Arsenic contamination in the Pak Panang Catchment, southern Thailand
The Pak Pa-Nang River Basin is located in southern Thailand. Environmental degradation has arisen because its catchment is mineralized with substantial deposits of tin forming part of the SE Asian Tin Belt. The presence of associated arsenopyrite gives rise to high arsenic concentrations, which are mobilized and available due to past mining activity. In order to evaluate the extent of the contamination, suitable techniques have had to be developed, for the extraction and measurement of arsenic species in a variety of environmental and biological samples. We have used trypsin and cellulase enzymatic extraction procedures to extract arsenic species from fish and plant samples, respectively. Arsenic species in sediments were determined following 1 M H3PO4 extraction in an open focused microwave system.
Anion-exchange HPLC was employed, coupled with ICP-MS for separation and detection of the important arsenic species, e.g. AsB, DMA, MMA, and inorganic arsenic in fish and plant samples while species of AsIII, AsV, MMA and DMA were determined in sediment samples. A nitric acid microwave digestion procedure, followed by carrier gas nitrogen addition (N2)-ICP-MS analysis, to overcome argon chloride (40Ar35Cl+) interference, was used to measure total arsenic. Validation for all these procedures was carried out using certified reference materials and real samples, mussel, cockle, green seaweed, brown seaweed and sediment collected from the Tamar Estuary, UK.
Fresh water and estuarine samples of fish and crustaceans, plants, soils, sediments and suspended solids from the Pak Pa-Nang catchment show a broad range for total arsenic concentration but indicate wide-spread contamination suspected. Of more concern was that the speciation measurements for arsenic indicated that the inorganic forms (as As III and V) are either in, or available to, the food chain. Temporal information, from core samples of the rivers and bay, indicates that this state could continue for some time. The natural and anthropogenically-altered hydrography of the catchment with its monsoonal-influence may well ensure this to be so.
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Publications
Foulkes, M.E., Rattanachongkiat, S., Utoomprukporn, W., Taiyaqupt, M., Tantichodok, P., Chongprasith, P. & Millward, G.E. (2007). Water chemistry and arsenic concentrations in Pak Panang Bay, southern Thailand: Influences of the north east monsoon. Journal of Coastal Research 23, 731-739.
Rattanachongkiat, S., Millward, G. E. and Foulkes, M. E. (2004). Determination of arsenic species in fish, crustacean and sediment samples from Thailand using high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Journal of Environmental Monitoring 6, 254-261.