## 2.3.2. Biocides

Author: Thomas Wagner

Reviewers: Steven Droge, Kevin Thomas

Learning objectives:

You should be able to:

- Understand the purpose of using biocides
- Distinguish different groups of biocides
- Understand the legislation concerning the production and use of biocides
- Understand the potential impact of biocides on ecosystems

Keywords: Biocides, product types, Biocidal Product Regulation (BPR), environmental impact

Introduction

European legislation describes a biocide as ‘chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means’. The US Environmental Protection Agency (EPA), an independent agency of the U.S. federal government to protect the environment, defines biocides as ‘a diverse group of poisonous substances including preservatives, insecticides, disinfectants and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products’. The definition by the EPA includes pesticides (Chapter 2.3.1). In the scientific and non-scientific literature, the distinction between biocides, pesticides and plant protection products is often vague.

Biocides are used all around us:

- The toothpaste that you used this morning contains biocides to preserve the toothpaste
- The water that you used to flush you mouth is prepared with biocides for disinfection
- The clothes that you are wearing are impregnated with biocides to prevent smells
- The food that you ate for breakfast might have contained biocides to preserve the food
- The construction materials around you have surface coatings that contain biocides to prevent biological degradation of the material

A biocide contains an ‘active substance’, which is the chemical that is toxic to its target organism, and often contain ‘non-active co-substances’, which could help in reaching desired product parameters, such as a viscosity, pH, colour, odour or increase its handling or effectiveness. The combination of active substances and non-active substances together makes up the ‘biocidal product’. An example of a well-known biocidal product is TriChlor, which contains active substance chlorine that is used to disinfect swimming pools. Because it is impractical to store chlorine gas for the treatment of swimming pools, TriChlor tablets are added to the pool water. TriChlor is trichloroisocyanuric acid (Figure 1). When dissolved in water, the Cl atoms are replaced by H atoms, forming chlorine (Cl-) and cyanuric acid (Figure 2). The free chlorine is able to disinfect the swimming pool.

Figure 1. Trichloroisocyanuric acid (A) Figure 2. Cyanuric acid and chlorine (B)

A biocidal product can also contain multiple biologically active substances to enhance its effectivity, such as AQUCAR™ 742 produced by DuPont. It contains glutaraldehyde (Figure 3) and quaternary ammonium compounds (Figure 4) that have a synergistic toxic effect on microorganisms that are present in oilfields and could form biofilms in the pipelines.

Figure 3. Glutaraldehyde Figure 4. Quaternary ammonium compound

Product types

The biocidal products are classified into 22 different product-types by the European Chemicals Agency (ECHA) (Table 1). It is possible that an active substance can be classified in more than one product types.

Table 1. The classification of biocides in 22 product types (www.echa.europe.eu)

Main group 1: Disinfectants and general biocidal products
Product type 1 – Human hygiene biocidal products
Product type 2 – Private area and public health area disinfectants and other biocidal products
Product-type 3 – Veterinary hygiene biocidal products
Product type 4 – Food and feed area disinfectants
Product-type 5 – Drinking water disinfectants
Main group 2: Preservatives
Product-type 6 – In-can preservatives
Product-type 7 – Film preservatives
Product-type 8 – Wood preservatives
Product-type 9 – Fibre, leather, rubber and polymerised materials preservatives
Product-type 10 – Masonry preservatives
Product-type 11 – Preservatives for liquid-cooling and processing systems
Product-type 12 – Slimicides
Product-type 13 – Metalworking-fluid preservatives
Main group 3: Pest control
Product-type 14 – Rodenticides
Product-type 15 – Avidicides
Product-type 16 – Molluscicides
Product-type 17 – Piscicides
Product-type 18 – Insecticides, acaricides and products to control other arthropods
Product-type 19 – Repellents and attractants
Product-type 20 – Control of other vertebrates
Main group 4: Other biocidal products
Product-type 21 – Antifouling products
Product-type 22 – Embalming and taxidermist fluids

Legislation

In Europe, biocides are authorised for production and use by the Biocidal Products Regulation (BPR, Regulation (EU) 528/2012) of the ECHA. The BPR ‘aims to improve the functioning of the biocidal product market in the EU, while ensuring a high level of protection for humans and the environment.’ (https://echa.europe.eu/legislation). This is an alternative regulatory framework than that for the plant protection products, managed by the European Food Safety Authority (EFSA). All biocidal products go through an extensive authorisation process before they are allowed on the market. The assessment of a new active starts with the evaluation of a product by the authorities of an ECHA member state, after which the ECHA Biocidal Products Committee forms an opinion. The European Commission then makes a decision to approve or reject the new active substance based on the opinion of ECHA. This approval is granted for a maximum of 10 years and needs to be renewed after it reaches the end of the registration period. The BPR has strict criteria for new active substances, and meeting the following ‘exclusion criteria’ will result in the new active substance not being approved:

- Carcinogens, mutagens and reprotoxic substances categories 1A or 1B according to CLP regulation
- Endocrine disruptors
- Persistent, bioaccumulative and toxic (PBT) substances
- Very persistent and very bioaccumulative (vPvB) substances

In very special cases, new active substances will be allowed on the market when meeting this exclusion criteria, if they are important for public health and public interest and there are no alternatives available. To lower the pressure on public health and the environment, there is also a candidate list for active substances to be substituted for less harmful active substances when the old active substances meet the following criteria:

- It meets one of the exclusion criteria
- It is classified as a respiratory sensitizer
- Its toxicological reference values are significantly lower than those of the majority of approved active substances for the same product-type and use
- It meets two of the criteria to be considered as PBT
- It causes concern for human or animal health and for the environment even with very restrictive risk management measures
- It contains a significant proportion of non-active isomers or impurities

The impact of environmental release

The release of biocides in the environment can have huge consequences, since these products are designed to cause damage to living organisms. A classic example is the release of tributyltin from shipyards, harbours and on sailing routes from the antifouling paint on the hulls of ships (De Mora, 1996). Tributyltin was used in the antifouling paint from the 1950s on to prevent microorganisms from settling on the hulls of ships, which would increase the fuel costs and repair costs. However, the release of tributyltin from the paint resulted in a toxic effect on organisms at the bottom of the food chain, such as algae and invertebrates. Tributyltin then biomagnified in the food web, this way affecting larger predators, such as dolphins and sea otters. Eventually, tributyltin entered the diet of humans. The first legislation on the use of tributyltin for ships dates back to the 1980s, but it was not until the Rotterdam Convention of 2008 that the complete use of tributyltin as an active biocide in antifouling paints was banned. Biocides can also have an effect on the capability of the environment to deal with pollution. Microorganisms are responsible for cleaning polluted areas by using the pollutant as food-source. McLaughlin et al. (2016) studied the effect of the release of biocide glutaraldehyde in spilled water from hydraulic fracturing on the microbial activity and found that the microbial activity was hampered by the biocide glutaraldehyde. Hence, because of the biocide, the environment was not or slower capable to return to its original state.

References

De Mora, S.J. (1996). Tributyltin: case study of an environmental contaminant, Vol. 8, Cambridge Univ. Press

McLaughlin, M.C., Borch, T., Blotevogel, J. (2016). Spills of hydraulic fracturing chemicals on agricultural topsoil: Biodegradation, sorption and co-contaminant interactions, Environmental Science & Technology 50, 6071-6078