| Abstract | The study aimed to assess mercury (Hg) contamination in environmental matrices adjacent to a large-scale municipal waste incinerator (MWI) on Samui Island, Thailand, which has been in operation for over 10 years with a capacity of 140 tons/day. In order to fulfill the objective of this study, a series of both Hg sources (municipal solid waste, bottom ash, fly ash, and leachate from the incinerator) and environmental samples (soil, sediment, precipitation and local plant species) were collected at the Samui municipal waste incinerating plant and adjacent areas during the years 2005 and 2006 for Hg analysis. Secondary data dating back to the year 1999, the date the incinerator began operating, were also obtained from the Samui municipal waste incinerating plant and the municipality. This information was used for earlier composition of solid waste fed into the incinerator. Total Hg concentrations were determined in municipal solid waste, soil and sediment within a distance of 100 m to 5 km from the incinerator operation in both wet and dry seasons. Hg analyses conducted in municipal solid waste showed low levels of Hg ranging between 0.15-0.56 mg/kg. The low level was due to the type of waste incinerator. Waste such as electrical appliances, motors and spare parts, rubber tires and hospital wastes are not allowed to feed into the plant. As a result, low Hg levels were also found in fly ashes, bottom ashes, and leachate (0.1-0.4 mg/kg, ≤ 0.03 mg/kg, and ≤ 1.0 μg/l respectively). Low Hg level was also detected from rain water at the study site (Samui incinerator) with the values between 9-12 ng/l. Stack concentration of Hg were less than 0.4 μg/Nm3. Since Hg emissions were at low concentrations, Hg in soil from atmospheric fallout near this incinerator including uptake by local weeds were very low ranging from non detectable to 399 μg/kg. However, low but elevated levels of Hg (76-275 μg/kg) were observed in surface soil and deeper layers (0-40 cm) in the predominant downwind direction of incinerator over a distance of between 0.5-5 km. Soil Hg concentrations measured from a reference/background track opposite of the prevailing wind direction were lower ranging between 7-46 μg/kg. Nevertheless, the trend of Hg build up in soil was clearly seen in the wet season only, suggesting that wet deposition process is a major Hg pollution source. Hg concentrations in the sea bottom sediment collected next to the last station track was small with values between N.D.-61μg/kg. Bioconcentration factors (BCFs) of mercury were calculated as quotient of the total mercury in local plants to soil concentrations. Among species studied, Dactyloctenium aegyptium (L.) P.B. was characterized by the highest ability to accumulate mercury, and the BCF value in aboveground portion and root was 2.1and 4.3 respectively. This finding indicated that Dactyloctenium aegyptium (L.) P.B. might be used in phytoremediation of mercury-contaminated soil or used as bioindicator for monitoring mercury contamination in soil. Based upon the overall findings, in terms of current potential environmental risk, the environment has not yet been appreciably contaminated from Hg emissions produced by this incinerator. However, the increase of Hg measured in downwind direction of the incinerator should be monitored for future potential risk. |