Interactions of sodium azide with triazine herbicides: Effect on sorption to soils

Abstract

Sodium azide (NaN 3) is one of the biocides commonly used to inhibit microbial growth during sorption experiments. However, a few reports have suggested that NaN 3 can react with the analyte of interest. In this study, the interactions of NaN 3 with triazine herbicides were investigated and the effect of atrazine transformation on its sorption to soil was evaluated. The concentration of atrazine in the presence of NaN 3 decreased significantly over period of time. After 14 days, only 38% of the initial atrazine concentration (10 mg l −1) was detected in a solution containing 1000 mg l −1 NaN 3 at pH 5.5. The magnitude and the rate of atrazine transformation increased with increase in NaN 3 load and with decrease in pH. In contrast to atrazine behavior, the concentrations of prometon and ametryn did not change during the experiment. GC/MS analysis indicated that the chlorine atom of atrazine is replaced by the azide group yielding 2-azido-4-(ethylamino)-6-(isopropylamino)- s-triazine. Atrazine transformation by NaN 3 significantly affected sorption of herbicide to soil. The presence of NaN 3 affects indirectly the sorption of atrazine due to competitive effect of its derivative. Our results demonstrated that the application of NaN 3 as a biocide in sorption–desorption experiments must be carefully evaluated. This issue is vital for sorption experiments conducted over long periods of time or/and with concentration of NaN 3 higher than 100 mg l −1.