UC Riverside

The agricultural use of treated wastewater (TWW) offers significant economic, societal, and environmental benefits. However, its application raises concerns due to the introduction of contaminants of emerging concern (CECs) into the agroecosystem, which can transfer from soil to the edible parts of crops, posing potential risks to human health. This dissertation examined the impact of alternating irrigation sources between TWW and conventional freshwater on the accumulation of CECs in vegetables, proposing a viable mitigation strategy.The initial study conducted under hydroponic conditions served as a proof-of-concept, where tomato and lettuce seedlings cultivated in CEC-rich solutions showed significant reductions in contaminant levels after switching to CEC-free media, attributed to plant metabolism, growth dilution and back release to culture media. Subsequent greenhouse experiments under soil conditions confirmed that alternating irrigation could effectively decrease CEC levels in edible parts of crops through mechanisms such as reduced chemical input, soil degradation, plant metabolism, and growth dilution. Structural equation modeling highlighted the strategy's efficacy, particularly for chemicals with high bioaccumulation potential and short half-lives. Field studies further validated the practical applicability of this strategy, assessing a diverse set of 32 CECs—including PFASs, pharmaceuticals and personal care products, and tire wear particle chemicals—in radish, lettuce, and tomato. Alternating TWW with freshwater significantly lowered CEC levels, with notable reductions for short-lived chemical and some persistent compounds like PFAS. Among the tested vegetables, lettuce had the highest frequency and levels of contaminant detections, while radish was particularly responsive to the irrigation change. This research systematically explored, from mechanisms to practical implementation, the effectiveness of alternating TWW and freshwater irrigation in reducing CEC accumulation in vegetable crops. The findings underscore the potential of this irrigation alternation approach as a scalable and effective method to enhance the safe use of non-conventional water sources in agriculture, simultaneously enhancing environmental sustainability and reducing human exposure to CECs, thus marking a significant advancement in agricultural practices.