concentration than other sites and the comparative account for the
distribution of Cd concentration in different years is represented in
Fig. 2.
The pH of all samples was pH 7–9 (alkaline) at all sites. The
elevated pH of the soil in addition to rainfall event in the winter
season dilutes the soil solution more which increases the pH of
the soil. This increase in pH increases the ability of soil to adsorb
and fix Cd.
The quality guidelines for Cd concentration developed in
certain countries indicate wide variations. In France, the soil
threshold level of Cd is 0.07 mg/kg [19]. The mean and range of
total Cd concentration in normal soil reported by London (1984)
were 0.35(0.01–2.0) mg/kg. Furthermore, limits for the total
concentration of Cd in soil according to EEC (1986) [20] was
3.0 mg/kg while the Dutch reference values [21] was 0.8 mg/kg.
Singh and Saha in 1997 [22] reported in their all India
coordinated research project that Cd varies from 0.04 to
0.96 mg/kg in the surface soil. The critical limit for classifying
sites as toxic for Cd was 1.0 mg/kg. This indicates that the results
from our studies for Cd reflect that the values of Cd in the
industrial soil, road side sample, field sample are greater than the
normal concentration of Cd in the soil. Cd added to the soil remains
for a long time and it may take about 100–1000 years for leaching