The reaction laws and toxicity effects of synthetic phenolic antioxidants (SPAs) in wastewater and atmosphere: A theoretical investigation

Synthetic phenolic antioxidants (SPAs) are widely added to fats and fried foods as food additives. Their hazards to humans and the environment cannot be ignored. The degradation mechanism of three SPAs (butyl hydroxyanisole (BHA), dibutyl hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ)) by superoxide radical (O₂^•-), SO₄•^-, O₃ and •OH is investigated using density functional theory (DFT) method. In the atmosphere, the •OH-addition products of TBHQ will react with O₂ and NO, and in the wastewater, TBHQ-OH intermediates will react with O₂ and HO₂• to generate products. The results showed that the activation energies (ΔG^≠) of the addition reactions of TBHQ with OH and O₃ in wastewater systems were 2.59–6.23 kcal/mol and 10.29–20.35 kcal/mol, respectively, which were significantly lower than those of the gas-phase reactions (4.91–9.74 kcal/mol and 16.69–24.57 kcal/mol), indicating the high efficiency of liquid-phase degradation. The rate constants for the degradation of the three SPAs by different ROS are in the following order: •OH ≈ SO₄•^- > O₃ > > O₂^•-. The half-life t_1/2(SO₄•^-) of SPAs is 0.013–151.06 s in the range of 273–313 K and [SO₄•^-] of 10⁻¹³ to 10⁻⁹ mol L⁻¹. These three SPAs are hardly persistent in the environment. As for TBHQ, the toxicity of the ring-opening products P2, P3, P4 and P5 was significantly lower relative to TBHQ. The degradation half-lives (t_1/2) of SPAs by advanced oxidation processes (AOPs) based on SO₄^- in the range of 273–313 K were 0.013–151.06 s, indicating their efficient degradation properties.The toxicity of its degradation products of SPAs are effectively reduced. This work provides theoretical support for the degradation of SPAs by advanced oxidation processes (AOP) based on SO₄•^- and •OH.