Changes in Chemical Composition and Copepod Toxicity during Petroleum Photo-oxidation

Photoproducts can be formed rapidly
in the initial phase of a marine
oil spill. However, their toxicity is not well understood. In this
study, oil was irradiated, chemically characterized, and tested for
toxicity in three copepod species (Acartia tonsa, Temora longicornis, and Calanus finmarchicus). Irradiation led to a depletion
of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes
in oil residues, along with an enrichment in aromatic and aliphatic
oil photoproducts. Target lipid model-based calculations of PAH toxicity
units predicted that PAH toxicities were lower in water-accommodated
fractions (WAFs) of irradiated oil residues (“irradiated WAFs”)
than in WAFs of dark-control samples (“dark WAFs”).
In contrast, biomimetic extraction (BE) measurements showed increased
bioaccumulation potential of dissolved constituents of irradiated
WAFs compared to dark WAFs, mainly driven by photoproducts present
in irradiated oil. In line with the BE results, copepod mortality
increased in irradiated WAFs compared to dark WAFs. However, low copepod
toxicities were observed for WAFs produced with photo-oxidized oil
slicks collected during the Deepwater Horizon oil spill. The results
of this study suggest that while oil photoproducts have the potential
to be a significant source of copepod toxicity, dilution and dispersion
of these higher solubility products appear to help mitigate their
toxicity at sea.

海洋溢油初期可快速生成油基光产物，但当前学界对其毒性的认知仍存在显著不足。本研究对原油开展辐照处理，进行化学表征，并针对三种桡足类物种（Acartia tonsa、Temora longicornis及Calanus finmarchicus）开展毒性测试。
辐照处理可导致油残留中的多环芳烃（polycyclic aromatic hydrocarbons, PAHs）与正构烷烃含量显著降低，同时提升油样中芳香族与脂肪族光产物的富集水平。
基于目标脂质模型的多环芳烃毒性单位计算预测，辐照油残留的水相可溶组分（water-accommodated fractions, WAFs，简称“辐照WAFs”）的PAH毒性低于暗对照样品的水相可溶组分（简称“暗WAFs”）。
与之相反，仿生萃取（biomimetic extraction, BE）检测结果显示，“辐照WAFs”中溶解组分的生物富集潜力较“暗WAFs”有所提升，这一现象主要由辐照油样中存在的光产物所驱动。与仿生萃取结果一致，“辐照WAFs”组的桡足类死亡率较“暗WAFs”组有所升高。但针对深水地平线（Deepwater Horizon）溢油事件中采集的光氧化油膜制备的WAFs，并未观测到显著的桡足类毒性。
本研究结果表明，尽管油基光产物可能是引发桡足类毒性的重要来源，但这类高溶解度产物的海上稀释与扩散过程，可有效缓解其在海洋环境中的毒性效应。