Comprehensive cytotoxicity assessment of treated produced water from thermal distillation using human cell lines

Produced water (PW) could be an alternative water resource after treatment for fit-for-purpose applications. However, comprehensive studies assessing the impact of treated PW exposure on human health are still lacking. Herein, we evaluated the effect of untreated and treated PW from the Permian Basin after two thermal distillation systems followed by granular activated carbon (GAC) and zeolite on human cell lines, including intestinal epithelial (Caco-2) cells, breast cancer cells (MCF-7), and embryonic kidney (HEK293) cells. Cells were exposed to untreated PW, thermal distillate, and post-treated PW after GAC and zeolite treatment. Various in vitro toxicity assays were conducted to assess cell viability, necrosis, apoptosis, oxidative stress, estrogenicity, and aryl hydrocarbon receptor (AhR) activation after PW exposure. Overall, untreated PW caused significant cytotoxicity, reduced cell viability, induced oxidative stress, and apoptosis, whereas distillate and GAC+zeolite-treated PW did not induce significant toxicity. As shown by E-screen assays, significant estrogenic activity was observed in feed PW and the distillate but not in the post-treated PW. CYP1A1 gene upregulation was observed in the distillate, suggesting activation of AhR by residual organic compounds. Post-treated PW did not induce AhR activation, highlighting the need for post-treatment following thermal distillation to mitigate residual xenobiotic organic compounds. Given that thermal distillation followed by GAC and zeolite filtration eliminated all adverse impacts on human cell lines, this integrated treatment process demonstrates strong potential for safe discharge and beneficial reuse of treated PW.