Air-monitoring systems used in Malta and overseas only give partial information about the toxicity of the air we breathe and may be resulting in underestimating lung cancer risks, a new study has shown.
The air contains a complex mixture of carcinogenic compounds, most of which are not included in the international list of mandatory compounds to be monitored, according to the study that alerts policymakers that lung cancer risks are being underestimated.
Titled Evaluation of the cancer risk from PAHs by inhalation: are current methods fit for purpose?, the study was funded by the UK Natural Environment Research Council and carried out by Noel Aquilina, from the University of Malta’s Department of Chemistry, and Roy Harrison, from the University of Birmingham, UK. It was published in the influential scientific journal Environment International.
Excluding tobacco smoking and radon, it is well documented that exposure to fine particulate matter is one of the main causes of lung cancer caused by air pollution. Among these fine particles, one finds polycyclic aromatic hydrocarbons (PAHs), which are a class of compounds emitted by any combustion process – be it a forest fire, the burning of a candle or a tyre or exhaust from vehicles, combusting a fossil fuel. When inhaled, these particles travel deep into the lung and may cause lung cancer later.
Noel Aquilina.“When it comes to the knowledge about the toxic particles we are inhaling, we have a gap. For the carcinogenic PAHs, European policymakers follow the binding obligations outlined in the Air Quality Directive. Data from a few international studies, looking into a bigger range of PAHs, some of which are more toxic than the ones we are measuring, has been used to show we are underestimating the carcinogenicity,” said Aquilina.
According to the WHO’s International Agency for Research on Cancer (IARC), globally, 11.4 per cent (2.2 million) of the new cancers in 2020 were lung cancers, being at a similar incidence and occurrence of breast cancer.
When it comes to the knowledge about the toxic particles we are inhaling, we have a gap
Normally, about 90 per cent of lung cancer cases are related to tobacco smoking and about two per cent are accounted for by outdoor air pollution and second-hand smoke. When it comes to Malta, according to the IARC, in 2020, lung cancer ranked third of all new cancers (10.3 per cent) and first for the number of cancer deaths (20.1 per cent).
Over the past 50 years, both the US Environmental Protection Agency and the European Commission, through the Air Quality Directive, have made the monitoring and reporting of 16 legacy PAHs (of which seven are proven carcinogenic) mandatory.
Aquilina explained that, in recent years, scientists have become aware that there are more than 100 PAHs; yet, to date, only the 16 legacy or seven carcinogenic ones are routinely monitored.
Aquilina and Harrison analysed six international studies that together looked at eight other PAHs which are more carcinogenic than Benzo[a]pyrene (B[a]P) but not included in the routine monitoring. They calculated that if these eight compounds are added to the mixture of the seven carcinogenic PAHs, the carcinogenicity increases by up to 12 per cent.
This new information underscores the fact that the use of B[a]P as a marker compound of the PAH mixture or of the seven carcinogenic PAHs to derive the risk attributable to PAH exposure presents high uncertainty.