Effects of NTA on the Fate of Heavy Metals in Sediments

Sodium tripolyphosphate (STPP), which is widely used as a builder in synthetic detergents, was found as one of the major factors of eutrophication in rivers and lakes. Many countries have used nitrilotriacetate (NTA) in detergents to replace STPP, but it induced another pollution problem. Because NTA is an effective chelating agent, it will dissolve heavy metals from the sediments and affect the fate of metal species in rivers. The purpose of this study is to investigate the effect of the mobilization of heavy metals from sediments by NTA. The experimental results indicated that NTA increases the mobilization of heavy metals as the shaking time increases and reaches an apparent equilibrium concentration after 24–48 hours. Typical results show that using 20mg/l of NTA and shaking time of 6 days, the fraction mobilized is about 8 to 15% for Cu, 1 to 7% for Zn, 7 to 10% for Pb, and 7 to 30% for Cd. Hardness of the water affects the formation of heavy metal-NTA complexes significantly. Biodegradation of the trisodium salt of NTA starts after 6–9 days with degradation time of the metal-NTA complexes decreasing in the order of Cu > Cd > Zn > Pb > Ca.