Impact assessment of landfill on soil health and water quality in a waste disposal site

Abstract

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.