Chapter 4 - Fate of engineered nanomaterials in agroenvironments and impacts on agroecosystems

Abstract

Engineered nanomaterials (ENMs) are one of the major emerging contaminants of concern in recent times. The impact of ENMs in agroenvironments is still not well understood. In order to enhance our knowledge, we have carried out a comprehensive literature survey covering areas such as their fate in soil, exposure effects on soil biota, and trophic transfer potential. Data have shown that the transport and retention of ENMs in soil are predominantly influenced by physiochemical properties of soil (composition, pH, cation exchange capacity, porosity, and texture), ENMs properties (morphology, surface coating, types of ENM, and zeta potential), and existence of cocontaminants. On the other hand, exposure of plants to ENMs has shown diverse results. Soil-based exposure to several metal-based ENMs, as well as foliar applications, at concentrations less than 100mg/kg, has yielded beneficial effects. These positive effects are attributed to the biofortification and disease suppression capabilities, whereas soil exposure at higher concentrations (>500mg/kg) has shown negative effects in plants. Very few results have been shown from foliar exposure. On the other hand, soil biota such as bacteria, fungi, and invertebrates are affected more negatively by the ENM exposure, irrespective of the exposure conditions. The diversity, abundance, and mortality of all the aforementioned biota have shown to be affected. Although there is evidence about the trophic transfer of ENMs in terrestrial habitats, data are still incomplete. These depend on the mode of exposure, age, and excretory capacity of the organisms involved. In conclusion, multiple biotic and abiotic factors influence the fate and effect of ENMs in agro-environments. Furthermore, the stakeholder’s approach, knowledge, understanding, and discretion cannot be underestimated. Thus more research is still needed in this crucial research area.