School of Environment, Tsinghua University, Beijing 100084, China.
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
Environ Int. 2020 Nov;144:106040. doi: 10.1016/j.envint.2020.106040. Epub 2020 Aug 13.
Agricultural soil contamination in seasonally frozen land threatens food security. It is necessary to investigate the effects of freeze-thaw cycles on heavy metal bioavailability so as to select suitable immobilization agents. In this study, the soil was collected from a mid-latitude agricultural site in Liaoning Province, China, which was spiked with cadmium (Cd) and lead (Pb). Four immobilization treatments were set up, including (i) corn stover biochar, (ii) organic fertilizer, (iii) combined biochar and organic fertilizer, and (iv) the control group. The immobilized soils were subjected to 16 freeze-thaw cycles to temperatures of -10 °C, -20 °C, and -30 °C. It was found that freeze-thaw cycling increased the labile cadmium (Cd) and lead (Pb) content in the soil (i.e., exchangeable). The organic fertilizer treatment performed best in short-term immobilization, which was demonstrated by the amount of diethylenetriaminepentaacetic acid (DTPA) extractable lead (Pb) being 17.3-53.3% lower than that of the other treatments, and 7.2-31.5% lower for cadmium (Cd). Biochar, on the other hand, displayed better long-term performance under freeze-thaw cycling. This is probably because the biochar's organic carbon content is relatively stable, and therefore, releases relatively little dissolved organic carbon (DOC) which could re-mobilize heavy metals. Furthermore, additional sorption sites are formed and the abundance of oxygen-containing functional groups increased when biochar breaks down during freeze-thaw cycles. Overall, the joint application of biochar and organic fertilizer had the greatest immobilization effect, which inhibited the cracking of soil aggregates, reduced the labile metal content, and displayed both short- and long-term immobilization effectiveness. It is suggested that combined biochar and organic fertilizer may offer an effective strategy for the sustainable agricultural management of cadmium (Cd) and lead (Pb) contaminated in seasonally frozen land.
季节性冻土区农田土壤污染威胁粮食安全，有必要研究冻融循环对重金属生物有效性的影响，从而选择合适的稳定剂。本研究采集了中国辽宁中纬度农业区受 Cd 和 Pb 污染的土壤，设置了 4 种稳定剂处理：（i）玉米秸秆生物炭、（ii）有机肥、（iii）生物炭和有机肥混合、（iv）对照组。稳定后的土壤进行了 16 次冻融循环，温度分别为-10℃、-20℃和-30℃。结果表明，冻融循环增加了土壤中可交换态 Cd 和 Pb 的含量。短期来看，有机肥处理对 Pb 的固定效果最好，DTPA 可提取态 Pb 含量比其他处理低 17.3%-53.3%，Cd 含量低 7.2%-31.5%。相比之下，生物炭在冻融循环下表现出更好的长期性能。这可能是因为生物炭的有机碳含量相对稳定，因此释放的溶解有机碳（DOC）较少，不会重新活化重金属。此外，生物炭在冻融循环过程中分解时会形成更多的吸附点位和含氧官能团，增加了对重金属的固定。总的来说，生物炭和有机肥的联合施用具有最大的固定效果，抑制了土壤团聚体的破裂，降低了可移动金属的含量，表现出短期和长期的固定效果。因此，联合施用生物炭和有机肥可能是季节性冻土区 Cd 和 Pb 污染农田可持续管理的有效策略。
