Past, Present, and Future Options for Preservatives in Coatings
EEC and more recently, in June 2015, the
Dangerous Preparations Directive (DPD)
1999/45/EC. This has updated the classification and labeling requirements within
the EU.
In the context of isothiazolinone biocides, there was a recent key change in labeling that was introduced in the second
Adaptation to Technical Progress (ATP)
update to the CLP Regulation (published
in 2011), which contains changes in the
classification and labeling criteria for
substances and mixtures regarding sensitization. This change potentially places
a new obligation onto the customer’s
preserved products that was previously
not required. This potential change may
impact the suitability of a sensitizing biocide in a customer’s product. Note that
this regulation is not specific to isothiazolinones but rather covers any chemical
associated with a sensitization classification. However, as mentioned earlier, all
of the commonly used isothiazolinone
biocide active agents are either known or
potential skin sensitizers.
The CLP regulation now establishes
two sub-categories of skin sensitizer:
• Category 1A High Potency
• Category 1B Moderate-Low Potency
In the past, a mixture had to be clas-
sified as sensitizing if it contained >= 1
of a sensitizing component, unless the
legal classification from Annex VI for the
CLP contained a different specific con-
centration limit (SCL).
Any mixture not classified as sensi-
tizing but containing a sensitizing com-
ponent at >= 0.1% needed to carry an
additional statement on the label, the
so-called“Allergen Phrase” -- “Contains
(name of sensitizing substance). May pro-
duce an allergic reaction.”
This wording was already required in
the former EU DPD. The revised CLP in-
troduced a differentiation for substance
classification between “high-potency
sensitizers” and “moderate-low potency
sensitizers”. The concentration threshold
for the classification of mixtures has been
lowered to >= 0.1% for strong sensitiz-
ers; other sensitizers stay at 1%.
In addition, the concentration
threshold for elicitation (the Allergen
Phrase) has been lowered to 0.01% for
strong sensitizers. For any sensitizing sub-
stance with an SCL of less than 0.1% the
limit has been set to one tenth (1/10) of
the SCL.
Under CLP the Allergen Phrase is
referred to as EU H208. It is important
to note that this phrase and the application criteria are not part of the UN GHS
model regulations but a specific “EU
add-on.” This phrase is not mandatory
outside the EU.
To summarize, within the European
Union, hazard communication requirements for chemical mixtures in the context of sensitizing chemicals changed in
June of 2015. Many of the preservative
systems currently selected by coatings
formulators within the European Union
were selected to meet the challenge of
avoiding the EU H208 allergen phrase.
However, in the time since June of 2015
a new challenge for coatings formulators has appeared on the horizon. Once
again, in developing an understanding of
the future challenge, it is helpful to first
review some background.
As described above, for some sensitizing compounds, Annex VI for the CLP
describes individual specific concentration limits (SCL). If such a compound is
present in a coating formulation above
its specific concentration limit, then
the coating formulation attracts the EU
H317 phrase, and it is also required to
carry an associated GHS pictogram. If
the sensitizing compound is present below its SCL but above one tenth (1/10)
of its SCL, then the coating formulation
attracts the EU H208 allergen phrase.
No pictogram is required with EU H208.
Therefore a consumer is more likely to
notice the hazard communication associated with EU H317.
For one member of the isothiazolinone class of preservatives, there is a
recommendation to change its specific
concentration limit. In March 2016,
the Risk Assessment Committee (RAC)
of the European Chemicals Agency
(ECHA) published an opinion to reduce
the SCL, and associated EU H317 trigger concentration, for MIT (2-Methyl-
4-isothiazolin-3-one) from 1000 ppm to
15 ppm. The ECHA RAC committee is
responsible for preparing the opinion of
ECHA on proposals for harmonized classification and labeling. However, the final
decision for proposals for harmonized
classification and labeling is taken by the
European Commission through a committee procedure. So in the case of MIT,
while a proposal has been made, a final
decision has not yet been reached.
As mentioned above, many of the preservative systems currently selected by
coatings formulators within the European
Union were selected to meet the challenge
of avoiding the EU H208 allergen phrase.
Significantly, many of these preservative
systems contain MIT. Therefore, if the
classification proposal that has been put
forward by the RAC committee is approved and therefore adopted by ECHA,
then the coating formulator’s challenge
of achieving robust preservation while
avoiding hazard phrases will become
much more difficult.
Preservation – Future?
Given the adverse trends impacting the
historically popular in-can preservative
active agents, there is likely to be a reevaluation of antimicrobial active agents
from other use patterns. For example,
the pyrithione active agents, which were
traditionally used as fungicides, are finding increased use as co-biocides for in-can preservation. Use of a co-biocide
makes possible a strategy whereby robust
preservation is achieved by using a low
level of isothiazolinone preservative as a
base, and supplementing this base with
a sufficient concentration of one of the
pyrithione active agents. One benefit of
this strategy is that a powerful antimicrobial effect is achieved by combining these
two complimentary active substances,
for example by combining 1,2-benziso-
thiazolin-3-one and sodium pyrithione.
Pyrithiones target microbial membranes
by acting as a chelating agent and disrupting essential ion gradients. Bacteria use
these gradients to store energy, and fungi
as a source of energy for nutrient transport. BIT is electrophilically active and
reacts with microbial enzymes containing
thiol groups, thus disrupting a number of
vital metabolic (energy) processes.
