Using acid volatile sulfide–simultaneous extracted metals as an assessment tool for metal pollution risk in the upper gulf of Thailand

Surface sediment samples from 30 station in the upper Gulf of Thailand (U-GOT) and 16 stations at the Chao Phraya river mouth collected in August 2010 and March 2011, respectively. The sediment samples were analyzed for Acid Volatile Sulfide (AVS) by purge and trap (colorimetric) technique. Simultaneous Extracted Metals (SEM) was determined by atomic absorption spectrophotometer. The study revealed that the concentrations of AVS in the U-GOT were in the range of 0.008-1.367 µmol/g dry weight, average of 0.188±0.303 µmol/g dry weight. The concentrations of AVS in sediments at the Chao Phraya river mouth were in the range of 0.011-3.339 µmol/g dried weight, average 1.753±1.070 µmol/g dry weight). The summation of metals (∑SEM) in the U-GOT and Chao Phraya river mouth sediments were in the range of 0.30-2.48 and 1.4-3.17 µmol/g dried weight, respectively. Possible toxicity related to these metals was examined using (i) ∑SEM/AVS ratios, (ii) ∑SEM – AVS difference, and (iii) ∑SEM – AVS/foc criteria. According to the criteria, some stations in the Chao Phraya river mouth and the U-GOT have shown a potential risk of metal pollution. However, two stations from the Chao Phraya river mouth showing metal pollution risk were being suboxic condition with low concentration of AVS in the sediments. For more accuracy assessment of metal risk in the upper Gulf of Thailand, sequential extraction procedure and factors controlling AVS behavior should be further investigated.