EFFECTS OF SEWAGE SLUDGE APPLICATION ON THE HEAVY METAL CONTENT OF WHEAT AND FORAGE CROPS

A growth chamber experiment was employed to investigate the effect of digested sewage sludge application on the heavy metal content of wheat and brome-alfalfa forage crops. Samples of wheat were also obtained from farm fields which had received heavy applications of sludge. No adverse effects on yields or appearance of crops were noted. The tissue levels of Hg, Cr and Pb were unaffected by sludge treatment. Cu levels in wheat kernels and straw were only slightly increased, but Cu levels in the forage crop were elevated by the sludge treatment. There was a considerable increase in the Zn content of all crops, but levels were not excessive. Sludge treatment produced up to a sixfold increase in the Cd content of wheat kernels and a considerable increase in the Cd content of the forage crop. The increased cadium levels are undesirable, but can be controlled by restricting the sludge application rate. There was little or no effect of sludge treatment on Cd levels in wheat straw.