A potential source of pollution is from the release of waste gases through incinerator stacks. It is necessary to fit heavy duty scrubbing equipment including bag filters to remove the pollutants. There are a number of health concerns associated with both air emissions from incinerators. Recent EU legislation, the Waste Incineration Directive, implemented by the UK in December 2002, tightened up rules on incinerator emissions. The occurrence of heavy metals in association with ex-industrial sites may result in land being designated as contaminated and therefore requiring remedial action. The merits of incineration technology are questionable, and much of the debate is on the treatment options of residual waste. Plastics are likely to end up with residual waste in an incinerator. Plastics are fossil fuel based and so emit greenhouse gases.