Heavy metal uptake by some vegetables grown on sewage sludge-treated soils
Loading...
Date
2003
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine University of Agriculture
Abstract
A glasshouse pot experiment was conducted to determine the uptake of heavy metals
by Chinese cabbage (Brassica chniensis), lettuce (Lactuca sativa L.) and cowpea
{Vigiza unguiculatd) from sewage sludge-treated soils. A sandy loam (pH 6.9) and a
loamy sand (pH 7.1) were amended with sewage sludge at rates of 0, 10, 20 and 30
ton/ha (oven-dry weight basis). Total and extractable heavy metals in soils and
sludge, plant materials, vegetable heavy metals concentrations and uptake, were
determined. Results on characterization of the soils and the sludge indicated that the
soils contained small amounts of heavy metals, thus having a low potential for
causing pollution and the sludge had elevated levels of heavy metals. Amendment
with sewage sludge significantly (P=0.05) increased the yields of all vegetables.
ry.y •
1
;
—F
Chinese cabbage dry matter yields ranged from 3.34 to 15.89 and 9.83 to 17.09
g/plant for Msimbazi and Mjimpya soils, respectively. For lettuce they ranged from
3.43 to 14.29 and 6.69 to 13.63 g/plant for Msimbazi and Mjimpya soils,
respectively, while for cowpea they ranged from 5.89 to 15.74 and 13.77 to 19.94
g/plant for Msimbazi and Mjimpya soils, respectively. The highest yields were
observed with applications of sewage sludge at 30 ton/ha. The analysis of the edible
parts of vegetables for heavy metals revealed higher uptake of Cd, Cu and Zn by all
vegetable species with increased rates of sewage sludge application. The uptake of
Pb and Cr by the vegetables was low and not consistent with the rates of sewage
sludge application. There were, significant differences between the uptake of heavy
metals by the different vegetable species. DTPA-extractable Cu and Zn
concentrations in post-harvest soil increased significantly with sewage sludge
application rate. However, the increase of DTPA-extractable Pb and Cd was not consistent with the rates of application of sewage sludge. Chromium was not
detected in the post harvest soil. Vegetables grown in amended soils showed higher
N and P concentrations than control plants. The results indicate that there should be
close monitoring over the use of the sludge for edible crop production.
Description
Dissertation
Keywords
Heavy metal, vegetables grown, reated soils, contol plant