Intermediates formed during natural attenuation of C9 aromatics under simulated marine conditions: Identification, transformation pathway, and toxicity to microalgae

Abstract

C9 aromatics — benzene hydrocarbon containing nine carbon atoms among — leakage accident has caused serious damage to the marine ecology near Quangang District, Fujian Province, China. The ecological restoration of the accident sea area is basically realized through natural attenuation. To determine whether the natural attenuation of C9 aromatics in the marine environment will generate highly toxic intermediates, and thus cause more serious harm to marine ecology, the intermediates of C9 aromatics (n-propylbenzene, isopropylbenzene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and indene) in the process of natural attenuation were studied under the marine conditions simulated by a microcosm. The acute toxic effects of 12 intermediates with longer residual time on Phaeodactylum tricornutum were also ascertained. Twenty natural attenuation intermediates of C9 aromatics were identified. These products primarily include the derivatives of phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic acids, as well as an aromatic lactone compound. No intermediates of 1,3,5-trimethylbenzene and indene during the attenuation process were determined. The indirect photooxidation initiated by hydroxyl radical might play an essential role in the formation of intermediates of C9 aromatic. Based on the 96-h EC50 values for P. tricornutum, the toxicity of the 12 intermediates, in descending order, was: 4-ethylphenol, 2-methylacetophenone, 2,3-dimethylbenzyl alcohol, 4-methylacetophenone, 3-methylacetophenone, 1-phenyl-1-propanol, 1-(2-methylphenyl) ethanol, 2-phenyl-2-propanol, 3,4-dimethylbenzoic acid, 2,4-dimethylbenzoic acid, 2,5-dimethylbenzoic acid, then 4-tolylacetic acid. The 96-h EC50 values of the intermediates of C9 aromatics to P. tricornutum ranged from 8.4 to 199.1 mg/L, which were lower than that of their corresponding parent compound. The findings provided essential fundamental insights for the assessment of marine environmental risk of C9 aromatics leakage accidents, and subsequent emergency disposal countermeasures.