Smolders E, Brans K, Coppens F, Merckx R
Laboratory of Soil Fertility and Soil Biology, Katholieke Universiteit Leuven, Belgium.
Environ Toxicol Chem. 2001 Nov;20(11):2469-74. doi: 10.1897/1551-5028(2001)020<2469:pnraat>2.0.co;2.
A potential nitrification rate test (PNR) was used to identify metal toxicity in field-contaminated soils. The test was applied to metal salt-spiked soils, to 27 uncontaminated soils, and to 15 soils that are contaminated by former metal smelting activities. Four agricultural soils (pH 4.5-6.6) were spiked with various rates of CdCl2 (0-200 mg Cd/kg dry wt) or ZnCl2 (0-3,000 mg Cd/kg dry wt) and were equilibrated more than nine months prior to testing. The soil Zn EC50s of the PNR were between 150 and 350 mg Zn/kg dry weight. No continuous decrease of the nitrification with increasing Cd application was observed. The nitrification rate was reduced by between 50 and 80% at the highest Cd application in all soils. The PNRs of 27 uncontaminated soils varied widely (0-21 mg N/kg/d), but most of this variability is explained by soil pH (R2 = 0.77). The PNRs of the 15 contaminated soils were 0 to 44% of the values predicted for an uncontaminated soil at corresponding pH. Significant toxicity in field-contaminated soils was identified if the PNR was outside the 95% prediction interval of the PNR for an uncontaminated soil at corresponding pH and was found in seven soils. These soils contain 160 to 34,000 mg Zn/kg dry weight and 5 to 104 mg Cd/kg dry weight and had a pH >5.7. No toxicity could be detected below pH 5.6, where even a zero PNR value is within the 95% prediction interval of uncontaminated soils. It is concluded that the nitrification is sensitive to metal stress but that its power as a soil bioassay is low because of the high variability of the endpoint between uncontaminated soils. The ecological significance of the assay is discussed.
采用潜在硝化速率试验（PNR）来识别田间污染土壤中的金属毒性。该试验应用于添加金属盐的土壤、27种未受污染的土壤以及15种曾受金属冶炼活动污染的土壤。四种农业土壤（pH值4.5 - 6.6）分别添加不同比例的CdCl₂（0 - 200 mg Cd/kg干重）或ZnCl₂（0 - 3000 mg Cd/kg干重），并在测试前平衡九个多月。PNR试验中土壤锌的半数效应浓度（EC50）在150至350 mg Zn/kg干重之间。未观察到随着镉施用量增加硝化作用持续下降的情况。在所有土壤中，镉施用量最高时硝化速率降低了50%至80%。27种未受污染土壤的PNR差异很大（0 - 21 mg N/kg/d），但这种差异大多可由土壤pH值解释（R² = 0.77）。15种污染土壤的PNR为相应pH值下未受污染土壤预测值的0%至44%。如果PNR超出相应pH值下未受污染土壤PNR的95%预测区间，则表明田间污染土壤存在显著毒性，在七种土壤中发现了这种情况。这些土壤的锌含量为160至34000 mg Zn/kg干重，镉含量为5至104 mg Cd/kg干重，pH值>5.7。在pH值低于5.6时未检测到毒性，此时即使PNR值为零也在未受污染土壤的95%预测区间内。研究得出结论，硝化作用对金属胁迫敏感，但由于未受污染土壤之间终点变异性高，其作为土壤生物测定的能力较低。文中还讨论了该测定方法的生态意义。
