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What is biocide and why are biocides used in paint products?

Published 21.10.2021


People like to enjoy harmony of colours in their environment. Using various types of paint is one of the most popular ways for creating it. And often private consumers use various paint products without being aware that they are like complex chemical cocktails consisting not only solvents, binders and pigments, but also numerous additives that contribute to various product properties that extend far beyond just colour. Among the additive groups deserving certain attention are biocides - chemical substances intended to destroy, deter, render harmless or exert a controlling effect on any harmful organism.

This blog post provides an insight into the following topics:    

  • What is biocide
  • Biocides and paint product industry
  • Biocide impact on human health and environment
  • EU regulations regarding biocide use
  • Consumer choice and responsibility regarding biocides

What is biocide?

Biocides (bio-live; cide - poison) are poisonous chemical substances intended to destroy, deter, render harmless or exert a controlling effect on different harmful life forms from microbes to rodents (a1). Biocides are usually added to various liquid products in order to control and limit the biological activity.

Depending on their intended application biocides are:

  • Pesticides - fungicides, herbicides, insecticides, algicides, molluscicides, miticides, rodenticides;

  • Antimicrobials - germicides, antibiotics, antibacterials, antivirals, antifungals, antiprotozoals, antiparasitics (a).

There is also a distinction to be made in understanding biocides. Namely,  it distinguishes a biocidal active substance and a biocidal product. Simply put, a biocidal active substance is the only ingredient or one of the ingredients of a biocidal product.

Biocidal product

According to the Directive 98/8/EC (Biocidal Products Directive), the definition of a biocidal products is as follows: “Active substances and preparations containing one or more active substances, put up in the form in which they are supplied to the user, intended to destroy, deter, render harmless, prevent the action of, or otherwise exert a controlling effect on any harmful organism by chemical or biological means” (b).

In other words - biocidal products are derivatives or combinations of one or more biocidal active substances made into a certain purpose end products therefore targeting and controlling specific life forms. Paint manufacturers also use them to ensure additional intended product properties, such as viscosity, pH level, colour, etc. 

In Europe biocidal products are categorised in four main groups - Disinfectants, Preservatives,  Pest control and Other biocidal products. These four groups consist of 22 biocidal product types. 

Biocides and paint product industry

As majority of paints are water - based and filled in cans for distribution and handling, biocides are added as means of protection against microbes and bacteria as well as aquatic organisms and algae, thus increasing paint products’ shelf-life and paint film resilience through time. The main biological threats to paints and surface coatings are fungi, algae and bacteria, thus the biocide additives to paints are mostly fungicides, algicides and bactericides (c;d).

Paint products that fall under the category of biocidal products include three distinguished product types. Out of the above- mentioned 22 product types, paint and coating ingredients lie under PT 6: Preservatives for products during storage, PT 7: Film preservatives and also PT21: Antifouling products.

PT 6, Preservatives for products during storage (in-can preservatives)

In-can preservatives may be added to paints and coatings during the p     roduct formulation stage and they are intended to increase the paint product shelf- life. These biocide preservatives could remain on the coated surface during the service-life of the products depending on mechanical as well as environmental and other factors.

Typical in-can preservative chemicals include: isothiazolones and formaldehyde donors (g).

PT 7, Film preservatives

Film preservatives are biocidal products used to eliminate or      limit theactivity of undesirable microorganisms on the treated surface (film) of a material or object that includes both fungal and algal biocides. Most of the topcoat paints available on the market contain film preservatives.

Typical fungicides used in the paint industry for film preservation: chlorothalonil, IPBC, octyl isothiazolone, zinc pyrithione, heterocyclic N, S compounds and N-haloalkyl thiol compounds.

Typical algaecides used in the paint industry for film preservation: Diuron, Irgarol™, Terbutryn (e; f).

PT 21, Antifouling products

Biocidal products that control the fouling organism growth on treated surfaces that are exposed specifically to aquatic environments, for example, marine vessels and equipment (e; f).

Health impacts

If we focus on the health impacts from exposure to biocides surprisingly little is known or can be found in the available literature, which is easily accessible for consumers. Namely , there is very little data available about biocide emissions from paints which is surprising because even with the fact that biocides are regulated, they are widely used by people who are not fully aware of their potential harmful effects (g).

Knowing the role of biocides as preservatives in paints we can further explore some of these substances and their known health impacts (all other biocides mentioned in this article may be individually researched upon interest):

The Isothiozolinone family of preservatives

Methylisothiazolinone (MIT), Chloromethylisothiazolinone (CMIT) Benzisothiazolinone (BIT) belong to the Isothiozolinone family of preservatives widely used as paint preservatives because of limited alternatives. According to the information onPubchem, all three of them have corrosive and irritating properties and are hazardous to environment. Methylisothiazolinone and Chloromethylisothiazolinone also pose risks of acute toxicity. In addition these compounds are volatile, thus with potential harm through inhaling. The Isothiozolinone may cause allergic contact dermatitis or in greater concentrations also chemical burns. 

Labelling: In the European Union cans of paint containing Isothiozolinones must carry a label  indicating that it is a skin sensitizer. Some certified paints in the EU may also carry the label EUH 208: “May produce an allergic reaction” (h; i; j).

  • Iodopropynyl Butyl Carbamate (IPBC)

Iodopropynyl butylcarbamate (IPBC) has been long used in paint preservation as a fungicide and bactericide. Possible health effects form IPBC include allergic contact dermatitis, redness, swelling, itching, and fluid-filled blisters. Another possible health concern is possible adverse effects on the human immune system, although more research is necessary (k; l).

  • Bronopol

Bronopol is also a widely used bactericide in paints among other products. According to the US EPA, bronopol poses high toxicity by the dermal route (meaning through skin to bloodstream), while also being recognised as skin and eye irritant      and posing slight      toxicity when inhaled (m).

  • Diuron

Diuron is an algacid that is reported to cause bladder, kidney, and uterine cancers when fed to mice at moderate doses.  According to the European Chemicals Agency, diuron is a suspected human carcinogen as well and is under assessment as endocrine disruptant (n;o).

  • Formaldehyde

Formaldehyde is a gaseous carcinogenic compound that can be released from biocides added to paint. It can cause irritation of      skin, eyes, nose, and throat and elevated levels of exposure may cause various types of cancers. To read more about health and environmental impacts of formaldehyde, visit blogpost

To sumup, biocidal products can contain substances and VOCs that can cause allergic, ecotoxic and carcinogenic reactions in humans as well as endocrine disruptions, although more elaborate research regarding humans is necessary. Most affected groups are people working in the paint and varnish industry as well as non-professional users, chemically-sensitive people and pregnant women.

Environmental impacts

In order to understand the impact of biocides on the environment, it is necessary to look closer at the role of two major biocide groups discussed in the context of paint and coating products - pesticides and antimicrobials.

Pesticide and antimicrobial run-off with water can take place from the painted surface both indoors and outdoors through households, urban areas etc. At this point through the adsorption process chemical compounds may become bound to the water cycle further contaminating ground waters, surface waters, soils and biota. Namely, biocides can further act in the environment in accordance to their manufactured purpose - which is by definition to limit or control biological activity (p;r).

Pesticides as environmental contaminators

Pesticides are unique contaminants due to the high toxicity levels they impose, having the ability of harming life forms also beyond the ones initially targeted. In addition, the ability of pesticides to eliminate  species can further promote development or spread of other species prolonging further dependency on pesticides while simultaneously adding to the associated health and environmental risks of pesticide use.

 As concerns paint and coatings industry, the most frequently used pesticides are fungicides. Fungicide release in the environment can happen from run off of painted surfaces (buildings, rooftops etc.) in urban environments, contributing to a continuous fungicide contamination of aquatic ecosystems, where fungicides can be toxic to a range of non-target organisms (s; t).

Antimicrobial paint additives as environmental contaminators

Antimicrobial paints are mostly used in healthcare facilities      but they are also gaining popularity  for residential applications. Although the antimicrobial paints can kill germs including MRSA, Staph, and E. coli and in residential applications it is desirable due to mold and mildew limiting properties, the downside of using these paints is growing concerns of  antimicrobial resistance (AMR). AMR is a term describing ph     enomena “when bacteria, viruses, fungi and parasites change over time and no longer respond to medicines making infections harder to treat and increasing the risk of disease spread, severe illness and death” (u;v). 

Knowing the potential impact of pesticides and antimicrobial paint additives it is important to understand the concept of life cycle assessment of paint products and also to consider the end-of-life stage of  particular products. Knowing that the paint film will last on a surface for a limited number of years, certainly not forever, it is important to acknowledge all biocidal products as potential environmental contaminants.



Consumer knowledge and responsibility

Taking into account that the substances, which are effective in limiting microorganisms, have potential negative impact on human health and environment, it is important for consumers      before choosing      a biocidal product to think about the following aspects:

  1.      The purpose for the use of biocidal product.
  2.      Possible alternatives that probably pose a less significant threat to human health and environment.

EU regulations for biocides

The European Union has developed rules and evaluation systems for biocidal products and biocidal active substances, which are intended to protect human and animal health as well as the environment they inhabit. The requirements of the regulatory framework  makes it complicated, time-consuming and often expensive to release new biocidal products in the market. There are two significant documents controlling biocidal product availability in the EU market - the Biocidal Products Directive (Directive 98/8/EC) and the Biocidal Products Regulation (Regulation (EU) No 528/2012) (w).

In order to check, if specific paint product is an authorised biocidal product in the EU/EEA market according to both directives mentioned above, you can visit the website of the European Chemical Agency,  where over 5200 authorised biocidal products can be searched for individually or downloaded as a list (excluding the products that have been on market before year 2000).

However, according to the opposing view, the regulations for biocides of the last decades do not serve to the goals of cleaner environmental and human wellbeing.  In stead they pave the way to increase marketing of biocidal products through the developed systematic “authorisation procedure”, not clearly acknowledging  the effects these chemicals and their combinations have or might have on human health and ecosystems (z).


One of the most important tools empowering consumers to make safe and informed choices is a product label, bridging the gap between the manufacturer and the end-user.

For consumers who want to avoid biocidal products, the top ecolabels to look for are the followingEU Ecolabel, Nordic Ecolabel, Green Seal, GreenGuard and Cradle to Cradle.

In addition, consumers should avoid purchasing and using  antifungal paints, since most likely those  are biocidal products.

Eco labels

If it is no possible to avoid using biocidal products, then certain measures should be taken for safety reasons:

  • Read the product label to identify, if the product is authorised and approved as well as thoroughly follow the safety instructions.
  • Store biocides in a safe place tightly covered in the original container to avoid any spillage.
  • Dispose of biocides and the      containers of biocidal products according to the product label. If unsure about the proper way of disposal, contact your local      municipality waste disposal department or agency.
  • In case of emergency, inform the authorities about the authorisation number of biocidal product as well as the active substances it contains.




Biocides in paint products have potentially significant negative environmental impacts and impacts on human health. However, biocidal products are widely available in the market due to their useful properties and ease of application.

Thus, the responsibility for health impacts as well as impact on ecosystems related to the use of certain paint products to a wide extent is in the hands of private consumers, when they make their product choices for domestic use. Such tools as product labels and regulated product lists can raise their awareness levels and even ensure certain level of consumer protection. However, complete avoidance of hazardous chemicals while using most of the commercially available paints is almost  impossible. Therefore the safest choices are, when the use of biocidal products is limited to the minimum necessary, such as by using paints from trusted sources that produce biocide-free coatings orby using dry or powder paints that mostly do not require biocide use in the formulation stage.    


Author: written by Anse Romančuka, edited by Linda Kikuste






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