Keywords (Extracted from title, table of contents and
abstract of thesis)
Conurbations, Tubewell, Irrigation,
Cauliflower, Metals, Higher, Vegetables, Soil, Irrigated, Survey,
Accumulations, Minidams |
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Abstract
Pakistan is suffering from shortage of surface
supplies, which is being overcome by the conjunctive use of good
quality ground water for growing cereals in irrigated areas and
use of sewage/ industrial effluents for raising vegetables in city
conurbations. The farmers get good vegetable yields with sewage
water as it contains large amount of organic matter and plant
nutrients. However, sewage also contains some metals which could be
potentially toxic for biological life. The amount of each metal
accumulated in plant depends on the quality of sewage used for
irrigation. The metals which have been identified in sewage include
chromium, cadmium, copper, lead, nickel, zinc, cobalt, magnesium,
iron and arsenic.
This study was carried out in Rawalpindi area with the objective to
quantify the heavy metal accumulation in different vegetables and
soils irrigated with sewage. Study was carried out in two different
stages. In the first stage, field survey was carried out during 2003
and2004. During this survey, water samples from different irrigation
sources such as tubewells, wells, minidams and sewage were
collected. Vegetable leaf samples and soil samples (0-30 cm depth)
were obtained from the fields from where water samples were
collected. The collected samples were processed following standard
procedures and were analysed for lead, cadmium, chromium and nickel.
After the survey work, three experimental sites having good quality
tubewell water and sewage were selected in Taxila, Rawalpindi and
Gujar Khan area. In the second stage,
field experiments on the selected sites were conducted in Rabi, 2004
and Kharif, 2005. At each site, three treatments were tested viz, T1
= sewage irrigation, T2 = sewage and tubewell irrigation
alternativeely, T3 = tubewell irrigation. Each treatment was
replicated thrice following two factor factorial design. The plot
size was 10 x 5 meter square. Cauliflower was sown in august, 2004
and spinach was sown in November, 2004. Okra and squash were sown in
march, 2005. Each field was irrigated with measured quantity of
water depending upon their crop water requirements. Water samples
were collected before irrigation. Soil samples were collected from
0-30, 30-60 and 60-90 cm depth before and after each season. Leaves
samples were collected after 30, 60 and 90 days and fruit samples
were collected after 90 days of crop germination. The collected
soil, water and plant samples were analyzed for lead, cadmium,
chromium and nickel along with zinc, iron, copper and manganese.
The survey data showed variation in heavy metals concentration of
different water sources. All water samples for lead were within safe
limits. Heavy metals in tubewell irrigated vegetables were below the
safe limits and in sewage and industrial effluents irrigated
vegetables were above the safe limits. Heavy metals in soil samples
irrigated with different water sources were below the critical
levels.
The field experimental data showed that due to sewage application,
lead and copper contents were much higher in leaves of spinach,
leaves and fruits of cauliflower, okra and
squash as compared to tubewell irrigation at Taxila, Gujjar Khan and
Rawalpindi sites.Cadmium accumulation in all the vegetables
irrigated with sewage at all the three sites were also much higher
as compared to tubewell irrigation, but found less than lead and
higher than chromium. Like all the heavy metals, nickel showed the
similar trend for its accumulation in all the vegetables. The
accumulations of all metals in vegetables irrigated with alternate
treatment were even lower than those irrigated with sewage and
higher than tubewell irrigation. Similarly, heavy metals
accumulation in soil and vegetables were maximum at Taxila site, as
the sewage used for irrigation was more contaminated as compared to
other sites.
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