UMR ECOSYS, INRA, AgroParisTech, Université Paris-Saclay, 78026 Versailles, France.
INRA, Montpellier SupAgro, UMR 759 LEPSE, 34060 Montpellier, France.
Sci Total Environ. 2016 Nov 1;569-570:961-972. doi: 10.1016/j.scitotenv.2016.06.023. Epub 2016 Jul 1.
Structural equation models (SEM) are increasingly used in ecology as multivariate analysis that can represent theoretical variables and address complex sets of hypotheses. Here we demonstrate the interest of SEM in ecotoxicology, more precisely to test the three-step concept of metal bioavailability to earthworms. The SEM modeled the three-step causal chain between environmental availability, environmental bioavailability and toxicological bioavailability. In the model, each step is an unmeasured (latent) variable reflected by several observed variables. In an exposure experiment designed specifically to test this SEM for Cd, Pb and Zn, Aporrectodea caliginosa was exposed to 31 agricultural field-contaminated soils. Chemical and biological measurements used included CaC12-extractable metal concentrations in soils, free ion concentration in soil solution as predicted by a geochemical model, dissolved metal concentration as predicted by a semi-mechanistic model, internal metal concentrations in total earthworms and in subcellular fractions, and several biomarkers. The observations verified the causal definition of Cd and Pb bioavailability in the SEM, but not for Zn. Several indicators consistently reflected the hypothetical causal definition and could thus be pertinent measurements of Cd and Pb bioavailability to earthworm in field-contaminated soils. SEM highlights that the metals present in the soil solution and easily extractable are not the main source of available metals for earthworms. This study further highlights SEM as a powerful tool that can handle natural ecosystem complexity, thus participating to the paradigm change in ecotoxicology from a bottom-up to a top-down approach.
结构方程模型（SEM）在生态学中越来越多地被用作多元分析，可以表示理论变量并解决复杂的假设集。在这里，我们展示了 SEM 在生态毒理学中的应用，更确切地说是为了测试金属生物有效性的三步概念到蚯蚓。SEM 模型化了环境可用性、环境生物有效性和毒理学生物有效性之间的三步骤因果链。在模型中，每一步都是由几个观测变量反映的未测量（潜在）变量。在一项专门设计的暴露实验中，为了测试 Cd、Pb 和 Zn 的 SEM，Aporrectodea caliginosa 暴露于 31 种农业田间污染土壤中。用于化学和生物测量的包括土壤中 CaC12 可提取金属浓度、土壤溶液中自由离子浓度（根据地球化学模型预测）、半机械模型预测的溶解金属浓度、总蚯蚓和亚细胞分数中的内部金属浓度以及几种生物标志物。观察结果验证了 SEM 中 Cd 和 Pb 生物有效性的因果定义，但 Zn 则不然。几个指标始终反映了假设的因果定义，因此可以作为田间污染土壤中蚯蚓对 Cd 和 Pb 生物有效性的相关测量。SEM 强调，土壤溶液中存在的和易于提取的金属并不是蚯蚓可用金属的主要来源。这项研究进一步强调了 SEM 作为一种强大工具的作用，它可以处理自然生态系统的复杂性，从而参与从自下而上到自上而下的方法在生态毒理学中的范式转变。
