The origin and fate of TCP isomers were studied in Kurose River, Hiroshima, Japan. As main factors controlling the fate, the adsorption characteristics of TCP isomers onto sediment and biodegradation in river water and sediment were studied. Concentration of TCP isomers in river water, sediment and SS were the highest in autumn (about ten times as large as in winter). High concentration of o-TCP was noted except in spring. In contrast to other seasons, in summer the concentration of o-TCP was relatively low and m-TCP was not detected. These variations seemed to be due to the difference in the rate of biodegradation with temperature. The concentrations of TCP isomers increased with the increase in flow rate under flood conditions. TCP in the river originated from non-point sources and not from wastewaters or atmospheric origins. The adsorption of TCP isomers on sediment followed Freundlich isotherms. No equilibrium was observed between bottom sediment and river water, indicating TCP was biodegraded rapidly in the bottom sediment. The biodegradation rate in the sediment was lowest for o-TCP and highest for p-TCP. The biodegradation rate of m-TCP was small under low temperature, whereas it was large in high temperatures above 20°C. The most biodegradable isomer, p-TCP, was not detected in most cases.

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