Dr Lisa Bushby investigates the dangers to health of exposure to biocodes.

Biocides are widely used. In the EU, almost 400,000 tonnes of active substances are estimated to be sold each year. The reason for such wide-spread use is their ability to suppress those organisms, such as pests, moulds and bacteria that are harmful to human or animal health, with applications ranging from insect repellents and disinfectants to industrial chemicals.

This article uses the examples of anti-fouling paints, wood preservatives and metalworking fluids to investigate the major health effects associated with biocides (skin disorders, cancer and breathing disorders) — specifically as a result of their biocidal active substance ingredients.

Protecting workers

Through EU legislation, biocidal active substances are subject to a two-stage approval process — the so-called "active substances", which give biocidal products their properties, being approved by the EU (and listed in an Annex to the Directive), and the authorisation of the products themselves, which is left to the individual Member States, with provision being made for a product approved in one Member State to be used in another.

Risk characterisation

A requirement of active substance approval is a “risk characterisation”, that is, the estimation of the incidence and severity of the adverse effects likely to occur in a human population, animals or environmental compartments due to actual or predicted exposure to any active substance or substance of concern in a biocidal product. This may include “risk estimation”, ie the quantification of that likelihood.

However, there is a significant gap in terms of available information on the effects of exposure or environmental and health impacts in many cases, as well as regarding safer alternatives, and as a result, there are biocidal products with allergic, ecotoxic, carcinogenic and endocrine disrupting properties available on the market.

The revised Biocidal Products Directive comes into force in 2013. One of its aims will be to make the data available on biocides more freely available, while still retaining a level of corporate confidentiality.

Local defence

Finally, there are the control measures implemented at the workplace. The use of safer alternatives, restricting the number of employees who could be exposed to the biocide, limiting the quantity used and stored, and providing suitable respiratory and personal protective equipment.

Allergic response: anti-fouling agents

Copper compounds have successfully been used in paints to prevent the process of “antifouling”, and continue to be used as metal sheeting, although there is a debate as to the safety of copper.

Cuprous oxide and cuprous thiocyanate, used as anti-fouling agents in paints, are harmful if swallowed. Inhalation of droplets of copper salts is reported to cause irritation of the nasal mucous membranes and sometimes of the pharynx. The salts have an occupational exposure standard for dusts and mists of 1mg/m3 over an 8-hour reference period and 2mg/m3 over a 15-minute reference period.

In addition, the use of “booster biocides” in paints to improve the copper salt’s performance introduces additional health hazards. Some of the booster biocides approved for use in anti-fouling coatings, eg dichlofluanid, have the potential to cause skin sensitisation (or allergic contact dermatitis). This can damage the skin’s barrier function leaving it dry, cracked and scaly. A Health and Safety Executive study focusing on operator exposure to anti-fouling coatings during their application identified that the potential for skin contamination was high. It is therefore essential that adequate precautions are taken to control the associated risk of dermatitis.

Booster biocides can also be irritating to the respiratory system. The risk to health from exposure by inhalation should therefore be assessed and appropriate precautions taken.

The majority of anti-fouling coatings contain solvents which are harmful by inhalation and by skin or eye contact. They can have a narcotic effect resulting in headache, dizziness, irritability and mental confusion. Skin contact can cause defatting of the skin and dermatitis, either through their own action or by permitting other substances to affect the skin. If anti-fouling coatings are used which contain solvents, adequate precautions will need to be taken to protect against these hazards.

Cancer: wood preserving products

Still an active substance (for certain professional uses) in the EU, there have been concerns over the carcinogenic potential of the well-known wood preservatives of creosote and coal tar creosote for some time.

In 1994, to control the specification of the creosote in amateur products, the EU restricted the levels of one of the chemicals in amateur creosote products, benzo-α-pyrene, to less than 0.005% by mass, and this was implemented in Great Britain through restrictions on the specification of products approved under the Control of Pesticides Regulations 1986, as amended.

Since then, a study led an EU scientific committee concluded that creosote has a greater potential to cause cancer than previously thought, and the level of the risk gave the EU reasons for concern. To protect human health and the environment, the European Commission therefore took action to prohibit amateur use of creosote products and to restrict the use of creosote treated wood as a precautionary measure.

Approvals for professional and industrial creosote/coal tar creosote products were allowed to continue, subject to restrictions on the specification of the products and restrictions on where wood that has been treated with creosote/coal tar creosote could be used.

Concerns remain over other currently-approved wood preservatives, eg tebuconazole and boric acid, which are both classified as toxic for reproduction.

Breathing disorders: metalworking fluids

Owing to their method of application, metalworking fluids are often associated with breathing disorders, eg occupational asthma, bronchitis and irritation of the upper respiratory tract, breathing difficulties or, rarely, a more serious lung disease called extrinsic allergic alveolitis, which can cause increasingly severe breathing difficulties in recurrent episodes, following repeated exposure.

Added to prevent bacterial contamination, it can be the biocidal product itself that is responsible for these effects when it is inhaled as part of the mist, eg biocides such as glutaraldehyde (toxic by inhalation and may cause sensitisation by inhalation) and octhilinone (toxic by inhalation).

A word on formaldehyde

Although not an active substance, or added directly to metalworking fluids itself, formaldehyde has attracted a lot of opinion owing to those biocide additives (some bactericides) that act by releasing small amounts of formaldehyde under specific conditions. These are known as formaldehyde releasers.

It has been known for some time that chronic exposure of rats to formaldehyde vapour at high levels over their lifetime can lead to the formation of nasopharyngeal cancer. It is believed that the key contributory factor to this event is repetitive irritation of the nasal mucosal lining, leading to increased cell death and regeneration, ultimately resulting in cancer at the site of contact.

In 2004, following the publication of data from human epidemiological studies, the International Agency for Research on Cancer reclassified formaldehyde from Group 2A (probably carcinogenic to humans) to Group 1 (known human carcinogen). (Formaldehyde is currently classified as a Category 3 carcinogen in the EU.)

It is the opinion of the UK Lubricant Association that a review on the classification status of formaldehyde should wait until additional epidemiological information is available.

It should also be noted that biocides that rely on the action of formaldehyde use the substance bound strongly to other molecules and it is only present at very low concentrations. A major industry study conducted in the US (some years ago) with triazine (a formaldehyde release biocide) showed that very low levels were detectable in metalworking operations, and these were well below reporting levels and occupational exposure limits.

The next article in this series will take a deeper look at the legislative framework around biocides.

Last reviewed 8 August 2012