Persistent Free Radicals from Low-Molecular-Weight Organic Compounds Enhance Cross-Coupling Reactions and Toxicity of Anthracene on Amorphous Silica Surfaces under Light

Abstract

Polycyclic aromatic hydrocarbon (PAH) contamination has raised great environmental concerns, while the effects of low-molecular-weight organic compounds (LMWOCs) on PAH photodegradation at amorphous silica (AS)/air interfaces have been largely ignored. In this study, the phototransformation of anthracene (ANT) at amorphous silica (AS)/air interfaces was investigated with the addition of LMWOCs. ANT removal was attributed to •OH attacking and the energy transfer process via 3ANT*. Light irradiation induced the fractured SiO• or Si• generation on AS surfaces, which could react with absorbed H2O and O2 to generate •OH and further yield a series of hydroxylated products of ANT. The presence of citric acid and oxalic acid improved •OH generation and enhanced ANT removal by 1.0- and 2.2-fold, respectively. For comparison, the presence of catechol and hydroquinone significantly decreased ANT removal and produced coupling products. The results of density functional theory calculations suggest that persistent free radicals (PFRs) on AS surfaces from catechol or hydroquinone after •OH attacking prefer to cross-couple with ANT via C–C bonding rather than self-couple. Dianthrone and cross-coupling products might possess higher ecotoxicity, while hydroxylated products were less ecotoxic than their parent compounds based on Ecological Structure Activity Relationships (ECOSAR) estimation. The results of this study revealed the potential ecotoxicity of PAH-adsorbed particulates coexisting with LMWOCs and also provided a new insight into PAH transformation through PFR pathways.

Mesoporous Silica Nanoparticles Induce Intracellular Peroxidation Damage of Phytophthora infestans: A New Type of Green Fungicide for Late Blight Control

“…This activity is quite different from some metal nanomaterials, such as Ag or Au . Previous studies have suggested that hydroxyl radicals (•OH) can be produced by some silica. , Surprisingly, it was found that the SSNs, VSNs, and MSNs could not produce any free radicals or active substances under normal conditions in this work (Figure h). Meanwhile, EPR analyses indicated that the ROS, including hydroxyl radicals (•OH), superoxide radicals (•O 2 – ), and singlet oxygen ( 1 O 2 ), could be generated in the P.…”

Mechanistic Study of the Effects of Agricultural Amendments on Photochemical Processes in Paddy Water during Rice Growth

“…The LC 50 , EC 50 , and ChV parameters of the dimer were significantly lower than those of 2,4-DCP, which indicates that the dimer was much more toxic than 2,4-DCP. In addition, the dimer is less water-soluble and difficult to be metabolized by microorganisms, which may be accumulated in animal and human bodies through food chains, thus posing potentially high health risks . In contrast, the LC 50 (fish), LC 50 (daphnia), and EC 50 (green algae) of the dechlorinated product increased to 12.06, 107.41, and 3.89 mg/L, respectively, suggesting a lower toxicity than 2,4-DCP.…”

“…In addition, the dimer is less water-soluble and difficult to be metabolized by microorganisms, 53 which may be accumulated in animal and human bodies through food chains, thus posing potentially high health risks. 56 In contrast, the LC 50 (fish), LC 50 (daphnia), and EC 50 (green algae) of the dechlorinated product increased to 12.06, 107.41, and 3.89 mg/L, respectively, suggesting a lower toxicity than 2,4-DCP. Therefore, the oligomerization of 2,4-DCP mediated by 3 DOM* would produce more toxic dimer products, while • OH-mediated dechlorination and hydroxylation is a detoxification pathway transforming 2,4-DCP to less toxic product(s).…”

Pharmaceutical Transformation Products Formed by Ozonation—Does Degradation Occur?

“…Chronic toxicity (ChV) in fish assesses the effect of long-term exposure to a pollutant on the organisms. The classifications are very toxic (LC50/EC50/ChV ≤ 1), toxic (LC50/EC50/ChV ≤ 10), harmful (LC50/EC50/ChV ≤ 100) and not harmful (LC50/EC50/ChV > 100) [ 52 ].…”