Human Exposures of Engineered Nanoparticles from Plants Irrigated with Contaminated Water: Mixture Toxicity Issues and Challenges Ahead

The objective of this study was to understand issues in risk estimation of exposure of mixture of engineered nanoparticles (ENPs) during consumption of crops and to identify future steps to fill current knowledge gaps. Information about co-occurrence of ENPs in wastewater and surface water and their occurrence in edible plants were obtained from published reports and current knowledge gaps were identified. Analysis indicated that there is a data gaps on (1) co-occurrence of ENPs in irrigated wastewater and plants and (2) their mixture toxicity for oral exposure route. To address identified issues, a four-step approach was proposed: (1) Monitor concentrations of different ENPs in surface water as well as in wastewater, (2) Conduct co-occurrence analysis of different ENPs, (3) Conduct uptake studies in plants using mixture of ENPs and determine uptake of different ENPs in plants and identify interaction effects between ENPs during their uptakes by plants, and (4) Develop groups of co-occurring ENPs influencing a given endpoint from oral exposure route and obtain dose-response data during exposures of mixture of ENPs to animals. This study is one of the few efforts highlighting the issue of data needs for estimating health risks during use of ENPs-contaminated wastewater for irrigation.