Introduction
Anthropogenic activities such as mining, smelting, and waste disposal usually release multiple metal(loid)s into the environment (Macgregor et al., 2015; Tabelin et al., 2018; Tabelin et al., 2021). Ever-increasing levels of arsenic (As), antimony (Sb), and cadmium (Cd) have been found in the environment in Canada (Fawcett et al., 2015) and China (Fu et al., 2010; Fu and Wei, 2013; Fu et al., 2016). Therefore, it is important to simultaneously immobilize toxic metal(loid)s in soils to reduce their accumulation in crops.
Few technologies are explored to repair the contaminated soils by multiple metal(loid)s, especially for Sb contamination. Materials containing Fe are often used to remediate the contaminated soils by As (Chou et al., 2016), Sb (Van Caneghem et al., 2016) and Cd (Huang et al., 2018) via some mechanisms, such as promoting Sb adsorption by iron (hydr)oxides (Van Caneghem et al., 2016) or forming a stable tripuhyite under strong acidic conditions (Leverett et al., 2012). In addition, Fe will stimulate the formation of Fe/manganese (Mn) plaques on the surface of rice roots (Huang et al., 2012). However, the inhibition and stimulation of Sb uptake in plants resulting from the actions of root Fe/Mn plaques were simultaneously observed in many studies (Ren et al., 2014; Cui et al., 2015; Huang et al., 2012). The above contradictory results might suggest that there will be some factors controlling the outcomes of compounds containing Fe to restrict Sb uptake.
The normal cultivation pattern for rice plants needs a long-time submerged condition and a short-time dry farming for 5 to 10 days at the end of tillering stage or the beginning of jointing stage (Yao et al., 2012). This water cycle will increase the release risk of metal(loid) pollution in soils (Huyen et al., 2019). In China, there is plenty of rain within most of rice cultivation areas (mainly locate in the south provinces of China), where the situation of soil metal(loid) contamination is also heavy (Mao et al., 2019). Thus, it is possible that the time of dry farming for these contaminated paddy soils will not be enough. The submerged conditions will stimulate the release of metalloids into soil solution and result in their excessive accumulation in plants, such as As and Sb (Takahashi et al., 2004; Xu et al., 2008; Wan et al., 2013; Liao et al., 2016; Matsumoto et al., 2016). In contrast, high soil moisture will be beneficial to restrict Cd uptake in rice plants (Simmons et al., 2008; Liao et al., 2016) via combination of Cd with sulfur (S) to form an insoluble compound (CdS) under an anaerobic condition (Bingham et al., 1976). Some researchers have attempted to use the water management technology to control the availability of targeted metal(loid)s in soils and thus reduce their accumulation in crops (Hu et al., 2015). However, the optimal water management manner is not clear when using this technology to remediate the contaminated paddy soils by multiple metal(loid)s.
In addition, when using the compounds containing Fe or the technology of water management to reduce uptake of metal(loid)s in crops, few concerns were paid on their effects on quality of crop products. The fill-up of the above knowledge gaps will make people notice the risks when using FeCl3 or water management to remediate Sb and Cd co-contaminated soils under an impeded drainage condition. Therefore, this study was conducted using FeCl3 (under a continued submergence condition) and different water management patterns in potted experiments to investigate: (1) the efficiency and risks of FeCl3 and water management to reduce uptake of Cd and Sb in a rice plant (Yangdao No.6); (2) the geochemical evolution of pore water with elongation of exposure time; (3) the formation of root Fe/Mn plaques and their roles in controlling uptake of elements; and (4) the uptake of essential elements and the yield of rice plants.