The combination of warming and copper decreased the uptake of polycyclic aromatic hydrocarbons by spinach and their associated cancer risk.

Both climate warming and co-contamination of polycyclic aromatic hydrocarbons (PAHs) and heavy metals are environmental issues of great concern. However, the interactive effects of warming and heavy metals on PAH accumulation in edible plants and the PAH-associated health risk remain unclear. In this study, enclosed soil/water-air-plant microcosm experiments were conducted to explore the effects of copper (Cu), warming (+6 °C), and their combination on the uptake of four deuterated PAH (PAH-d) by spinach (Spinacia oleracea L.) in aged soil. PAH-associated health risks for soil, plant, and air exposure pathways were also assessed. The results showed that both individual Cu or warming decreased the PAH-d concentrations in root and shoot (non-normalized by lipid content) as well as the total PAH-associated cancer risk. Although antagonism existed between warming and Cu, compared to the presence of Cu, warming further reduced the spinach uptake of PAHs-d and total PAH-associated cancer risk, and the reductions were stronger at higher Cu levels. The inhibitory effect of the binary combination on PAH-d root uptake was attributed to decreased root lipid content and phytoavailable concentrations of PAHs-d in soil as a consequence of biodegradation, aging effect and cation-π interaction. The antagonism between warming and Cu on spinach uptake could be explained by their opposite effects on PAH-d biodegradation and the inhibition of the cation-π interaction caused by warming. Additionally, the shoot uptake of PAHs-d was mainly controlled by their soil to air to shoot partitioning. The findings suggest that the interactive effects of climate warming and co-existing pollutants should be taken into account for the assessment of plant uptake and health risk of PAHs.