Descrição
A greenhouse pot experiment was conducted to evaluate the effect of sewage sludge (SS), of sugar beet
sludge (SBS), or of a combination of both, in the remediation of a highly acidic (pH 3.6) metal-contaminated
soil, affected by mining activities. The SS was applied at 100 and 200 Mg ha 1 (dry weight basis),
and the SBS at 7 Mg ha 1. All pots were sown with Italian ryegrass (Lolium multiflorum Lam.). After 60 d of
growth, shoot biomass was quantified and analysed for Cu, Pb and Zn. The pseudo-total and bioavailable
contents of Cu, Pb and Zn and the enzymatic activities of b-glucosidase, acid phosphatase, cellulase, protease
and urease were determined in the soil mixtures. Two indirect acute bioassays with leachates from
the soil (luminescent inhibition of Vibrio fischeri and Daphnia magna immobilization) were also used.
The SS, in particular when in combination with SBS, corrected soil acidity, while increasing the total
organic matter content and the cation exchange capacity. The application of SS led to a decrease in the
level of effective bioavailable metals (extracted by 0.01 M CaCl2, pH 5.7, without buffer), but caused an
increase in their potential bioavailability (extracted by a solution of 0.5 M NH4CH3COO, 0.5 M CH3COOH
and 0.01 MEDTA, pH 4.7). Plant biomass increased more than 10 times in the presence of 100 Mg SS ha 1,
and more than five times with the combined use of 100 Mg SS ha 1 and SBS, but a considerable phytotoxic
effect was observed for the application rate of 200 Mg SS ha 1. Copper, Pb and Zn concentrations
in the shoots of L. multiflorum decreased significantly when using 100 Mg SS ha 1 or SBS. The activities
of b-glucosidase, urease and protease increased with increasing SS applications rates, but cellulase had
a reduced activity when using 200 Mg ha 1 SS. Both amendments were able to suppress soil toxicity to
levels that did not affect D. magna, but increased the soil leachate toxicity towards V. fischeri, especially
with the application of 200 Mg SS ha 1. This study showed that for this type of mine soils, and when
using SS of similar composition, the maximum SS application rate should be 100 Mg ha 1, and that liming
the SS amended soil with SBS did not contribute to a further improvement in soil quality.
; Palma, P. 
