Pesticide degradation in an integrated constructed wetland: Insights from compound-specific isotope analysis and 16S rDNA sequencing

Abstract

Carbon isotope analysis and the 16S rDNA sequencing were adopted to investigate the degradation process of chlorpyrifos during its transport in the integrated constructed wetland (ICW). Firstly, the extent of concentration decrease of chlorpyrifos was examined, and the removal efficiency in the first 36 h was found to be the highest. The removal rate reached 96.83 % after 96 h, and this process fit to the first-order kinetic model, with a kinetic constant (k) of 0.066 h−1. A significant carbon isotope fractionation was observed, with a change of the δ13C values from −26.54 ± 0.07 ‰ to −25.41 ± 0.08 ‰. The average chlorpyrifos biodegradation proportion reached 71.23 % (60.42 %–85.04 %), and it was predicted that about 11.79 %–36.41 % of chlorpyrifos removal in the ICW was attributed to abiotic factors. The outlet of the subsurface flow constructed wetland saw the highest D∗/B∗ value (1.38–3.88), indicating that the remaining fraction of dilution was much more significant than that of degradation in this period. The top 20 phyla of microbial community were identified in the ICW. Proteobacteria was the most dominant phylum, accounting for >40 % of the bacterial communities in all sampling locations. Acidobacteria and Bacteroidetes were the second and third dominant phyla. At the genus level, the microbial community composition differed more greatly in every stage of the ICW, and the spatial distribution difference was quite significant in the ICW. This study is important to figure out the migration and transformation of chlorpyrifos when the ICW was adopted as a removal tool for organic micro-pollutants, and more similar studies could be carried out in the future to promote the evaluation of pollutant removal capacity of the ICWs, and to further develop the application of stable isotope analysis of compounds in the natural environment.