PERSISTENCE AND TOXICITY OF ALKYLLEAD SALTS TO ANAEROBIC NITROGEN TRANSFORMATIONS IN SOIL

Using acetylene blockage and acetylene reduction techniques as parameters of denitrification and nitrogen-fixation respectively, four alkyllead chlorides (Me3 PbCl, Me2PbCl2, Et3PbCl, Et2PbCl2; Me=CH3, Et=C2H5) were separately tested (at 0.01, 0.1, 1.0, 5.0 or 10.0 μg/g) for their inhibitory properties against these nitrogen transformations in an agricultural soil. In the presence of added nitrate, glucose, and acetylene, alkyllead salts only marginally inhibited nitrous oxide, ethylene, and carbon dioxide accumulation in the head space above soil slurries which were incubated anaerobically for up to ten days. In contrast, the same levels of alkyllead toxicants appreciably modified the accumulation of these gases above incubations of supernatant from soilwater suspension. In general, dialkylleads were more inhibitory than their trialkyl homologs to nitrogen transformations and the activities of ethyllead salts were not appreciably different from their methyllead analogs. At the termination of the methyllead trials, residue concentrations of ionic aklylleads were appreciably greater in supernatant incubations than in soil slurry incubations. Tetramethyllead was present only in trace quantities and Me3Pb+ was present in both soil and supernatant incubations where Me2PbCl2 was the test toxicant. At the highest concentration of alkylleads tested in soil, no serious hazards to N transformations were detected. © 1990 Springer-Verlag New York Inc.