4.4. Mercury contamination
Total mercury in seawater and sediment of the Gulf of Thailand is shown in Table 6. Considering the data obtained from several surveys, it can be found that the mercury concentration in seawater during the period 1974–1980 is comparable to natural level as suggested by Kothny (1973), i.e. in the range of 0.01–0.38 ppb. High mercury concentrations (44.7–847 ppb) nevertheless were reported during 1983–1987. The levels were even higher than those detected in Minamata Bay, Japan (1.6–3.6 ppb). Whether these reported data are valid or not, there is a need for clarification both on sample collection and analytical methods. Most mercury concentrations in the sediments were still within the acceptable limit of 0.3 ppm (Ministry of Transport, Japan, 1976), except certain locations such as the Chao Phraya River estuary and the east coast of the Gulf. Higher mercury concentrations in such areas might be due to the contamination from urban and industrial areas.