ASSESSMENT OF HEAVY METAL CONTAMINATION OF THE SOIL IN MUNICIPAL OPEN-AIR DUMPSITES OF DHAKA CITY AND ITS OUTSKIRTS

Abstract

Disposal of the household originated and industrial hazardous materials with municipal solid waste (MSW) into the open dumping sites is the usual practice in Bangladesh. This experiment was carried out from July to December 2019 to assess the heavy metal contamination of the soil collected from the municipal open-air dumpsites of Dhaka city and its outskirts. The samples were collected from four dumpsites as Aminbazar and Matuail dumpsites of Dhaka; Konabari dumpsite of Gazipur and Shiddhirganj dumpsite of Narayanganj to analyze the soil characteristics (soil texture, pH, organic content) with heavy metals content (Cd, Pb, Ni and Cr). Samples were collected by auger sampling method from three soil depth (10-15 cm, 15-30 cm and 30-45 cm) directly from the dumpsite soil (DSS) and non-dumpsite soil (NDSS) with a duration of thirty days (December, 2019). It was observed that soil sample from all the sites was loamy type, pH was almost neutral and contained low amount of organic matter. The results of the analysis showed that the metals content dumpsite soil (DSS) were (Cd: 0.23 – 0.98 mgkg -1 ; Pb: 13.2 – 39.7 mgkg -1 ; Ni: 6.87 – 29.31 mgkg -1 and Cr: 14.32 – 43.49 mgkg -1 ) from all three depth of soil from all areas was higher than the content of non-dumpsite soil (NDSS) (Cd: 0.21 – 0.48 mgkg -1 ; Pb: 4.5 – 18.1 mgkg ; Ni: 4.23 – 18.65 mgkg -1 and Cr: 2.45 – 28.56 mgkg -1 ). All the sample contained heavy metal concentration not exceeding the permissible limits. Cadmium was richer in Aminbazar, Dhaka but other three metals, lead, nickel and chromium was richest in Shiddhirganj, Narayanganj. There was negligible correlation between all the heavy metals and pH and strongly negative correlation between heavy metals and soil depth. The outcome of this study gives the idea of heavy metals content in dumpsite soil (DSS) samples comparing the non-dumpsite soil (NDSS) samples and indicates the necessity of solid waste stabilization for heavy metal immobilization within the solidified matrix bond and re-use of solidified/stabilized products for sustainable solid waste management.