Indoor and outdoor air pollution health risks in Mabopane and Soshanguve townships in the City of Tshwane, South Africa

Abstract

EXECUTIVE SUMMARY

Background: Air pollution is a major threat to human health. Low – and middle-income countries are faced with many challenges, such as urbanisation and modernization, industrialization, traffic density, and an increase in the human population. Children are uniquely vulnerable to air pollution due to their physiologic characteristics (i.e., narrow airways and immature immune systems). Approximately 7 million people die worldwide annually due to exposure to indoor and outdoor air pollution. In South Africa, more than 28,000 people die annually due to exposure to air pollution. Therefore, air pollution is responsible for about R94.7 billion in economic costs every year. There is strong evidence that the majority of communities in the City of Tshwane Metropolitan Municipality are exposed to high levels of pollution during the winter and daily during rush hours, mostly in residential areas.

Aim: To evaluate indoor and outdoor air pollution health risks at Mabopane and Soshanguve townships in the City of Tshwane, South Africa.

Method: The study was conducted in Mabopane and Soshanguve Townships in the City of Tshwane Metropolitan Municipality, Gauteng Province. A cross-sectional study design was applied following the International Study on Asthma and Allergies in Childhood (ISAAC) Phase III. A total of 1844 parents and guardians of preschool children completed the modification. However, a total of 4 questionnaires were discarded due to incorrect completion by the participants. As a result, a total of 1840 questionnaires were included in the statistical analysis. Ambient PM2.5 samples were collected on the rooftop of the Mabopane fire station from 04 May 2022 to 28 February 2023, over 24 hours every six (6) days. In total, 60 PM2.5 samples were collected, including 10 duplicates. PM2.5, soot, black carbon (BC), and organic carbon (OC) levels were measured using gravimetric techniques, reflectometers, optical transmitters, energy-dispersive X-ray fluorescence, and Hybrid Single-Particle Langrangain Integrated Trajectory software. The United States Environmental Protection Agency’s (US EPA) human health risk assessment (HRA) model was followed to conduct the health risk assessment of ambient PM2.5 and trace elements.

Results and discussion The study shows that the prevalence of severe asthma symptoms, asthma, rhinoconjunctivitis, eczema (EE) ever, and current eczema symptoms (current ESs) among preschool children in Mabopane and Soshanguve was 15.4%, 6.8%, 18.5%, 11.9%, and 13.3%, respectively. The use of gas for cooking or heating significantly increased the risk of current severe asthma symptoms among preschool children by 20% (CI: 2.08 – 4.91; p-value < 0.001). Furthermore, the use of open-fire sources (paraffin, wood, or coal) increased the risk of severe asthma symptoms among preschool children by 87% (CI: 0.98 – 3.55; p-value = 0.057).

The use of gas and open fire sources (paraffin, wood, or coal) increased the likelihood of asthma (OR = 3.69; 95% CI: 1.22 - 11.2) and allergic rhinoconjunctivitis (OR = 2.48; 95% CI: 1.55 - 3.96). Trucks passing near homes almost the whole day during the weekdays increased the likelihood of allergic rhinoconjunctivitis (OR = 1.31; 95% CI: 0.72-1.38). Environmental tobacco smoke (ETS) exposure at preschool increased the likelihood of asthma (OR = 2.11; 95% CI: 1.49 – 2.97). ETS exposure at home increased the likelihood of allergic rhinoconjunctivitis (OR = 1.95; 95% CI: 0.52 - 7.38).

The use of open fires (paraffin, wood, or coal) increased the likelihood of EE (OR = 1.63; 95% CI: 0.76 – 3.52) and current ESs (OR=1.94; 95% CI: 1.00 – 3.74). Additionally, ETS exposure at home increased the likelihood of EE (OR = 1.66; 95% CI: 1.08 – 2.55) and current ESs (OR = 1.61; 95% CI: 1.07 – 2.43). Lastly, mothers or female guardians smoking cigarettes increased the likelihood of EE (OR = 1.50; 95% CI: 0.86 – 2.62) and current ESs (OR = 1.23; 95% CI: 0.71 – 2.13).

Parents should be informed about the health risks associated with exposing their children and community to smoking. The National Department of Health should speed up the process of promulgating indoor air pollution standards. South African road management policies should encourage integrated transport to decrease vehicle usage and promote lift clubs to reduce road traffic.

The mean levels of PM2.5, soot, BC, and OC were 10.4 μg.m-3, 1 m−1x 10–5, 0.9 μg.m-3, and 1.0 μg.m-3 respectively. The 24-hour mean PM2.5 exceeded the WHO air quality guidelines (5 μg.m-3) but did not exceed the 24-hour annual South African National Ambient Air Quality Standards (SANAAQS) (20 μg.m-3), respectively. There was no significant seasonal variation of PM2.5, with the highest mean observed in spring (13.1 μg.m−3) (p > 0.05). However, there was a temporal variation of PM2.5 on weekdays and weekends, with the highest levels observed on weekdays (11.8 μg.m−3) (p < 0.05). Six geographic air masses were observed: Cluster 1: Southeastern Indian Ocean (23%); Cluster 2: North Limpopo (32%); Cluster 3: Northern Cape (14%); Cluster 4: Short Eastern Indian Ocean (23%); Cluster 5: Long Southeastern Indian Ocean (6%); and Cluster 6: Long Southwest Atlantic Ocean (3%).

A total of 19 elements were determined: Ag, Ba, Br, Ca, Cl, Cu, Fe, K, Mn, Ni, P, S, Sb, Si, Sr, Ti, U, V, and Zn. The trace element that recorded the highest mean level for the entire sampling campaign was Fe (243 ng.m−3), followed by Si (222 ng.m−3), S (158 ng.m−3), Ca (107 ng.m−3), and K (84 ng.m−3), with no significant seasonal variation during the dry and wet seasons (p > 0.05). Fe and Si are associated with soil dust, while S and Ca are linked to industrial and construction air, such as power generation industry and construction dust. The Hazard Quotient (HQ) for total PM2.5 for adults, children, and infants was 2.1, 11.1, and 20.1, respectively, exceeding the WHO benchmark (5 μg.m−3). The HQs for trace elements S and Ti were also above 1 for infants. The Ni excess cancer was 1.2 x 10-6, and the exposure to Ni was a risk factor for cancer throughout the year.

According to the HYPLIT model, air pollution in Mabopane is affected by several provinces, namely Mpumalanga, Limpopo, Northern Cape, Eastern Cape, and Free State. Additionally, the pollution is influenced by both long- and short-range factors in the Indian Ocean. Some of these provinces are known for their air pollution sources, including mining activities, coal power plants, and biomass combustion. Therefore, the South African government should strengthen air quality management to prevent transboundary air pollution. The City of Tshwane Metropolitan Municipality should enforce air quality bylaws that include vehicle emission tests to penalise road users who do not comply with the air quality legislation.

Conclusion and Recommendations: The study has found that exposure to both outdoor and indoor air pollution sources can increase the risk of asthma, severe asthma symptoms, allergic rhinoconjunctivitis, and atopic eczema among preschool children aged 7 years old and below in Mabopane and Soshanguve. The sources of indoor and outdoor air pollution include environmental tobacco smoke, household fuel use (such as gas, wood, paraffin, and coal), and vehicle emissions (specifically from trucks).

The study also found that although the levels of outdoor PM2.5 did not exceed the South African National Ambient Air Quality Standards (SANAAQS), they exceeded the World Health Organisation (WHO) guidelines. The health risk assessment showed that even exposure to PM2.5 levels below the SANAAQS poses a risk to adults, children, and infants in Mabopane. The study suggests that the current SANAAQS for PM2.5 needs to be reviewed to better protect human health.

The study also highlighted the carcinogenic hazard of nickel (Ni), which poses a risk throughout the study period. This study contributes to the understanding of health complications associated with exposure to indoor and outdoor air pollution in the communities of Mabopane and Soshanguve. It also provides knowledge about the air distance sources contributing to air pollution in Mabopane, thus providing scientific evidence for South African policymakers to promulgate indoor and household air pollution legislation and strengthen the current air pollution legislation.

This study serves as a baseline for further epidemiology studies among preschool children aged 7 years old and below. The study recommends conducting epidemiological studies to understand the burden of respiratory diseases and their association with specific air pollutants in South African townships, as well as a source apportionment study to understand the sources of air pollution in Mabopane.

Keywords: Air pollution, PM2.5, Preschool, Health risk assessment, HYSPLIT, Trace elements, Mabopane, Soshanguve, South Africa.