In vivo tracing of endogenous salicylic acids as the biomarkers for evaluating the toxicity of nano-TiO to plants.

Currently, nano-titanium dioxide (nTiO) is considered an emerging environmental contaminant. Bottlenecked by the traditional destructive and lethal sampling methods, nTiO's effect in living plants is poorly investigated. Here, in vivo tracing of endogenous salicylic acids at regular intervals was performed by using solid phase microextraction (SPME) technique for evaluating the effects of nTiO on plants. By planting aloe in soil containing varying amounts of nTiO, the titanium (Ti) element accumulated in the leaves to concentrations and then reached the maximum of 1.1 ± 0.4 μg/g after nTiO exceeding 0.1 g/kg. The levels of salicylic acid (SA) and acetylsalicylic acid (ASA) were up-regulated upon the exposure to nTiO, while were positively correlated to the contents of Ti. Moreover, the increased malondialdehyde, decreased total superoxide dismutase and fluctuated glutathione along with the addition of nTiO demonstrated the oxidative stress caused by nTiO. Meanwhile, apparent growth indicators including leaf elongation, plant fresh weight and root development were influenced, which further confirmed the toxicity of nTiO imparted on aloe. This study presents the possibility of using salicylic acids as biomarkers for revealing the toxicity of nTiO on plants in addition to the other biomarkers and biomass data, and the in vivo SPME technique is powerful for their monitoring.