Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam
Concentrations of arsenic and ammonium ions well above drinking water standards have been detected in aquifers which supply Hanoi, the capital of Vietnam, with fresh water. Chemical analyses showed arsenic and ammonium ion concentrations varying between 27 – 264 μg/l in freshwater and 1.8 – 34.7...
| Autor principal: | |
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| Formato: | L3 |
| Lenguaje: | Inglés sueco |
| Publicado: |
SLU/Dept. of Soil Sciences
2007
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| Materias: |
| _version_ | 1855571923914719232 |
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| author | Harms-Ringdahl, Peter |
| author_browse | Harms-Ringdahl, Peter |
| author_facet | Harms-Ringdahl, Peter |
| author_sort | Harms-Ringdahl, Peter |
| collection | Epsilon Archive for Student Projects |
| description | Concentrations of arsenic and ammonium ions well above drinking water standards have
been detected in aquifers which supply Hanoi, the capital of Vietnam, with fresh water.
Chemical analyses showed arsenic and ammonium ion concentrations varying between
27 – 264 μg/l in freshwater and 1.8 – 34.7 mg/l in groundwater. The current Vietnamese
drinking water guidelines for arsenic and ammonium are set at 10 μg As/l and 1.5 mg
NH4/l.
The aim of this thesis is to investigate the fate of arsenic and nitrogen and the processes behind the mobilization of these elements in the Nam Du area, situated 10 km southeast of Hanoi. Two possible processes affecting the As concentration are investigated: (1) oxidation of arsenopyrite or (2) desorption of arsenite/arsenate bound to iron hydroxides due to iron reduction. Regarding ammonium ions, previous projects have
identified two possible sources which were investigated further in this study: (a) mineralisation of organic matter in sedimentary peat layers and (b) ammonium ions
derived from anthropogenic sources, such as fertilisers or leakage of waste water. The
methods used in this study were: analyses of N-, O- and H-isotopes, the ionic composition and redox potential in the groundwater, combined with a conceptual model of the groundwater flow in the area.
There were large spatial variations in ammonium and arsenic levels within the Nam Du
area. According to tritium (3H) analyses the water was quite young, indicating recent
mobilisation processes. The redox potential, pH and sulphate concentration in the water
indicate that arsenic is mobilised by reduction of iron hydroxides rather than oxidation of arsenopyrite. Furthermore, the isotopic composition of N combined with increasing levels of ammonium ions over time, the C/N ratios and the age of the water, suggest that
mineralisation of peat is not occurring to such an extent that this process could explain
the currently high ammonium levels. The isotopic composition of the ammonium ions
and the rising concentrations in the aquifers rather imply that the ammonium ions derive
from one or several sources with a high 15N/14N ratio, such as waste water, organic
fertilisers or urea. |
| format | L3 |
| id | RepoSLU11710 |
| institution | Swedish University of Agricultural Sciences |
| language | Inglés swe |
| publishDate | 2007 |
| publishDateSort | 2007 |
| publisher | SLU/Dept. of Soil Sciences |
| publisherStr | SLU/Dept. of Soil Sciences |
| record_format | eprints |
| spelling | RepoSLU117102017-11-23T12:04:35Z Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam Harms-Ringdahl, Peter groundwater contamination sources ammonium ions arsenic species redox potential stable isotopes Hanoi Vietnam Concentrations of arsenic and ammonium ions well above drinking water standards have been detected in aquifers which supply Hanoi, the capital of Vietnam, with fresh water. Chemical analyses showed arsenic and ammonium ion concentrations varying between 27 – 264 μg/l in freshwater and 1.8 – 34.7 mg/l in groundwater. The current Vietnamese drinking water guidelines for arsenic and ammonium are set at 10 μg As/l and 1.5 mg NH4/l. The aim of this thesis is to investigate the fate of arsenic and nitrogen and the processes behind the mobilization of these elements in the Nam Du area, situated 10 km southeast of Hanoi. Two possible processes affecting the As concentration are investigated: (1) oxidation of arsenopyrite or (2) desorption of arsenite/arsenate bound to iron hydroxides due to iron reduction. Regarding ammonium ions, previous projects have identified two possible sources which were investigated further in this study: (a) mineralisation of organic matter in sedimentary peat layers and (b) ammonium ions derived from anthropogenic sources, such as fertilisers or leakage of waste water. The methods used in this study were: analyses of N-, O- and H-isotopes, the ionic composition and redox potential in the groundwater, combined with a conceptual model of the groundwater flow in the area. There were large spatial variations in ammonium and arsenic levels within the Nam Du area. According to tritium (3H) analyses the water was quite young, indicating recent mobilisation processes. The redox potential, pH and sulphate concentration in the water indicate that arsenic is mobilised by reduction of iron hydroxides rather than oxidation of arsenopyrite. Furthermore, the isotopic composition of N combined with increasing levels of ammonium ions over time, the C/N ratios and the age of the water, suggest that mineralisation of peat is not occurring to such an extent that this process could explain the currently high ammonium levels. The isotopic composition of the ammonium ions and the rising concentrations in the aquifers rather imply that the ammonium ions derive from one or several sources with a high 15N/14N ratio, such as waste water, organic fertilisers or urea. Höga nivåer av ammoniumjoner och arsenik har rapporterats förekomma i de akvifärer som förser Vietnams huvudstad, Hanoi, med färskvatten. Resultat från detta projekt visar arsenik- och ammoniumkoncentrationer mellan 27 – 264 μg As/l respektive 1.8 – 34.7mg N/l, vilket kan jämföras med WHOs gränsvärde på 10 μg/l för arsenik, och 1.5 mg/l för ammonium. Syftet med examensarbetet har varit att undersöka vilka processer som leder till de nivåer av ammonium och arsenik som idag föerkommer i Nam Duområdet, beläget 10 km sydost om Hanoi. Två av de möjliga processerna bakom mobiliseringen av arsenik är undersökta. (1) oxidation av arsenopyrit och (2) reduktion av järnhydroxider med åtföljande mobilisering av vattenlöslig arsenik. Tidigare undersökningar visar på två möjliga ammoniumkällor: (a) kvävemineralisering i torvlager som förekommer naturligt i marken och (b) antropogena källor såsom kvävegödsel och läckage av kväverikt avloppsvatten. Metoderna som använts är N- O- och H-isotopanalyser, samt undersökningar av grundvattenflöden, redoxförhållanden och vattnets innehåll av lösta ämnen. Insamlade data har kombinerats med en konceptuell flödesmodell över området. Resultaten visar en betydande rumslig variation både beträffande ammonium- och arsenik koncentrationerna. Tritium (3 H)-analyser visar att vattnet i akvifärerna är yngre än tio år vilket tyder på att de ämnen vi finner i grundvattnet har mobiliserats under denna period. Redoxförhållanden, pH värden och sulfatkoncentrationen i grundvattnet tyder inte på att arseniken mobiliseras genom oxidation av arsenopyrit utan förmodligen genom reduktion av järnhydroxider och åtföljande frigörande av arsenik. Vidare tyder isotopsammansättningen, stigande ammoniumhalter och C/N kvoter på att kvävemineraliseringen i torven inte sker i en sådan omfattning att den kan förorsaka de ammoniumkoncentrationer som observerats. Isotopsammansättningen och grundvattenflödena tyder snarare på en ytlig ammoniumkälla med höga 15N/14N kvoter. Källan utgörs sannolikt av gödselmedel eller kväverikt avloppsvatten. SLU/Dept. of Soil Sciences 2007 L3 eng swe https://stud.epsilon.slu.se/11710/ |
| spellingShingle | groundwater contamination sources ammonium ions arsenic species redox potential stable isotopes Hanoi Vietnam Harms-Ringdahl, Peter Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam |
| title | Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam |
| title_full | Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam |
| title_fullStr | Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam |
| title_full_unstemmed | Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam |
| title_short | Identifying possible sources of ammonium ions and arsenic in groundwater in the Nam Du area, Vietnam |
| title_sort | identifying possible sources of ammonium ions and arsenic in groundwater in the nam du area, vietnam |
| topic | groundwater contamination sources ammonium ions arsenic species redox potential stable isotopes Hanoi Vietnam |