| Research Abstract |
Groundwater in Hanoi City is contaminated with ammonia, organic matter, and arsenic, but the source and the mechanisms of groundwater contamination was not yet been fully elucidated. In this study, mono-(MMA), di-methylamines (DMA), and the MMA/DMAratio were used as tracers investigatete source and mechanism of groundwater contamination due to ammonia and organic matter in Hanoi City. Water samples (n=116) were collected in August 2000, December 2000, and September 2001, andadditionally soil core samples (n=61) were collected in September 2001. In the contaminated groundwater, strong correlation between ammonia, MMA and DMA indicated that both ammonia and Mas originated from organic degradation. Contaminated surface waters had higher MMA/DMA ratio than in the groundwaters. These results suggest that the major source of MMA in the surface waters is degradation of glycine in proteins contained in domestic wastewater and fish baits, whereas the major source of DMA and MMA in groundwaters is degradation of tri-methylamine (TMA). As a by-product of anaerobic TMA decomposition, DMA accumulates in groundwaters. These different mechanisms of MMA and DMA enrichment in surface and groundwaters makes it possible to use these primary and secondary amine species as tracers of groundwater contamination. Together with the degree of adsorption, namely DMA > MMA > ammonia, which was explained both by the basicity of the free compounds and the solvation behavior of their protonated analogues, we can conclude that the MMA/DMA ratio can be used to identify in situ sources of ammonia and organic matter in underground.
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