On the contribution of background sources to the heavy metal content of municipal sewage sludge

The role of human excretion, drinking water, and deposition as a source of heavy metals to municipal sewage was investigated and compared with common levels in sludge for soil application. These sources contributed more than half of the copper (Cu), zinc (Zn), and lead (Pb) content of municipal sewage sludge for soil application, while other sources dominated the fluxes of chromium (Cr) and cadmium (Cd). Drinking water was an important source for Cu and Zn. Deposition contributed about 40% to the Pb flux. Faecal excretion commonly caused less than 10% of the heavy metal load, while urinary excretion was here a negligible heavy metal source.