## 1 Introduction
Heavy metals can induce ROS formation in plants, such as superoxide radicals (O), hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)), and hydroxyl (HO\({}^{-}\)), which damage oxidative pigments, proteins, membrane lipids, and amino acids, ultimately leading to plant cell death [35; 36]. Plants respond to ROS by producing antioxidant enzymes, such as catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) and their metabolites [37]. Antioxidant enzymes can scavenge oxygen free radicals (O\({}^{\bullet-}\), \({}^{1}\)O\({}_{2}\), H\({}_{2}\)O\({}_{2}\), HO\({}^{\bullet}\), HO\({}^{-}\)) and their products, and repair damaged cells [38; 39; 40]. The effect of heavy metals on antioxidant enzymes in remediation experiments has been reported by numerous studies [39; 41]. Therefore, the activities of soil enzymes and plant antioxidant enzymes can be used as indicators to evaluate the remediation effect of soil amendments. With the rapid development of urbanization, a large amount of construction waste is inevitably generated [42]. Most of the construction waste includes waste concrete, waste cement, steel bars, gravel, and wood [43]. At present, most of the construction waste is directly transported to the suburbs for open-air stacking or landfill without treatment, and a small amount of construction waste is used as roadbed material [44]. With the rapid development of utilization technology for mineral admixtures, a large quantity of natural zeolite and fly ash is used as auxiliary cementitious material to partly replace cement in the preparation of mortar and concrete. Therefore, most of the fine powder in construction waste contains zeolite, fly ash, and cement. The pore size distribution, specific surface area, and active groups formed by elements such as Al, Si, and Fe contained in fly ash make it an excellent heavy metal adsorbent through physical and chemical adsorption [45]. At the same time, the physical and chemical properties of fly ash can improve the physical properties, chemical properties and biological activities of the soil. Addition of FA to soils has been reported to increase pH and reduce the availability of heavy metals [46; 47]. As a clay mineral, zeolite has the characteristics of large specific surface area, strong adsorption, and environmental friendliness. The results show that zeolite was effective in the remediation of heavy metal-contaminated soil [48]. Zeolites are important low-costsoil amendments that improve soil stability, health, and productivity, thereby mitigating the toxicity of heavy metals. Therefore, waste cement containing fly ash and zeolite can be recycled as a new type of heavy metal immobilizing agent. [PERSON] et al. have confirmed that waste cement can remove cadmium from wastewater and reduce the mobility of cadmium in the soil [23]. [PERSON] [22] found that the high pH and ANC of demolition waste (cement paste and lightweight concrete) can improve the heavy metal adsorption capacity of soil and soil ANC. The results of [PERSON]'s [49] study showed that concrete particles (0.5-1 mm) (cement slurry) could increase the pH value of wastewater and had a high removal efficiency of Cr, Cu, Ni, Pb, and Zn through adsorption and precipitation. However, there are no reports on the effect on soil enzyme activities and plant antioxidant enzyme activities in the contaminated soils that have been amended with waste cement. Therefore, in this study, we used three types of waste cement based on ordinary Portland cement and carried out a soil incubation and pot experiment. The soil Cd bioavailability was evaluated through DTPA extraction to estimate its immobilization by waste cement. An enzyme activity assay was used to estimate the toxicity of Cd in simulated contaminated soil before and after remediation. Pot experiments were carried out to evaluate Cd effects in lettuce plants, lettuce biomass, the MDA content in lettuce, and plant antioxidant enzyme activities before and after remediation.