There are more than 100 different PAHs and they generally occur as complex mixtures in combustion products such as soot.
PAHs are known by several names, including polycyclic organic matter (POM), polynuclear aromatic hydrocarbons, polynuclear aromatics (PNAs) and polynuclear hydrocarbons. They can occur in the air, either attached to dust particles or as solids in soil or sediment.
The health effects of individual PAHs are not universal. There are 17 PAHs that are suspected to be more harmful than the others and the chances of exposure to these are comparatively higher.
PAHs have long been recognised as chemical carcinogens and may be a major cause of human cancers. Benzo[a]pyrene (BaP), for example, is a ubiquitous environmental pollutant derived from the incomplete pyrolysis of organic materials, and appears to be among the most active carcinogenic agents to which humans are exposed.
PAHs and the environment
PAHs mainly enter the environment from the exhausts of trucks, firewood burning, chimneys, forest fires, etc. They enter surface water through industrial plant discharge and wastewater treatment plants. Properties such as solubility in water and volatility determine the distribution of PAHs in the environment.
Generally, PAHs are less solubility in water; they are present in the atmosphere either as vapours or particles stuck to the surfaces of small dust motes.
Once emitted to the atmosphere, weight influences the fate of gaseous PAH mixtures. Heavier PAHs tend to adsorb to particulate matter, whereas lighter PAHs tend to remain gaseous until removed by precipitation. PAH concentrations in water tend to be low because of their weak solubility, which leads to accumulation in sediments and aquatic organisms. PAHs can be absorbed by plants and subsequently accumulate in soil.
They are known travel long distances before rainfall brings them back down to Earth. Some PAHs evaporate into the atmosphere from surface water, but most adhere to solid particles and settle at the bottoms of rivers. In soils, PAHs become very tightly bound. Some PAHs do evaporate from surface soils to the air, and some have been known to contaminate underground water.
The PAH content of plants and animals living on the land or in water can be many times higher than the actual content of soil- or water-bound PAHs.
Human exposure to PAHs
“As PAHs are present throughout the environment, avoiding exposure — either at home, outside or at work — is difficult,” says Dr Benny Antony, Joint Manging Director, Arjuna Natural Extracts. “And you won’t be exposed to an individual PAH, but a mixture of PAHs.”
Exposure to PAH vapours or PAHs that are attached to dust and other particles in the air is most likely. PAHs have been found in some drinking water supplies in the United States, and food grown in contaminated soil or air may also contain PAHs. Cooking meat or other foods at high temperatures, such as during grilling, actually increases the amount of PAHs in the food.
Physiology and PAHs
PAHs can enter the body through the lungs while breathing contaminated air. However, it is not clearly understood how rapidly or completely the lungs absorb PAHs. Drinking water, food, soil or dust particles that contain PAHs also represent routes of entry for these chemicals, but absorption is generally slow when PAHs are swallowed. Under normal conditions of environmental exposure, PAHs could enter the body if your skin comes into contact with soil that contains high levels of PAHs.
The rate at which PAHs enter your body by eating, drinking or through the skin is influenced by the presence of other compounds that you may be exposed to at the same time.
PAHs mostly end up in adipose tissues and any other areas of the body that contain fat. They are stored mostly in the kidneys, liver and fat tissues. A small amount is found in the spleen, adrenal glands and ovaries.
PAHs are converted in the body into many other different substances. Some of these new substances are more harmful and some are less harmful than the original PAHs. Results from animal studies show that PAHs are not stored in the body for a long time. Most PAHs that enter the body leave the body within a few days, primarily through faeces and urine.
Health and PAHs
The association of human cancer with exposure to polycyclic aromatic hydrocarbons (PAHs) dates back to Sir Percivall Pott’s analysis of chimney sweeps’ cancer in 1775. PAHs can be harmful to human health under certain circumstances. Several PAHs have caused tumours in laboratory animals when the air breathed or food eaten contained these substances, or after long periods of skin contact.
Studies of the effect of PAHs on people show that individuals exposed by respiration or skin contact for long periods to mixtures that contain PAHs and other compounds can also develop cancer.
Mice fed high levels of benzo[a]pyrene during pregnancy had difficulty reproducing and so did their offspring. The offspring of pregnant mice fed benzo[a]pyrene also showed other harmful effects, such as birth defects and decreased body weight. Similar effects could occur in people; but, as yet, we have no information to show that these effects do occur.
Studies in animals have also shown that PAHs can cause harmful effects on skin, body fluids and the immune system after both short- and long-term exposure. These effects have not been reported in people. The Department of Health and Human Services (DHHS) has determined that some PAHs are known animal carcinogens. The International Agency for Research on Cancer (IARC) has determined that some are carcinogenic to humans.
EU regulation on PAHs
Herbal health supplement manufacturers may currently be unaware of the new regulation on PAHs. On 27 October 2015, the European Commission published Regulation (EU) No. 2015/1933, amending Annex to Regulation (EC) No. 1881/2006, with regard to maximum levels of polycyclic aromatic hydrocarbons (PAHs) in foodstuffs.
The EU has set maximum levels for PAHs in foodstuffs via Regulation (EC) No. 1881/2006 amended by Regulation (EU) No 835/2011. Recently, the EU published Regulation (EU) No. 2015/1933 with regard to maximum levels of PAHs in cocoa fibre, banana chips, food supplements, dried herbs and dried spices.
In the light of recent scientific evidence and the opinion adopted by the European Food Safety Authority's (EFSA) Scientific Panel on Contaminants in the Food Chain (CONTAM Panel) in 2008, the Commission has determined that PAH contamination will be measured by the sum of four PAH substances — benzo[a]pyrene, benz[a]anthracene, benzo[b]fluoranthene and chrysene — as opposed to the level of benzo[a]pyrene as a single substance.
The new Regulation sets out maximum values for both the sum of the four substances and benzo[a]pyrene on its own, which will be maintained to ensure comparability of previous and future data.
Analysis methods
There are several well-established procedures for the analysis of PAHs. Most of them involve pretreatment of the sample, wherein the PAHs are extracted from the complex mixtures in which they are present into a new matrix by liquid/liquid, solid-phase and/or ultrasonic extractions. Pretreatment methods often serve as a precleaning step for interfering compounds and also a preconcentration step.
The application of ultrasound to accelerate or assist PAH (and other inorganic and organic compounds) extraction from solid materials is sometimes used. Extracts are measured by either HPLC or GC (depending on the nature of the sample and its volatility) with the detectors being mass spectrometer (MS), ultraviolet (UV) or fluorescence spectrophotometers.
PAH elimination in health supplements
In nutraceuticals and food supplements, PAHs may be formed during processes such as drying, roasting, baking, frying or grilling. Direct fire-drying and heating processes used during the production of some oils of plant origin can also result in high levels of PAHs.
Dr Benny Antony explains: “Although the effective removal of PAHs is possible, alternative methods that avoid the initial formation of PAHs should be used whenever possible.” Vegetables may be contaminated by the deposition of airborne particles and/or by being grown in contaminated soil. The waxy surface of vegetables and fruits can concentrate low molecular mass PAHs by surface adsorption.
The concentrations of PAHs are generally greater on the plant surface, such as the peel or outer leaves, than in internal tissue. Consequently, washing or peeling may remove a significant proportion of the total PAH bioburden. Particle-bound high molecular mass PAHs that remain on the surface are easily washed off, whereas low molecular mass compounds that are in the vapour phase can penetrate the waxy layer of fruits and vegetables and are less efficiently removed by washing.
In response to the European Union regulations to prevent polycyclic aromatic hydrocarbons (PAHs) and other contaminants in food supplements, Arjuna offers its Safe Pure line of products.
“The main challenge is to not remove the required and active components of the extracts, as this results in products with potentially lower efficacies. It can even change the profile of the components significantly to an extent that the product does not reflect its natural properties,” notes Dr Benny Antony.
There are techniques available today that remove contaminants, such as supercritical carbon dioxide, activated charcoal and hexane, but they are non-selective processes that can cause the loss of active ingredients, be harmful to the environment or pose a risk of toxicity. Arjuna Natural Extracts has developed its own technology that completely removes PAHs, complies with EU specifications and has been tested and validated within its own and international laboratories.
