Center for Bioenergy Recycling, ASHBACK, Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Universitetsparken 15, DK2100, Copenhagen, Denmark.
Center for Bioenergy Recycling, ASHBACK, Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Universitetsparken 15, DK2100, Copenhagen, Denmark.
Environ Pollut. 2018 Nov;242(Pt B):1510-1517. doi: 10.1016/j.envpol.2018.08.034. Epub 2018 Aug 14.
Small heterotrophic protists (flagellates and naked amoebae) are very abundant in soil and play a key role in maintaining soil services. Hence, knowledge on how xenobiotics affect these organisms is essential in ecosystem management. Cadmium (Cd) is an increasing environmental issue as both industrial deposition and recycling of heavy metal rich waste products have led to Cd enrichment of soils. Evaluation of toxicity of Cd to micro-organisms is often performed using a solution of pure Cd (e.g. CdCl) in liquid culture. This approach may be highly misleading as interactions between Cd and other substances, e.g. various ions or inherent soil components often strongly modify Cd toxicity. Hence, we compared the toxic effect of Cd to small heterotrophic protists in soil microcosms and liquid culture. We also evaluated how zinc (Zn) affects Cd toxicity, as Zn usually accompanies Cd in a ratio of c. 100:1, and is known to impede Cd toxicity. In the soil microcosms, we also monitored the primary food source of the protists, i.e. culturable bacteria, and used soil respiration as a proxy of soil functioning. Finally, we examined to what extent Cd actually sorbs to soil. We found 1) that c. 10 times more Cd was required to obtain the same effect in the soil microcosms compared to the liquid culture, 2) that soil sorption explains why Cd, even though highly toxic in aqueous solutions, has very limited effect when applied to soil, and 3) (very surprisingly) that in our experimental systems Zn was as toxic as Cd. Our study suggests that Cd toxicity to soil protists will be small because most Cd in soil will be sorbed to the soil matrix and because the Zn:Cd ratio of 100:1 in most substances, incl. pollutants, will mean that lethal Zn effects will occur before Cd reaches toxic levels.
小型异养原生生物（鞭毛虫和裸变形虫）在土壤中非常丰富，在维持土壤服务方面发挥着关键作用。因此，了解外源化学物质如何影响这些生物对于生态系统管理至关重要。镉 (Cd) 是一个日益严重的环境问题，因为工业沉积和富含重金属的废物回收导致土壤中镉的富集。通常使用纯 Cd（例如 CdCl）的溶液在液体培养中评估 Cd 对微生物的毒性。这种方法可能具有很大的误导性，因为 Cd 与其他物质（例如各种离子或固有土壤成分）之间的相互作用常常强烈改变 Cd 的毒性。因此，我们比较了 Cd 对土壤微宇宙和液体培养中小型异养原生生物的毒性作用。我们还评估了锌 (Zn) 如何影响 Cd 的毒性，因为 Zn 通常与 Cd 以约 100:1 的比例伴随存在，并且已知会阻碍 Cd 的毒性。在土壤微宇宙中，我们还监测了原生生物的主要食物源，即可培养细菌，并将土壤呼吸用作土壤功能的替代物。最后，我们研究了 Cd 实际上吸附到土壤中的程度。我们发现：1）与液体培养相比，在土壤微宇宙中获得相同效果需要大约 10 倍的 Cd；2）土壤吸附解释了为什么 Cd 在水溶液中具有很高的毒性，但当应用于土壤时毒性非常有限；3）（非常令人惊讶的是）在我们的实验系统中，Zn 与 Cd 一样具有毒性。我们的研究表明，Cd 对土壤原生生物的毒性将很小，因为土壤中的大部分 Cd 将被吸附到土壤基质上，并且由于大多数物质（包括污染物）中的 Zn:Cd 比例为 100:1，这意味着在 Cd 达到毒性水平之前，致命的 Zn 效应将发生。
