Fluid catalytic cracking (FCC) process plays an important role in petroleum refining industry, and FCC catalyst is the key for FCC process. FCC catalyst will become spent FCC catalyst (SFCCC) due to the deposition of nickel (Ni), vanadium (V), and other metal components from crude oil. FCC catalyst is the largest refining catalyst consumed, and the annual output of SFCCC exceeds 500,000 tons worldwide (Cheng et al., 2023). With the increase of global demand for oil energy, the amount of SFCCC production is growing steadily (Shan et al., 2023). The metal composition in SFCCC is complex and difficult to dispose, rich in Ni, V, antimony (Sb), cobalt (Co), lanthanum (La), cerium (Ce), and other components, which has environmental risk (Pathak et al., 2021). SFCCC is one of the most concerned dangerous solid wastes in the petrochemical field (Crespo et al., 2023). However, to the best of our knowledge, there are few studies on research of toxicity and human health risk of SFCCC. SFCCC has been listed as hazardous waste in the “National Hazardous Waste List” in China (Zhang et al., 2022). Subsequent studies have been carried out on the toxicity and danger of SFCCC (Liu et al., 2016; Zhang et al., 2019; Bin et al., 2019; Wang and Li, 2021; Wang et al., 2021; Fu et al., 2021).

However, current research on toxicity assessment of SFCCC is still insufficient. With the development of related research, the understanding of the critical toxic factors of SFCCC is constantly changing. SFCCC was listed into the “National Hazardous Waste List” mainly due to the consideration of the high toxicity of Ni. However, subsequent studies have shown that Ni in SFCCC does not exist in the form of highly toxic substances such as oxidized nickel and carbonyl nickel (Fu et al., 2021), and there are also views that highly toxic oxidized nickel only exists on the surface of SFCCC particles (within 10 nm) (Bin et al., 2019). In addition, some studies have evaluated the leaching concentrations of various metals in SFCCC, and found that Sb is more easily leached than other metals. Leaching of Sb from SFCCC may lead to excessive concentrations of Sb in groundwater or surface water (Bin et al., 2019). In reference to the research on toxic components and metal leaching of SFCCC, the “National Hazardous Waste List (2021 Edition)” in China partially exempted part of SFCCC and only listed SFCCCs produced by catalytic cracking with blunt nickel agent (the main source of Sb) as hazardous waste.

However, considering that the metal composition of SFCCCs is very complex, it is difficult to truly reflect the toxic effects of SFCCCs by a single chemical analysis method, and it is impossible to accurately determine which metals are the main hazard factors. Therefore, the critical toxic factors of SFCCCs are still unclear and controversial. Under the influence of acidic precipitation during the nonstandard landfill disposal or stockpiling of SFCCC, the harmful metal components will leach to the water environment, which will affect human health. Therefore, direct toxicity studies on SFCCC can reflect their health toxic. There are no reports on health toxicity of SFCCC. In order to fully identify the health hazards and critical toxic metal factors of SFCCC, the cytotoxicity assessment of various SFCCC was performed in this study to investigate the effects of SFCCC on human health. In vitro toxicity evaluation of 7 human cell lines and 3 mouse fibroblasts was performed to explore the health risks of SFCCC and identify critical toxic metals.