Impact of iron and manganese nano-metal-oxides on contaminant interaction and fortification potential in agricultural systems – a review Elizabeth C. Gillispie, A,D Stephen E. Taylor, A,B Nikolla P. Qafoku A and Michael F. Hochella Jr A,C A Subsurface Science and Technology Group, Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA. B Department of Crop and Soil Science, Washington State University, Richland, WA 99354, USA. C Department of Geoscience, Virginia Tech, Blacksburg, VA 24061, USA. D Corresponding author. Email: elizabeth.gillispie@pnnl.gov Environmental context. Nanominerals are more reactive than bulk minerals, a property that strongly influences the fate of nutrients and contaminants in soils and plants. This review discusses applications of Fe- and Mn-nano-oxides in agricultural systems and their potential to be used as fertiliser and contaminant adsorbents, while addressing potential phytotoxicity. We discuss areas where significant advances are needed, and provide a framework for future work. Abstract. Rising population growth and increase global food demand have made meeting the demands of food production and security a major challenge worldwide. Nanotechnology is starting to become a viable remediation strategy of interest in farming. Ultimately, it may be used as a sustainability tool in agricultural systems. In these roles, it could be used to increase the efficiency of techniques such as food monitoring, pathogen control, water treatment and targeted delivery of agrochemicals. In addition to these uses, nanoparticles, particularly nano-metal-oxides (NMOs), have been engineered to act as contaminant scavengers and could be applied to a wide range of systems. Numerous studies have investigated the scavenging ability of NMOs, but few have investigated them in this role in the context of agricultural and food systems. Within these systems, however, research has demonstrated the potential of NMOs to increase crop health and yield but few have studied using NMOs as sources of key micronutrients, such as Fe and Mn. In this review, we address previous research that has used Fe- and Mn-NMOs in agricultural systems, particularly the worldwide crop production of the four major staple foods – rice, wheat, maize and soybeans – highlighting their application as fertilisers and sorbents. Fe- and Mn-NMOs are strong candidates for immobilisation of agricultural contaminants in soils and, because they are naturally ubiquitous, they have the potential to be a cost-effective and sustainable technology compared with other remediation strategies. Additional keywords: agricultural nanotechnology, nutrient uptake. Received 18 February 2019, accepted 14 June 2019, published online 23 July 2019 Introduction The Earth’s human population continues to grow, and espe- cially in the shadow of climate change, the demands for more and better distributed food production have created an ongo- ing global challenge. Nanotechnology has become a remedi- ation strategy of interest as a sustainable tool in agricultural systems, where it aims to increase efficiency in food pro- duction monitoring, pathogen assessment and solutions, water quality, and targeted delivery of agrochemicals (Rodrigues et al. 2017; Prasad et al. 2017). In addition to these needs, nanoparticles, such as nano-metal-oxides (NMOs), have been engineered to act as contaminant scavengers and could be applied to a wide range of additional needs. Although there are several studies that focus on the scavenging ability of NMOs, few have applied this to agricultural and food systems (Shao et al. 2016; Li et al. 2019; Huang et al. 2018). Key properties, such as ultra-small size, exceptionally high surface to volume ratios, and enhanced chemical reactivity, make NMOs ideal sorbents, in addition to the possibility of adding metal selec- tivity (Khan et al. 2017). Despite the promise of NMOs for metal(loid) scavenging, few studies have focussed on these oxides in cropping systems. A review on the effect of metal-oxide nanoparticles on growth and physiology of crops (Rizwan et al. 2017) highlighted that certain nano-oxides, such as those with cerium, copper, silver and titanium, can both decrease and increase seed germination, growth, yield and quality. Observed system interactions and characteristics depend on the type of crop, and the type and amount of nano-oxide used. However, only one of the studies testing the effect of NMOs on seed germination cited in the review (Rizwan et al. 2017) considered Fe-NMOs (Feizi et al. 2013). This study showed that lower concentrations of CSIRO PUBLISHING Environ. Chem. 2019, 16, 377–390 https://doi.org/10.1071/EN19063 Journal compilation Ó CSIRO 2019 www.publish.csiro.au/journals/env 377 Review RESEARCH FRONT