly ash quench water 1 0.005 Stack emission 3 8.44' 3.65-14.12 2.29 1.69-3.18 4 . 5 X IO-' 3.37 X 10-"6.26 X lo-' 2nd Day municipal solid waste 3 0.59 0.34-0.80 Residue 1 0.08 b Residue quench water 1 Fly ash quench water 1 0.005 Stack emission 2 2.43' 1.95-2.91 0.78 0.41-1.14 1.59 X 10-j 8.90 X 10---2.28 X 3rd Day municipal solid waste 3 0.52 0.50-0.55 Residue 1 0.11 b Residue quench water 1 Fly ash quench water 1 0.014 b Stack emission 4 a
Traveling grate, two furnaces, continuous feed, 22-ton-per-hour capacity, one furnace operating. None detected. Micrograms of selenium per gram of particulate collected.
Table 111. Municipal Solid Waste Composition during a Three-Day Incineration Study Type of solid waste by wt.) Tons burned in Food 23 hr. waste Garden Paper Plastic Textiles Wood Metal
(z
Day
1st Day 2nd Day 3rd Day Av.
241 247 245 244
14.1 0.5 13.8 9.5
0.9 0.2 1.4 0.8
68.6 60.4 54.9 61.3
indicates a more eficient burning in Incinerator I (Table I) than in the incinerator used for the three-day study (Table 11). The daily results obtained from the three-day study were consistent with each other, except that on the third day, no selenium was detected in the stack emission sample. This absence is not totally accounted for by the decreased paper content in the refuse and the increased selenium concentration in the residue and fly ash on the third day. It must be remembered, however, that since the entire 200 pounds of sorted material was not actually burned during the sampling period, the composition values of municipal solid waste are only indications of what might be expected from refuse incineration. Another solid waste processing method that must be considered as a source of environmental exposure to selenium is the composting process. The use of compost as a soil conditioner creates the possibility of increasing the selenium content of the soil and subsequently affecting its vegetation and water runoff. The selenium concentration in finished compost material from two different compost plants were compared, and the levels seen, 0.4 to 0.9 pg. per gram, were within the range found for raw refuse (Table I). These values are similar to those found for normal soils and although an additive effect might be seen, the level of selenium in compost-treated soil would remain below toxic levels of 2 to 10 pg. per gram found in seleniferous areas (Bear, 1964).
Conclusions Data have been reported on the emission of selenium to the environment as a result of various solid waste disposal processes. Particular attention has been given to incineration, 852 Environmental Science & Technology
0.9 12.0 3.2 5.4
0.9 1.9 0.0 0.9
4.1 10.2 2.8 5.7
1.4 5.8 10.4 5.9
Glass
Inerts
7.3 2.8 3.5 4.5
1.8 6.2 10.0 6.0
since samples could easily be collected in conjunction with another group interested in incinerator operation parameters. To confirm the implications of the selenium increase that occurs in our environment through the use of compost and landfill operations, soil and groundwater must be investigated. When a degree of representativeness of solid waste samples has been established, other means of disposal can also be investigated as potential environmental pollution mechanisms for selenium as well as other toxic materials. Interpretation of present and subsequent data will be greatly enhanced by refinements in solid waste sampling and by the firmer establishment of environmental tolerance levels for selenium. In the data presented here, maximum values of 0.002 mg. per m.3 and 0.014 mg. per liter are reported for stack emission and quench water samples, respectively. These values compare favorably with presently recommended levels of 0.2 mg. per m.3 for an 8-hr.-day working environment (Amer. Conf. Govt. Ind. Hyg., 1969) and 0.01 mg. per liter (McKee and Wolf, 1963) for drinking water. Further work will establish whether similar results are obtained when seasonal and geographical variations as well as extreme changes in refuse composition are considered. Ackno wledgrnent The author thanks the Technical Assistance and Investigation Branch, Division of Technical Operations, Bureau of Solid Waste Management, for the provision of incinerator effluent samples and incinerator operating information, and the Waste Handling and Processing Branch of the Division of Research and Development, Bureau of Solid Waste Management, for hammermill samples.
Literature Cited American Conference of Governmental Industrial Hygienists, 31st Annual Meeting, Chicago, Ill., May 1969. Bear, F. E., Ed., “Chemistry of the Soil,’’ 2nd ed., Reinhold, New York, 1964, p. 134. Cerwenka, E. A., Cooper, C. W., Arch. Enciron. Health 3, 71-82 (1961). Clark, R. E. D., Analyst 82, 182 (1957). Dye, w. B.9 Bretthauer, E., S e h H. J.3 Blincoe, c.3 Anal. Chem. 35, 1687-93 (1963). Lott, P. F., Cukor, P., Moriber, G., Solga, J., Anal. Chem. 35,1159-63 (1963). McKee, J. E., Wolf, H. W., “Water Quality Criteria,” California State Water Quality Control Board, Pub. No. 3-A, 253 and 254, 1963.
Schwartz, K., Foltz, C. M., J. Amer. Chem. Soc. 79, 3292 and 3239 (1957) u.s. Department Health, Education, and Welfare, Public Health Service Pub. No. 1729, “The Surgeon General’s Conference on Solid Waste Management,” 1967. Watkinson, J. H., Anal. Chem. 32, 981-3 (1960). Watkinson, H., ibid. 38, 92-7 (1966). Chemical and Engineering News, 45 (23), 12 and 13, May 29, (1967) west, p. w:, ~ ~stateuniversity, ~ ~~t~~ i R ~ ~ L ~ .~ i, private communication, 1968.
Af
J.
Received for reuiew January 5, 1970. Accepted May 18, 1970. Mention of commercial products does not constitute endorsement by the US.Public Health Service.
COM M UN I CAT1ON
Syringe Sampling Technique for Individual Colorimetric Analysis of Reactive Gases Marston C. Meador and Robert M. Bethea Chemical Engineering Department, Texas Tech University, Lubbock, Texas 79409
A flow apparatus for continuously producing small quantities (up to 280 liters per hour) of humidified air containing constant known amounts of atmospheric contaminants is described. Contaminant levels up to 400 p.p.m. NOz, SO?,CL are reproducibly maintained for periods in excess of eight days by use of Teflon permeation tubes filled with the desired material. A comparison of the standard bubbler technique, and glass and polypropylene syringe gas sampling showed the polypropylene syringe technique to be superior for the analysis of NO? by the Lyshkow-modified Saltzman method over the range 0.07 to 60 p.p.m. of NOr in air. The improved syringe technique was extended to the colorimetric analysis of SO2, Clz, HC1, and H F in dynamically polluted air. The Lyshkow method for SO?is applicable in the range of 0.17 to 50 p.p.m. The orthotolidine method for free chlorine is applicable in the range of 0.12 to 50 p.p.m. The modified method of Iwasaki, Utsumi, et al. (1956) for HCl is satisfactory in the range of 0.5 to 50 p.p.m. The bleaching reaction of Andrew and Nichols (1961) for H F is marginally acceptable in the 5 to 50 p.p.m. region.
I
n recent research to study the removal of trace amounts of reactive contaminants (NO2, SO?, Cln, HCl, and HF) from simulated spacecraft atmospheres, several methods were evaluated from a microkinetic viewpoint. Evaluation of the removal techniques required analytical capability for each reactive gas in the range of 1 to 50 p.p.m. This report is an account of the development of a combined, single-step syringe sampling technique for the individual analyses of NO>,SOr, C ~ ZHCl, , and H F in dynamically polluted air by colorimetric techniques. Experimental
The experimental system consisted of two distinct systems. The first system was an atmosphere preparation train capable of providing a reliable supply of synthetically prepared, polluted air of specified composition, humidity, and pressure.
The second system consisted of the sampling and analysis sections. Atmosphere Preparation Subsystem. Oil-free, breathablegrade air containing no measurable amounts of any reactive gas was supplied in commercial compressed air cylinders. The air passed through a standard pressure regulator, through a microfilter, and then through a flow regulating needle valve. A Hastings-Raydist mass flowmeter (model LF-20K) was used to measure the air flow. After flow measurement, the dry air was then split into two streams. One of these streams was then routed through a flow control valve to a water-filled, ceramic packed humidification tower. The humidifier was a 150-cm.-long section of 15.3-cm.4.d. steel pipe packed with 1.2-cm. ceramic Berl saddles. The cross-sectional area in the humidifier lowered the linear air velocity sufficiently so that water entrainment was not a problem. The fully saturated air was then combined with CO? and mixed with contaminated air. The CO? concentration was adjusted to the desired level by metering C 0 2 through a Brooks rotameter (model R-2-15AA, 15-cm. tube, spherical stainless steel float with integrally mounted Flo-Mite needle valve and differential pressure regulator) into the air stream after the humidifier. The other air stream was passed over a sealed Teflon tube which contained the pure liquid contaminant. The contaminant diffused through the walls of the tube into the flowing air stream. This stream of contaminated air was mixed with the humid air containing CO? to yield air at 50 relative humidity, 22” C., containing 0.5 % C 0 2 ,and the desired contaminant level. The combined air stream then passed into a manifold and split into constant composition streams for absorption and kinetic studies. The pressure control valve maintained a constant pressure in the system downstream of the flow control valve and vented any excess contaminated air. AS this system was designed to produce contaminated air in quantities suitable for small-scale studies, the volume available for analyses was small: approximately 5 of the system output of 280 standard liters per hr. Permeation Tube Technique. The Teflon (FEP) permeation tubes were used in two ways: to serve as direct calibration Volume 4, Number 10, October 1970 853
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