Spearmint planting in combination with its leaf amendment spurred dissipation of polycyclic aromatic hydrocarbons in soil

Oil-bearing aromatic plants are superior to traditional crops and grasses in phytoremediation due to their high stress tolerance and ornamental value. Here, spearmint (<i>Mentha crispa</i>), a model aromatic plant species, with or without spearmint leaf amendment, was used in a pot experiment to evaluate the phytoremediation effects on a PAHs-contaminated soil. After 180 days, the planted pots amended with essential oil-containing spearmint leaves exhibited a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>∑</mml:mo><mml:mrow><mml:mn>16</mml:mn><mml:mtext>PAHs</mml:mtext></mml:mrow></mml:mrow></mml:math> removal rate of 26.80%, significantly higher (<i>p</i> < 0.05) than that by the planted pots added with essential oil-deprived leaves (9.75%) and planting alone (5.13%). The 4-ring PAHs tended to be preferentially removed, leading to compositional alterations of PAHs. Also, the substrate-assisted PAHs degradation was not at the cost of appreciable loss of stable soil organic carbon. Further, combination of planting and oil-containing leaf amendment exhibited relatively more root exudates in abundance which could serve as biostimulants for PAHs rhizodegradation. Spearmint roots and leaves harvested accumulated 2868.42 and 3698.97 ng/g PAHs which were mostly translocated to essential oils during hydistillation, implying that essential oils may be PAHs dissipation enhancers. These results manifest the oil-bearing leaf amendment a spur to phytoremediation of PAHs by spearmint. Spearmint holds promising in remediation and rejuvenation of PAHs-contaminated urban soils.