Fraction transformation is the intrinsic driving force of risk formation and the evolution of sites polluted with heavy metals. This process is usually a long, slow and spontaneous process characterized by a gradual linear release of the most stable to the most mobile fractions, in accordance with fraction stability, leading to the thermodynamic static risk of the site. However, this process may be altered by drastic changes in environmental conditions, showing nonlinear characteristic and resulting in a nonlinear surge of some mobile fractions over a certain period of time. This process not only greatly increases the static risk but also induces the dynamic transient risk of the site. By applying a sequential extraction procedure, the delayed geochemical hazard methodology and statistical analysis, the transformation of arsenic fractions at a polluted site and their potential geochemical paths was investigated, which confirmed the above hypothesis. The transformation process was found to be mainly nonlinear. Taking water-soluble arsenic, surface-adsorbed arsenic, and acid-extractable arsenic as the endpoints, these nonlinear paths might lead to a surge in those three endpoint fractions when their associated arsenic fractions accumulate in the soil beyond a critical content, inducing dynamic risk and raising the static risk. These results provide new insights into site risk assessment, namely, that site risk highly depends on fraction transformation, especially on nonlinear transformation; therefore, both static and dynamic risks should be involved in site risk assessment. From this perspective, the case site (A total of 42 topsoil samples from Shimen realgar mine, Hunan) had a medium risk in terms of static risk, with a probability of 4.76%–7.14% of a possible burst of dynamic risk due to high arsenic accumulation in its some areas.

分数转化是风险形成的内在驱动力以及重金属污染场地的演变。该过程通常是一个漫长，缓慢且自发的过程，其特征在于，根据馏分的稳定性，将最稳定至最易流动的馏分逐渐线性释放，从而导致该位点的热力学静态风险。但是，此过程可能会因环境条件的急剧变化而改变，从而表现出非线性特征，并导致在一定时间段内某些可移动馏分的非线性激增。该过程不仅大大增加了静态风险，而且还引发了站点的动态瞬态风险。通过采用顺序提取程序，延迟地球化学灾害方法和统计分析，对砷在污染地点的转化及其潜在的地球化学路径进行了研究，证实了上述假设。发现变换过程主要是非线性的。以水溶性砷，表面吸附砷和酸可萃取砷为终点，当它们的相关砷组分在土壤中累积超过临界含量时，这些非线性路径可能导致这三个终点组分激增。并增加了静态风险。这些结果为现场风险评估提供了新的见解，即现场风险高度依赖于分数变换，尤其是非线性变换；因此，现场风险评估中应同时考虑静态和动态风险。从这个角度来看，