VOC: everything you need to know

Have you ever heard of VOCs? Did you know that many of the products and materials we have in our homes emit volatile organic compounds? What can this entail?
Don't worry, you will find the answers to your doubts in this article.

In recent decades, there has been an increasing focus on air pollution and much has been done on emission control and the reduction or elimination of pollutants. Although there is much concern about outdoor pollution, it is equally important to consider indoor pollution!

Read the article to find out what VOCs actually are, what hazards they have, how to choose the best products and try to reduce emissions in work and home environments, because with a little extra care we can do a lot for our health and the environment!

Now let us take a step back and first see the definition of an organic compound. Article 268 of Legislative Decree No 152 of 2006 ('Norme in materia ambientale') provides us with one. An organic compound is any compound containing at least the element carbon (C) and one or more of the elements hydrogen (H), oxygen (O), fluorine (F), chlorine (Cl), bromine (Br), iodine (I), sulphur (S), phosphorus (P), silicon (Si) or nitrogen (N), with the exception of carbon oxides (e.g. CO₂ ) and inorganic carbonates and bicarbonates.

The same decree also gives the definition of a volatile organic compound: any organic compound that has at 293.15 K (i.e. at 20 °C) a vapour pressure of 0.01 kPa or more, or that has a corresponding volatility under particular conditions of use.

"Vapour pressure? Volatility? OK, but I don't know anything about these things!" you might think. Actually, these are scientific terms describing rather simple physical phenomena. The two terms define the aptitude of solid or liquid substances to change to the vapour state (in the first case we speak of sublimation, in the second of evaporation).

The European Directive 2004/42 defines a VOC as 'any organic compound having an initial boiling point of 250 °C or less, measured at a standard pressure of 101.3 kPa'.

To this is added a further subdivision provided by the World Health Organisation, which has identified four classes:

• very volatile organic compounds (VVOCs) that have a boiling point of < 0 to 50-100 °C;
• volatile organic compounds (VOC) that have a boiling point of 50-100 to 240-260 °C;
• semi-volatile organic compounds (SVOCs) that have a boiling point of 240-260 to 380-400 °C;
• organic compounds associated with particulate matter (POM) that have a boiling point above 380 °C.

The VOC definitions in the two standards mentioned above refer to two different physical properties: the first is based on vapour pressure (also called vapour pressure) and is related to evaporation, the second is based on boiling point. What is the difference? Both boiling and evaporation are phase changes in which substances pass from the liquid to the gaseous state (vaporisation), but whereas with evaporation only the surface of a liquid is involved, with boiling the entire volume is involved. It follows that some compounds may be considered VOCs on the basis of one criterion but not the other, although it should be made clear that most volatile organic compounds fulfil both conditions.

The recent European Directive No 2284 of 2016 introduced the definition of non-methane volatile organic compounds (NMVOCs), understood as "all organic compounds, other than methane, that can produce photochemical oxidants by reaction with nitrogen oxides in the presence of solar radiation". This definition - which took over and modified the one in the previous Directive 2001/81/EC - takes into account the fact that VOCs can produce, through chemical reactions catalysed by solar radiation, the so-called photochemical smog, i.e. the set of polluting compounds present in the air.

To summarise the concepts seen above, we can say that volatile organic compounds are a class comprising different chemical compounds characterised by easy vaporisation at room temperature and capable of reacting in the troposphere to form polluting compounds. They include aliphatic (e.g. butane, n-hexane) and aromatic (e.g. benzene, toluene) hydrocarbons, halogen derivatives (e.g. dichloromethane), aldehydes (e.g. formaldehyde), ketone (e.g. ketamine), and alkyl derivatives (e.g. ketone). formaldehyde), ketones (e.g. acetone), alcohols (e.g. ethanol, butanol), esters (e.g. ethyl acetate) and other compounds (e.g. acetic acid, acrylamide, nicotine, acetonitrile).

VOCs can be divided into two categories according to their origin. One therefore speaks of:

• Biogenic VOCs, if the compounds are emitted in nature (e.g. terpenes);

• Anthropogenic VOCs, if the compounds are emitted by human activities (e.g. oil-derived solvents).

Then there are biogenic compounds that are extrapolated and used in the production of products, thus becoming anthropogenic.

VOCs may originate from vehicle or industrial emissions (outdoor sources), but also from many products and materials present or used in public and private buildings (indoor sources). Volatile organic compounds may come from building materials - e.g. paints, varnishes, glues, upholstery - or from cleaning products, deodorants, pesticides, cosmetics, disinfectants, cigarette smoke and heating appliances.

Let's look in detail at some of the compounds:

• Aliphatic hydrocarbons can be found in fuels, perfumes, propellants, refrigerants, paints or insecticides. Propane, for example, is used as a fuel, as a refrigerant, as a solvent and as a propellant; butane is used as a fuel, as a refrigerant and as a reagent; hexane is used as a fuel and as a solvent; limonene is used as a perfume, solvent and insecticide;

• halogen derivatives can be found in pesticides, degreasers and refrigerants. Chloroform, for example, is used as a solvent, refrigerant or glue; dichloromethane is used as a solvent; CFCs (chlorofluorocarbons) were mainly used as refrigerants; pentachlorophenol (PCP) is used as an insecticide, antifouling and preservative; tetrachloroethylene is used in dry cleaning and as a degreasing solvent;

• aromatic hydrocarbons can be found in varnishes and paints, in glues, in detergents, in fuels. Benzene has been widely used in fuels, lubricants, paints, detergents and to make other chemicals, but it can also be found in tobacco smoke; toluene is used in fuels and as a solvent and reagent; xylene is used as a solvent, diluent and detergent;

• alcohols can be found in detergents, disinfectants, paints, cosmetics and adhesives. In addition to being found in alcoholic beverages, perfumes and disinfectants, ethanol is used as a solvent and fuel; methanol is used as a solvent, as a fuel and as a reagent in industrial chemical processes;

• aldehydes can be found in resins, disinfectants, biocides and furniture. Formaldehyde is used as a disinfectant, bactericide, preservative, reagent, and glue in both wall and ceiling panels and wood-based panels; acetaldehyde, besides being used as a reagent in industrial synthesis processes, can also be found in traces in tobacco smoke.

By now we are used to using the word outdoor to define the outdoor environment, while by the term indoor we mean all those non-industrial environments that are used for living, leisure, work and transport, thus including in this definition public and private offices, community facilities (schools, hospitals, banks, hotels, etc.) and those intended for social activities (restaurants, sports facilities, cinemas, etc.), public and private means of transport and, of course, our homes.

Numerous surveys of people's lifestyles have shown that most of their time is spent in confined environments. Whereas 20 years ago people spent an average of only 10-12% of their time outdoors, they now spend as little as 5-6%. Furthermore, various studies have shown that the pollutants in the outdoor air are the same as those in the indoor air, but that the concentration of the latter is often higher: we are therefore more exposed to indoor emissions than to outdoor emissions.

As we mentioned in the previous section, VOCs can be released into the external and internal environment. The major external sources are of both anthropogenic and biogenic origin, such as certain compounds emitted by plants (especially isoprene, monoterpenes and other terpenoids), compounds from the biological decomposition of organic matter, or methane from fermentation that may occur in manure farms or landfills. External sources of anthropogenic origin are vehicle exhaust gases, industrial solvent emissions and, in a lesser form, fumes from thermal power plant combustion.

The main indoor sources of VOCs are anthropogenic and come from cleaning products, building materials, furniture, cosmetics, deodorants, insecticides, heating devices, cigarette smoke, printers and copiers, glues, paints, adhesives and various solvents.

A report by the Istituto Superiore di Sanità (ISS) on 'Monitoring Strategies for Volatile Organic Compounds Indoor' explains that a distinction can be made between VOC sources according to trends in emission levels over time. Generally, VOC emissions can be distinguished into continuous or intermittent. In turn, the former can be divided into constant or irregular, and the latter into recurring or occasional.

Continuous and constant sources are those that generate emissions that are uniform over time, such as linoleum, cork, wood finishes or furniture that emits formaldehyde (the emission may last for several years). On the other hand, continuous but irregular sources are those that produce emissions that decrease over time: examples are paints, glues and enamels.

A classic example of a recurring intermittent source is the cooking of food, whereas room fragrances are an occasional intermittent source.

VOCs that are released into the environment, whether indoors or outdoors, can pose a risk to human health.

In recent decades, there has been an increasing focus on air pollution and much has been done on emission control, the reduction or elimination of polluting components and the identification of maximum allowable concentrations for different categories of compounds. Although there is much concern about outdoor pollution, as we have seen, it is equally important to consider indoor pollution, since it can be responsible for the onset of pathologies or the aggravation of existing pathologies.

The extent of exposure to volatile organic compounds in indoor environments changes depending on various factors:

• the evaporation rate of volatile organic compounds;
• the concentration of VOCs;
• room ventilation;
• the individual's exposure time.

Several studies have shown that VOCs indoors, in the presence of indoor emission sources and reduced air recirculation, can be present in quantities as much as 10 or 20 times higher than in the outdoor environment.

VOCs can cause two types of toxicity:

• acute (short-term) toxicity, which is the result of a single exposure or several repeated exposures over the course of a day. Effects include headaches, nausea, irritation of the eyes, throat and nose, dizziness and asthma;
• chronic (long-term) toxicity, which is the result of long-term exposure. Effects include (depending on the compound generating them) damage to the central nervous system, kidneys or liver.

It should be remembered that not all volatile organic compounds present specific dangers to humans: examples are methane or propane. Others have even been classified by the IARC (International Agency for Research on Cancer) as carcinogenic: these include formaldehyde and benzene.

In Appendix B of the ISS report on 'Monitoring Strategies for Volatile Organic Compounds in Indoor Environments' you can see the list of the main VOCs that may be present in indoor environments and their CAS numbers, specific to each substance. You can go to the ECHA website (European Chemicals Agency) and enter the CAS numbers to check the specific hazards of individual compounds.

To date, numerous studies have been conducted on health effects based on exposure to individual chemicals, while fewer studies have been conducted on combined chemicals.

In this respect, European Directive 42/2004 is important because it requires an assessment of the total VOCs emitted by paints, varnishes and bodywork products.

Over the years, several regulations, both European and Italian, have come out regarding VOC emissions. Among the most important are:

• European Directive No 42 of 2004 on the 'limitation of emissions of volatile organic compounds due to the use of organic solvents in certain paints and varnishes and in certain vehicle refinishing products', which was followed by Italian implementation with Legislative Decree No 161 of 2006 and subsequent amendments. This European legislation aims to reduce air pollution from VOCs, as they contribute to the formation of tropospheric ozone. Paints and varnishes may therefore only be placed on the market if they have a content equal to or lower than the values indicated in the directive and if they are appropriately labelled (for further details, read the section 'VOC limits and declaration');

• Directive (EU) 2016/2284 (repealing Directive 2001/81/EC) on the 'reduction of national emissions of certain atmospheric pollutants', transposed by Italy through Legislative Decree No 81 of 2018, was enacted to achieve levels of air quality that do not pose significant risks and negative impacts to the environment and human health. This European legislation stipulates the reduction of anthropogenic atmospheric emissions of sulphur dioxide (SO₂ ), nitrogen oxides (NO_x ), non-methane volatile organic compounds (NMVOCs), ammonia (NH₃ ) and fine particulate matter (PM_2,5 ) and requires the development and implementation of national air pollution control and monitoring programmes. Until 31 December 2019, it will be possible to apply the national emission limits under the previous Legislative Decree no. 171/2004, which set a limit of 1159 kilotonnes of VOCs per year. The current Italian decree instead sets the reduction of VOC emissions compared to 2005 at 35% from 2020 to 2029 and 46% from 2030;

• Directive 2010/75/EU on "industrial emissions (integrated pollution prevention and control)", transposed by Italy through Legislative Decree No. 46/2014, establishes rules aimed at avoiding, or at least reducing, emissions from industrial activities into the air, water and soil and the generation of waste, in order to protect the environment;

• Legislative Decree No. 152/2006 on 'Regulations on environmental matters' and also known as the 'Environment Consolidation Act' or 'Environment Code', lays down rules on soil and water protection, waste management, reduction of air pollution, environmental impact assessment and compensation for environmental damage. The decree has undergone numerous amendments over the years, the latest being introduced by Legislative Decree No. 21 of 2018.
  Part Five of the TU deals with 'regulations on air protection and reduction of emissions into the atmosphere'. Going into more detail, Title I legislates on 'prevention and limitation of atmospheric emissions from plants and activities' by establishing 'emission values, prescriptions, methods of sampling and analysis of emissions and criteria for assessing the conformity of measured values'. Article 275 deals specifically with VOC emissions.

Many of the VOCs we mentioned at the beginning of this article present specific hazards, both to humans and to the environment. While some have even gone so far as to ban their use in various areas, for the entire category of volatile organic compounds, legislation has been in place for years to limit their emissions, as we have seen in the previous section 'VOC regulations'.

In addition to the limits set for overall VOC emissions (excluding methane) defined in Legislative Decree No. 81/2018, there are, as we have already seen, precise limits also for emissions from paints, varnishes and bodywork products.

According to Annex I of Directive 2004/42/EC, paints and varnishes are defined as ‘coatings applied to buildings, their trim and fittings, and associated structures for decorative, functional and protective purpose’. They are subdivided into:

1. ‘matt coatings for interior walls and ceilings’;
2. ‘glossy coatings for interior walls and ceilings’;
3. ‘coatings for exterior walls of mineral substrate’;
4. ‘interior/exterior trim and cladding paints for wood, metal or plastic’;
5. ‘interior/exterior trim varnishes and woodstains’;
6. ‘minimal build woodstains’;
7. ‘primers’;
8. ‘building primers’;
9. ‘one-pack performance coatings’;
10. ‘two-pack performance coatings’;
11. ‘multicoloured coatings’;
12. ‘decorative effect coatings’.

Article 4 of both the European directive and the Italian decree define the labelling of these types of products. Therefore, they can only be placed on the market if they are indicated on the label:

• the type of product (as defined in Annex I) and its VOC limit value expressed in g/l (as defined in Annex II);

• the maximum VOC content the product may contain, expressed in g/l of ready-to-use product.

The legislation outlines both the limit values for the various categories, distinguishing between water- and solvent-based products (Annex II), and the analytical methods for calculating VOCs (Annex III): ISO 11890-1, ISO 11890-2 or ASTMD 2369 where reactive diluents are present in the product.

With regard to analytical methods, we would like to emphasise that it is impossible to obtain an analysis with a VOC value of zero. Therefore, you should be wary of those products that are labelled 'VOC zero' or 'VOC free', as this is untrue and misleading. Proof of this can be found by requesting a VOC analysis certificate stating this fact.

Can we do something to reduce VOC emissions? Of course we can!

We can act on several fronts, starting with the use of transports. Obviously the bicycle is the most environmentally friendly vehicle, but if one decides to use a motor vehicle, it is good to remember that the release of hydrocarbons into the atmosphere is related to the characteristics of the fuel itself. While methane usually burns completely, moving towards increasingly dense mixtures (LPG > petrol > diesel) proportionally increases the likelihood of unburned hydrocarbons and other compounds being released into the atmosphere.

As is also indicated in a Ministry of Health brochure on volatile organic compounds, activities aimed at reducing VOCs in indoor environments can be numerous:

• minimise the use of materials/products containing VOCs (detergents, room perfumers, pesticides, etc.);
• favour water-based products with low certified VOC values;
• correctly follow the instructions for use on product labels;
• adequately ventilate rooms, especially after the installation of building materials, wall coverings and furniture;
• carry out adequate and regular maintenance of cooling/heating devices;
• make regular checks on mechanical ventilation systems;
• do not smoke;
• dry-clean clothes only when strictly necessary;
• use the ventilation hood with exhaust to the outside when cooking;

In short, with a little extra care we can do a lot for our health, that of our animal friends and for the environment!

We hope with this article we have clarified your doubts and given you food for thought. If you have any other questions and curiosities, do not hesitate to write to us!

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