Abstract：
Photochemical processes are typically not incorporated in screening-level substance risk assessments due to the complexity of modeling sunlight co-exposures and resulting interactions on environmental fate and effects. However, for many substances, sunlight exerts a profound influence on environmental degradation rates and ecotoxicities. Recent modeling advances provide an improved technical basis for estimating the effect of sunlight in modulating both substance exposure and toxicity in the aquatic environment. Screening model simulations were performed for 25 petrochemical structures with varied uses and environmental fate properties. Model predictions were evaluated by comparing the ratios of predicted exposure concentrations with and without light to the corresponding ratios of toxicity thresholds under the same conditions. The relative ratios of exposure and hazard in light vs. dark were then used to evaluate how inclusion of light modulates substance risk analysis. Results indicated that inclusion of light reduced PECs by factors ranging from 1.1- to 63-fold as a result of photodegradation, while reducing PNECs by factors ranging from 1- to 49-fold due to photoenhanced toxicity caused by photosensitization. Consequently, the presence of light altered risk quotients by factors that ranged from 0.1- to 17-fold, since the predicted increase in substance hazard was mitigated by the reduction in exposure. For many structures, indirect photodegradation decreases environmental exposures independently of the direct photolysis pathway which is associated with enhanced phototoxicity. For most of the scenarios and chemicals in the present work, photosensitization appears to be mitigated by direct and indirect degradation from sunlight exposure.
摘要：
由于对阳光共同暴露进行建模的复杂性以及由此产生的对环境命运和影响的相互作用，光化学过程通常不会纳入筛选级物质风险评估中。然而,对于许多物质，阳光对环境退化率和生态毒性有着深远的影响。最近的建模进展为估计阳光在调节水生环境中的物质暴露和毒性方面的影响提供了改进的技术基础。对25种具有不同用途和环境归宿特性的石化结构进行了筛选模型模拟。通过比较在相同条件下有和没有光的预测暴露浓度的比率与相应的毒性阈值比率来评估模型预测。光暴露和危害的相对比率与然后使用黑暗来评估包含光如何调节物质风险分析.结果表明，由于光降解，光的掺入使PEC减少了1.1到63倍，同时由于光敏化引起的光增强毒性，将PNEC减少了1至49倍。因此,光的存在改变了风险商的范围从0.1倍到17倍，因为预期的物质危害增加是通过减少暴露来缓解的。对于许多结构，间接光降解独立于与增强的光毒性相关的直接光解途径降低了环境暴露。对于当前工作中的大多数场景和化学品，光敏化似乎可以通过阳光照射的直接和间接降解来减轻。
