In a tributary stream of the upper Muromi river, located west of Fukuoka city, as the spring water containing CO2 and about 10ppm (Fe) of dissolved iron flows downstream, a large amount of hydrous iron (III) oxide (Fe(OH)3) precipitates on the stream bed. Judging from the variation in Fe, DO, HCO3 and dissolved CO2 concentrations, it is concluded that the Fe (OH)3 precipitation results from loss of CO2 from the stream water due to the sudden decrease in the CO2 partial pressure, followed by the hydrolysis and oxidation of ferrous ion.
On the other hand, MBPMC (2,6-di-tert-butyl-p-tolyl methyl carbamate; a carbamate herbicide) was detected in the stream water by GC-MS analysis. The MBPMC concentration decreased along the stream from 0.6 to 0.4 ppb, and the amount of the precipitated MBPMC approximately correlated with that of the Fe (OH)3. The Fe (OH)3 contains naturally-occurring organic materials, suggesting that MBPMC might be adsorbed on the surface of Fe (OH)3 which is covered with the naturally-occurring organic materials containing hydrophobic groups.
