Fate of 2,4,6-trichloro-(14C)-phenol bound to dissolved humic acid

Abstract

Batch microcosms were utilized to evaluate binding of 2,4,6-trichlorophenol (TCP) to dissolved humic acid (HA). Biodegradation of 2,4,6-TCP was then evaluated after addition of a bacterial culture previously acclimated to the substrate. Gel chromatography (size exclusion) was used to separate HA-bound 2,4,6-TCP from free (unbound) 2,4,6-TCP by molecular size before quantitative analysis.Dissolved HA can interact with free 2,4,6-TCP, forming an HA/TCP association in solution. Equilibrium isotherms of 2,4,6-TCP for dissolved HA are linear for 2,4,6-TCP concentrations up to 1000 μg/l and HA concentrations up to 100 mg/l. Distribution coefficients of 2,4,6-TCP for HA vary with dissolved humic concentration. Coefficients decreased with increasing HA concentration indicating a change in HA sorption characteristics with concentration.Acclimated bacteria, Pseudomonas aeruginosa, can mineralize up to 60% of the total 2,4,6-TCP in solution, however, total mineralization decreased with increasing HA concentration. Overall mineralization in HA-containing solutions was 5–15% less than in HA-free solutions. Biodegradation of free 2,4,6-TCP was very rapid while biodegradation of HA-bound 2,4,6-TCP was much reduced and appeared to be desorption controlled.