Foliar uptake of persistent organic pollutants at alpine treeline

Previous studies highlighted the role of temperature on the foliar uptake of persistent organic pollutants (POPs) based on their physicochemical properties. However, few studies have focused on the indirect impacts of low temperature on the foliar uptake of POPs due to the changed physiology of leaves. We measured the concen-trations and temporal variations of foliar POPs at the treeline on the Tibetan Plateau, the highest-altitudinal treeline on Earth. The leaves at the treeline showed high uptake efficiencies and reservoir capacity of dichlor-odiphenyltrichloroethanes (DDTs), which were two times to one order of magnitude higher than those in forests worldwide. Enhanced surface adsorption due to the increased thickness of the wax layer in a colder climate was found to be the primary contributor (>60 %) to the high uptake of DDTs at the treeline, and slow penetration controlled by temperature contributed 13 %-40 %. The relative humidity, related negatively to temperature, also influenced the uptake rates of DDTs by foliage at the treeline (contribution: <10 %). The uptake rates of small molecular-weight POPs (hexachlorobenzene and hexachlorocyclohexanes) by foliage at the treeline were quite lower than those of DDTs, relating probably with the weak penetration of these compounds into leaves and/or low-temperature-induced precipitation washout from leaf surface.

Automated summary

Previous studies have focused on the direct impact of temperature on the foliar uptake of persistent organic pollutants (POPs), but few studies have explored the indirect impacts of low temperature on foliar uptake. Our study at the treeline on the Tibetan Plateau found that colder climate conditions led to enhanced surface adsorption and slower penetration of dichlorodiphenyltrichloroethanes (DDTs) in leaves, resulting in higher uptake efficiencies and reservoir capacity. The relative humidity, correlated with temperature, also influenced the uptake rates of DDTs.