Determination of copper, zinc and lead in cabbage (Brassica oleracea sp.) heads and lettuce (Lactuca sativa sp.) leaves grown on soil amended with sewage sludge
Loading...
Date
2012-06-19
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Sewage sludge from KNUST treatment plant is currently being used by many farmers for cultivation of vegetables on large scales for human consumption. This study focused on some selected heavy metals (lead, zinc and copper) levels in the KNUST treatment sludge, the effect of sewage sludge on soil properties that affect heavy metal uptake and determined levels of metals in lettuce and cabbage which are grown on the sewage sludge amended soil. In this study, three treatments were used base on recommended application rates for both cabbage and lettuce. 100, 150 and 200 kg/ha application rates were used as treatments for lettuce while 160, 210 and 260 kg/ha application rates were used for cabbage. The experiment was pot experiment arranged in a completely randomized design and under climatic conditions of Kumasi. Heavy metals (53.10±0.22, 40.77±0.36 and 24.10±0.13 mg/kg for copper, zinc and lead respectively) were found to be present in the KNUST sewage sludge but were below EU acceptable limits. Effect of sewage sludge on soil properties such as pH, organic matter content and soil conductivity were determined. Soil organic matter content and soil conductivity increased significantly (P < 0.05) with increasing application rates. The soil pH was not affected significantly (P > 0.05) with the application of sewage sludge. Levels of metals in the soil increased significantly with increasing application rates. The controls for both plants recorded the lowest heavy metal uptake (0.48±0.13, 1.36±0.23 and 2.60±0.29 mg\kg for lead, zinc and copper respectively for cabbage and 0.34±0.19, 1.35±0.31 and 2.30±0.14 mg\kg for lead, zinc and copper respectively for lettuce) while highest metal uptakes were recorded at the highest application rates for both plants (0.66±0.17, 2.66±0.09 and 4.33±0.14 for lead, zinc and copper respectively for cabbage and 0.54±0.01, 2.24±0.17 and 3.88±0.19 mg/kg for lead, zinc and copper respectively for lettuce). The uptake of zinc and copper were statistically significant (P < 0.05) while lead uptake was insignificant (P > 0.05) for both plants. The levels of metals in both plants for all treatments used were below WHO safe limit. Yields increased significantly with increasing application rates for both plants. Heavy metals residual levels in the soil were found to be higher in the control (13.21±0.15 for cabbage and 14.32±0.12 for lettuce) than other treatments for both plants. The results of this study showed that applying the KNUST treatment sludge based on recommended rates can enhance yields and improve soil fertility. The study also revealed that the sewage sludge can also increase levels of metals especially copper and zinc in soils and consequently leading to uptake by lettuce and cabbage plants.
Description
A Thesis submitted to the Department of Theoretical and Applied Biology,
Kwame Nkrumah University of Science and Technology
in partial fulfillment of the requirements for the degree of Master of Science in Environmental Science, June-2012