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tual sites — where proper management practices were followed — have shown no disease transmission attributable to land apllication of sludge, according to EPA.
As for heavy metals, the presence of small concentrations of some — “trace elements” such as zinc, copper and selenium — need not be considered a liability, according to EPA. In fact, very small concentrations of such trace elements are essential for plant and animal metabolism. Often, however, soils are deficient in these trace elements. Thus, when sludge contains proper concentrations, it may actually help to make up nutrient deficiencies in soils and crops.
But unlike the trace elements, two contaminants often found in sludge — cadmium and PCBs (polychlorinated biphenyls) — can be extremely toxic, even in low concentrations. Usually, these turn up only ini sludge from plants that process industrial wastes. But, as * safety precaution before beginning land application of sludge from any sewage treatment plant, EPA rec(Continued
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