The toxicity of heavy metals (HMs) to soil enzymes is directly influenced by the status of the enzyme (free vs. immobilized on minerals) and the duration of exposure. However, little information is available on the interaction effect of HMs, mineral, and exposure time on soil enzyme activities. We investigated the interaction mechanism of alkaline phosphatase (ALP) with minerals (montmorillonite and goethite) and the response of free and immobilized ALP to cadmium (Cd) toxicity under different exposure times. The adsorption isotherms of ALP on both minerals were L-type. The maximum adsorption capacity of goethite for ALP was 3.96 times than montmorillonite, although both had similar adsorption constant (K). Goethite showed a greater inhibitory effect on ALP activity than montmorillonite. The toxicity of Cd to free- and goethite-ALP was enhanced with increasing exposure time, indicating a time-dependent inhibition. However, Cd toxicity to montmorillonite-ALP was not affected by the exposure time. The inhibition of Cd to soil enzyme activity is influenced by the properties of mineral complexes and the duration of exposure. A further understanding of the time pattern of HMs toxicity is helpful for accurately assessing the hazards of HMs to soil enzyme activity.

重金属（HMs）对土壤酶的毒性直接受酶的状态（游离与固定在矿物质上）和暴露持续时间的影响。但是，关于HM，矿物质和暴露时间对土壤酶活性的相互作用影响的信息很少。我们研究了碱性磷酸酶（ALP）与矿物质（蒙脱土和针铁矿）的相互作用机理，以及在不同的暴露时间下游离的和固定的ALP对镉（Cd）毒性的响应。ALP在两种矿物上的吸附等温线均为L型。针铁矿对ALP的最大吸附能力是蒙脱石的3.96倍，尽管两者的吸附常数相似（K）。针铁矿对蒙脱石的抑制作用大于蒙脱石。镉对游离和针铁矿-ALP的毒性随着暴露时间的增加而增强，表明时间依赖性抑制作用。但是，镉对蒙脱石-ALP的毒性不受暴露时间的影响。镉对土壤酶活性的抑制作用受矿物复合物的性质和暴露时间的影响。对HMs毒性时间模式的进一步了解有助于准确评估HMs对土壤酶活性的危害。