Preliminary investigation of reductive degradation of 1,3-dinitrobenzene contaminated soils with natural weed Sphagneticola trilobata

Abstract

Purpose

1,3-dinitrobenzene (1,3-DNB) is a nitroaromatic compounds (NACs), that is a commonly seen persistent contaminant when spilled into soil media. The nitrogen atom of a NACs’ nitro group contains a + III nitrogen oxidation state, which is prone to accepting electrons and is reducible. Sphagneticola trilobata is a wildly distributed weed and contains polyphenols, which may act as a natural electron supplier. This study investigated the potential application of S. trilobata to treat 1,3-DNB contaminated soils.

Materials and methods

The soil slurry experiments were performed to evaluate the proposed processes of mixing weeds and contaminated soil with water under different dosages of weeds and soil/water mass ratios. S. trilobata weeds were collected from the campus of National Chung Hsing University. Characterization of S. trilobata reaction systems was initially conducted. In the weeds/contaminated soils slurry experiments, 30-mL reaction bottles were prepared as follows: 5 g of contaminated soil was mixed with 2, 5, 10, and 15 mL of water, each with a fixed concentration of 10 g-weed L⁻¹, corresponding to 4, 10, 20, and 30 g-weed kg⁻¹-soil. An additional set of reaction bottles was prepared for the soil (g)/water (mL) ratios 5/2, 5/5, 5/10, and 5/15, with a fixed 90 g-weed kg⁻¹-soil.

Results and discussion

The total phenolic content of S. trilobata was determined to be 11.832 ± 0.038 mg g⁻¹, as gallic acid. The UV–Vis spectroscopy analysis verified that the weed polyphenols can play a crucial role in degrading 1,3-DNB. Furthermore, in the soil slurry experiments, S. trilobata dosage and water addition volume are two critical factors influencing the degradation efficiency. For low concentrations of 1,3-DNB in soil (14.46 mg kg⁻¹), the weed dosage of 10 g kg⁻¹-soil at a soil/water ratio of 5/5 (g/mL) was able to achieve > 99% removal rate, while for treating a higher concentration of 1,3-DNB (215.65 mg kg⁻¹), a greater weed dosage and water volume were required. 1,3-DNB can be transformed to the less toxic intermediates, 3-nitroaniline (3-NA) and 1,3-phenylenediamine (1,3-PDA).

Conclusions

The mechanism of 1,3-DNB degradation by S. trilobata’s polyphenols follows the formation of 3-NA and 1,3-PDA. This study verified the potential chemical reductive reaction with S. trilobata as a reducing reagent for degrading reducible contaminants such as 1,3-DNB, by the in situ field application of mixing S. trilobata weeds with contaminated soils, and providing an appropriate soil water ratio. The results of this study may serve as a reference for remediating NAC contaminated soils.