TRACE METAL RISK ASSESSMENT IN VEGETABLE CROPS IRRIGATED WITH SEWAGE WATER AND SLUDGE ALONG KUBANNI RIVER DRAINAGE BASIN IN ZARIA METROPOLIS, NIGERIA.
TRACE METAL RISK ASSESSMENT IN VEGETABLE CROPS IRRIGATED WITH SEWAGE WATER AND SLUDGE ALONG KUBANNI RIVER DRAINAGE BASIN IN ZARIA METROPOLIS, NIGERIA.
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Date
2008-08
Authors
HARUNA, ADAMU
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Abstract
The concentration levels of trace metals in spinach and lettuce irrigated with sewage
water on agricultural lands in metropolitan Zaria were determined in a 3-month monitoring
programme (February − April, 2008). The investigation was carried out in the biggest sewage
water - irrigated vegetation in the city, which is a fadama land (flood plain) along river
Kubanni drainage basin. Samples of spinach, lettuce, sewage water, sewage sludge and soil
from the study area, as well as samples of tube-well water, soil, spinach and lettuce from a
control area were analysed for five trace metals (Zn, Ni, Cu, Pb and Cd) using atomic
absorption spectrophotometry (AAS). The physico-chemical characteristics of the sewage
water, tube-well water, sewage sludge and soil samples, and the fertility of the sewage sludge
were also evaluated. The results obtained showed that sewage water quality characteristics
were mostly beyond the permissible limits as recommended by the Food and Agriculture
Organisation (FAO) and United State Environmental Protection Agency (USEPA). The levels
of Cd, Cu, Pb, Cl− and NO3
− in sewage water samples analysed were also found to be higher
than the respective reference values for irrigation water.
Furthermore, the results indicated a substantial build-up of trace metals in soil and
vegetables that were grown with sewage water. The levels of Cd, Cu and Ni in soils, as well as
the levels of Cd and Pb in vegetables were beyond the permissible limits recommended by
FAO, USEPA and EU, suggesting that irrigation with sewage water resulted in an obvious
increase of trace metal content in soil (P > 0.05). In fact, metal transfer factors from soil to
spinach and lettuce were found significant for Pb, Ni and Cu. The mobility and bioavailability
of the five metals in sewage sludge and soil samples were also assessed using a six step
selective sequential extraction scheme for partitioning the metals into different chemical forms.
The results obtained showed that the residual fractions of both sewage sludge and soil samples
were the most abundant pool for all the trace metals examined. The mobility and the potential
bioavailability of the metals investigated were in the order: Pb > Zn > Cu > Ni > Cd and Ni >
Zn > Pb > Cd > Cu for soil and sewage sludge samples, respectively.
Description
THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA
IN PARTIAL FULFILMENT FOR THE AWARD OF
MASTERS OF SCIENCE IN ANALYTICAL CHEMISTRY
DEPARTMENT OF CHEMISTRY,
AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA.
AUGUST, 2008
Keywords
TRACE METAL,, RISK ASSESSMENT,, VEGETABLE,, IRRIGATED,, SEWAGE,, SLUDGE,, KUBANNI,, DRAINAGE BASIN,, ZARIA METROPOLIS, NIGERIA.