Mercury contamination and potential impacts from municipal waste incinerator on Samui Island, Thailand

In recent years, mercury (Hg) pollution generated by municipal waste incinerators (MWIs) has become the subject of serious public concern. On Samui Island, Thailand, a large-scale municipal waste incinerator has been in operation for over 7 years with a capacity of 140 tons/day for meeting the growing demand for municipal waste disposal. This research assessed Hg contamination in environmental matrices adjacent to the waste incinerating plant. 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 and bottom ashes (0.1-0.4 mg/kg and 0.03 mg/kg, respectively). Stack concentration of Hg were less than 0.4 g/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 g/kg. However, low but elevated levels of Hg (76-275 g/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 g/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 35-67 g/kg. 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.