It is easy to forget that we are not out of reach of pollutants inside our homes. Research investigating polycyclic aromatic hydrocarbons (PAHs) in the Hudson Bay community, San Francisco, U.S. indicates that the public health concerns of
these pollutants are notable to developing girls.
PAHs come from tobacco smoke, vehicle exhaust, smoked meats and coal-star sealings from pavements.
Other natural sources of this chemical include coal, crude oil and gasoline. Moreover, PAHs are also classified as a probable human carcinogen as it can disrupt the endocrine system.
Exposure to these pollutantsㅡclassified as priority pollutants by the Environmental Protection Agency (EPA)ㅡcan occur through inhalation of vapours, skin exposure and ingestion of contaminated water sources.
The Centers for Disease Control and Prevention (CDC) measured PAH metabolites in the urine of more than 2,504 girls aged
six years and older during a survey from 2003 to 2004. This was possible because these chemicals are excreted through urine.
When introduced into our bodies through the skin, respiratory and gastric tract, these potential endocrine disruptors are metabolised into monohydroxy-PAHs (OH-PAHs) before they are expelled from the body.
However, OH-PAHs have the ability to interact in a similar way to oestrogenㅡa hormone which plays a role in women’s development and reproduction. Since OH-PAH has a similar molecular structure
to oestrogen, it has the ability to bind to oestrogen
receptors in the body, referred to as oestrogenic activity.
‘PAHs are also classified as a probable human carcinogen as it can disrupt the endocrine system.’
In the human body, when a molecule such as a hormone binds with a receptor, like a lock and key, it is often to initiate or stop a reaction. When OH-PAH engages in oestrogenic activity, research shows that it may cause a disruption in the
endocrine system, where reactions may occur when they are not supposed to happen. This type of activity has the potential for a developmental susceptibility, particularly throughout puberty.
A Bay Area, California, study on developing girls
The LEGACY (Lessons in Epidemiology and Genetics of Adult Cancer from Youth) cohort study was carried out on a group of girls living in California, United States. Researchers examined the link between pubertal timing and urinary PAHs
The LEGACY Girls study surveyed 359 girls, finding strong evidence of exposure to various PAHs. In particular, girls in the cohort from 10 to 13 years old appeared to have higher concentrations of this pollutant in urine samples compared to
The study also included a series of questionnaires to assess lifetime exposure to PAHs: outdoor sources such as traffic, type of neighbourhood and indoor sources including fuel used for home heating and cooking (electric, gas, coal,
firewood, synthetic logs). It assessed the use of fireplaces, candles, incense, smoking and finally if the girls and their mothers consumed grilled or barbecued foods.
‘This type of activity has the potential for a developmental susceptibility, particularly in an individual going through puberty.’
The racial implications of high-traffic environments
Living near a vehicle-congested environment can carry a risk of air pollution. Within the study, most girls lived in residential neighbourhoods (91%), and almost half lived in neighbourhoods with moderate or heavy traffic (46%).
According to questionnaires, Hispanic girls and mixed race girls were more likely to live in residential areas with low walkability due to traffic and live in homes with smokers. These vehicle-congested areas can carry higher concentrations
of naphthalene and fluorene, two types of PAH metabolites, compared with neighbourhoods where traffic is lighter. Benzo(a)pyrene, another car-exhaust
pollutant, was found in lower concentrations in these environments.
PAHs pollutants found in the home
Central heating can be a considerable source of indoor PAHs in homes. Gas heated homes in particular can carry several types of phenanthrene exposure compared to electric heating.
Candles and incense were found to be associated with naphthalene pollutants, although frequent use was not associated with higher concentrations. Interestingly, the same PAH pollutant mentioned was also linked to the consumption of smoked
or grilled meat and fish.
‘Vehicle-congested areas can carry higher concentrations of naphthalene and fluorene, two types of PAH metabolites.’
Additionally, some of these pollutants associated with the consumption of smoked or barbecued meats were more concentrated within two days of sample collection, aligning with similar studies.
Hispanic girls and mixed race girls were also more likely to be living in homes with smokers than the rest of the cohort, but the results found no PAH metabolites associated with exposure to cigarette smoke. However, girls who smoked within
two days of proving samples had detectable levels of various PAH metabolites.
Girls and young women of colour bear the brunt of PAH exposure
Moreover, results uncovered various PAH chemicals appearing at higher levels in girls and young women of colour including African-American, Hispanic, and Asian-American girls. In particular, several naphthalene metabolites were found in
higher concentrations than those associated with traffic, smoking, and candle-lighting use.
The study included girls with various ethnicities: 48% White, 29% Hispanic, 13% Asian-American, 6% African-American and 4% mixed race. The higher risk for Hispanic, Black and Asian girls was also found in similar studies which assessed the
risk of cancer in prepubescent girls.
‘Naphthalene metabolites were found in higher concentrations than those associated with traffic, smoking and candle-lighting use.’
Pollution may be exacerbated by summer temperatures
The study concluded that samples collected over the summer months had higher concentrations of PAHs metabolites compared to samples taken over autumn and winter. In particular, those associated with traffic, smoked and grilled meat
pollution, may be found at higher levels as the air temperatures rise.
Researchers talk about the fact that given how grilling food may be an activity preferred in summer months, combined with the PAHs tendency for volatility, there can be more chances for exposure. The risks exist when the pollutant is
airborne and inhaled, as well as when it is directly consumed.
PAH pollutants found in the home in line with other studies
Overall, PAHs metabolite levels were considered high and in line with similar cancer cohort and CDC studies, notably the Breast Cancer and the Environment Research Program (BCERP) study. The vehicle exhaust associated pollutants in these
cancer studies was found at higher levels in this study.
This type of car PAH-related pollutant was detected in most samples of the Bay Area study and in what is considered to be high concentrations. This pollutant is considered a possible carcinogen, but how widespread is it?
Most children living in urban areas may be exposed to vehicle pollution for levels depending on area of residence and various other factors. For example, a study on children living in the Valencian region in Spain found that nine out of
eleven PAH metabolites were detected in the systems 78% of the population size of 566. Most importantly, the study emphasises that multiple sources of PAH may be at play when evaluating exposure.
While it is important in medicine to address vulnerable populations, the study suggests exposure and frequency to these different exposure is where the vulnerability lies. We may not be able to remove vehicle exhaust from the air so easily,
but it may be possible to reduce exposure to cigarette smoking, candles and grilled and barbecue foods which add on to the pollution to our bodies.
As always, representation is important to be able to apply the results found in any scientific study, and studies such as this one, which monitored the effects of pollution on developing children and adolescents, should strive to include
more people of colour the same way the recruitment of 50:50 female and male is considered desirable in clinical studies.
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