Tannery solid wastes and CrCl3 were applied to two Oxisols in a greenhouse pot experiment. Soils used were a Typic Eutrorthox (Dusky-Red Latosol - LRe) and Typic Haplorthox (Red-Yellow Latosol - LVA) of which the main difference was the manganese reducible content. The tannery wastes were sludge from the liming process with a total dry matter chromium content of 0.06 g kg-1 (LCL) and the primary sludge (LCR) with a total dry matter chromium content of 17 g kg-1. The sludges were applied at three different rates taking into account their total nitrogen content (10, 20 and 30 Mg ha-1 for the LCL and 19, 38 and 57 Mg ha-1 for the LCR, both at a dry weight basis). CrCl3 was applied at rates of 330, 660 and 990 kg ha-1 of chromium, equivalent to the rates of applied LCR sludge. Cr6+ was measured after 1, 6, 14, 28, 54 and 86 days of incubation. After the 56th day, a one month old lettuce seedling (Lactuca sativa L.) was planted and grown for 30 days. The Cr3+ oxidation was detected only at the CrCl3 treatment of the LRe soil, being the highest amount found after the first day of incubation (0.72 to 1.16% of the total applied Cr), decreasing afterwards to non detection limits in the 54th day. The application of both sludges increased the electrical conductivity (1.40 to 5.07 dS m-1) and the sodium adsorption rate (3.05 to 14.12). It affected lettuce development causing death of the plants at the highest rates. LCR and CrCl3 treatments increased the levels of chromium in the plant tops but not always proportionally with the increasing applied rates. Both ocurrences were more pronounced for the LVA soil. Under the conditions of the experiment, lettuce growth was limited primarily by salt than by chromium content.
sludges; hexavalent chromium; electrical condutivity; RAS