a case study of Wiang Pa Pao, Chiangrai Province, Thailand Suntorn Uppamarn creator Preeda Pakpian Chairperson Thammarat Koottatep Examination Committee Vilas Nitivattananon Examination committee National Science and Technology Development Agency (NSTDA), Thailand Scholarship donor text series technical report th Pathum Thani, Thailand Asian Institute of Technology 2010 continuing eng 93 leaves : ill. + 1 online resource Wiang Pa Pao abandoned tin mining sited in the north region of Thailand. At present, it changed land use to growing food crops and small communities. It is interesting that arsenic concentration in this area especially, sedimentation area and ore dressing area was very high at 176 mg kg-1 dw. (PCD, 2008) where the arsenic concentration level in soil for growing plants is the same. The objective of this study was designed to find out the significant pathways and distribution pattern of arsenic that released from this mine site into the environmental media including soil, surface water, groundwater and sediment. Contour lines of arsenic distribution pattern, evaluation of environmental and human health risk by using hazard quotient, surveying and monitoring program at the study mining site in Chiang Rai Province, Thailand were conducted to cover both rainy and dry season if the seasonal effect may have influence As toxicity. Stratified and grid sample methods used to collecting the environmental samples in the study area such as soil, surface water and plants. Surface water samples and seasonal plants sample were obtained in both rainy and dry season. In reflection of dry season, soil, sediment, groundwater, and snail could be collected only in the rainy season. The concentration of arsenic water samples were higher than standard with the value range from 53-234 mg L-1. The concentration of arsenic in sediment, snail and plants was in the range of 53.75 {u2013}147.50 mg kg-1 dry weight (dw), 16.46 {u2013}1,568.62 mg kg-1wet weight (ww), and 0.23 {u2013}46.88 mg kg-1 dw, respectively. The concentration of arsenic in every samples were higher than the limit (guideline and standard). However, arsenic concentration in soil was relatively high at mining site (201.39 ± 65 mg kg-1, topsoil), dressing area (157.35 mg kg-1, topsoil) and sedimentation area (850.24 mg kg-1, topsoil) as estimated. All of soil samples nearby mining area have high As (average 41 mg kg-1) than limit of Thailand standard at 27 mg kg-1(PCD). From arsenic distribution patter map, it shown high dispersion of arsenic from sedimentation area in mining boundary and had been accumulating with other heavy metal such as; cooper, iron, lead and manganese. Environment and human health risk assessment was determined in the aquatic biota including surface water, groundwater, sediment and snail. The hazard quotient (HQ) values in all samples were very high and all of them are greater than one with the value range from 5-23.4 (HQ: water samples). There was highly potential risk in aquatic media at the study area. However, human health risk assessment in three villages was conducted based on the intake of contaminated foods and water (plants and snails) where they live in this area. The highest value of HQ is estimated from the mining area (Ban Pong Nam Ron), following by Downstream village (Ban Cham Bon), Upstream village (Ban Pa Tong), respectively. In view of the mining area where people living and working (plantation) there, this site has very high risk. It is a point source where many operations occurred would bring in arsenic for exposure. Moreover, HQ values in all zones were higher than one. Then, human health is measured as at very high risk for arsenic. While arsenic dispersion from this mining was very serious and cleanup site or rehabilitate program should be suggested for the site immediately. A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science in Environmental Engineering and Management Thesis (M.Sc.) - Asian Institute of Technology, 2010 Abandoned mines Risk assessment Thailand Chiang Rai Arsenic Physiological effect Risk assessment Thailand Chiang Rai Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B02484 http://203.159.5.9/ait-thesis/detail.php?q=B02484 110103 20260818100204.0