Human health risks posed by exposure to PM10 for four life stages in a low socio-economic community in South Africa

Introduction Mine ash dumps, industries and domestic fuel use have a great impact on air quality and PM10 (particles with a diameter equal to or less than 10 μm) is a pollutant of particular concern. Methods The objective of this study was to assess the human health risks posed by exposure to PM10 among a low socio-economic community. The Human Health Risk Assessment (HHRA) framework (i.e. hazard assessment, dose-response assessment, exposure assessment and risk characterization) was applied. PM10 concentrations were monitored for one month during winter and summer, respectively. A HHRA was conducted to assess whether the community was exposed to PM10 concentrations that may pose carcinogenic and non-carcinogenic health risks. Results Generally, the residents were exposed to higher concentrations of PM10 during winter than summer, resulting in a higher risk to health during winter. Results of the HHRA showed that infants were exposed to a higher dose of PM10 than the other life stages when exposed to the same concentration due to differences in inhalation rates and the ratio between inhalation and body weight. However, they were at the same risk of developing adverse effects from exposure to the same concentration of PM10 as the other life stages were exposed to, because the ‘safe’ dose was also higher for infants and since all life stages, in general, are similarly affected by PM unless the chemical composition of the PM is known. Conclusion This study recommends that infants and children, in particular, should not be exposed to air pollution from domestic fuel burning as one positive step to try and reduce their dose.


Introduction
Particulate matter (PM) is a complex, heterogeneous mixture of smoke, soot, dust, salt, acids, and metals and varies in concentration, size, chemical composition, surface area and sources of origin [1]. PM may comprise, among others, sulphate, nitrate, ammonia, chloride and organic carbon particles [2]. PM10 is defined as particles with a diameter of equal to or less than 10 microns.
Exposure to 10 in particular, poses a definite risk to health because it is more likely to be inhaled and the fine fraction of PM10 (i.e. PM2. 5) is respirable and may reach the alveolar region of the lung. Ultrafine PM (i.e. PM0.1) that is inhaled settles in the lung by Brownian motion and some may be exhaled before it deposits in the lungs [3].

Methods
The study comprised two parts namely an ambient air quality monitoring and a Human Health Risk Assessment (HHRA).

Ambient air quality monitoring
A TOPAS airborne particulate monitor (Sira MC 090158/00) was used to measure the ambient PM10 concentrations to which the population of eMbalenhle were exposed. The monitor was installed at eMbalenhle Sasol Club, alongside the Department of Environmental Affairs (DEA) monitoring station (GPS coordinates: S26°33,039' and E29°04,747'). Ambient PM10 concentrations were monitored for one month during winter (August 2010) and one month during summer (February 2011). DEA monitoring station data were also extracted for the same periods as the TOPAS instrument was installed for comparison purposes.
The particulate monitor was calibrated and maintained according to the manufacturers specifications. The fibre filters were replaced once after two weeks. Monitored data used to assess the health risks posed by exposure to PM10 in the population of eMbalenhle were compared with the South African National Ambient Air Quality Standard (NAAQS) [4]. The PM10 concentrations were measured in 15 minutes intervals, the raw data output was divided by a calibration factor of 2 and the 24-hour averages were calculated.
The monitored PM10 concentrations were compared with the NAAQS which were originally set to protect human health.

Human Health Risk Assessment
HHRA is a useful tool to estimate human health risks posed by exposure to a given environmental pollutant. HHRA have been applied in previous studies in South Africa, for example to estimate kerosene [5] and sulphur dioxide-related health risks [6]. However, a HHRA on PM10 has never been conducted in eMbalenhle. The HHRA framework applied in this study comprised four parts: hazard identification, exposure assessment, dose-response assessment and risk characterisation. The formal identification of PM10 as a hazard as well as the types of health risks that may occur as a result of exposure to PM10 was done from existing literature.
Dose-response assessment, i.e. how an individual will react to a particular exposure, was not performed in this study as the extent of the work requires comprehensive screening and additional health data presently not available in South Africa. Instead, the measured levels of PM10 were compared with the NAAQS. This national standard was therefore used as a benchmark value.
The information obtained during the hazard identification and the exposure assessment was used to estimate the concentrations of PM10 that are likely to cause significant health risks in humans. The PM10 monitored data were used to estimate how the different levels of exposure to PM10 can impact on the likelihood and severity of health effects.
It was postulated that the population of eMbalenhle was exposed to levels exceeding the NAAQS for PM10 that may have a negative impact on their health. It was assumed that inhalation was the most Page number not for citation purposes 3 important route of exposure (not ingestion or dermal contact) and that people were exposed for 24 hours per day.  ED (Exposure Duration) expressed in years. For non-carcinogens assumed to be one year. BW is the average body weight of the receptor over the exposure period (kg). AT is the period over which exposure is averaged (1 year = 365 days). For non-carcinogens the AT equals ED (years) multiplied by 365 days [7].
The long-term inhalation rates for adults and children (including infants) were presented as daily rates (m 3 /day). It was assumed that the 95 th percentile inhalation rates for long-term exposures for infants, children and adults (males and females combined, unadjusted for body weight) range from 9.2 m 3 /day for infants from birth to 1 year, 16.6 m 3 /day for children aged 6 to 10 years to 21.4 m 3 /day for adults aged 31 to 40 years [7].
The Safe Average Daily Dose (SADD) was calculated as follows: Where: SADD is the dose that the population of eMbalenhle may be exposed to without suffering negative health risks, expressed in µg/kg/day. In this case the concentration C represents the South African 24-h standard for PM10 expressed in µg/m 3 . The rest of the formula is the same as described above.
The risks caused by exposure to PM10 in the population of eMbalenhle were characterised in terms of the potential risk to illness or symptoms in the exposed population. The information developed in the previous three steps (hazard identification, exposure assessment and dose-response assessment) was brought together in the risk characterisation step to quantify the potential health risks in the exposed population, expressed as a Hazard Quotient (HQ).
The HQ was calculated using the following equation [7]: Where: HQ is the Hazard Quotient (which is always unit less) FADD is the Field Average Daily Dose calculated (in µg/kg/day) SADD is the "safe" average daily dose calculated (in µg/kg/day) Guidelines for interpreting HQ calculations are (Lemly, 1996)

Measured results of PM10
The measured 24-hour average PM10 concentrations for winter (August 2010) and summer (February 2011) using both the TOPAS and DEA instruments are presented in Figure 1 and  which means that even if the population of eMbalenhle was exposed to that average concentration of PM10, negative health impacts would be unlikely, as concentrations were below the 24-hour average NAAQS of 120 µg/m3, although some individuals may still be sensitive to relatively low PM10 concentrations [8].  Hence, to determine the worst-case scenario risk estimates, the TOPAS data were used for the HHRA.

Human health risk assessment in eMbalenhle
The respectively. It was assumed that the BW of an infant is 9.2kg, that of a child 52.5kg and that of an adult 118kg [7] . The results of the FADD for the PM10 concentrations measured in winter for the different life-stages are given in Table 2.
The results of the FADD for the PM10 concentrations measured in summer for the different life-stages are given in Table 3. For each life-stage, the winter dose was higher than the summer dose.
In order to characterise the health risks posed by exposure to  Table 4 and Table   5. In winter (August 2010), the HQ was 2.97, indicating a moderate risk according to [9] and in summer (February 2011) the HQ was 0.53, indicating that adverse health effects were unlikely, thus a low risk.
The calculated HQs using the IRIS formula, of dividing the concentration by a benchmark concentration, were between 1.1 and 10 for the winter period, which means that the population of eMbalenhle were at moderate risk of negative health effects from exposure to PM10. In summer, the HQs were above 0.1 but below 1, which means that the population of eMbalenhle were at low risk and it is unlikely that they may have experienced negative health effects due to PM10 exposure.

Discussion
This study aimed to determine the human health risks posed by ambient PM10 concentrations to residents of eMbalenhle in an air pollution hotspot area in South Africa. Similar studies have been carried out elsewhere in the world [10][11]. Our results showed that ambient PM10 concentrations were higher during the winter month Several studies have considered the health impact of air pollution on children and infants [12][13][14]. Children in eMbalenhle may be more exposed to ambient PM10 concentrations than infants and adults, because they spend more time outdoors by walking to school, playing outside during school breaks and have sport activities in the afternoons [15]. Infants will be mostly indoors. However, if there are indoor sources of PM10 such as domestic fuel use, these infants may be exposed to even higher concentrations than outdoors. The adults living in eMbalenhle may have different exposure levels, depending on their occupation and age. Caregivers and the elderly may be exposed to high levels of PM10 if they mostly stay indoors and use domestic fuel. The exposure levels of workers may differ depending on their occupation and whether they work indoors or outdoors. [16] showed that outdoor air pollution in urban areas in South Africa was estimated to cause 3.7% of the national mortality from cardiopulmonary disease and 5.1% of mortality attributable to cancers of the trachea, bronchus and lung in adults aged 30 years and older, and 1.1% of mortality in children under 5 years of age.
The results of the human health risk assessment showed that the infant had the highest calculated dose per kilogram body weight, followed by the child and then the adult, yet the risk was the same

Conclusion
The study found that even though eMbalenhle is surrounded by industries and other sources of PM10, emissions at ground level from domestic fuel burning, may contribute mostly to the levels of particulate pollution in eMbalenhle, especially in winter. The results of the HHRA indicated that the infant, child and adult are at equal risk from exposed to the same levels of PM10 for the same duration and individuals are more at risk during winter than summer. More studies should be conducted to assess the indoor exposure to air pollution focussing on the more vulnerable groups such as infants, the elderly and those suffering from other respiratory and cardiovascular diseases.