Volatile Organic Compounds Are Hazardous to Health
Volatile organic compounds (VOCs) have been extensively studied over recent years and have been implicated as perhaps the most important feature of sick building syndrome (recently relabeled as tight building syndrome). VOCs are known to have the potency to cause symptoms like headache; eye; nose and throat irritation; respiratory distress; mental fatigue and flu like symptoms.
The Concentration Level that VOCs Become Hazardous
VOCs and their reaction products (ozone and aldehydes) are increasingly regarded as posing unacceptable risks to public and occupational health.
Scientists currently believe that the symptoms of chemical sensitivity [cell-meditated allergy] are seldom caused by exposure to single compounds (except in the occupational setting), they are generally caused by exposure to a group of compounds. This is often referred to as the total stress load or cocktail effect.
To express the effect of multiple chemical exposure, scientists must take consideration of the total volatile organic compounds (TVOC) in the environment being studied. Furthermore, a line cannot be drawn between the indoor and outdoor environments, as the TVOC inside and outside can react cumulatively and/or synergistically. This is important because most dwellings in the UK are naturally ventilated.
The effect of individual VOCs cannot be extrapolated and used to determine the effects of the TVOC because individual VOCs in the non-industrial environment rarely exceed the relevant occupational threshold limits.
Scientists have suggested that the TVOC threshold in the non-industrial settings should be less than 0.16mg/m3. It is important that the health of the subjects is taken into consideration as the threshold limit outlined above may have to be significantly reduced, especially for individuals with impaired immune systems or if children are likely to be exposed. Special consideration may also have to be given to individuals in the population who have multiple chemical sensitivity (MCS), individuals with MCS can react adversely to minute concentrations of chemicals.
VOCs can be Detected by Smell
Many VOCs exist below the threshold of smell and therefore cannot be detected by the human nose. As the concentration of a compound increases, the more likely it will rise above the odour detection threshold. Some compounds can be detected at fairly low levels, for example the odour detection threshold fo formaldehyde is 0.06mg/m3.
Terpenes and related terpenoid compounds, among the most widely distributed of naturally occurring compounds, are often referred to as isoprenoid compounds because of the occurrence in their structure of the five-carbon skeleton of isoprene.
In the strict sense terpenes are volatile aromatic hydrocarbons of empirical formula C10 H16: In the wider sense they include sesquiterpene, diterpenes and higher polymers, as well as various oxygen-containing compounds derived from the terpene hydrocarbons considered as polymers of isoprene, they may be acyclic, monocyclic, or dycyclic. Terpenes have a characteristic, usually pleasant (but sometimes unpleasant) odour, and show olefinic properties, being easily oxidised and ozmized.
A great number of oxygen-containing isoprenoid compounds are known (e.g.- linalool), in addition to their olefinic properties, to have the characteristics of the functional group, primary or secondary alcohol, aldehyde or ketone. Many are optically active.
VOCs Emitted By Other Vegetation
Although isoprene and monoterpene components (eg, pinene, liminene, myrcene) are widely emitted by pine trees and oak trees, forests are generally confined to poor quality arable land on mountainous terrain which presumably would be sparsely populated. Forests grown on low ground adjacent to residential areas may give rise to similar health complaints from residents, however, due to the geographical location of both the forests and the residents it must be acknowledged that the residents (in most cases) would have made a conscious decision to live in tandem with nature in the country. Most hardy country folk are very much aware of the naturally elevated levels of pollen, fungal spores and terpenes, and yet still prefer to live there.
Ozone is one of many secondary pollutant produced by photochemical reactions. Others can be produced by ozone interacting with the aliphatic and olefinic compounds emitted from oilseed rape, producing further secondary pollutants like aldehydes and organic gases. Interestingly, the production of secondary organic gases increases with increased humidity and temperature. The following monoterpenes have the characteristic to interact with ozone:- pinene, sabinene, myrcene, ocimene and limonene.
Isoprene, terpenes, alcohols, carbonyl compounds and esters are the major components released by plant emissions (Gaedel, 1986). Some of these can actively participate in photochemical smog pollution, being extremely reactive with OH radicals and ozone (Dimitriades, 1981; Atshuller, 1983). Research in this field has focused mainly on the quantitative determination of isoprene and monoterpene components (e.g. alpha-pinene, beta-pinene, carene, limonene, myrecene) as these exhibit high potentials for ozone production.
Layzell reported in 1991; one suggestion which is likely to affect all mammalian species is ‘invisible’ air pollution, such as low level ozone - this is worse in rural areas, and ozone is known to affect bronchial hyperreactivity (Lioy, 1985).
Seaton, (now retired) chairman of the Government’s Expert Panel on Air Quality Standards and has recommended that the present maximum level of ozone be reduced from 60 ppb to 40 ppb following measurements in London which revealed that ozone levels regularly exceed 95 ppb. Seaton advised that the new figure was set very low, at a level at which no health effects were likely in any circumstances. It interesting, and perhaps concerning, to note that today ozone levels in rural areas regularly exceed 200ppb.
The author believes that in light of the excessive levels of harmful ozone found in rural areas, and with the knowledge that oilseed rape (major ozone producer) cultivation has increased by a phenomenal figure in excess of 100 fold over the last thirty years, this must raise serious questions about the ability of oilseed rape to produce harmful pollutants, thereby considerably elevating the natural levels of pollutants present in the rural environment.
It is also extremely important to note one of Soutar’s conclusions in her 2004 oilseed rape research paper; The general prevalence of seasonal symptoms in rural areas is of interest, and a proportion of these cases is likely to be caused by factors other than allergy [non-immunological]. Release of chemicals by plants and natural rises in summer ozone levels may be contributors.
The TVOC Concentration
At the very least, the multiplicity of VOCs from oilseed rape may act cumulatively on the bodies immune system, and the effects will be compounded. In this type of situation multiple VOCs are generally described as the total VOC (TVOC) concentration. Individual occupational threshold exposure limits listed in occupational safety standards become irrelevant, as each of the compounds in the group could well be below their individual threshold limits.
If multiple VOCs from oilseed rape act synergistically, the VOCs become interactive and can result in the production of other compounds which can be far more harmful than the cumulative effects of the compounds. In this situation, the data from the resulting compounds of synergism should then be cumulative with all the other non-reactive compounds present.
The Definition of Irritant
Outside the scientific setting irritant is used to describe a perceived sensation, like smell, which can give rise to complaints from individuals who are disturbed by the smell. In general terms, things that stimulate our sense of touch, smell or taste but do not affect the function of the body in any way, should be described as irritants. In the occupational setting however, any substance which is recognised as a controlled substance which can affect the functions of the body is also called an irritant. Irritant, when described in occupational medicine, is wide ranging and is frequently used to describe carcinogens, mutagens, allergens and toxins, etc. It is important to realise that when health professionals [i.e. research scientists] advise the public that a substance is an irritant, the public perception of that irritant is likely be something quite different.
Some Important Considerations about VOCs
Inhalation of VOCs appear to be the most important route of exposure. Among the chemical properties lipophilicity and solubility in water are extremely important for the behaviour of a compound in the body.
In general, VOCs are lipid soluble and easily absorbed through the lungs.
The distribution of a VOC and its metabolities largely depends on the route of transportation in the body. In the case of lipophilic compounds, this may mainly be the lymphatic system. The VOC first passes the respiratory system before it is circulated in the blood. [A lipophilic compound is therefore a good candidate for causing cell-mediated allergy].
Specific attention to VOCs on the immune system have been, for the most part, ignored. Toxicologists have tended to concentrate on the effects of VOCs on target organs, toxicokinetic properties and interactions, and the bio-transformation of VOCs. Consequently, research into immune system dysfunction caused by VOCs is a relatively new field studied by immunotoxicologists.
In 1976, Seinen and Willems were surprised to find that organotins were immunotoxic to rats. This effect was previously overlooked because knowledge of the immune system was rarely incorporated in protocol of toxicology at that time. During the last thirty years many studies have focussed on the adverse effects of organotins on the immune system. Because of the large amount of information available, they are regarded nowadays as immunological model compounds with suppressive effect on T-cell development and function.
In 1985, Ravnskoy hypothsized that hydrocarbons had two mechanisms of action, toxicological and immunological. Ravnskov proposed that hydrocarbons were immunosuppressive, causing defective elimination of antigen.
Johnnsen, et al, hypothesized that lipophilic VOCs may destabilize the lipid multilayer of tear fluid, and that this mechanism could be at least partly responsible for eye irritation and allow irritants to easily penetrate the lipid multilayer. A degreasing effect of lipophilic VOCs dissolving the lipid multilayer of the tear fluid has been proposed as a mechanism of eye irritation.
Only little is known about the effects of low level VOC exposures characteristic for non-industrial environments (Molhave). Evidence from experiments and investigations indicates the following about the most frequent effects of VOCs on humans.
Generally, the responding tissues are mucousal membranes in eyes, nose and throat; skin in face, neck and hands; upper and lower airways.
The most frequent effects seem to be acute. They may, like perception of odours, show adaptation. Some effects may be sub-acute in which they, like headache, are expected to increase with increasing exposure time. [Molhave doesn’t look beyond the lipid layer].
Author - Armitage; copyright 2007