Acclimation to and biodegradation of nitrilotriacetate (NTA) at trace concentrations in natural waters

Abstract

Acclimation to and biodegradation of nitrilotriacetic acid (NTA), an organic builder used in synthetic laundry detergents as the sodium salt, was studied at trace concentrations (ppb) in several river waters. The river waters tested ranged from those where extensive NTA exposure via detergents had not occurred, to those where NTA exposure had been continuous for several years. In rivers not previously exposed to NTA, acclimation and degradation were observed at the lowest initial concentration tested, 5 μg 1 −1. Degradation of NTA after acclimation followed apparent first order kinetics, and half lives for NTA removal ranged from 7 to 138 h at initial NTA concentrations of 50 and 5 μg 1 −1, respectively. Degradation of NTA in water samples where prior NTA exposure had already occurred required no acclimation and was less variable than in unexposed rivers. First order rate constants varied only slightly over a 1000-fold initial concentration range (1–1000 μg 1 −1) and NTA half lives ranged from 7 to 17 h. In general, our results indicate that microflora present in natural waters can acclimate to and degrade NTA, even if exposed to only trace levels in laboratory experiments. However, rates of NTA biodegradation are more rapid and less variable in river waters where natural NTA exposure has already occurred.