Effect of soil conditions on natural attenuation of 2,4,6-trinitrotoluene (TNT) by UV photolysis in soils at an active firing range in South Korea

Abstract

Naturally occurring 2,4,6-trinitrotoluene (TNT) degradation by UV photolysis is one of important TNT degradation mechanisms in TNT-contaminated soils, in particular, at sites such as active firing ranges where active remediation techniques cannot be used. Thus, it is important to find the key factor that affects TNT photolysis to enhance naturally occurring TNT degradation. This study investigated the effect of soil water content, iron oxide content, and potassium ion (K+) content on the extent of 2,4,6-trinitrotoluene (TNT) photolysis in TNT-contaminated soils using a lab-scale batch tests. TNT degradation rates in soils by UV photolysis increased by approximately 7 and 21 times with increasing soil water contents from 0 to 50 % and 100 %, respectively. This suggests that a greater TNT loss is expected during a wet season than during a dry season. On the other hand, the iron oxide content in soils did not significantly affect TNT degradation as long as UV irradiation was available. In addition, TNT photolysis did not depend on the presence and abundance of K+ in TNT-contaminated soils at the field water holding capacity (16 %) although K+ increased TNT sorption in soils. Overall, this study showed that soil water content is the key factor affecting TNT degradation by UV photolysis in TNT-contaminated soils. Also, since the experiments simulated TNT photolysis of top soils at sites, ploughing of top soils would greatly enhance the naturally occurring TNT photolysis.