Palladium (Pd) is a trace metal of the platinum group elements, representing an emerging contaminant for the environment. It is of great interest to characterize the bioaccumulation and toxicity of Pd to improve our toxicological knowledge for this contaminant. Under standardized toxicity testing conditions, we analyzed Pd accumulation and toxicity effects on the duckweed Lemna minor exposed to nominal concentrations from 2 to 50 µM. The inhibitory effect was significant (p < 0.05) from 8 µM of Pd, starting with 9.5% of growth inhibition and a decrease of 1 cm for the root size. Under 12.5 μM of Pd, the bioaccumulated Pd of 63.93 µg/g fresh weight inhibited plant growth by 37.4%, which was caused by a strong oxidative stress in the cytosol and organelles containing DNA. Under 25 and 50 μM of Pd, bioaccumulated Pd was able to deteriorate the entire plant physiology including chlorophyll synthesis, the photosystem II antenna complex, and the photochemical reactions of photosynthesis. In fact, plants treated with 50 μM Pd accumulated Pd up to 255.95 µg/g fresh weight, causing a strong decrease in total biomass and root elongation process. Therefore, we showed several growth, physiological, and biochemical alterations which were correlated with the bioaccumulation of Pd. These alterations constituted toxicity biomarkers of Pd with different lowest-observed-effect dose, following this order: root size = growth inhibition < catalase activity = carotenoid content = reactive oxygen species production = total thiols < chlorophyll a/b = variable fluorescence to maximal fluorescence intensity ratio = absorbed-light energy transfer from the chlorophyll a antenna to the photosystem II reaction center = performance index of photosystem II activity < V_J. Therefore, the present study provides insight into the toxicity mechanism of Pd in L. minor plants under standardized testing conditions. Environ Toxicol Chem 2021;40:1630–1638. © 2021 SETAC

中文翻译：

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浮萍（小浮萍）中钯积累的毒性反应：生物标志物的测定

钯 (Pd) 是铂族元素中的一种微量金属，是一种新兴的环境污染物。表征 Pd 的生物蓄积性和毒性以提高我们对该污染物的毒理学知识非常有意义。在标准化毒性测试条件下，我们分析了 Pd 积累和对暴露于 2 至 50 µM 标称浓度的浮萍的毒性影响。抑制作用显着（p < 0.05) 从 8 µM Pd 开始，从 9.5% 的生长抑制开始，根部尺寸减少 1 cm。在 12.5 μM 的 Pd 下，63.93 μg/g 鲜重的生物累积 Pd 抑制了 37.4% 的植物生长，这是由含有 DNA 的细胞质和细胞器中的强氧化应激引起的。在 25 和 50 μM 的 Pd 下，生物蓄积的 Pd 能够破坏整个植物的生理机能，包括叶绿素合成、光系统 II 天线复合体和光合作用的光化学反应。事实上，用 50 μM Pd 处理的植物积累的 Pd 高达 255.95 μg/g 鲜重，导致总生物量和根伸长过程的强烈下降。因此，我们展示了几种与 Pd 的生物积累相关的生长、生理和生化变化。a / b = 可变荧光与最大荧光强度比 = 从叶绿素a天线到光系统 II 反应中心 的吸收光能量转移= 光系统 II 活性的性能指数 < V _J。因此，本研究提供了在标准化测试条件下深入了解 Pd 在L. minor植物中的毒性机制。环境毒物化学2021；40:1630–1638。© 2021 SETAC