Cadmium in the water and sediments of the Chao Phraya River and associated waterways, Bangkok, Thailand

As part of a research programme designed to examine the effect of cadmium on various biochemical responses in fish, a preliminary survey was carried out of cadmium concentrations in water and sediments sampled at 26 sites within the Chao Phraya River system in the Bangkok area of Thailand. Compared with values in the literature, the results of total cadmium analysis of both river water and sediments gave no indication of extreme pollution with cadmium, although two sites were identified with substantially higher than average sediment cadmium concentrations. More detailed sampling at these sites, over several months, compared with nearby 'pristine' sites, confirmed their elevated cadmium status. The forms of cadmium present in the sediments at these sites, as determined by sequential fractionation, also provided evidence for the presence of contamination. However, considerable temporal variations in water and sediment cadmium concentrations were observed at individual sites, most probably related to seasonal high water levels and sediment flushing.