The use of biocides is recommended to maintain the microbiological quality of a product and to protect it against contamination. However, with the current trend away from heavy metals and phenolic-based biocides to more environmentally acceptable ones, manufacturers may find that the use of biocides alone may not prevent the paint from becoming spoiled. If paints spoil in spite of the use of biocides, then the technical knowledge of the biocide manufacturer as well as the effectiveness of the biocide may be questioned. In fact, the issue is not the effectiveness, but the nature of these current biocides, which happen to degrade quickly in the environment. An integral strategy, which involves both the use of biocides and preventive measures to control microbial contamination, should be applied. This article outlines such an integral approach.
Depending on the growth conditions (nutrients, minerals, gas composition, temperature, pH, water activity, etc.), microorganisms can reproduce very rapidly in the paint. The growth of microorganisms, such as bacteria that reproduce by binary fission in a closed system, can be plotted as the number of cells versus the time. The resulting curve is composed of four different phases (see Figure 1).