September 4, 2025 — JNU Integrated Media Center

A groundbreaking study led by Professor Xiang Lei from the research team of Professor Mo Cehui at Jinan University has been published in Water Research, a top-tier international journal in environmental science. The study systematically uncovers, for the first time, the synergistic toxic effects and underlying molecular mechanisms between xanthates—typical organic flotation agents used in mining—and the heavy metal cadmium (Cd). It reveals that xanthates and Cd can form soluble tridentate coordination complexes, which significantly enhance Cd accumulation in crops and lead to synergistic toxicity. These findings offer new insights for ecological risk assessment and pollution control related to organic flotation agents in mining activities.

Xanthates are organic reagents widely used in the flotation of sulfide ores. A large portion of these compounds enter the environment via flotation wastewater and can pose risks to aquatic organisms even at very low concentrations. Xanthates can also form complexes with heavy metals such as cadmium, copper, and zinc, altering the environmental behavior and bioavailability of both the metals and the reagents, potentially exacerbating toxicity. However, studies on the combined toxicity and interaction mechanisms between xanthates and heavy metals have been limited, particularly regarding the bonding process and ecological effects, which has hindered the development of effective pollution prevention strategies.

To address this research gap, the team selected three common xanthates (ethyl, isopropyl, and butyl xanthate) and Cd—a heavy metal often associated with sulfide ores—as target pollutants. Using cabbage seedling cultivation experiments combined with multiple analytical techniques—including atomic force microscopy (AFM), quantum chemical simulations, high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), and isothermal titration calorimetry (ITC)—the researchers investigated the complexation behavior and toxicity mechanisms.

The results showed that all three xanthates formed soluble tridentate coordination complexes with Cd, exhibiting a symmetrical trigonal pyramidal structure involving four σ bonds and 1.5 π bonds. This coordination mechanism corrects the previously held misconception that xanthates and Cd form bidentate complexes. The formation of Cd–xanthate complexes inhibited the degradation of xanthates, increasing their environmental persistence. Moreover, these complexes markedly enhanced the bioavailability of Cd, leading to a 2.8-fold increase in Cd accumulation in cabbage seedlings compared to Cd-only exposure. The combined stress also disrupted photosynthesis and transpiration by inhibiting electron transport, stomatal conductance, and transpiration rates, resulting in severe membrane lipid peroxidation and significant biomass reduction.

Notably, unlike Cd, copper (Cu) formed insoluble precipitates with all three xanthates, leading to significantly reduced toxicity. This difference stems from the much higher complexation affinity between Cu and xanthates (pKsp ≈ 20) compared to that of Cd (pKsp ≈ 14). The results indicate that soluble complexes with synergistic toxicity are likely to form between xanthates and metals with moderate affinity, highlighting a previously underestimated ecological risk.

This study provides the first molecular-level insight into the synergistic toxicity of xanthates and heavy metals, offering important theoretical support for pollution control in mining areas and the safety of agricultural products. Professor Xiang Lei of the College of Life Science and Technology at Jinan University is the first author of the paper, with Professor Mo Cehui and Associate Researcher Zhao Haiming serving as co-corresponding authors. The research was supported by the National Natural Science Foundation of China (Grant No. 42030713) and the Guangdong Provincial Natural Science Foundation Outstanding Youth Project (2025B1515020043).

Image Descriptions

Figure 1: Effects of combined exposure to Cd and xanthates on cabbage root growth and heavy metal accumulation.

Figure 2: Impact of Cd–ethyl xanthate combined stress on transpiration, chlorophyll content, and photosynthesis.

Figure 3: High-resolution mass spectra and natural Cd isotope patterns for Cd–xanthate complexes.

Figure 4: NMR spectra showing chemical shift changes upon Cd–ethyl xanthate coordination.