The use of biocides in plastics is commonplace. They are added to protect the plastic itself from degradation by microbes or alternatively to provide an external antimicrobial hygienic surface. The choice of suitable test method and the appropriate biocide can be difficult, as the different ways in which biocides work will affect how they perform under certain test protocols.

A list of frequently used test methods and commonly available biocides is provided with details of their strengths and weaknesses. In an ever-changing regulatory environment, an examination is also made of the influence of legislation on the current and future use of such biocides.

Biocides are additives used in a variety of articles including plastics. When used in plastics the annual biocide sales volumes are in excess of 2,500 tons with a value of over $175 million (147). They are used traditionally to prevent degradation of the plastic itself or more recently to impart an external anti-microbial or hygienic effect. They achieve this by killing or preventing the growth of microbes that may otherwise consume nutrients within the plastic or settle and grow on its surface. Microorganisms grow by adopting some of the raw materials within the plastic as their nutrient carbon source (food) but in addition need the correct pH, trace elements and crucially, water. When these organisms grow (and use the plastic's ingredients) it may cause the plastic to relinquish its mechanical properties. It could become brittle and lose its conductivity or flexibility. Alternatively organisms may colonise...