¹³C/¹²C and ¹⁵N/¹⁴N Isotope Analysis To Characterize Degradation of Atrazine: Evidence from Parent and Daughter Compound Values

Atrazine (Atz) and its metabolite desethylatrazine (DEA) frequently occur in the environment. Conclusive interpretation of their transformation is often difficult. This study explored evidence from ¹³C/¹²C and ¹⁵N/¹⁴N isotope trends in parent and daughter compounds when Atz was dealkylated by (i) permanganate and (ii) the bacterium <i>Rhodococcus</i> sp. NI86/21. In both transformations, ¹³C/¹²C ratios of atrazine increased strongly (ε_{carbon/permanganate} = −4.6 ± 0.6‰ and ε_{carbon/<i>Rhodoccoccu</i>s} = −3.8 ± 0.2‰), whereas nitrogen isotope fractionation was small. ¹³C/¹²C ratios of DEA showed the following trends. (i) When DEA was formed as the only product (Atz + permanganate), ¹³C/¹²C remained constant, close to the initial value of Atz, because the carbon atoms involved in the reaction step are not present in DEA. (ii) When DEA was formed together with desisopropylatrazine (biodegradation of Atz), ¹³C/¹²C increased but only within 2‰. (iii) When DEA was further biodegraded, ¹³C/¹²C increased by up to 9‰ giving strong testimony of the metabolite’s breakdown. Two lines of evidence emerge. (a) Enrichment of ¹³C/¹²C in DEA, compared to initial Atz, may contain evidence of further DEA degradation. (b) Dual element (¹⁵N/¹⁴N versus ¹³C/¹²C) isotope plots for dealkylation of atrazine agree with indirect photodegradation but differ from direct photolysis and biotic hydrolysis. Trends in multielement isotope data of atrazine may, therefore, decipher different degradation pathways