Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Herbicide Photodegradation via Safener-Induced Photosensitization: A Mechanistic and Predictive Study on Solid Surface

The environmental persistence of herbicides in soil is a significant agricultural challenge. Although certain safeners, such as benoxacor, have been shown to accelerate herbicide photodegradation, the broader influence of safeners, their mechanisms, and their behavior across herbicide classes remain poorly understood. To address this gap, we investigated the photodegradation of nine herbicides from multiple chemical classes on an inert quartz surface, both alone and in the presence of eleven structurally diverse safeners under simulated sunlight. Decay kinetics revealed that, except for metolachlor and mesotrione, most herbicides degraded slowly (9 × 10⁻⁴ to 1.4 × 10⁻² h⁻¹). Safeners, however, consistently enhanced clopyralid degradation, with enhancement factors between 1.3 and 6.68. Notably, atrazine exhibited a 6.68-fold faster decay when combined with cloquintocet-mexyl or isoxadifen-ethyl, substantially reducing its half-life. Similar improvements were observed for chlorimuron-ethyl, prometryn, and others, while mesotrione showed weaker enhancement (0.52–1.24-fold), likely due to its strong nitro group. Mechanistic probing with chemical scavengers indicated that reactive oxygen species, particularly singlet oxygen (¹O₂) and direct interactions with the safener’s triplet state, drive the observed photosensitization. Predictive QSAR models (R² > 0.99) further highlighted low hydrogen-bonding capacity as the most critical molecular feature for maximizing safener-induced enhancement. Overall, these findings reveal a dual role for safeners: enhancing crop tolerance while accelerating herbicide dissipation, offering a chemistry-based path to more sustainable agrochemical design.