Enhancing the release and plant uptake of PAHs with a water-soluble purine alkaloid

The effect of a common plant alkaloid, caffeine, on the release and plant uptake of some polycyclic aromatic hydrocarbons (PAHs) in soils was investigated. Cucurbita pepo (ssp. pepo cv. Gold Rush) was grown in PAH-spiked media in the presence and absence of caffeine. Solubility tests initially confirmed the ability of caffeine to dissolve PAHs mixtures of anthracene, phenanthrene, pyrene, benzo[a]pyrene and benzo[ghi]perylene. Extraction experiments also highlighted its potential as a PAH-releasing agent from an aged soil. Phytoextraction from a low organic sand medium (fOC = 0.056 ± 0.03%) indicated a significant enhancement of pyrene uptake with three weeks daily watering with 500 mg L−1 caffeine solution. The average pyrene content of roots was 35.3 and 16.0 μg g−1, in caffeine and non-caffeine set-ups, respectively. In the shoots, the corresponding values were 3.60 and 1.67 μg g−1. Both showed more than twofold increase with caffeine. Caffeine also accumulated mainly in the leaves of the treated samples at 2800 mg kg−1 dry weight. Further tests with a 1-year aged soil (fOC = 5.2 ± 1%) containing a mixture of phenanthrene and pyrene yielded parallel results. However, lower PAH content in these samples were observed due to the stronger PAHs partitioning in aged-soil matrix. After four weeks of caffeine, phenanthrene in shoots and roots increased by one and a half and four times, respectively. The corresponding enhancements for pyrene were two and a half and three and a half times.