Interactions between organic matter (OM) and metals in soils are important natural mechanisms that can mitigate metal bioaccumulation in terrestrial environments. A primary source of OM in soils is straw return, accounting for more than 65% of OM input. Straw-OM has long been believed to reduce metal bioaccumulation, e.g., by immobilizing metals in soils. However, there is growing evidence that straw return could possibly enhance bioavailability and thus risks (i.e., food safety) of some metals in crops, including Cd, Hg, and As. Poor understanding of straw return-induced increases in metal bioavailability would add uncertainty in assessing or mitigating risks of metals in contaminated farming soils. Here, 863 pieces of literature (2000–2019) that reported the effects of straw return on metal bioavailability and bioaccumulation were reviewed. Mechanisms responsible for the increased metal mobility and bioavailability under straw return are summarized, including the effects of dissolution, complexation, and methylation. Effects of straw return on the physiology and the absorption of metals in plants is also discussed (i.e., physiological effect). These mechanisms are then used to explain the observed increases in the mobility, bioavailability, and bioaccumulation of Cd, Hg, and As under straw amendment. Information summarized in this study highlights the importance to re-consider the current straw return policy, particularly in metal-contaminated farmlands.

土壤中有机物（OM）与金属之间的相互作用是重要的自然机制，可以减轻地球环境中金属的生物积累。土壤中有机质的主要来源是秸秆还田，占有机质输入的65％以上。长期以来，人们一直认为Straw-OM可通过例如将金属固定在土壤中来减少金属的生物富集。然而，越来越多的证据表明，秸秆还田可能会提高生物利用度，从而增加作物中某些金属（例如镉，汞和砷）的风险（即食品安全性）。对秸秆还田引起的金属生物利用度增加的理解不充分，将增加评估或减轻污染的耕作土壤中金属风险的不确定性。在这里，回顾了863篇文献（2000-2019年），这些文献报道了秸秆还田对金属生物利用度和生物累积的影响。归纳了导致秸秆还田时金属迁移率和生物利用度增加的机理，包括溶解，络合和甲基化的影响。还讨论了秸秆还田对植物生理和金属吸收的影响（即生理作用）。然后将这些机制用于解释在秸秆改良下，Cd，Hg和As的迁移率，生物利用度和生物蓄积性的增加。本研究总结的信息强调了重新考虑当前秸秆还田政策的重要性，尤其是在金属污染的农田中。还讨论了秸秆还田对植物生理和金属吸收的影响（即生理作用）。然后将这些机制用于解释在秸秆改良下，Cd，Hg和As的迁移率，生物利用度和生物蓄积性的增加。本研究总结的信息强调了重新考虑当前秸秆还田政策的重要性，尤其是在金属污染的农田中。还讨论了秸秆还田对植物生理和金属吸收的影响（即生理作用）。然后将这些机制用于解释在秸秆改良下，Cd，Hg和As的迁移率，生物利用度和生物蓄积性的增加。本研究总结的信息强调了重新考虑当前秸秆还田政策的重要性，尤其是在金属污染的农田中。