PhD

The study entitled “Impact assessment of landfill on soil health and water
quality in a waste disposal site” was undertaken with an objective to assess the impact
of dumping Municipal Solid Waste (MSW) on soil and water quality, spatial
variability in the level of biological and chemical contamination along the leachate
zone and identification of a few bioremediators and their possible effectiveness in
decontaminating the landfill materials.
As a part of this study, geo-referenced
sampling points have been identified initially for dumped waste materials (from the
existing two landfill sites), soil (from two depths) and leachate samples along the
leachate flow zone at a regular interval of 50 m within the plant area and ground
water samples outside the area were collected. All the samples were monitored from
these geo-referenced sampling points in three successive seasons, viz., pre-monsoon,
monsoon and post-monsoon. The values for all the physico-chemical parameters in
landfill materials were high during pre-monsoon period and only a marginal variation
observed in heavy metal content in three seasons of study. Soil samples were acidic
in reaction and a reduction in N, P, K and heavy metals were observed as the depth of
sampling increased. Comparatively high values were observed in all parameters
during pre-monsoon period than the other two seasons both in soil and leachate
samples. Fe, Al and Hg content in leachates were very high and the concentrations of
Fe, Al, Pb, Cd and Hg in ground water exceeded the acceptable level insisted by BIS.
The leachate samples also recorded a high value for biological oxygen demand,
chemical oxygen demand and coliform count than the ground water samples.
Fifteen profusely growing weed species were identified and collected along
the leachate flowing zone and the shoot and root portions were analyzed separately
for various heavy metals to assess their selective retention capacities. Most of the
weed species except Sphagneticola trilobata, Commelina diffusa, Ricinus communis,
and Mikania micrantha were found to retain more toxic metal load in the root portion
than the shoot portions. Among them, Alternanthera tenella was identified as the
best hyper accumulator with respect to its gross uptake of the metals like Mg, Mn, Pb,
Cd, Ni, Co and Cr. Hence, this plant was selected for the sand culture study along
with other established hyper accumulator plants namely; Indian mustard, sunflower,
globe amaranth and marigold analyzed for selective retention capacity under four
graded doses of lead, cadmium and nickel.
This study identified three best plants species (sunflower, globe amaranth and
marigold) showing highest hyper accumulation capacities and hence they were
carried forward to another pot culture study employing contaminated and degradable
landfill materials for the final revalidation of claims. The experiment consisted of ten
treatments and the treatments where the growing medium was re-constituted with
different proportions of degradable landfill materials and virgin soil with and without
the AMF inoculation. The plants which were grown for three months were analyzed
separately for root and shoot portions for the exact quantum of selective retention
status of metals like Al, Zn, Cu, Fe, Pb, Cd, Ni, Co, Cr and Hg. Lower levels of
metal accumulation was recorded in all the plant parts where AMF had been
inoculated in the media than its pairing treatment without inoculation, indicating the
specific effect of AMF in preventing the uptake of heavy metals by plants and at the
same time permitting the absorption of other ions needed for growth. Sunflower had
been adjudged as the best plant that removed maximum load of studied heavy metals
from the contaminated growing media except nickel and chromium. Similarly globe
amaranth had been specifically identified as an excellent accumulator of nickel.
Marigold was identified to be efficient accumulator of chromium.
From the investigation it can be concluded that the soil and water bodies near
the dumpsite sufficiently contaminated with the heavy metals like Zn, Mn, Cu, Fe,
Pb, Cd, Ni, Co, Cr and Hg. As the distance from the dumpsite increased the extent of
various chemical and biological contaminations showed a decreasing trend.
Sunflower, globe amaranth and marigold were found to be effective hyper
accumulators for the area in decontaminating the soils.