Risk assessment of BTEX concentration from 2 combustion of coal in a controlled laboratory 3 environment 4

A D-grade type coal was burned under simulated domestic practices in a controlled 17 laboratory set-up, in order to characterize emissions of volatile organic compounds (VOCs); viz. 18 benzene, toluene, ethylbenzene and xylenes (BTEX). Near-field concentrations were collected in a 19 shack-like structure constructed using corrugated iron, simulating a traditional house found in 20 informal settlements in South Africa. Measurements were carried out using the Synspec Spectras 21 GC955 real-time monitor over a three-hour burn cycle. The 3-hour average concentrations (in μg/m3) 22 of benzene, toluene, ethylbenzene, p-xylene and o-xylene were 919 ± 44, 2051 ± 91, 3838 ±19, 4245 41 23 and 3576 ± 49, respectively. The cancer risk for adult males and females in a typical SA household 24 exposure scenario, was found to be 1.1 -1.2 and 110-120 folds higher than the US EPA designated 25 risk severity indicator (1E-6), respectively. All four TEX compounds recorded the Hazard Quotient 26 (HQ) of less than 1, indicating a low risk of developing related non-carcinogenic health effects. The 27 HQ for TEX ranged from 0.001– 0.05, with toluene concentrations being the lowest and ethylbenzene 28 the highest. This study has demonstrated that domestic coal burning may be a significant source of 29 BTEX emission exposure. 30


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The introduction of several chemicals in the atmosphere has been widely associated with 34 increased health risks (1,2). Anthropogenic sources of higher exposure to air pollutants is suggested

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There is a growing concern globally, regarding pollutant inventories in order to understand 41 major sources of emissions and their impacts (7). There is an emerging body of knowledge which air pollution(10,11). Majority of households, especially in developing countries, rely on multiple 45 energy sources combusted daily using inefficient devices in poorly ventilated environments (12,13).

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Emission of volatile organic compounds (VOCs) under these conditions may present an important class of pollutants as it has been associated with several health and environmental impacts 48 (14-16). It is reported that VOCs, even at low concentrations, can produce several health effects 49 including nausea, eye and throat irritation, induction of asthma attacks, fatigue, dizziness and mental 50 confusion (17-21). VOCs in general are quite numerous however; emphasis is given to mono-51 aromatic volatile organic compounds termed BTEX (benzene, toluene, ethyl benzene and xylenes).

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This group of VOCs are often considered carcinogenic (22,23). Particularly, benzene and 53 ethylbenzene exposure is linked with increased risk of leukemia and hematopoietic cancers (24-26).

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Toluene and xylene are non-carcinogenic but may produce reproductive adverse effects; especially 55 when exposures are chronic at low to high concentrations (27).

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Efforts to create an exposure inventory for BTEX is mainly done in occupational environments, 57 while less information is available at non-occupational settings (28-34). The sources of BTEX in 58 residential areas are diverse including domestic care products; life style related chemicals such 59 cigarette smoke; and combustion energy-related sources (35). It has also been suggested that the 60 risk of exposure is higher in indoor environments relative to outdoor environments (36-41).

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Exposure to airborne pollutants is influenced by many factors such as emission rate at the source,

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In regulating exposure to toxic compounds on human health, many countries use risk 70 assessments as a tool to determine the relative risk and develop action plans based on the emissions 71 or concentration. However, risk assessment considers various factors in estimating a possibility of a 72 biological response. Factors such as hazard source identification, exposed group, exposure pathway, 73 concentration of the contaminant, target organ and potential biological response dose which might 74 trigger a response are investigated (32,42). Hematotoxicity

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The study was carried out at the University of Johannesburg's Sustainable Energy and Research

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Centre in South Africa. The stove was placed at the center of the combustion lab. The combustion 106 laboratory is built simulating a typical informal house colloquially known as a shack, constructed   sealing of openings were not comprehensive enough to contain all emitted pollutants, which might 117 be similar to a typical shack. The stove was placed at the center of the combustion lab and 118 measurements were taken at 1 m above the floor and 1.2 m away from the stove as shown in Figure   119 1. Domestic coal fire is generally associated with high heat generation, simultaneously increasing the 120 indoor temperature significantly. Due to the sensitivity of the monitoring equipment care was given    stove from the indoor spaces before going to bed. We therefore, used this scenario to estimate the 157 exposure duration.

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In general, we have conducted risk assessment to estimate the potential exposure to BTEX from domestic 159 coal burning and similar to other studies, used the data to assess the risk to human health (48,57,58). Risk

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For the exposure assessment we have considered the estimated dose expressed as chronic daily intake 180 (mg/kg/day). Due to inadequate available methodologies to determine the internal dose we used near 181 field breathing zone concentration for the exposure assessment. We assumed that the breathing zone 182 concentration is equal to the near field concentration or emission zone (61). The driving factors in dose 183 estimation were exposure pathway (air) including route of entry (inhalation), frequency to which one is 184 expected to be exposed, duration of exposure and population age group (Adults male and females).

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Since, this was a laboratory based study simulating the experience of residents, where population index 186 is not present, the study adopted some of the parameters for the exposure scenario from the US EPA's 187 risk assessment guidelines and South African Statistics as in Table 1(61,64).

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ED is the exposure duration as in equation 2 (11.5 days);

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BW is the average body weight (70 kg, 60 kg for male and female adult respectively);

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AT is the number of days per year.

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However, default values as contained in Table 1, assume a daily intake of pollutant over a 24-hour 208 period, is often constant and can be extrapolated over a year. In our study, there was a variation on 209 exposure duration due to the nature on how households use the technology.

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In equation 2, we determined a procedure used to estimate exposure duration in a typical winter period 211 in South Africa. The limitation of this method is that the exposure duration seeks to be confined to coal

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For non-carcinogenic pollutants a hazard quotient (HQ) was used to estimate the potential health risk of 281 dwellers. Where a HQ value is greater than one, it is regarded as a hazardous exposure; while HQ value 282 of less than one means there is a low probability of developing associated health effects. In equation 6, 283 the procedure for calculating HQ is shown.            Peer-reviewed version available at Int. J. Environ. Res. Public Health 2018, 16, 95; doi:10.3390/ijerph16010095 determined 1.2 E -4 and 1.1 E -4 respectively. The cancer risk for woman was found to be higher than 373 that of males. This finding suggest that women will be more vulnerable than men even though the 374 exposure concentration is the same. As shown in table 5, the cancer risk for women suggest that 120 375 people will be at risk of cancer per 1E 6 of the exposed population. Furthermore, in table 6, results

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show that 110 men per million exposed will be at risk of carcinogenic health effects. In both exposure 377 scenarios (male and female) the cancer risk was found to be higher than the acceptable risk levels of 378 1E -6 and 1E -4 .

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The cancer risk in adult female and male were found to be 120 and 110 folds higher than the 389 designated cancer severity indicator of 1E -6 , respectively. These findings confirm those reported by

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The results presented in our study indicate that there is a lower probability of non-carcinogenic health 407 effects as a result of exposure to domestic coal combustion technology as described in this study.

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Despite, the non-carcinogenic effects rated hazard quotient of less than one, this might change

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The study further, attempted to utilise breathing zone near field BTEX concentration as averaged 440 over a 3-hour burning cycle in adult female and male to estimate carcinogenic and non-carcinogenic 441 health effects, simulating practices in informal settlements. The cancer risks were found to be 110 to 442 120 folds higher than the designated cancer severity indicator of 1E -6 .

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The health risk assessment of TEX, through calculating the hazard quotient, was below the

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Notably, risk assessment is a comprehensive and iterative process to assess the relative risk for 453 several exposure scenarios. It must be understood that risk assessment has several uncertainties, the