Purpose

Heavy metal soil-pollution is of concern due to its adverse effects on the ecosystem and human health. However, conventional ecological risk assessments considering only chemical concentration have limitations because of an increased uncertainty in assessing soil-risk. Therefore, this study applied the Triad approach, using a tier system, for assessing site-specific ecological risk in heavy metal-contaminated soil. In addition, risk-level was determined to analyze the necessity of remediation in a contaminated site.

Materials and methods

Soil samples from six different sites, including heavy metal-contaminated regions (S1–S5) and a control site (C, unpolluted with heavy metals) were collected. Soil properties were assessed based on a tier system to evaluate the ecological risk of each site. The first step tier-1, involved calculating the soil pollution index (SPI) and the second, tier-2, involved assessing site-specific ecological risk based on three lines of evidence (LoEs), viz., chemistry (ChemLoE), ecotoxicology (EcotoxLoE), and ecology (EcoLoE). The total and bioavailable fractions of heavy metals in soil and bio-accumulated heavy metals in earthworms (Eisenia fetida) were measured for ChemLoE. A bioassay involving mortality and weight reduction rates of earthworms, and a root-elongation test of lettuce (Lactuca sativa sp.) was conducted for EcotoxLoE. Soil biological properties, soil basal respiration, and soil enzyme activities, were evaluated for EcoLoE. Final integrated risk (IR) was obtained by combining the risk-values of each LoE, determined using IR values and deviation of each LoE.

Results and discussion

Although three out of the five sampling sites had SPI > 1 in tier-1, all five sampling sites were subjected to tier-2 to evaluate site-specific ecological risk. In tier-2, ChemLoE (0.53–0.99) was higher than EcotoxLoE (0.05–0.43) and EcoLoE (0.00–0.29), indicating that chemical aspects impacted risk evaluation more than the toxicological and ecological aspects. The final IR ranged between 0.24 and 0.85; risk-level was classified as low (S2, S3, S5), moderate (S1), and high (S4) according to the IR value. Based on the risk-level, site S4 could require remediation for agricultural land-use.

Conclusions

The IR of each sampled site varied depending on the impact of heavy metals. Based tier-1 and tier-2 results, a thorough site-specific evaluation is required to understand the adverse effects of heavy metals on soil ecosystems, and the triad approach could be useful for managing heavy metals in soil.

中文翻译：

---

利用三元法评估重金属污染土壤的生态风险

目的

重金属土壤污染因其对生态系统和人类健康的不利影响而令人关注。然而，由于评估土壤风险的不确定性增加，仅考虑化学物浓度的常规生态风险评估存在局限性。因此，本研究采用Triad方法，采用分层系统，评估了重金属污染土壤中特定地点的生态风险。此外，确定了风险水平以分析在受污染场地进行补救的必要性。

材料和方法

收集了六个不同地点的土壤样品，包括重金属污染区（S1-S5）和一个对照地点（C，未被重金属污染）。根据等级系统评估土壤性质，以评估每个地点的生态风险。第一步（第一步）涉及计算土壤污染指数（SPI），第二步（第二级）涉及基于三个证据线（LoEs），即化学（ChemLoE），生态毒理学评估特定地点的生态风险（EcotoxLoE）和生态（EcoLoE）。测量了ChemLoE中土壤中重金属的总含量和生物利用率，以及earth （Eisenia fetida）中生物富集的重金属含量。一项涉及mortality死亡率和减重率的生物测定法，以及生菜的根伸长测试（Lactuca sativasp。）进行了EcotoxLoE。评价了EcoLoE的土壤生物学特性，土壤基础呼吸和土壤酶活性。通过合并每个LoE的风险值（使用IR值和每个LoE的偏差确定）来获得最终综合风险（IR）。

结果和讨论

尽管五个采样点中的三个在一级采样中的SPI> 1，但所有五个采样点都进行了二级采样，以评估特定于现场的生态风险。在第2层中，ChemLoE（0.53-0.99）高于EcotoxLoE（0.05-0.43）和EcoLoE（0.00-0.29），表明化学方面对风险评估的影响大于毒理学和生态方面。最终IR在0.24至0.85之间。根据IR值，风险级别分为低（S2，S3，S5），中（S1）和高（S4）。根据风险水平，站点S4可能需要对农业土地使用进行补救。

结论

每个采样点的IR取决于重金属的影响而变化。根据1级和2级结果，需要进行全面的针对特定地点的评估，以了解重金属对土壤生态系统的不利影响，并且三合会方法可能对管理土壤中的重金属有用。