Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food crops, thus raising food safety and environmental concerns. Since little is known about Ag NP behavior in wash water during typical commercial washing of fresh produce, this study assessed the temporal changes in Ag NP behavior when exposed to 2–100 mg/L free chlorine (Cl 2 ) in simulated lettuce wash water for up to 10 days. Aggregate size and zeta potential of Ag NPs (5 mg/L) were evaluated in the presence and absence of dissolved lettuce extract (DLE, 0.1%), with Ag NPs in deionized water serving as the control treatment. In the presence of chlorine, greater aggregation of Ag NPs occurred over time (49 to 431 nm) compared to the control treatment ( P < 0.05). Lower zeta potentials (-39 to -95 mV) were observed in the chlorine-only treatments, likely due to the formation of AgCl particles. Larger aggregates and lower zeta potentials were also observed in the presence of DLE (84–273 nm and -28 to -32 mV, respectively), as compared to the control treatment. After 7 to 10 days, larger aggregates were seen in the chlorine-only treatments as compared to the DLE treatments, despite their lower zeta potentials, probably facilitated by nucleation and crystal growth of AgCl. Transmission electron microscopy with energy dispersive spectroscopy confirmed the formation of AgCl-Ag NP composite particles in the presence of chlorine and the embedding of AgCl and Ag NPs in the DLE matrix. Thus, DLE might stabilize and protect Ag NPs from chlorine. These findings indicate that chlorine and plant-released organic material can substantially change the behavior of Ag NPs, which may in turn impact both their removal from fresh-cut produce during washing and their environmental fate.

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