Polycyclic aromatic hydrocarbons (PAHs)

PAHs comprise a group of over 100 different chemicals that are produced during the incomplete burning of fuels, garbage or other organic substances such as tobacco, plant material or meats. These combustion processes produce a mixture of chemicals with soot being a well known example.

Tobacco smoke contains many chemicals including PAHs which are found in the tar that accumulates in the lungs of smokers.

Some of these PAHs are manufactured for research or are used in medicines, dyes, plastics and pesticides such as naphthalene found in mothballs. PAHs can also be found in coal tar, bitumen, crude oil, creosote and roofing tar.

The distribution of PAHs in the environment is extensive and the general public may be exposed to PAHs found in soil/dust, air, water, food or household products.

PAHs of greatest concern

The most common PAH is naphthalene which is found in mothballs

17 PAHs have been identified as being of greatest concern with regard to potential exposure and adverse health effects on humans and are thus considered as a group. These are:

• acenaphthene
• acenaphthylene
• anthracene
• benz[a]anthracene
• benzo[a]pyrene
• benzo[e]pyrene
• benzo[b]fluoranthene
• benzo[g,h,I]perylene
• benzo[j]fluoranthene
• benzo[k]fluoranthene
• chrysene
• dibenz[a,h]anthracene
• fluoranthene
• fluorene
• indeno[1,2,3-c,d]pyrene
• phenanthrene
• pyrene

PAHs usually not found singularly, but as mixtures with many different types present at the same time. This makes assessing the health effects of individual PAHs very difficult.

Health effects

PAHs can be harmful to health under some circumstances, and will depend mainly on the:

• length of time a person is exposed
• the amount one is exposed to
• the PAHs you have been exposed to
• how you were exposed - inhalation, ingestion or skin contact.

A variety of other factors can also affect health impacts from such exposure, including pre-existing health status and age.

Studies using pregnant mice fed a specific PAH known as benzo[a]pyrene showed that PAHs may interfere pregnancy. Data from these studies suggest there is a potential to product adverse reproduce effects in humans, however there are no human data to confirm this conclusion.

Those at a higher risk

The following groups have an increased susceptibility to the effects of PAHs:

• elderly who have declining organ function
• young children with immature and developing organs
• people who smoke (and therefore inhale PAHs and thus have higher exposure)
• have a history of excessive sun exposure (enhanced skin cancer response if simultaneously exposed to PAHs via skin)
• have liver and skin diseases
• women of child bearing age.
• an unborn foetus as it is recognised that PAHs may cross the placenta.

Symptoms of PAHs exposure

Short term exposure

The ability of PAHs to induce short-term health effects in humans is not clear. Occupational exposures to high levels of pollutant mixtures containing PAHs has resulted in symptoms such as:

• eye irritation
• nausea and vomiting
• diarrhoea
• confusion.

However, it is not known which PAH in the mixtures cause these effects. Mixtures of PAHs are known to cause skin effects in animals and humans such as irritation and inflammation. 

Anthracene, benzo(a)pyrene and naphthalene are direct skin irritants

Anthracene and benzo(a)pyrene are reported to be skin sensitisers, for instance cause an allergic skin response in animals and humans.

The effects of short-term exposure to children are the same as for adults. However children, who have lower bodyweights than adults, do not require as great an exposure to experience the same health effects as adults.

Long term exposure

Health effects from chronic or long-term exposure to PAHs may include:

• cataracts
• kidney and liver damage aplastic anaemia (effect on the bone cells in bone marrow that produce red blood cells)
• skin damage and photosensitisation (sensitisation to sun light)

Repeated contact with skin may induce redness and skin inflammation. Naphthalene, a specific PAH, can cause the breakdown of red blood cells if inhaled or ingested in large amounts.

Animals exposed to levels of some PAHs over long periods in laboratory studies have developed lung cancer from inhalation, stomach cancer from ingesting PAHs in food and skin cancer from skin contact.

Long-term studies of workers exposed to mixtures of PAHs and other workplace chemicals have shown an increased risk of:

• skin cancer
• lung cancer
• bladder cancer
• gastrointestinal

These studies have also reported asthma-like symptoms, lung function abnormalities, chronic bronchitis and decreased immune function. However, it is not clear from these studies whether exposure to PAHs was the cause as other potential cancer causing agents were also present.

How you may be exposed to PAHs

Most authorities indicate there are no safe level of exposure

There are a wide range of sources of PAHs, the most common being cigarette smoke, but bushfires, residential wood fires and exhaust from vehicles and fire-works are the largest producers of PAHs.

Due to the complexities of PAHs, it is best practice to minimise any exposure to any PAHs.

Where soil or water has been contaminated, appropriate management is required to reduce or prevent people contacting the PAHs. This may include preventing dust from being produced and vapours from entering homes from the soil or water. This ensures the exposure to surrounding areas is minimised and does not result in significant exposure to surrounding residents.

Testing for PAHs

For those who have a bore, it is important to test the water for bacteria and chemicals to ensure it is safe to use for its intended purpose. Contact a National Association of Testing Authorities (NATA) accredited water testing laboratories to determine if your bore water is safe for its intended purpose. 

Not sure if you have been exposed?

It is not usual to test a person to see if they have been exposed to PAHs, unless exposed in a workplace or if there is some good reason to suspect exposure to high levels of PAHs. Due to the complexity of the chemistry and the fact the body turns the PAHs into other chemicals a urine test is required, and the analysis done at specialist laboratories.

Regulations have limited the amount of PAHs in food and water, and SA Health encourages smokers to quit. The Environment Protection Agency (EPA) manages soil and water that has been contaminated to minimise exposure.

Reducing your exposure to PAHs

Contaminated soil

If you live in an area where the soil has been contaminated with PAHs, the following steps can help to reduce your exposure:

• it is not recommended vegetables are grown in contaminated soil
• to prevent dust, the soil should be covered with a thick layer of mulch (300mm) and regularly replenished or covered with a thick layer of soil, or some hard surface such as pavers.
• stabilising the soil with a ground cover can also be used as a measure to reduce dust
• wear gloves and dust masks if you need to deal with contaminated soil
• wash gardening equipment and footwear before going indoors
• have groundwater tested to ensure it is suitable for the intended purpose
• wash your hands before eating and after playing in the yard
• do not allow pets to come into contact with contaminated soil
• have bore (ground) water tested to ensure it is suitable for the intended purpose for both bacteria and chemical contamination

Some PAHs may evaporate from contaminated soil and result in the detection of odours. Should odours arising from ground sources be detected, avoid the inhalation of these odours and contact SA Health's Scientific Services for advice.

Do not remove naphthalene balls from their child resistant containers. In small children it has been found that half a mothball can cause serious adverse effects requiring hospitalisation.

Reducing your child's exposure

As young children are more at risk, refer to the following the tips to reduce their exposure to PAHs:

• do not allow young children to come into contact with the contaminated soil
• wash your child's hands before eating
• wash your child's hands after playing outdoors
• ensure toys are cleaned before being brought inside
• children should be excluded from areas where odours from ground contamination are noticed

Further information

For further information on PAHs, contact SA Health's Scientific Services.