The general perception is that exposure to pollutants leading to several health problems, in particular some cancers are exclusively associated with the outdoor air quality. In part this is true if one stays outside for a long time in streets through which substantial volume of vehicles passes through, if one lives in very close proximity to urbanised areas with these characteristics and heavy industrialised areas.
The local scenario is different from the typical polluted cities elsewhere. In Malta, at 316 km2 a good part of the island is highly urbanised and densely populated. Local traffic goes through the network of relatively narrow streets and bypass roads which connect the different districts. Added to this, several industrial activities are intertwined or are found in the vicinity of residential areas.
Although any combustion of fossil fuels (fuels, wood, gas etc.) emits several pollutants and generally is linked to outdoor activities, in the indoor environment, normal daily activities such as cooking, space heating, use of fireplaces, burning of candles and incense and others are the common sources of fine dust generation. If tobacco smoking occurs in a residence, that would be the overpowering source of fine dust generation and hence the probability of an enhanced exposure.
Infiltration of fine dust in our homes cannot be ignored because it adds up to the indoor generated dust. The chemical composition of the infiltrated dust is largely determined by the outdoor activities such as traffic exhaust, shipping fumes, power generation, construction, industrial activities, sea salt, desert dust and due to secondary particle formation.
The above mentioned scenario makes it quite an interesting, yet a distinct case to study. If our country is relatively dry all year round, and the presence of settled house dust (SHD) is ubiquitous in every Maltese residence, no matter the location, type of dwelling and apertures and/or ventilation practises, what is the SHD composed of? Is it harmful? What are the implications of continuous exposure to SHD by either inhalation, dermal contact or ingestion?
Combustion from tobacco smoke or others activities generate some very nasty, potent carcinogens to humans. Of particular interest are the levels of class 1 carcinogens (proven to cause cancer in humans) such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone [NNK] and N′-nitrosonornicotine [NNN] (which are tobacco-smoke related) and Benzo (a) Pyrene [B(a)P] and Dibenz (a,h) Anthracene [D(ah)A] (which are combustion related).
In a new, peer-reviewed publication from , from the Department of Chemistry, in collaboration with the University of California San Francisco (UCSF), analyses were carried out to characterise the chemical composition of SHD in Malta in relation to combustion activities. The study was published in the .
Samples of indoor SHD and whenever possible, outdoor settled dust were collected from several locations in Malta in 2016. For this purpose, participants were asked to allow three days without sweeping, wet dusting or washing the floors to collect enough dust mass for analysis.
This research addressed if there is significant difference in the levels of these carcinogens across the five districts in Malta and also calculated the mean carcinogenicity of polycyclic aromatic hydrocarbons in the local SHD. At UCSF, Dr Aquilina developed and optimised an efficient method to extract, clean and analyse tobacco smoke and combustion related pollutants from a very complex and challenging matrix to clean, such as dust.
Unfortunately the carcinogenicity of the mixture of several carcinogens could not be determined as the scientific basis has not been developed yet. This was the first international study to report concurrent levels of a mixture of tobacco smoke and combustion derived carcinogens from SHD.
For all pollutants analysed, there is no statistical difference in the tested dust across the different districts in Malta, no matter how much we think that some areas are more polluted more than others. In residences where smoking occurs the tobacco pollutants overpower other combustion sources compared to non-smoking houses. In non-smokers’ houses, NNK and NNN are easily detected. An analysis of PAH diagnostic ratios indicate that there is a difference between indoor and outdoor settled dust and the main sources of PAHs in our residences are infiltrated from vehicle emissions and grass and wood combustion. The important B(a)P/B(ghi)P ratio, indicator of the carcinogenic contribution, is directly linked to traffic emissions.
In comparison with other studies, our SHD has concentration levels of the nasty carcinogens similar to what was obtained in Palermo. Although the carcinogenicity of the PAHs in our SHD is on the lower end, it cannot be ignored, given that relatively fresh SHD was analysed. There is not much that can be done to avoid the build-up of these nasty chemicals in our homes. We cannot choose not to breathe and the best approach to reduce our exposure to these nasty carcinogens is to ventilate well our residences but more importantly to wash or wet dust our floors with water only, as frequently as possible.
