The Danger of Cadmium
Cadmium is the heavy metal that is very close to toxic levels in the general environment -- therefore it is imperative to use all methods available to lower the proliferation of Cadmium into the environment and especially into the food chain. Any further increase will result in an equivalent increase of kidney failures.
Sewage sludge is highly contaminated -- on the average levels around 40 mg Cd/kg P compared to 3 mg Cd/kg P for source separated urine and 2 mg Cd/kg P for the best chemical fertilers. For this reason alone we should stop spreading sludge on food producing land. Some proponents of agri-sludging, even in EPA and FDA, will argue that soils can tie up Cadmium as long as the pH is within a certain range. This is true but a very dangerous gamble, since the natural buffers in many soils is used up because of acid rain from coal burning power plants --- to evenly "regulate" pH is not as easy in practice as the proponents seem to believe.
This is a fact sheet on Cadmium Poisening prepared for the Ontario Ministry of Labour. It includes land application of sewage sludge as a source of cadmium exposure. It also provides good background on the impact of cadmium poisening. Cadmium is the heavy metal that is closest to toxic levels in the ambient environment at present.