In the cross hairs: Biocidal active substances

By Gabi Büttner, Umco.

Biocidal active substances are needed more urgently than ever before in the paints and coatings sector. Solvent-based products are increasingly disappearing, for the protection of humans and the environment and as a result water-based systems are steadily becoming more widespread – but these require the use of biocidal active substances.

Biocidal products containing these active substances are used as in-can preservatives and film preservatives to prevent the formation of mould and algae in damaged paint and façade coatings, amongst other uses. The first active substance approvals for in-can preservatives are starting to impact companies in the form of restrictions.

Product-Types 6 and 7 – overlaps

In-can preservatives (product-type 6) are intended to protect water-borne paints in containers from microbial deterioration, which could otherwise discolour them or alter their viscosity. Film preservatives (product-type 7), by contrast, are intended to protect walls and facades from microbial deterioration and algal growth which would otherwise discolour the surface and damage the coating. Despite the different fields of application, there is substantial overlap as far as the active substances employed are concerned: the two most important of these are zinc pyrithione and the isothiazolinone class of substances. Active substances for approval for each product-type have been systematically reassessed over many years as part of the Existing Substances Review Programme. Active substances falling under product-type 6 are scheduled for review before those of product-type 7. Particularly where identical active substances are concerned, current approvals results for in-can preservatives may suggest the results that can be expected for film preservatives. According to the timetable for the approval of active substances, all product-type 6 and 7 open approvals decisions must be made within the next five years. Initial results from the approval processes are falling in the direction of either the substitution of active substances or stricter classifications and labelling.

Exclusion and substitution

The exclusion and substitution of active substances presents a challenge, as they are essentially based on hazard criteria and not on a risk assessment. This points to a possibility that substance classes per se will be excluded. For example, the classification of formaldehyde as a carcinogen had a negative impact on the entire group of formaldehyde releasers that are used as in-can preservatives. Regardless of whether its use is in product-types 6 or 7, the future of zinc pyrithione as an active substance is still uncertain because it could suffer the same fate as that of the formaldehyde releasers. Zinc pyrithione is currently under review for a harmonised classification as toxic to reproduction, the outcome is still undecided.

Labelling limits – Tantamount to a ban

However, exclusion and substitution are not the only reasons for the substantial, continuous decline in active substances and families of active substances. Further restrictions on use result from the substance-specific labelling limits. For example, isothiazolinones are known to have a skin sensitisation potential and are rightly assessed very carefully. Dashing the hopes of the industry, however, the legislator has adopted a hazard-based rather than a risk-based approach to the assessment of active ingredients. Consequently, less importance is attached to use and safe handling than to the hazard potential. This is shown in the RAC’s proposal for the substance MIT. The isothiazolinone mixture CMIT/MIT has been subject to a labelling limit of 15 ppm since 2002 because of its high potential for skin sensitisation. The RAC is proposing to apply this limit to MIT as well, when in fact MIT is actually an alternative because of its lower skin sensitisation potential. Unlike CMIT/MIT, MIT in this concentration does not effectively preserve products during storage, and so the labelling limit is tantamount to a ban on MIT use by the public. It remains to be seen what decisions be will taken concerning the other isothiazolinones for both in-can preservatives and film preservatives. Decisions made to date would suggest that the choice of active substances available for the various applications will continue to shrink due to these labelling limits.

Assessing active substances in isolation

The question as to if preservation and film protection have been examined sufficiently in the round can be answered with a clear “no” for the moment. The problem with assessing active substances for the coatings industry in isolation is that any such assessment will mask a critical decline in the number of available alternatives, and this will only be realised when it is too late. In the case of in-can preservatives, the associations present call for all active substances of a given product-type to be assessed concurrently is going unheeded. This request, aimed at keeping the big picture of possible preservative alternatives in mind, may also have an effect of the future of film preservatives. It would seem that currently everything in the industry is up in the air. Novel, innovative active substances will not be available in the short term and the hazard-based approach is not expected to be replaced by a more risk-based approach. The challenge facing the industry is to combine the few remaining active substances available with a view to covering a huge range of uses for in-can preservatives and film preservatives.

The BPR takes a nuanced approach to the exclusion or restriction of an active substance:

• Article 5 – Exclusion criteria:
  • Active substances which are classified as being of concern due to their properties (CMR, PBT/vPvB, endocrine-disrupting) shall not be approved.
• Article 10 – Active substances which are candidates for substitution:
  • Inhalation allergens, active substances which meet two of the three criteria for being PBT, as well as active substances which fall under Article 5, but whose use is indispensable, e.g., for socio-economic reasons, are considered candidates for substitution. They can receive conditional approval, but such approval has a shorter period of validity as they are to be replaced to the largest possible extent in the medium term.
• Article 23 – Comparative assessment of biocidal products:
  • The competent authority concerned must carry out a comparative assessment before authorisation of a biocidal product containing an active substance as referred to in Article 10. In this case, it needs to be verified whether there are alternatives with less hazardous active substances which are at least as effective and whether the chemical diversity of the remaining active substances is adequate to prevent the occurrence of resistance.
• CLH:
  • In addition and at any time, an active substance can be assigned a specific concentration limit (SCL) via the harmonised classification and labelling process, and this can have a substantial impact on use.

Book tip

Microbicides in Coatings by Frank Sauer gives a comprehensive overview of the working mechanisms and possible applications of microbicides for coatings – invaluable for formulators and technicians as well as for business people with a basic knowledge of chemistry and biology.