Nano-Biofortification of Food Crops: A Critical Review of Mechanisms, Efficacy, Biosafety and Barriers to Field-scale Application

Abstract

Micronutrient deficiencies, particularly of zinc, iron and selenium, remain widespread in populations that depend on cereal-based diets, and agronomic biofortification is one of several strategies used to raise micronutrient concentrations in edible crop tissues. Engineered nanomaterials have been proposed as a means of improving the efficiency of this strategy through slower nutrient release, altered foliar penetration and targeted delivery. The literature has expanded rapidly, yet its conclusions are frequently stronger than its evidence. This critical narrative review examines whether nano-enabled delivery of zinc, iron and selenium offers demonstrable advantages over conventional fertilisers for food-crop biofortification, through which mechanisms, at what biosafety cost, and with what prospects for field-scale use. Literature was identified through structured searches of multidisciplinary and biomedical indexes, supplemented by citation tracking and institutional guidance, and was appraised for experimental setting, choice of comparator, dose normalisation, nano-specific characterisation and research integrity. The evidence indicates that most nutrient delivered from metal-oxide and elemental nanoparticles enters plant tissues after dissolution or biotransformation, so that nano-specific benefit arises chiefly from release kinetics, reduced leaf injury and formulation chemistry rather than from uptake of intact particles. Field and radiotracer studies with zinc show that nano-formulations can raise grain zinc to nutritionally relevant concentrations but seldom outperform soluble salts or chelates on an equal-dose basis. Evidence for selenium is more favourable, including field data showing conversion to organic selenium species and absence of particulate selenium in grain, whereas evidence for iron remains largely confined to pot studies. Soil microbial effects appear dose- and soil-dependent, and risk assessment is constrained by short experiments, unrealistic exposure concentrations and insufficient characterisation. Contested large-scale deployment of nano-fertilisers illustrates the consequences of commercialisation that precedes independent evidence. Nano-biofortification is best regarded as a promising but conditionally supported refinement of agronomic biofortification. Its advancement depends on multi-site field trials with conventional comparators, human bioavailability endpoints, life-cycle and economic assessment, and harmonised nano-specific regulation.