作者：Bravo, A., Hilmarsson, T., Koehler, B. et al.

Photodegradation in lakes is a major sink for the toxin methylmercury (MeHg) in forest-wetland-lake ecosystems. Previous attempts to estimate annual rates of MeHg photodegradation in lakes have followed a "black-box approach", where the process has been related to incident sunlight rather than photon absorption. Here we use experimental data from three contrasting dark and clear boreal lakes to develop the first apparent quantum yield (AQY) model for spectral MeHg photodegradation rates in lakes. The model was proven universal by its ability to predict experimental data from 22 lakes representing five global regions, covering wide ranges in dissolved organic carbon (DOC), specific UV absorbance at 254 nm, and pH (1.8-39.5 mg C L-1, 1.7-5.7 L mg-1 C m-1 and 4.8-8.5, respectively). The AQY model manifests a dual role played by dissolved organic matter (DOM) as a sensitizer, by producing reactive transient species (RTS) upon photon absorbance, and as an inhibitor, by scavenging of RTS by antioxidants associated with aromatic structures in DOM. Using site-specific data on direct and diffuse solar irradiance, MeHg concentrations, and spectral light absorption properties in 1033 lakes, we estimate an annual MeHg photodegradation rate of 12.1 kg y-1 in the total volume of Swedish lakes. This value corresponds to 24% of the estimated 51 kg of MeHg that annually is transported with runoff from soil into the same lakes. By the AQY model, we calculate the first regional estimates of MeHg photodegradation in lakes of boreal and temperate Europe, temperate North America, subtropical North America, and tropical South America, providing a basis for the establishment of regional MeHg cycling models.

湖泊中的光降解是森林—湿地—湖泊生态系统中甲基汞（MeHg）的主要汇。以往估算湖泊MeHg年光降解速率的研究多采用“黑箱方法”，即将该过程与入射太阳辐射直接关联，而非与光子吸收量相关联。研究利用三个明暗对比显著的北方湖泊的实验数据，建立了首个湖泊中光谱分辨的MeHg光降解速率表观量子产率（AQY）模型。该模型的普适性得到验证：其成功预测了代表全球五个区域、共22个湖泊的实验数据，这些湖泊涵盖广泛的溶解有机碳（DOC）浓度（1.8-39.5 mg C·L⁻¹）、254 nm波长比紫外吸光度（1.7-5.7 L·mg⁻¹ C·m⁻¹）和pH（4.8-8.5）。AQY模型揭示了溶解有机质（DOM）的双重角色：其一是敏化剂作用——DOM吸收光子后产生活性瞬态物种（RTS）；其二是抑制剂作用——DOM芳香结构所伴随的抗氧化物质会清除RTS。基于1033个湖泊的实测直射与散射太阳辐照度、MeHg浓度及光谱吸收特性数据，估算瑞典全国湖泊水体中MeHg的年光降解速率为12.1 kg·y⁻¹，约占每年随地表径流由土壤输入这些湖泊的MeHg总量（估算为51 kg）的24%。借助AQY模型，首次估算了中国东北部与欧洲温带、北美温带、北美亚热带及南美热带地区湖泊的MeHg光降解速率，为建立区域性MeHg循环模型奠定了基础。

(来源：Environmental Science & Technology 2026 Issue 23  DOI: 10.1021/acs.est.5c18570）