Uptake and Phytotoxicity of TNT in Onion Plant

Abstract

The uptake of 14C-2,4,6-trinitrotoluene (TNT) in hydroponics was studied using onion plants. Of the total TNT mass (5 µM concentration), 75% was in the roots, 4.4% in the leaves, and 21% in the external solution at 2 days. The percent distribution in roots was lower with higher concentration in the external solution, but in leaves it was comparable at all concentrations (5–500 µM). Root concentration factor (RCF) in hydroponics was more than 85 in constant hydroponic experiment (CHE) at 5 µM and 150 in nonconstant hydroponic experiment (NHE) at 5 µM. The maximum RCF values in the hydroponic system were greater with lower solution concentration. Transpiration stream concentration factor (TSCF) values in the present study (NHE only: 0.31–0.56) were relatively similar to the values with predicted values (0.43–0.78), increasing with higher external TNT concentration. All predicted values for RCF and TSCF were derived in the literature from equations using log K ow (log10 octanol–water partition coefficient). For phytotoxicity tested in hydroponics and wet paper method, 500 µM was toxic to onion plant, 50 µM was nontoxic for plant growth but limited the transpiration rate, and 5 µM was nontoxic as control.