Predicting the environmental fate of anthropogenic chemicals remains a top priority for scientists and regulators; however, these efforts are hindered by the complexity of environmental systems. For example, in aquatic photodegradation, multiple photochemically produced reactive intermediates (PPRI) are present simultaneously, such as hydroxyl radicals (˙OH), singlet oxygen (¹O₂), and triplet excited states of chromophoric dissolved organic matter (³CDOM*). This makes it difficult to isolate contributions of individual PPRI to overall photodegradation as well as to measure bimolecular reaction rate constants with target contaminants (k_PPRI), which could subsequently be used to predict degradation rates under variable environmental conditions and in engineered water treatment systems. As an alternative approach, simplified model systems can be used to isolate reactions with each PPRI. Yet, a systematic comparison of the results obtained in different model systems has not been conducted. In this study, at least two model systems were used to quantify k_PPRI between each PPRI (i.e., ˙OH, ¹O₂, and three ³CDOM* proxies) and each of the 28 pesticides evaluated. Results were consistent for most pesticides across the set of model systems used to evaluate a given PPRI. However, significant discrepancies were observed in some cases. For some pesticides, reactions with ˙OH appeared faster than the diffusion-controlled limit, suggesting additional reactions with unidentified PPRI were occurring. In ¹O₂ model systems, unexpected reactions occurred between some pesticides and the triplet excited states of the model sensitizer. Lastly, there was not a consistent trend between the calculated k_PPRI and the photochemical properties of the three ³CDOM* proxies evaluated, as suggested in previous studies. Overall, the results from this study showed that model systems are a powerful tool for investigating indirect photodegradation reactions and should be adopted in formal evaluations of the environmental fate of anthropogenic chemicals. Key considerations and recommendations to ensure accurate and reliable use of model systems are provided and areas benefiting from further investigation are identified.

预测人工化学物质的环境命运仍然是科学家和监管机构的首要任务；然而，这些努力受到了环境系统的复杂性的阻碍。例如，在水生光解过程中，同时存在多种由光化学产生的反应中间体（PPRI），如羟基自由基 (˙OH)、单线态氧 (¹O₂) 和有色溶解有机物的三重激发态 (³CDOM)。这使得很难单独区分每个 PPRI 对总体光解作用的贡献，也无法测量与目标污染物之间的双分子反应速率常数（k_PPRI），这些数据可以用于预测在不同环境条件下和工程水处理系统中的降解速度。作为一种替代方法，简化模型系统可用于隔离与每种 PPRI 的反应。然而，尚未对不同模型系统中获得的结果进行系统的比较。在此研究中，至少使用了两种模型系统来量化 28 种农药评估中每种 PPRI（即 ˙OH、¹O₂ 和三种 ³CDOM 代理）之间的 k_PPRI。在用于评估特定 PPRI 的模型系统集合中，大多数农药的结果是一致的。然而，在某些情况下观察到了显著差异。对于一些农药，与 ˙OH 的反应似乎比扩散控制极限更快，这表明还发生了与其他未识别 PPRI 的额外反应。在 ¹O₂ 模型系统中，意外地发生了一些农药和模型敏化剂的三重激发态之间的反应。最后，在计算 k_PPRI 与评估的三种 ³CDOM* 代理的光化学特性之间没有一致的趋势，这与以往的研究建议不符。总体而言，本研究的结果表明，模型系统是探究间接光解作用反应的强大工具，并应在人工化学品环境命运的正式评价中采用。提供了确保准确和可靠使用模型系统的关键考虑因素和建议，并确定了需要进一步调查的领域。