The traditional method of removing the toxic metals, such as lead, cadmium, arsenic, mercury and chromium, from emissions utilizes particulate control devices such as electrostatic precipitators or baghouses (fabric filters). The former, while being very robust, are not efficient, and the latter, though more efficient, suffer from breakage and blockage and need careful, regular and expensive maintenance.

Mercury is particularly difficult to control. At the temperature of combustion it is a gas, and evades the particulate controls. Because of this, waste incineration has been a major source of environmental mercury. Many incinerators use activated carbon to absorb the mercury, but this is another expensive item, and requires continuous monitoring. This does not occur, and so there is little hope of knowing just what has been released.

Mercury that is removed still resides in the activated carbon and fly ash. Whether the carbon is sent for reactivation or is burnt in the incinerator, that captured mercury will still enter the environment. The mercury in bottom ash will leach from landfill, and evaporate in heat.

The WHO recently announced that the toxicity of mercury was, in fact, 3000 times higher than had been previously believed. Recently the news has featured fly ash not even being buried, and in fact, after lying in open tips, being used for building materials. This is hardly acceptable.

"Modifications to counteract one pollutant can lead to increases in others:

"The incineration industry has had to develop on the fly. New scientific and environmental findings trigger new pollution control devices and expensive retrofits. Incinerators are built and financed with the expectation that they will operate at least 20 years. However, incinerators operating today look very different from those built 20 years ago. We can anticipate that those operating 20 years from now will look very different from today's. The trouble with making changes on the fly, is that a solution to one pollutant problem, may make other pollutant problems worse.

"For example, the demand for higher furnace temperatures and better combustion to combat the dioxin problem, led to higher nitric oxide formation, the greater liberation of toxic metals, and reduced mercury control (less soot available for mercury absorption). Both the desire to capture energy via water boilers and the use of electrostatic precipitators for particulate control, increased the post combustion formation of dioxin. The use of lime and baghouse scrubbing combinations has led to a more toxic fly ash product. The public has had to live through this ongoing experiment for many years, and continues to do so."

- Municipal waste incineration: A poor solution for the twenty first century, Dr. Paul Connett, 4th Annual International Management Conference 1998