Accumulation characteristics and control technologies of heavy metal contamination in facility soil of China: A review

This review aims to evaluate the prevalence and severity of heavy metal contamination in facility soil across China. Through a systematic analysis of 46 articles published between 2018 and 2023, data were extracted pertaining to 128 facility farming sites spanning 31 provincial administrative regions. The findings reveal that these reported locales are severely impacted by heavy metal contamination, with most facility soil exhibiting mild to moderate levels of pollution. Specifically, cadmium (Cd) is identified as a major concern, posing significant risks to soil health and agricultural yield. In addition, other heavy metals such as lead (Pb), chromium (Cr), arsenic (As), mercury (Hg), and copper (Cu) also contribute to the overall contamination, albeit to varying degrees. Agricultural practices, primarily the utilization of chemical fertilizers, manure, and pesticides, have been pinpointed as the principal pathway for heavy metal infiltration into soil, accounting for a substantial share ranging from 69.7% to 86.7% of the total input. There is an urgent need for more sustainable agricultural practices to minimize the influx of heavy metals into the soil environment. Nature-based Solutions (NbS) offer a promising approach for sustainable production in facility soil by utilizing natural resources alongside organic waste. A technical system can be devised to mitigate heavy metal pollution in these soils. Therefore, a risk mitigation strategy has been proposed which includes preemptive source control, process blocking, and terminal remediation measures. The preemptive control at the source aims to reduce contaminant inputs of heavy metals at the origin of the soil environment, particularly focusing on agricultural inputs such as fertilizers, pesticides, and irrigation water. Process blocking utilizes innovative techniques to hinder the mobilization and bioavailability of heavy metals in the soil, thereby minimizing their toxicity during plant uptake. Plant species or varieties with lower heavy metal accumulation potential and the use of water-soluble fertilizers are also encouraged. Terminal remediation strategies primarily involve various functional amendments to immobilize heavy metals in the soil. Additionally, crops with specific tolerance, accumulation, or detoxification capabilities for heavy metals are selected for bioremediation purposes. Furthermore, sustainable practices should be prioritized to mitigate risks while optimizing agricultural productivity. These strategies emphasize waste management, soil health maintenance, and improved practices, especially for the secure and effective utilization of contaminated soil. However, there is a scarcity of research on integrated controlling technologies for soil heavy metal contamination in China's facility agriculture. Nevertheless, case studies have validated the effectiveness of integrated approaches compared to single-technology solutions, highlighting their practicality and broad applicability. In summary, a conceptual framework was formulated to tackle heavy metal contamination in facility soil. The findings provide valuable insights to guide future research and practical strategies. These efforts are imperative in mitigating the hazards posed by heavy metal contamination in facility soil, thereby advancing sustainable agricultural practices.