PCBs are insulating liquids used for their non-flammable properties, mainly in transformers, whether a fire would be unacceptable and as the dielectric in capacitates. Unfortunately the mineral oil used in transformers has become cross contaminated over the years. As PCBs are fairly non-biodegradable and tend to collect in food chains legislation was brought in to prevent wide-spread contamination. Liquids containing over 50 mg/kg must be classed as injurious substance and disposed of via costly high temperature incineration. It is therefore essential those responsible for plant know their level of contamination and have strict controls on oil movements to site.