SPECIATION OF TRACE ELEMENTS IN LEACHATES FROM LANDFILLS IN RELATION TO WATER QUALITY ASSESSMENT

摘要

Speciation studies on arsenic and selenium were carried out on water samples taken from rivers in the vicinity of landfill areas used as land-based waste disposal system. These rivers are used as water intake points and the raw water is treated prior to distribution for domestic and industrial uses. Leachates from these landfill areas are capable of contaminating the river water through underground seepage or overflowing especially after a heavy downpour. The quantitative aspects of the arsenic and selenium species were evaluated by looking at water quality parameters taken during the sampling procedure. Preconcentration of the chemical species was done using a mixture of ammonium pyrrolidinethiocarbamate-chloroform (APDTC-CHCl_3). Since only the reduced forms of both arsenic and selenium species could be extracted by the preconcentrating mixture, suitable reducing agents such as 25% sodium thiosulphate for As(III) and 6M HC1 for Se(IV) were used throughout the studies. Care was taken to exclude the interfering elements such as the alkali and alkali earth metals from the inorganic arsenic and selenium species by introducing 12% EDTA solution as the masking agent. The extracted mixture was irradiated in a thermal neutron flux of 4 × 10~(12) n.cm~(-2) s~(-1) from a TRIGA Mk.II reactor at the Malaysia Institute of Nuclear Technology Research (MINT). Gamma rays of 559 keV and 297 keV from the ~(76)As and ~(75)Se respectively were used in the quantitative determination of the inorganic species. Mixed standards of As(III) and Se(IV) used in the percentage efficiency procedure were prepared from salts of Analar grade. Water quality evaluation was viewed not only from the ratio of the inorganic species present but also from other physical and chemical parameters normally used in water quality studies.