European Coatings: June 2017
In the course of the systematic re-evaluation of all available biocidal active substances which is being carried out under the biocidal products regulation, it is emerging that the range of suitable active ingredients for in-can preservatives is narrowing more and more. With no major innovations expected in the biocides market, a bottleneck is looming that threatens the future of water-borne technologies according to a paper by Dr Christof Walter, German Paint and Printing Ink Association (VdL), Martin Glöckner, German Construction Chemicals Industry (Deutsche Bauchemie) and Dr Axel Heßland, German Adhesives Industry Association (Industrieverband Klebstoffe).
Recent decades have seen solvent-borne products largely being superseded by their water-borne counterparts in adhesives, paints, coatings and construction chemicals, as well as many other products that can be processed as liquids. However, welcome this development may be in terms of protection of occupational health, consumers and the environment, there is a downside to the replacement of organic solvents by water: susceptibility to mould and bacteria. Consequently, it is essential that products be protected against microbial attack.
IMPORTANCE OF PRESERVATION
Even when the level of industrial hygiene is very high, the introduction of germs and spores can never be completely ruled out, e.g. via the residual water content of pigments and fillers. Colonisation generally renders such products unfit for purpose and so they have to disposed of at great cost. This can be prevented by using suitable biocidal active ingredients (in-can preservatives), an approach that makes many water-borne technologies practicable in the first place.
Adequate range of biocidal active ingredients needed
From a cursory glance at the list of in-can preservatives that are undergoing or have received authorisation as part of the review of existing active substances, it would seem that they are available in sufficient number. The problem is that not all active ingredients are suitable for all applications. Thus, sensitivity to oxidation and stability in the correct pH range play a role, but odour and possible discolouration also need to be considered. In addition, most active ingredients target certain organisms only. In order that gaps may be avoided and resistance build-up prevented, what is needed is a kind of "tool box” of biocidal active ingredients, which are each employed at different concentrations. The maxim governing the use of biocides is "as little as possible, as much as necessary”. If the biocidal concentrations are too low, the biocides will not be effective at all or there is a risk that resistance will build up, as we have seen in the field of antibiotics.
Which active ingredients are still available?
For the time being, essentially two classes of compounds can still be used (see box), namely isothiazolinones and formaldehyde releasers. With the classification of formaldehyde as a category 1B carcinogen, formaldehyde releasers have come under considerable pressure. As for isothiazolinone-based preservatives, harmonised classification and labelling led to the imposition several years ago of a substance-specific labelling threshold of 15 ppm for CMIT/MIT (3:1 mixture) – the most effective active substance in this class. As a result, CMIT/MIT has been extensively replaced by other active ingredient combinations (e.g. those based on MIT; see box). As CMIT has a markedly higher skin sensitisation potential than MIT, the number of sensitisation cases has declined markedly in recent years.
However, the opinion of the ECHA Risk Assessment Committee is that a labelling threshold of 15 ppm should also apply to MIT. This raises the fear that an upper threshold of 15 ppm will be imposed on DIY applications, as happened in the case of CMIT/MIT, during active ingredient authorisation. When one considers that MIT (as opposed to CMIT/MIT) is not effective at that concentration, this would be tantamount to a ban on MIT. Given the limited availability of alternative substances – for which further restrictions can be expected (see box) – manufacturers would be forced to use CMIT/MIT instead of MIT-based preservatives, a step that would not chime with consumer and occupational health and safety because of the heightened sensitisation potential.
Unfortunately, the innovations which authorities often call for cannot be conjured up out of a hat. In most cases, occupational hygiene alone will not solve the problem. What is more, there are applications in which it is simply impossible to have a germ-free environment, such as in some printing processes where the ink is in contact with the paper via the rollers. New, innovative active ingredients are needed. Yet innovations in the biocides market are unlikely in view of the huge research effort needed, enormous fees for authorising active substances, uncertainty over whether the active ingredient will ultimately be granted authorisation, and the comparatively small market for in-can preservatives.
A holistic approach is required
For this reason, the Association of the German Paint and Printing Ink Association (VdL), the German Construction Chemicals Industry (Deutsche Bauchemie) and the German Adhesives Industry Association (Industrieverband Klebstoffe) are advocating a holistic approach to the evaluation of biocidal active ingredients which takes their high functional benefits into account. In the absence of an holistic approach, the future of water-borne technologies is under threat. The use of active substances with a higher sensitising potential or even reversion back to solvents would be a huge step backwards in terms of occupational, environmental and consumer protection. The manufacturing industry is therefore appealing to all stakeholders to do everything in their power to ensure that this retrograde step is not taken and that the positive progress made in recent years continues and is not jeopardised.