Source: Canadian Council of Ministers of the Environment, 2008, revised 2010

Polycyclic aromatic hydrocarbons

Soil contamination by polycyclic aromatic hydrocarbons (PAHs) is widespread in Canada because of the almost ubiquitous nature of their main sources, the rejection of various petroleum hydrocarbons or products of coal, and various methods / types combustion, such as vehicle exhaust and a wide variety of industrial processes.

PAHs are complex hydrocarbon groups containing at least two benzene rings juxtaposed.

Sources of polycyclic aromatic hydrocarbons

Some come from anthropogenic sources, other natural sources - usually, it is the by-products of combustion or modified terpenoids and heterocyclic compounds of plant origin. Note that forest fires and volcanic eruptions are also natural sources of PAHs.

Degradation of polycyclic aromatic hydrocarbons

The adsorption and biodegradation are the modes of the most important developments, particularly for PAHs with molecular weight is high - they remain firmly attached to the ground. PAHs with five or six cycles may have a very low bioavailability to terrestrial organisms (soil contact) or to aquatic organisms (transfer of substances takes place through groundwater).

In general, the microbial degradation of PAHs in soil is the most important process in terms of changes in the short and medium term the quantity of substances (USEPA, 1990, Wild et al, 1991.). Resistance to microbial degradation in soil or in water tends to increase also the molecular weight and the number of cycles.

If naphthalene degrades rapidly in the majority of cases, PAH four, five or six cycles tend to degrade much more slowly. In general, biodegradation is much faster under aerobic than anaerobic conditions (Neff, 1979).

Polycyclic aromatic hydrocarbons and health

With regard to human health, it focuses mainly on the carcinogenic effect of PAHs whose carcinogenic potential is known or suspected. There is sufficient scientific information on the mechanisms of genotoxicity and carcinogenicity of PAH based on in vitro studies (mammalian cell cultures and bacterial cultures) and in vivo (rodents laboratory) to conclude that PAHs considered here are known carcinogens or potential.