Domestic air pollution from biomass burning in Kenya

Atmospheric Enu~mnment Vol. 23, No. 8, pp. 1677 Printed in Great Brcain.

DOMESTIC

CQO+6981/89

1681. 1989.

S3.03+0.00

Pergamon Press plc

AIR POLLUTION FROM BIOMASS BURNING IN KENYA

JAN S. M. BOLEIJ,* P~ETER RUIGEWAARD and FRED HOEK Wageningen Agricultural University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands H.

THAIRU

Kenyatta University, Nairobi, Kenya E. WAFULA

and F. ONYANGO

University of Nairobi, Kenya

and HENK

DE KONING

World Health Organization, Geneva, Switzerland (First

receioed

I3 July 1988 and receiued for publication 6

February

1989)

Abstract-Biomass fuels, mainly wood, are burned under often primitive and inefficient conditions by about half the world’s population as the major source of domestic energy. In a rural area in Kenya, air pollution measurements were carried out inside dwellings during the rainy season in connection with a WHO epidemiologic survey to the incidence of acute respiratory infections among children aged below 5 years. Respirable particles and NO, were found in the order of, respectively, 10 times higher (mean 1400 pg mm3) and as high (mean I80 pg rnm3)as recommended air quality guidelines for the general population. Also the levels of polycyclic aromatic hydrocarbons were very high. No relation could be detected between the number of acute respiratory infection episodes of the children and indoor air quality. This could be explained by the fact that the concentrations were very homogeneously distributed among the population. Key word index: Indoor air quality, exposure, biomass, wood burning, developing countries, acute respiratory infections.

INTRODUCTION

Indoor

air quality is increasingly being associated with acute respiratory infections (ARI) in children in developing countries. The indoor air pollution is mainly due to traditional biomass fuel combustion in dwellings under primitive, inefficient conditions resulting in high exposures of the occupants. Biomass fuels are used by about half the world’s population as the major source of domestic energy. A review prepared by the World Health Organization (WHO, 1984) of the scientific literature on indoor air pollution caused by biomass fuel showed that there is a potentially serious problem. However, the extent and severity of health effects associated with biomass fuel combustion are not well established. A relation has been found in a study in Nepal (Pandey et al., 1987) between the number of AR1 episodes in infants and the time spent near the fire as a proxy for the level of exposure. To assess the impact of air pollutants from biomass burning in developing countries, WHO has decided to * To whom correspondence should be addressed. AE

23:8-D

undertake a number of field surveys within the framework of ongoing studies on AR1 among children in various countries. The main objectives of these surveys are given below. To measure various air pollutants associated with biomass in a representative number of houses. To evaluate the main factors contributing to high indoor exposure for children aged below 5 years. To explore the feasibility of determination of the relationship between indoor air quality and the incidence of ARI. The first survey conducted in the rural area of Maragua, Kenya, is described (WHO, 1987a).

MATERIALS Population

and

housing

AND METHODS characteristics

The survey was incorporated into the organizational setting of an epidemiologic study of AR1 among children aged below 5 years, supported by the WHO and the U.S. National Academy of Science. The study population is within 250 houses and comprises

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JAN S.

M. BOLEIJ et al.

470 children. The average household has seven members. Most families have only a small area of land of about 2-4 acres where they grow corn and beans for their own consumption and some cash crops like bananas and coffee. The women do the actual farming as well as the collection of firewood, the cooking and the upbringing of the children. The size of the houses is between 25 and 35 m2 with on average three rooms. They have dirt floors with walls usually made of mud and wood. Eighty percent of the roofs consist of corrugated iron sheets while 20% are thatched. Cooking is carried out on traditional three stone open fires within the house in 58% of the homes and in 42% of the houses in a separate kitchen. Most fuel used is wood of different types and quality, but sometimes agricultural waste from bananas, sisal and corn is used. The smoke of the fire circulates through the whole house as the walls between the rooms do not reach up to the roof. The windows, mostly simple open spaces in the mud wall, the outside door and an open space between the wall and the roof provide ventilation. Typically the fires are burning for about 7 h each day, while about 50% of that time the children are near the fire mainly during the evening when the family is gathered round the fire. From the 250 households in the area 36 were randomly selected within four subgroups stratified according to roofing (thatched, corrugated) and kitchen (attached, separate) arrangements. Study design and methods

The field study had two components; 24 h averaging time measurements in all 36 houses and daily pollution pattern measurements each hour, during 1 day in three houses. In all 36 houses 24 h average measurements for suspended particles (SP) and NO, were made twice with an interval of about 1 week between two measurements. For measuring SP a battery powered pump (DuPont, P2500) was used with a flow of 2 L min - 1 and a PAS-6 filter holder (Kuile, 1984) with glass fibre filters (Whatman GF/A, 2.5 cm diameter). PAS-6 sampling heads measure in the inspirable range (50% cut off at 30 pm) according to the IS0 definition (ISO, 1981, 1983). Weighing of the filters before and after sampling was performed with a digital microbalance after equilibration of the filters for at least 24 h in a desiccator at a relative humidityof 45% (above a saturated potassium carbonate solution). At the beginning and the end of each sampling period the flow of the pumps was checked with a flowrator (Brooks, R-16-1 5-A, glass) which was calibrated against a soapbubble meter. Measurements with flow differences in excess of 10% were considered inaccurate and not used for further analysis. The pump and an extra battery, to allow a sampling time of 24 h, were installed in a wooden box for protection and noise reduction. Attached to this box was an Al pole through which the sampling tube was led to the filter holder. The sampling height was 80 cm, correspond-

ing with the breathing height of the children. The equipment was placed at a distance of about 1 m from the fireplace where the family was gathered during the evening. For comparison five measurements were performed simultaneously with a 10 mm cyclone preseparator (Casella) which measures particles in the respirable range (ISO, 1981, 1983). Also five randomly selected duplicate measurements were done to check the precision. In 20 filters the amount of polycyclic aromatic hydrocarbons (PAH) was determined according to the Dutch standard method (NVN 2798, 1986). The glassfibre filters were kept in the dark in a refrigerator at - 18°C for a period of about 6 months before analysis. For the 24 h average NO2 measurements Palmes diffusion tubes (Boleij et al., 1986) were used in duphcate. The tubes were placed on the same support as the filter holders. To observe the variation in concentrations during the day in three houses between 6 a.m. and 10 p.m., each hour instantaneous measurements of CO (Drager indicator tubes, CH 25601), CO, (Drager indicator tubes, CH 30801) and respirable suspended particles (Respirable Aerosol Mass Monitor, model 3500, Therm0 Systems Inc.) were performed. Each hour also observations on time budgets and activities were made in the three houses. Fieldwork

The fieldwork was done during the rainy season (April, May) in 1986. The equipment was prepared, charged and stored in a room at the Maragua Rural Health Training Centre, from where also the fieldwork of the AR1 study was carried out. The local AR1 fieldworkers made the necessary arrangements with the families prior to the first installment of the equipment. They acted as interpreters and assisted with completing a questionnaire administered to the mother of the under 5 year old child, on house characteristics, fuel used for cooking, duration of the fires, types of food cooked and activities of the mother and children during the time of the measurements. Each measuring day six sets of equipment were placed in the kitchens of six homes and were collected the next day. RESULTS

Suspended particles (24 h averaging time)

The five duplicate PAS-6 measurements resulted in a total coefficient of variation of 9.8%. The five simultaneously measured samples of respirable and inspirable particles were within 10% of each other indicating that all particles were in the respirable range. Complete data sets of repeated measurements were available for 30 homes; in six homes the results of one measuring period were missing due to technical failures or absence of the family during the second period. The results of the two measuring periods are summarized in Table 1.

Domestic air pollution from biomass burning Analysis of variance (SAS, 1985) of the repeated measurements showed that 69% of total variance was due to the difference between the first and second measurement in the same house. Only 31% of the variance was caused by the differences between the houses. This resulted in a true geometric standard deviation of 1.5. Analysis of variance (SAS, 1985) using the logtransformed data did not show significant differences in mean concentrations for the different kitchen and roofing arrangements. Only a tendency was found for both separate kitchens and corrugated iron roofs to have somewhat higher levels.

PAH The resutts of the PAH analysis of 20 filters loaded with particles are summarized in Table 2. On the basis of four duplicate measurements, including sampling, a

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mean coefficient of variation of 32% for the various PAH was calculated (see also Table 2). N*z Based on the duplicate samples an overall coefficient of variations was calculated of 30%. Again complete data sets of repeated measurements are available for 30 homes. The results are summarized in Table 3. Analysis of variance (SAS, 1985) of the repeated measurements showed that 67% of the variance was attributed to differences within the kitchens and 33% to differences between the kitchens, resulting in a true geometric standard deviation of 1.3. As for the suspended particle data no significant differences could be detected between the NO, levels for the various housing characteristics. A tendency was found for houses with thatched roofs to have somewhat lower concentrations than those with iron roofs.

Table 1. Means and standard deviations of 24 h average suspended particle concentration for both measuring periods (in pg m - ‘)

Period 1

2 l-l-2

H 35 32 67

Arithmetic mean

Standard deviation

1390 1400 i4Ou

850 1140 1000

Geometric standard deviation

Geometric mean

1.9 2.2 2.0

1150 1050 1100

Table 2. Filter content and calculated air concentrations of 20 filters containing suspended particles from 24 h measuring periods

Compound (1) F~uoranthene (2) Pyrene (3) Benza(a)anthracene (4) Chrysene (5) Benzo(b)Ruoranthene (6) Benzo(k)fluoranthene (7) Benzo(a)pyrene (8) Benzo(gki)perylene (9) Dibenz(a,h)anthracene (101 Indeno( 1,2.3-cll)pyrene

CV,I

n

29 57 40 17 33 33 37 2I 34 19

20 20 20 20 20 20 20 18 18 19

Filter content AM SD kgg-‘1 180

540 190 180 70 30 60 180 100 40

Air* concentrations AM Max. Min. (ngm-“) (ngmW3) (ngmd3)

210 550 140 If0 50 20 50 120 90 20

780 270 260 110 40 90 250 140 50

780 2390 840 800 320 110 260 770 440 160

30 loo 40 30 10 10 10 30 20 10

*Air concentrations were calculated on the basis of the mean filter content and the mean, maximum and minimum air concentrations of the suspended particles. t Total coefficient of variation based on four duplicate measurements.

Table 3. Means and standard deviations of 24 h average NO, concentrations for both measuring periods (pgmm3)

Period

n

Arithmetic mean

1 2 1+2

33 31 64

200 160 180

Standard deviation 104 80 94

Geometric mean 170 150 160

Geometric standard deviation 1.7 1.5 1.6

JAN S. M. BOLEIJ er al.

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Correlation between NO, and suspended particles

ARI incidence

Regression analysis (SAS, 1985) of the logtransformed concentrations of the simultaneously measured particle levels 24 h average NO, and suspended resulted in a correlation coefficient of 0.36. Based on this correlation a predicted value can be calculated for the suspended particle concentrations from NOz measurements. The predicted value and the 95% prediction interval for the suspended particle concentration based on one and ten NOz measurements are given in Table 4 for the lowest and highest NO, level in this study.

During a 42 week period the number of AR1 episodes was recorded by the local field workers during biweekly visits for the children aged below 5 years living in the houses where the measurements took place. The children on average had 7.2 episodes of AR1 with a standard deviation of 2.4. Analysis of covariance (SAS, 1985) showed no relation between the number of AR1 episodes and the suspended particle concentrations, the NO, levels, the housing characteristics, or combinations of these variables.

DISCUSSION

Daily pollution pattern measurements The information obtained from the hourly visits to one of the three houses is presented in Table 5. The results of the two other houses showed a similar pattern. Burning times and presence near the fire The mean burning time of the fires during the 24 h measuring periods was 7 h with a standard deviation of 3 h. Almost all children and mothers stayed 25-75% of that time near the fire.

Table 4. Predicted suspended particle concentration and 95% prediction interval based on 1 and 10 NO, measurements for the highest and lowest NO, level in this study (in pgrnm3)

NO, 40 560 40 560

level

n

Predicted value

1

95% prediction interval

390 1600 390 1600

I IO 10

loo< 350~ 230< 690~

>1540 > 7280 > 660 13700

Table 5. Hourly measurements in a typical house with thatched roof and attached kitchen

Time

co (ppm)

co, W)

7.00 8.20 9.20 10.20 11.20 12.20 13.20 14.20 15.20 16.20 17.20 18.20 19.30 20.00

20 5 2 7 4 10 0 0 0 0 50 20 5 4

0.10 0.06 0.05 0.06 0.04 0.04 0.03 0.05 0.04 0.04 0.10 0.08 0.08 0.06

nd = Not detectable.

Suspended particles (pgm-‘) 9350 1000 nd 1500 150 nd 250 nd nd nd 12,250 4050 150 nd

Fire condition Moderate Low No Moderate Very low Very low No No No No High Low Moderate Very low

The suspended particles in this study were in the respirable range, which is in agreement with laboratory studies to wood combustion emissions (Cooper, 1980; Dasch, 1982; Zeedijk, 1986; Smith et al,, 1983). The suspended particle concentration levels found in the kitchens are very high. The WHO (1987b) recommends a maximum in the order of 100 to 150 ,ugmm3 for total suspended particles with an averaging time of 24 h as a maximum for the general population. In case the fire was out, hardly any suspended particles were measured. This means that the average concentration during 7 burning h is about 350&4000 pgrnm3. Most mothers and children stay near the burning fire during 25-75% of the time especially in the evening when according to the daily pollution pattern measurements the highest concentrations occur. During that time very high peaks were registered. Little or no difference could be detected for the various house characteristics on which the stratification of the houses was based. This is explained by the fact that most of the variance in concentration levels was within the houses and only little among the houses. The calculated true geometric standard deviation also indicates that concentrations of suspended particles were homogeneously distributed among the population. The CO concentrations found during cooking are lower than recorded in many other studies (WHO, 1984; Smith, 1987) in developing countries. This might be due to differences in sampling locations. We were also able to measure much higher concentrations above the fire in the smoke plume. However, these concentrations are not likely to be inhaled as people tend to avoid direct inhalation of smoke. The air concentrations of the various PAH were very high. They reflect the high particle concentrations. In western societies similar concentrations can only be found in heavily cigarette smoke polluted environments (IARC, 1985). The mean filter content for benzo(a)pyrene in this study is in agreement with the content of filterable fireplace emissions for various kinds of wood (Dasch, 1982). For six of the measured PAH there is sufficient evidence that they are carcinogenic to experimental animals (IARC. 1983). All

Domestic air pollution from biomass burning measured PAH are major components of soot, which human carcinogenicity in the form of lung cancer has been demonstrated by several cohort studies among chimney sweeps (IARC, 1985). Even though a thorough evaluation of the carcinogenic risk is not easily possible for this situation as all studies so far have been performed in western societies, the levels observed in this study can be considered as a real threat to the population. The 24 h average NO, concentrations in this study are approximately at the same level as the recommended air quality guidelines by WHO (WHO, 1987b). At these levels, in some studies, minor lung function changes and chronic obstructive lung disease symptoms have been found (WHO, 1987b). Also for NO, a low true geometric standard was found with little or no influence of the various house characteristics again

indicating a homogeneously distributed exposure among the population. The levels of NO, and suspended particles considered in relation to air quality guidelines indicate that the suspended particles represent a greater health hazard than NO,. It has been suggested to use NO, measurements as an indicator for the suspended particle concentrations, as NO, measurements are much simpler and applicable on a larger scale. Based on the relation in this study the feasibility is very doubtful as a large overlap exists between the 95% prediction interval for the particle concentrations derived from the highest and lowest NO, level. Graphical presentation of the relation indicated a non-linear relationship which can be explained by the fact that different processes in the fire lead to suspended particle and NO2 emissions, respectively. Suspended particles and NO, levels are known to affect the incidence of ARI. No relation could be detected, however, between the number of AR1 episodes of the children and the measured suspended particle levels, the NO, levels, or a combination of both. Also no correlation was found with the house characteristics. This is explained by the fact that the pollution levels were very homogeneously distributed among the houses in which the children lived with hardly any influence of the house characteristics on the variation of the concentration levels. Including the time budgets for the children to arrive at actual exposure data did not improve the analysis, as also the time budgets were very homogeneous among the children. Furthermore the time budgets were not very reliable, because they were obtained by interviewing the mothers, who generally had a poor notion of time. Reliable data can only be obtained by observations. In the ongoing AR1 study in the Maragua area the effect of smoke exposure is only likely to be detected if an intervention is incorporated in the study to create a sub-population with lower exposure levels.

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Acknowledgement-Many thanks are due to the field workers and employees of the Maragua Rural Health and Training Centre. The cooperation of the technical staff of the Kenyatta University and the University of Nairobi was greatly acknowledged. The study was financed by a grant from the WHO.

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