Distribution of trace metals in the Gulf of Thailand and East Coast of Malay Peninsula

Abstract

The water samples and sediment samples were taken from 81 stations in the Gulf of Thailand and East Coast of Malay Peninsula during April-May 1996. The water samples were analyzed using the cobalt-APDC coprecipitation technique. Sediment samples and suspended particulate samples were digested with hydrofluoric acid (HF) and aqua regia. The concentrations of cadmium, copper, iron, nickel and lead in the samples were measured using a Graphite Fumace atomic absorption spectrophotometer. Trace metals of interest: cadmium, copper, iron, nickel and lead in the Gulf of Thailand and East Coast of Malay Peninsula were mostly present in dissolved form except for iron. The concentration of dissolved cadmium, copper, iron, nickel and lead in the study area were 0.025-0.134, 1.03-8.87, 4.38-59.80, 1.66-8.71 and 0.06-0.93 nM, respectively. The concentration of suspended particulate cadmium, copper, iron, nickel and lead were 0.001-0.090, 0.27-5.65, 21.30-629.26, 0.16-1.96 and 0.02-0.65 nM, respectively and the concentration of cadmium, copper, iron, nickel and lead in surface sediment were 0.01-0.94 mu g/g, 10.30-61.00 mu g/g, 6.30-23.80 mg/g, 15.23-52.61 mu g/g and 5.24-91.00 mu g/g, respectively. Of all the trace metal studied, only cadmium showed a nutrient-type behavior. Iron was enriched in the bottom layer but no obvious trend was observed for copper, nickel and lead. Besides the five major rivers in Thailand namely Bang Pakong, Chao Praya, Mae Klong, Ta Chin and Tapi River, the Mekong River in Vietnam appears to be a vital source of water to the Gulf of Thailand and some contribution was from bottom water from the South China Sea. The total discharges of cadmium, copper, iron, nickel and lead were 35, 2,735, 985,843, 2,830 and 1,574 tons/year, respectively. The calculated budget indicated that there must be an unknown sources of these metals, especially for Fe and Pb to account for the sedimentation of cadmium, copper, iron, nickel and lead of 7.2, 1,697, 1,226,198, 1,553 and 2,410 tons/year, respectively. The estimate residence time of cadmium, copper, iron, nickel and lead in the Gulf of Thailand were 1.23, 0.76, 0.14, 0.73 and 0.52 years, respectively.