Interaction of titanium dioxide nanoparticles with soil components and plants: current knowledge and future research needs - a critical review

Titanium dioxide nanoparticles (nano-TiO2), one of the most produced engineered nanoparticles (ENPs), are used in pigments, photocatalysis, food additives, and personal care products. This broad variety of applications has led to the unusual and widespread distribution of nano-TiO2 in several environmental sectors, with different effects on living organisms. In the last decade, several publications have shown fragments of information about the interaction, detection, uptake, and translocation of nano-TiO2 in plants. This review includes a discussion of the current knowledge about factors affecting the interaction of nano-TiO2 with soil and plants. We also discuss the role of particle size, crystal phase, surface coating, and techniques employed to study the interaction of these nanoparticles with plants. Concluding results from synchrotron based, microscopic, physiological, and biochemical analyses of plants exposed to nano-TiO2 are presented. However, the current information leaves no doubt that there are still many aspects in need of additional investigations to fully understand the effects of nano-TiO2 in plants. For instance, little is known about the transgenerational effects of nano-TiO2 exposure and the changes at agronomical and physiological levels. The effects of such ENPs in proteins and other metabolites are also not well understood. In addition, more information is needed about the interaction of nano-TiO2 with other ENPs-and-organic co-contaminates and the effects of plants. Since nano-TiO2 have been found in edible tissues, it is expected that they will be in the food chain; thus, studies on their trophic transfer are required. The authors hope that, besides contributing to a better understanding of current data about the effects of nano-TiO2 in soil and plants, this review will help to drive future investigations and will contribute to the general knowledge on the environmental interactions of engineered nanomaterials.