Emergence of toxic trace elements in plant environment: Insights into potential of silica nanoparticles for mitigation of metal toxicity in plants

Emergence of trace elements at potentially toxic concentrations in the environment has become a global issue in recent times. Owing to the rapid population growth, unregulated industrialisation, intensive farming practices and excessive mining activities, these elements are accumulating in environment at high toxic concentrations. The exposure of plants to metal-contaminated environments severely influences their reproductive and vegetative growth, eventually affecting crop performance and production. Hence, it is crucial to find alternatives to mitigate the stress caused by toxic elements, in plants of agricultural importance. In this context, silicon (Si) has been widely recognized to alleviate metal toxicity and promote plant growth during various stress conditions. Amending soil with silicates has shown to ameliorate the lethal effects of metals and stimulates crop development. However, in comparison to silicon in bulk form, nano-sized silica particles (SiNPs) have been demonstrated to be more efficient in their beneficial roles. SiNPs can be used for various technological applications, viz. Improving soil fertility, agricultural yield, and remediating heavy metal-polluted soil. The research outcomes of studies focussing on role of silica nanoparticles to specifically mitigate the metal toxicity in plants have not been reviewed earlier in depth. The aim of this review is to explore the potential of SiNPs in alleviating metal stress and improving plant growth. The benefits of nano-silica over bulk-Si fertilizers in farming, their performance in diverse plant varieties, and the possible mechanisms to mitigate metal toxicity in plants have been discussed in detail. Further, research gaps are identified and future prospects are envisioned for advanced investigations in this field. The growing interest towards nano-silica related research will facilitate exploration of the true prospective of these nanoparticles for mitigation of metal stress in crops and in other fields of agriculture as well.