Envlron. Scl. Technol. 1986, 20, 684-689
Rapid Changes in Peat Fly Ash Mutagenicity after Release into the Atmosphere: A Controlled Dilution Bag Study Matt1 J. Jantunen,* t Arl Lllmatalnen,t Thomas Ramdahl,591i and Ahtl Itkonent Department of Environmental Hygiene and Toxicology, National Public Health Institute, Neulaniementie 4, SF 7021 0 Kuopio, Finland, University of Kuopio, 7021 1 Kuopio, Finland, and Center for Industrial Research, Blindern, 0314 Oslo 3, Norway
Effects of moisture condensation on fly ash mutagenicity, when the effluent of a peat-fired power plant is dispersed into cold and humid air, were investigated. A 140-m3flow-type dilution bag was used to dilute flue gas collected after the electrostatic precipitator with ambient air and to age this mixture for approximately 2 min. Fly ash was sampled by size fractionating aerosol samplers preand postdilution. Organics were extracted from the samples, fractionated by semipreparative high-performance liquid chromatography, and assayed for mutagenicity by the Ames method (TA98 and TAlOO with and without S9). The smallest particles were the most mutagenic in both pre- and postdilution samples. Mutagenicity of the fly ash increased strongly in the dilution bag. This was most pronounced in the medium- and low-polarity organic fractions. In the predilution samples most of the mutagenicity was found in the most polar fraction. Postdilution of this fraction showed a modest increase for TA98 and TA98 S9 but not for TAlOO or TAlOO + S9. Direct mutagenicity and mutagenicity with activation were comparable. In the postdilution samples most of the mutagenicity was found in the nonpolar and medium polarity fractions. The mutagenicity of the nonpolarity and medium polarity fractions increased strongly after aging 2 min in the mixing bag. In these fractions predilution mutagenicity with and without activation was comparable. Following dilution and aging the mutagenicity with activation increased to a much greater extent than the direct mutagenicity. W
+
Introduction The production of energy often involves combustion of carbonaceous fuels: oil, coal, gas, or biomass. Incomplete combustion of these fuels produces toxic byproducts, which are emitted into the environment. Many of these compounds exhibit mutagenic and carcinogenic properties (1, 2 ) . Coal fly ash contains both inorganic (3) and organic (4) mutagens. Polycyclic aromatic hydrocarbons (PAH) and several more polar derivatives of PAH, like nitro-PAH (5),polycyclic aromatic ketones (6),and quinones (3, are among the most frequently identified mutagens in combustion emissions. Many of these organic substances react in the atmosphere with copollutants such as NO,, SO,, Ox, and free radicals (8). As a result of these reactions the initial mutagenicity of the organic matter may be altered. This has been observed, for instance, with automobile emissions, where a shift toward more polar mutagenic compounds has been observed as the emissions age in the atmosphere (9). The atmospheric fate of organic emissions is usually studied in reaction chambers under controlled conditions. One approach has been to fill outdoor Teflon chambers with exhaust gases (10) or flue gases (11,12) and air and to expose them to sunlight and injected copollutants. In t National
Public Health Institute. *University of Kuopio. Central Institute for Industrial Research. "Present address: Norsk Hydro A.S., P.O. Box 4313, N-5013 Nygaardstangen, Norway. 684
Environ. Sci. Technol., Vol. 20, No. 7, 1986
Table I. Statistics of the Variations of the Major Operation Parameters of the Studied Boiler Plant during Sampling (n = 997-1078)" parameter
mean
SD
min.
max.
fuel heat input, MW 131 24 39 218 proportion of heat from oil, % 9.2 1.8 76 flue gas temp, K 414 7.2 395 442 effective heat value of peat 21.1 0.3 20.4 21.5 dry subst, MJ/kg peat moisture, % 40.5 47.4 2.1 51.5 flue gas 02, % 5.7 1.1 4.0 10 flue gas flow, H,O-free 0.482 0.534 0.01 0.556 (m3/MJ), at STP, 10% C02 outdoor temp, K 274.6 271.0 279.3 "All data obtained from the plant control eauipment.
these studies flue gas concentrations have been low and reaction times long (4-8 h). In a study of the mutagenicity of wood combustion products Kamens and co-workers observed a transformation of the emissions with time into more polar mutagenic substances (11), in agreement with the results from the automobile emissions study mentioned earlier. When Kamens and co-workers tested dilute wood and peat smoke in outdoor chambers, they found that aging or sunlight alone did not increase the mutagenicity. In dark 3-h experiments, using tester strain TA98 - S9, addition of 0.57 ppm of O3increased the mutagenicity by a factor of 4.4, addition of 0.54 ppm of NOz by a factor of 4.1, and addition of 0.37 ppm of O3 with 0.55 ppm of NOz by a factor of 19. The enhancement of direct-acting mutagens occurred within minutes. Metabolic activation with S9 strongly increased the initial mutagenicities of the samples but had a varying effect on the final levels (12). When low-grade organic fuels with high moisture content are burned, the flue gas may contain up to 30% HzO. Released into cool and humid atmosphere, this moisture condenses on smoke particles, and a transient cloud of water aerosol is formed. Numerous gaseous flue gas components are water soluble and reactive. Flue gas contains fine fly ash particles, which are coated with a thin layer of metals and metal oxides (13, 14). Some of these metals can act as catalysts, and in water droplets, which absorb SO, and NO,, conditions for chemical transformations of organic compounds should be favorable. Our research hypothesis was that organics adsorbed on the fly ash particles will undergo chemical transformations, which affect their mutagenicity, when water condenses on these particles in the plume. Experimental Section A 200-MW corner fired boiler, fired with milled peat (90-95%) and residual oil, in a municipal electric power and heat generating plant, was chosen for this study. Its operation parameters during our sampling were obtained from the plant control room and are presented in Table I. The power level varied considerably due to test runs of the new boiler. The plant is equipped with an electrostatic precipitator (ESP). As milled peat contains
00 13-936X/86/0920-0684$01.50/0
0 1986 American Chemical Society
RESIDENCE
TIME
100
-
120 s
HIGH VOLUME SAMPLER W I T H A 4 STAGE IMPACTOR
w
CASCADE C E N T R I P E T E R - PARTICULATE s A r m i . R
-
GASEOUS SAMPLER
Figure 1. Flue gas and amblent air mixing apparatus with the locations and types of samplers.
40-55% H20, the flue gas H20 content is high, ranging from 15 to 25%. Apparatus. The exerimental apparatus presented in Figure 1 was used to sample large quantities of flue gas, to emit it into a constant flow of ambient air, and to age this mixture for a few minutes. This dilution bag was located outdoors. The largest bag, which would fit the available space at the ESP platform of the power plant, was prepared from reinforced, undyed white and translucent PVC-cloth, originally produced for food packing. Samples of several alternative materials were prepared for mutagenicity tests and tested by the same procedure as the flue gas sampling filters. The chosen PVC-cloth released no mutagenic extracts in any test with TA98 or TA100, with or without S9. Sampling. Flue gas was sampled from the stack through a 100 mm i.d. insulated aluminum tubing and a small flue gas blower. Because sampling temperatures around 100 "C are critical for condensation of combustion product mutagens ( 4 ) ,the flue gas was cooled to 70-90 "C by mixing with ambient air in a 1 to 1ratio to maximize organic vapor condensation before sampling. Any water condensation at this stage would have flooded our predilution sample. The overall sampling duration was 268 h, out of which 97 h were lost in eight intervals for either power plant failures or sampling equipment problems. Filters were changed according to particulate loading, on the average, every 2 h. Before dilution a side flow of 1.5 L/min was taken, dried in a permeation distillation dryer (Permapure), and analyzed for C02,SO2,NO, and CO by a portable single beam, variable path IR analyzer (Wilks Foxboro, Miran 1A) (15). Fly ash was sampled by University of Kuopio modified cascade centripeters (Bird & Tole), with four centripeter stages and a backup filter (15). After the 140-m3dilution bag a standard GMW highvolume sampler with a four-stage slot impactor (Sierra series 230) was used for particulate sampling. To prevent the sampled fly ash from being washed from the filters, the sample flow was dried by heating to 30-40 "C with an electrical wire heater. Gas temperatures were monitored in the stack, in the flue gas sampling manifold, outdoors, in the diluted flue gas flow at the end of the bag, and just
Table 11. Temperatures Involved in the Sampling System
("C) av
flue gas in stack flue gas in the sampling manifolda outdoor air flue gas-air mixture in the bag heated sample before the Hi-Vol sampler
range
141 122-169 83 64-96 1.5 -2.2-6.1 16 9-23 34 30-40
To maximize organic vaoor condensation.
before the high volume sampler. Mean temperatures and their ranges are given in Table 11. Sampling was continued fram 11-16-1982 at 03.00 to 11-27-1982at 07.30. The weather varied little during the period. It was mostly overcast, windy, cold (-2.2 to +6.1 "C), and humid (75-100%). Average daylight hours were 09.00-15.00, with the maximum height of sun at 6". The water vapor content in the dilution bag was assumed to be equal to 100% RH, as condensation was visible at all times. The total water content in the bag air was computed from the measured water and known hydrogen content of the fuel peat and the relative humidity observed at the local airport weather service. The mixing ratio could not be kept constant but varied due to the load-related presure variations in the flue gas channel. Actual mixing ratios were computed from heat balance. The water aerosol content in the bag was computed by subtracting the water vapor from the total water. All sampled particle size fractions were studied by scanning electron microscopy to determine particle sizes and shapes. The backup filter of the slot impactor contained the smallest but also some of the largest particles, presumably due to particle bounce. Because condensation prefers the smallest particles (13), particle bounce in effect lowers the organics concentration in the backup filter sample. Extraction. All particulate samples of a given size fraction, as well as the two largest size fractions ( d A> 13 pm) of the predilution samples, were combined to obtain enough organic extract for chemical fractionation and mutagenicity tests. Therefore, the mutagenicity test results represent a single integrated value for each particle Environ. Sci. Technol., Voi. 20, No. 7, 1986
685
Table 111. Step Gradient Program for Fractioning of Peat Fly Ash Organics time,min
% hexane
% DCM
% ACN
0-10 10-29 29-39 39-44 49-74
95 95-0 0 0 0
5 5-100 100 100-0 0
0 0 0 0-100 100
Fractions were collected at the following times: I, 0-19 min; 11, 19-35 min; 111, 35-50 min; IV, 50-74 min. Solvent flow rate was 2.0 mL/min.
size range and polarity fraction for the sampling period. The centripeter and impact filters were Soxhlet extracted for 24 h with dichloromethane (DCM). Aliquots of the extracts were filtered through a PTFE membrane filter (0.5 pm, Millipore) and reduced to approximately 100 pL under a gentle stream of nitrogen at approximately 30 "C. Fractionation was performed with a Waters HPLC system consisting of two Model 600 A pumps, a Model U6K injector, a Model 720 system controller, and a Model 440 absorbance detector operating at 254 nm. The column was a 300 X 7.8 mm i.d. semipreparative pPorasil column (Waters). The column was flushed with acetonitrile (ACN), with DCM, and finally for 15 rnin with a mixture of 5% DCM in n-hexane to establish a blank. The samples
were quantitatively injected onto the column and fractionated by using the program shown in Table 111. Before each separation the mobile phase was reverse-programmed to the original elution conditions, and the column was flushed for 15 min with 5 % DCM in n-hexane (16). Mutagenicity Testing. The HPLC fractions were evaporated, dissolved in 1 mL of dimethyl sulfoxide (Me2SO),and assayed by the Ames Salmonella/microsome test using tester strains TA98 and TAl00 with and without metabolic activation (Aroclor 1254 induced rat liver homogenate, 10% S9 in S9 mix) (17). Tester strains were kindly provided by Dr. B. Ames, and their genotypes were regularily checked by the recommended procedures (17). All tests were made in duplicate and average values were used. Background and positive control test results are given in Table IV. Mutagenicity, measured as the slope of the initial part of the dose-response curve (net revertants vs. milligrams of fly ash), was computed by zero-forced regression analysis. Mutagenicity levels are presented as revertants for a given polarity and particle size fraction in 1 g of fly ash. Therefore, the total mutagenicity of the fly ash is
where i = polarity fractions 1-4, j = particle size fractions 1-5, and m = total mass of fly ash in the sample.
Table IV. Background and Positive Control Mutagenicity Test Results background tests mean rev" no. of per plate f SD plates TA98 TA98 + S9 TAlOO TAlOO S9
25 f 4 31 f 5 168 A 20 157 A 18
+
45 36 44 36
amount used per plate, pg
positive compd used 4-nitrophenylenediamine benzo[a]pyrene sodium azide benzo [a]pyrene
control testa mean net rev per plate f SD
5 2
1400 f 14 380 f 70 450 f 60 660 f 170
1 2
no. of plates 7 14 7 14
Mean rev, mean revertants. Table V. Statistics of the Basic Pollutant Emissions of the Studied Boiler Plant during S a m p l i n e emission
mean, ng/JC
med.
total partic d A < 1.5 pm 1.5-4.6 pm 4.6-13 pm 13-52 pm 52 pm > d A
140 29 39 52 13 10 27 120 250
73 16 17 25 4.6 2.7 24
co
NO
so2
SD, % of mean
Sgb
min., ng/J
3.7 3.1 4.2 4.5 6.2 5.6 1.7
8.4 2.2 0.52 1.4 0.056 0.063 10 51
24 29
max., ng/J
280 490 160
comment
log-normal distribution
I
81
"For particulates n = 71; for gaseous emissions n = 748. bGeometric standard deviation. cIn average 1 MJ = 0.47 ms at STP, [CO,] = 11.7% in wet flue. The values are computed from mg/m3 to ng/J using real time, [CO,], and temperature values. Table VI. Flue Gas-Outdoor Ajr Mixing Parameters' parameter mass rate, kg/s volume rate, m3/s water content -vapor, g/m3 -aerosol, g/m3 SOZ, mg/m3 NO: mg/m3 particulate, mg/ms
mean 0.088 0.106 160 NDb 530 260 300
flue gas min. 0.0
140 ND 170 110 19
max. 0.16 175 ND 1500 430 2600
air min.
max.
mean
1.08 0.841
1.08
1.08
1.17 0.963
4.8 ND 0.03c NA 0.02c
3.0 ND
5.6 4.8 0.OSc
mean
0.llC
17 0 41 20 6.5
mixture min.
max.
1.08
1.2
12
22
9.6
"The flow velocity in the bag was 0.10 m/s, and the flue gas residence time in the bag was 120 s. bNot detectable. CReference19. dNOz has not been measured. Typically in a power plant flue gas less than 5% of NO, is NOz (18).Ignoring any NO NO2 conversion in the bag would give an NOz concentration of
