Uptake of selected heavy metal from municipal sewage sludge by tall fescue, lettuce and radish plants

The objective of this greenhouse study was to determine the effects of a municipal sewage sludge on the uptake of Cd, Cu, Ni, Pb, and Zn by lettuce (Lactuca sativa L., cv. "Black Seeded Simpson"), radish (Raphanus sativus L. cv. "Early Scarlet Globe") and fescue (Festuca arundinacea) grown on a Decatur silt loam, a Rhodic Paleudult. Two lime levels, zero and 6700 kg/ha, were employed to ascertain the extent of soil pH effect on metal uptake. Three soil extractants, 0.005 M DTPA, 2N NH₄OAc, and 0.5 N acetic acid, were used to determine their suitability for pre-dicting metal uptake by each of the three crops. Plant uptake was affected to the greatest extent by the level of sludge applied to the soil. Generally, the 20% and 30% sludge application levels (by weight) caused all plants to increase their metal uptake over the zero rate. At the 10% level, the uptake differences were not as consistent. It was found that liming the soil did not always have a depressing effect on metal uptake of any crop. It was found that Cd was accumulated into lettuce and radish tops to a much greater extent than in radish roots or in tall fescue. Copper was found in higher concentra-tions in both radish tops and roots than lettuce or tall fescue. Tall fescue, on the other hand, accumulated more Ni than radish or lettuce plants. Lead was found to be present in highest amounts in radish plants while both radish and lettuce crops accumulated more Zn than tall fescue. All three soil extractants were found to correlate well with Zn uptake for all plant species. DTPA was found to show the highest corre-lation with plant uptake of metals of the extracts tested. Liming generally reduced r values as compared to unlimed treatments.