FATE OF DYES IN AQUATIC SYSTEMS .3. THE ROLE OF SUSPENDED SEDIMENTS IN ADSORPTION AND REACTION OF ACID AND DIRECT DYES

The behavior of nine acid and five direct dyes was examined in suspens ions of lake and river sediments. Seven of the dyes demonstrated varia ble kinetics of loss from water. In most cases, there was an initial d rop in water concentration due to sorption. Transformation kinetics of CI Acid Reds 4, 18, and 88 were first order in dye concentration and apparently first order in sediment concentration. CI Acid Reds 4 and 1 8 also exhibited an initial lag period. Transformation and sorption of CI Acid Red 114 and CI Acid Red 151 could not be studied because of p recipitation. CI Acid Yellow 151, DY 1 and CI Acid Blue 92 were lost f rom solution by pathways that were not first order. Of these, CI Acid Blue 92 was transformed at a rate that was too fast to measure reliabl y, but CI Acid Yellow 151 and DY 1 were very stable in the suspensions . Products of azo group reduction were found for CI Acid Reds 1 and 4 and CI Direct Red 24. The results suggest that many acid and direct dy es will be stable in aquatic systems for long periods of time unless o ther transformation pathways (e.g. photochemical) are rate determining . Freundlich adsorption isotherms were measured for 12 of the dyes wit h both sediments. Because of competitive transformation and sorption, isotherms were measured on boiled sediments after equilibration for 24 h. The data show that the dyes are not strongly sorbed and that the e xtent of sorption to boiled sediment is within a factor of two to thre e of that with natural sediment.