Bromide ion enhancing the phytodegradation of emerging phenolic pollutants and its mechanisms mediating wheat resistance to phenolic pollutants stress

The phytodegradation of emerging phenolic pollutants (EPPs) has attracted widespread attention. However, the impact of bromide ions (Br−) on the phytodegradation of EPPs and its mechanism mediating wheat resistance to EPPs stress have rarely been reported. Our research discovered that Br− enhanced the removal of EPPs (7.5, 15 mg/L) in a dark hydroponic wheat system. The degradation efficiency of acetaminophen (ACE), bisphenol A (BPA) and 1-naphthol (1-NP) increased 2.2, 2.8 and 1.28 times as Br− concentration increased from 0 to 1 mM, respectively. In the presence of Br−, the mono- and dibromo-products of ACE and BPA were produced in the dark hydroponic wheat system, while 1-NP showed higher degradation efficiency but no bromine substitution formation. EPPs induced oxidative damage and root growth inhibition in wheat. The addition of Br− enhanced the chlorophyll content, indole-3-acetic acid (IAA) content and antioxidant potential to alleviate EPPs stress. Principal component analysis (PCA) revealed significant separation of different Br− stimuli, that is, the low concentrations of Br− (0.1 mM) enhanced the content of IAA by 28.6%, while higher concentrations of Br− (0.5, 1 mM) alleviated membrane lipid peroxidation by improving peroxidase (POD) activity. This is the first report that Br− could stimulate the synthesis of IAA via indole acetonitrile (IAN) pathway and hydrolysis of IAA-conjugates. This study provides more support for the feasibility of phytoremediation techniques for phenolic pollutants and references for the assessment of ecological risks and health hazards of EPPs.