Monitoring of polycyclic aromatic hydrocarbon emissions from biomass combustion in Kenya using liquid chromatography with fluorescence detection

The Science of the Total Environment, 138 (1993) 77-89 Elsevier Science Publishers B.V., Amsterdam

77

Monitoring of polycyclic aromatic hydrocarbon emissions from biomass combustion in Kenya using liquid chromatography with fluorescence detection A.N. Gachanjaa and P.J. Worsfoldb "School of Chemistry, University of Hull, ltull HU6 7RX bDepartment of Environmental Sciences, University of Plymouth, Plymouth PL4 8AA UK (Received June 1st, 1992; accepted June 20th, 1992) ABSTRACT Sampling and reversed-phase liquid chromatographic anabsis with fluorescence detection of polycyclic aromatic hydrocarbons (PAHs) released from biota,ass coy,~bustion sources is presented. PAH emissions from charcoal obtained from Acacia r,~earns~i and Newtonia buchananii trees, combusted in two charcoal burning stoves common~, used in Kenya (traditional metal and ceramic-lined) are compared. Particulate bound and gaseous PAH were sampled onto a glass microfibre filter and an XAD-2 resin cartridge, respectively. PAH results from samples collected in kitchens in the Kenyan Highlands are also presented and discussed in relation to indoor air pollution in developing countries. Key words: fluorescence; polycyclic aromatic hydrocarbons; biomass fuels; liquid chromatography; indoor air pollution

IWIRODUCTION

Fifty per cent of the world's population relies principally on biomass fuels, e.g. wood, charcoal, animal dung and crop residues, for their household cooking [1]. In Africa, Asia and Latin America about 500 million people, mostly children, are exposed to high levels of pollutants arising from the combustion of traditional biomass fuels [2]; In Kenya, 80% of the urban homes and 10% of rural homes (about half a million households) use charcoal burning stoves for cooking and the: remainder of the rural population use firewood [3]. As the urban populaILion continues to increase, charcoal usage will also increase in importance. Cooking with charcoal has a number of advantages over firewood e.g. it is easier to transport, store and distribt;te and produces less emissions when burnt. There is a health concern over i;l~eemissions from wood smoke, not only because of the mass and chemi,~al nature of the pollutants but also ~48-9697/93/$06.00

© 1993 Elsevier Science~Publisher's B.V. All rights reserved

78

A.N. GACHANJA AND P.J. WORSFOLD

because of their respirable nature (50-75% of the particulates emitted are in the inhalable size range). Polycyclic aromatic hydrocarbons (PAHs) form the largest group of environmental carcinogens known today [4] and are produced when biomas~ fuels are burnt [5]. Cooper [6] has reported~.emission factors for wood combustion in fireplaces in the range of 1-24) g kg -I and 0.1-9.0 mg kg -! for particulates and benzo[a]pyrene, respectively. In Kenya, carcinoma of the nasopharynx has been reported to occur more commonly among populations living in the Highlands (altitude > 2000 m above sea level) where cooking is clone in small, poorly, ventilated kitchens compared with populations living at lower altitudes (0-2000 m) [7]. The thai'coal used for this study was obtained from Acacia mearnsii and Newtonia buchananii trees. Both are fast growing trees (regeneration time approximately 10 years), produce softwood and are common sources of firewood and charcoal on the slopes of Mt. Kenya, Kenya. Acacia mearnsii is also an important source of vegetable tannin because its bark has a high content of phenolic compounds while the bark of Newtonia buchananii is chewed as an aphrodisiac [8]. This paper describes a high performance liquid chromatographic procedure with fluorescence detection (HPLC-FL) for PAH analysis in emissions from the combustion of charcoal from Acacia mearnsii and Newtonia buchananii trees in two charcoal bunJin~ stoves (traditional and ceramic lined). The sampling and PAH analysis of samples collected in kitchens in the Kenya Highlands are also presented and the results obtained are discussed in relation to indo,,.~r air pollution in developing countries. Most of the carcinogenic PAHs have high molecular mass and are relatively non-volatile (boiling points above 400°C) [9]. HPLC with selective and sensitive fluorescence ~etection was the analytical method chosen since in trace environmental analysis for a small number of PAHs and'for relatively non-,~olatile solutes at normal GC working temperatures (< 300°C), HPLC is ~,lperior to capillary gas chromaography [10]. EXPERIMENTAL

Reagents and equipment Toluene (AnalaR grade), hexane (analyticalgrade) and dichloromethane (DCM) (analyticalgrade) were obtained from B D H and redistilledbefore use. Acetonitrile(ACN) (HPLC grade) and isopropyl alcohol (IPA) (Pronalys A R grade) were obtained from May and Baker and used as obtained. Tetrahydrofuran (THF) (glassdistilled)from Aldrich was used as obtained. Distilled deionised water was used throughout. Air sampling pump~ (Casella model AFC 123) and an air sampler (OHS

MONITORING POLYCYCLIC AROMATIC HYDROCARBON EMISSIONS FROM BIOMASS COMBUSTION

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fibre finder) together with flow meters (Precision Engineering RS 2 and RS 3) were used. PAH staadards of 95% purity and above (Aldrich) were used as obtained. XAD-2 resin (Alltech Associates; pre-cleaned by Soxhlet extraction) and glass microfibre filters (Whalman GF/D, 47 mm diameter) were used for sampling. The HPLC equipment consisted ~f a solv,mt pump (Waters 600 Millipore), a rotary sampling valve (Rheo¢tyne 7125) and a filter fluorimeter (LS-2B Perkin Elmer). Chromatograms were recorded using a strip chart recorder (Chessel BD 4004). PROCEDURES

Sampling Wood from Acacia mearnsii and Newtonia buchananii trees was burnt in a traditional Kenyan kiln to produce charcoal. Acacia mearnsii (4.1 g) and 4.5 g of Newtcmia buchananii charcoals were ground to a fine powder, placed in clean extraction thimbles and Soxhlet extracted with 200 ml toluene for 16 h (at approx. 4 cycles h-I). The charcoal was also burnt in a combustion apparatus designed so that all the combustion products were trapped on a glass microfibre filter and an XAD-2 resin cartridge. Two charcoal burning stoves commonly used in Kenyan households, traditional and ceramic lined stoves, were separately charged with charcoal from Acacia mearnsii and Newto, ia buchananii trees. The combustion products were sampled using a glass microfibre filter and an XAD-2 resin cartridge as shown in Fig. 1. The experimental parameters used are given in Table 1. Glass microfibre filters and XAD-2 resin were used to trap particulate bound apd gaseous PAHs, respectively in households in Kenya, during the time of preparation of the evening meal (between 1800 h and 2200 h). Sampling durations were in the range of 2-4 h. The sampling parameters used in kitchens in Kenya are given in Table 2. Samples were collected from households on the slopes of Mt. Kenya where either charcoal or firewood was used for cooking. The households were randomly selected. Sample extraction and clean-up Tile glass microfibre filters and XAD-2 resin cartridges were Soxhlet extracted with toluene fc,r 16 h (at 4 cycles h-I), the toluene was removed using a rotary vacuum evaporator (water bath temperature ~-45°C) [I I] and the residue obtained was redissolved in 100 ~1 hexane. C~8 prepacked cartridges were cleaned as follows before loading the sample. Five miUilitres of each of the following solvents were sequentially eluted through the column.

A.N. GACHANJA A N D P,J.WORSFOLD

80

ACN" THF (90:10) -- ACN : IPA (50:50) 1 hexane: IPA (50:50) ! hexane ! ACN" THF (97:3) - hexane : IPA (50:50) A sample (100/~1) was loaded on t',:e Cis cartridge and the aromatic fraction was recovered by washing with 3.0 m; of' 3% THF in ACN. The solvent was removed from the aromatic fraction using a ~low stream of nitrogen with the sample immersed in a warm water bath (40-45°C) in a fumehoodo The sample was redissolved in 100 ~l hexane/DCM (90:10). To reuse a C~s cartridge, it was washed with 3 ml ACN/IPA (80:20) to remove aliphatic compounds and 7 ml ACN/IPA (50:50) to remove long chain alipbatic compounds (n > 20 carbon atoms) and phthalates. The C,s cartridge was then conditioned with 5 ~nl ACN/THF (97:3) [12].

10 cm diameter filter runnel

/

/

in-line filter holder XAD-2 cartridge

~ ~ ,

toflowmeter and pump

((:1)

samplintl height Biomass combustion

equipment _~.t1==~--.-.~----- h t sWpa'm

~

~ . tnlet

traditional metal stove

Fig, I, Sampling of combustion products from charcGal burning stoves. (A) 0. I g XAD - 2 resin; (B) 0. ! g X A D - - 2 resin (back-up cartridge}. A and B separated with glass wc oi plugs.

MONrlORING POLYCYCLIC,~OMATIC HYDROCARBON EMISSIONS FROM BIOMASSCOMBUSTION

81

TABLE 1 Experimental parameters during sampling from charcoal burning stoves Charcoal Burnt

Cooking stove used

Height of sampling (m)

Volume of air sampled (cm3)

Blank Newtonia buchananii Acacia mearnsii

-Traditional Ceramic Traditional Ceramic

0.5 0.5 0.5 0.35 0.35

450 500 460 460 500

The final fractionation of the extracts was performed using a semi preparative normal phase HPLC column (250 mm × 10 mm i.d. packed with 8 ~tm amino-bonded silica; Dynamax). The solvent plogram started with hexane at a flow rate of 2.0 ml min-' for 10 rain, then changed to 10% DCM in hexane at a flow rate of 4.0 ml min -~ for 35 min during which time the column eluent was collected. This program was optimised using anthracene (eluted in 11 min) and benzo(ghi)perylene (eluted in 40 min). To ensure that all material was eluted, 10% DCM in hexane was pumped through the column for a further 10 min and the column was reconditioned with hexane (2.0 ml rain -|) for 5 min before injection of the next sample.

Analytical reversed-phase HPLC Samples (20 ~1) were separated on an analytical HPI.C system consisting TABLE 2 Sampling parameters in kitchens in Kenya Sample number

Volume of air (litre)

Type of cooking stove

Type of Biomass fuel

I00 I01 102 103 104 105 106 107 108

900 315 300 340 594 540 540 540 540

ceramic lined 3-stone 3,stone ceramic lined traditional 3-stone 3-stone 3-stone 3-stone

charcoal a Cypressius governi~nae wood Coffee wood charcoal" charcoal" Maize stalks Grevillae robusta wood Greviilae robusta wood Acacia mearnsii wood

aThe trees from which the charcoals were made could not be traced.

82

A.N. GACHANJA AND P.J. WORSFOLD

of a multisolvent pump (Waters 600 Millipore), a polymeric CI~ PAH cartridge column (Spherisorb ODS-2, 5/tm, 150 null X 4.6 mm i.d.) and a filter fluorimeter (LS-2B Perkin Elmer). A mobile phase flow rate of 1.0 ml min -m and a gradient elution program of ACN/water (70:30) to ACN (100%) in 20 min followed by 100% ACN for 15 rain was used. The column was then equilibrated with the initial mobile phase for 15 min before introduction of the next sample° To increase the sensitivity and selectivity for individual PAH, two separate excitation and emission wavelengths were used for fluorescence detection. Using a 340 nm excitation cutoff filter, pyrene, 3,6dimethylphenanthrene (3,6-DMP), benzo[a]anthracene (B[a]A), benzo[e]pyrene (B[e]P) and dibenz[a,h]anthracene (DB[a,h]A) were detected at an emission wavelength of 393 nm. An excitation cutoff filter of 375 nm and emission at 430 nm were used to selectively detect chrysene (CHR), fluoranthene (FLR), perylene (PER), benzo[a]pyrene (B[a]P), benzo[ghilperylene (B[ghi]P) and 3-methylcholanthrene (3-MCA). Standard solutions of PAHs were separately iinjected and a calibration graph of PAH concentration versus fluorescence emission plotted for each PAH. All samples were analyzed in duplicate. It was necessary to degas the mobile phase with helium in order to eliminate fluorescence quenching by dissolved molecular oxygen. RESULTS AND DISCUSSION

PAH emissions from charcoal combustion The retention times of individual PAHs were reproducible (Table 3) and in conjunction with the selective fluorescence detection conditions used, allowed identification of individual PAH in the samples. Linear calibration graphs (0.9928 < r < 0,9999) were obtained for all the PAHs i'~ the concentration ranges of 0--62 ng ml-' for benzo[a]pyrene (most sensitive) and 0-27 ~tg ml -~ for 3,6-dimethy!phenanthrene (least sensitive). For all samples, the means of duplicate analysis are reported. The reproducibility of duplicate analysis for all samples was less than 4.3%. The amounts of each PAH adsorbed on unburnt charcoals from Acacia mearnsii and Newtonia buchananii trees and the amount of each PAH produced when these charcoals were burnt is given in Table 4. For each PAH, the amount released on combustion is greater than the amount adsorbed on the unburnt material, proving that PAHs are produced during combustion, but no clear trend in the burnt: unburnt ratio for the PAHs was found. An exception was the amount of chrysene adsorbed on charcoal from Newtonia buchananii tree which was higher than the amount released when it was burnt. These results show that the amount of PAH emitted when charcoal is burnt is independent of the amounts adsorbed and dependent on the small organic radicals produced during the combustion processes. A chromatogram of the toluene extract from Acacia mearnsii charcoal is shown in Fig. 2.

MONITORING POLYCYCLIC AROMATIC H Y D R O C A R B O N EMISSIONS FROM BIOMASS COMBU~I'ION

83

FABLE 3 Detection limits (calculated at 3 x blank signal) and relative standard deviation (RSD) of LC retention times fbr individual PAH PAH

Retention time (s)

Capacity factor (k') a

RSD% (n = 10)

Detectiov limit (ng ml-')

Chrysene Fluoranthene Pyrene 3,6-DMP B[a]A Perylene iknzo[e]pyrene lknzo[alpyrene DB[a,h]A B[g&]P 3-MCA

477 918 1023 1082 1374 1383 1630 1787 1915 2047 2105

3.5 7.6 8.6 9.1 I 1.9 13.8 14.3 15.8 16.9 18.2 18.7

1.1 1.1 3.8 0.4 3.3

355 70 7 550 12 3 43 ! 13 9 8

1.9 b

3.0 0.7 2.8 1.0 0.6 b

~to= 64 s. bn:6.

TABLE 4 Comparison of amounts of PAH adsorbed and emissions produced on burning Acacia mearnsii and Newtonia buchananii charcoals PAH b

Amounts of PAH in og kg "~ charcoal Newtonia buchananii

Acacia mearnsii

Fluoranthene Chrysen~ Benzo[e]pyrene Peryle~e Benzo{~:]pyrene Dibei~[a,h]anthracene

adsorbed a

emitted c

adsorbed"

emitted c

19 ND 46 4 I

1530 226 372 12 119

ND I 120 ND ND ND

850 ND 536 ND 14

ND

ND

,7

139

ND

70

Benzolgh~lperylene

39

aToluene extractable amounts. bNone of the other PAH in ]'able 3 were detected. ¢Sum of particulate adsorbed and gaseous PAH. ND, not detecled.

279

84

A.N. GACHANJA AND P.J. WORSFOLD

0.7

0.6

05

0.4 oem

A

0 03

i

0.2

a o

"0.1

|

i

40

~0

ii

|

l

20

10

0

Time (min) Fig, 2, HPLC chromatogram of the tolueae extract from Acacia mearnsg charcoal, ke~ = 375 nm (cutoff filter), Xem= 430 rim. (A) fluoranthene, (B) perylene; (C) benzo[a]pyrene, and (D) dibenz[a, hlanthracene.

Charcoal has a high surface arep. with strong adsorption characteristics end ~i~es semi-quantitative recoveries for PAH using Soxhlet extraction. Activated coconut charcoal has been recommended for use in sampling of volatile organic molecules (b.p. < 100°C) [13]. The recoveries of 3,6-DMP, B[a]A and DB[a,h]A, cold spiked on pre-extracted Acacia mearnsg charcoal, using Soxhlet extraction were 76%, 65% and 58% (mean of duplicate extractions), respectively, which indicates that recovery decreases with increasin~ molecular mass of the PAH. Wright et al. [14] extracted PAHs spiked on activated charcoal and obtained extraction efficiencies of zero for chrysene and coronene using 16 h Soxhlet extraction with carbon disulphide and dichloromethane. Although PAH adsorbed on charcoal might, in general, not be easily extractable into the body once the charcoal dust is inhaled, the health

MoNrrORING POLYCYCLIC AROMATIC HYDROCARBON EMISSIONS FROM BIOMASS COMBUSTION

85

impact on people who are handling charcoal every day (either charcoal producers or dealers) may have some similarity to the reported occupational health problems of chimney sweeps [15]. The results of PAH analysis of the emissions produced when Acacia mearnsii and Newtonia buchananii charcoals were burnt in two charcoal burning stoves (traditional and ceramic lined) are given in Table 5. Soxhlet extraction of PAHs from particulates on glass microfibre filters and XAD-2 resin using toluene has been reported to be quantitative (> 90%) [16]. A separate analysis of the XAD-2 resin back-up cartridge showed that no PAH breakthrough occurred. Ramdahl et al. compared emissions of aldehydes, benzene and PAH from wood and charcoal burning stoves and reported emissions of 25-1000 times less when a charcoal burning stove was used [17]. The traditional charcoal burning stove is made of metal, spherical in shape and stands on three legs (Fig. l b). The lower hemisphere supports a grate which divides the upper shallow charcoal box from the lower compartment where ash is collected. The ceramic-lined stove is similar but has a ceramic liner (made from a mixture of clay and vermiculite) and a ceramic grate. The ceramic stove has a heat transfer efficiency of 30-40% compared with 15-20% for the traditional stove, consumes 25% less charcoal [3] and gives 33% less PAH emissions (see Table 5). Fewer PAHs are emitted when the ceramic stove is used and this is probably due to catalytic reactions on the surface of the ceramic lining and the higher temperatures that are reached (due to the insulating property of the ceramic lining). TABLE 5 PAHs emissions when Acacia mearnsii and Newtonia buchanat,ii charcoals were burnt in different cooking stoves PAH (rig m'3) a

Chrysene Fluoranthene

Newtonia buchananii

Acacia mearnsii

Traditional stove

Ceramic stovo~

Traditional stove

Ceramic stove

139 I 17

ND 20

ND 28

ND ND

i 70 16

I !9 6

161 ND

ND ND

Benzolalanthracene 3-MCA

ND, not detected. aAll PAH values have been corrected for blank values which were !~9 and 28 ng m "3 for chrysene and tluoranthene, respectively, the only PAHs detected in the blank. Hone of the other PAHs in Table 3 were detected

86

A.N. GACHANJA AND P.J. WORSFOLD

PAH in kitchens in Kenya In all households sampled (Table 2), the fire had not been maintained for longer than 3 h prior to sampling. Dry wood was burnt in 3-stone stoves in all cases. Due to the increasing scarcity of fuel wood in developing countries [18], some households use any combustible matter. Maize stalks, a poor fuel which bums at low temperatures leaving no coals, was used in the household where sample 105 was obtained. Sample 104 was obtained in a household where the fire was maintained at a very low level. An earlier similar study in a nearby district (Murang'a), conducted during the rainy season (April/May) for over 24 h sampling periods recorded a maximum of 260 ng m "3 and a minimum of 10 ng m -3 of benzo[a]pyrene [19]. The values obtained in this study (Table 6) are lower for all PAHs compared with the Murang'a study. A possible explanation for the lower values reported here is that sampling was done during the dry season (January/ February) when fires are maintained only during cooking periods and the woods burnt are dry. In contrast, the Murang'a study was performed during the rainy season, when fires are also used for space heating and the woods burnt are usually wet (producing more smoke and suspended particulate matter). In 1972, Clifford [7] reported values in the range of 85-166 ng m -3 and 79-515 ng m -3 for benzo[a]pyrene and benzo[a]anthracene respectively in five households, all using firewood, on the slopes of Mt. Kenya. The maximum concentration of benzo[a]pyrene reported in households in India [20] under monsoon conditions of 19 mg m -3 is comparatively high while the TABLE 6 PAH concentrations in Kenyan kitchens PAH/Sample

Chrysene Fluoranthene Pyrene B[a]A B[e]P B[alP Perylene DB[a, hIA B[ghiJP 3-MCA ND, n~t detected.

PAH concentration (ng m "3) 100

101

102

103

104

105

106

107

108

ND 85 54 64 63 5 ND ND 24 ND

210 ND 5 4 16 8 ND ND 3 ND

ND 1080 ND 540 790 145 ND ND ND 37

285 ND ND !I ND 2 ND ND ND ND

ND ND ND ND ND ND ND ND ND ND

ND ND II 8 20 1 ND ND 2 ND

ND ND 129 105 273 53 ND ND 38 ND

165 60 ND ND 100 28 ND ND ND ND

222 ND 48 39 23 93 ND ND ND 63

MONITORING POLYCYCLIC AROMATIC H Y D R O C A R B O N EMISSIONS F|~OM RIOMASS COMBUSTION

87

minimum concentration, 62 ng m -3, is within the range of values obtained in this study for Kenyan households. The potential concentration that might exist during indoor cooking with biomass fuels will be dependent on the fuelling rate, type of fuel, volume of kitchen and the effective air exchange rate (ventilation) [21]. The kitchens where sampling was done were small (<24 m 3) and had small windows (< 1 m 3) which were not opened during the sampling periods. Aggarwal et al. [22] postulated that the annual dose exposure (in the living environment) to both total suspended particulates and benzo[a]pyrene to persons in India and on the slopes of Mt. Kenya was the highest in the world. Crarnow [23] has reported that B[a]P concentrations of I/~g 1000 m -3 of air appear to be associated with a 5% incidence of lung cancer. Many of the PAH produced when biomass fuels are burnt are carcinogenic and although accurate extrapolation of experimental animal data to man is not necessarily justified, the cellular effects of PAHs are known to be cumulative and the total dose is therefore related to the duration of exposure and concentration [24]. The health implications and impact of biomass combustion pollutants on exposed individuals, particularly infants and the elderly, has act been fully assessed. CONCLUSIONS

Rever,,ed-phase LC undo: gradient elution using a polymeric C~s column coupled with fluorescence detection provides an analytical method for PAHs that is sensitive, selective and reproducible. Anab sis of the emissions from the two charcoal burning stoves used in this study showed that the ceramic stove produced significantly less PAH emission thorn the traditional stove. Combustion of charcoal from the Acacia mearnsll tree gave emissions which contained more PAHs (33% higher) than charcoal from the Newtonia buchananii tree. A maximum total PAH concentration of 2.6/~g m "3 was obtained in the kitchen samples. Chrysene, benzo[a]anthracene, benzo[a]pyrene, benzo[ghilperylene, 3-methylcholanthrene are all carcinogenic and were detected in the kitchen samples in the concentration range 1-540 ng m "3 (except in sample 104). In all the kitchen samples analysed (except 104 and 105), the benzo[a]pyrene concentration was above 1.0 ng m -3. ACKNOWLEDGEMENTS

One of us (A.N.G) would like to thank the British Council and Kenyatta University (Kenya) for their financial support.

88

A.N. G A C H A N J A A N D PJ. WORSFOLD

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20 A.L. Aggarwal, K.R. Smith and R.M. Dave, Air pollution and rural biomass fuels in developing countries: a pilot village study in India and its implications ibr research and policy. Atmos. Environ., 17 (1983) 2343-2362 21 WHO, Estimating the human exposure to air pollutants. Geneva, EFP/82, vol.31, 1982. 22 A.L. Aggarwal, K.R. Smith and K.R. Dave, Air pollution and rural biomass fuels. Abst. Selected Solar Technol., 5(4) (1983) 18-24. 23 B.W. Crarnow, Can air pollutants cause chronic lung diseases? Environ. Sci. Technol., 12 (1978) 1356-1358. 24 G. Becher and A. Bjorseth, Determination of occupational exposure to PAH by analysis of body fluids, in A. Bjorseth and T. Ramdahi (Eds.), Handbook of Polycyclic Aromatic Hydrocarbons, Vol. 2, Dekker, New York, 1985, pp. 237-252.