Bergami E, Pugnalini S, Vannuccini M L, Manfra L, Faleri C, Savorelli F, Dawson K A, Corsi I
Department of Physical, Earth and Environmental Sciences, University of Siena, Italy.
Department of Physical, Earth and Environmental Sciences, University of Siena, Italy.
Aquat Toxicol. 2017 Aug;189:159-169. doi: 10.1016/j.aquatox.2017.06.008. Epub 2017 Jun 15.
Plastic pollution has been globally recognized as a critical issue for marine ecosystems and nanoplastics constitute one of the last unexplored areas to understand the magnitude of this threat. However, current difficulties in sampling and identifying nano-sized debris make hard to assess their occurrence in marine environment. Polystyrene nanoparticles (PS NPs) are largely used as nanoplastics in ecotoxicological studies and although acute exposures have been already investigated, long-term toxicity on marine organisms is unknown. Our study aims at evaluating the effects of 40nm PS anionic carboxylated (PS-COOH) and 50nm cationic amino-modified (PS-NH) NPs in two planktonic species, the green microalga Dunaliella tertiolecta and the brine shrimp Artemia franciscana, respectively prey and predator. PS NP behaviour in exposure media was determined through DLS, while their toxicity to microalgae and brine shrimps evaluated through 72h growth inhibition test and 14 d long-term toxicity test respectively. Moreover, the expression of target genes (i.e. clap and cstb), having a role in brine shrimp larval growth and molting, was measured in 48h brine shrimp larvae. A different behaviour of the two PS NPs in exposure media as well as diverse toxicity to the two planktonic species was observed. PS-COOH formed micro-scale aggregates (Z-Average>1μm) and did not affect the growth of microalgae up to 50μg/ml or that of brine shrimps up to 10μg/ml. However, these negatively charged NPs were adsorbed on microalgae and accumulated (and excreted) in brine shrimps, suggesting a potential trophic transfer from prey to predator. On the opposite, PS-NH-formed nano-scale aggregates (Z-Average<200nm), caused inhibition of algal growth (EC=12.97μg/ml) and mortality in brine shrimps at 14 d (LC=0.83μg/ml). Moreover, 1μg/ml PS-NH significantly induced clap and cstb genes, explaining the physiological alterations (e.g. increase in molting) previously observed in 48h larvae, but also suggesting an apoptotic pathway triggered by cathepsin L-like protease in brine shrimps upon PS-NH exposure. These findings provide a first insight into long-term toxicity of nanoplastics to marine plankton, underlining the role of the surface chemistry in determining the behaviour and effects of PS NPs, in terms of adsorption, growth inhibition, accumulation, gene modulation and mortality. The use of long-term end-point has been identified as valuable tool for assessing the impact of nanoplastics on marine planktonic species, being more predictable of real exposure scenarios for risk assessment purposes.
塑料污染已被全球公认为海洋生态系统的一个关键问题，而纳米塑料是了解这一威胁程度的最后一个未被充分探索的领域之一。然而，目前在采样和识别纳米级碎片方面存在困难，难以评估它们在海洋环境中的存在情况。聚苯乙烯纳米颗粒（PS NPs）在生态毒理学研究中被大量用作纳米塑料，尽管已经对急性暴露进行了研究，但对海洋生物的长期毒性尚不清楚。我们的研究旨在评估40纳米阴离子羧基化聚苯乙烯（PS-COOH）和50纳米阳离子氨基改性聚苯乙烯（PS-NH）纳米颗粒分别对两种浮游生物的影响，即绿色微藻杜氏盐藻和卤虫，前者为猎物，后者为捕食者。通过动态光散射（DLS）确定PS纳米颗粒在暴露介质中的行为，同时分别通过72小时生长抑制试验和14天长期毒性试验评估它们对微藻和卤虫的毒性。此外，在48小时的卤虫幼虫中测量了在卤虫幼虫生长和蜕皮中起作用的靶基因（即clap和cstb）的表达。观察到两种PS纳米颗粒在暴露介质中的行为不同，对两种浮游生物的毒性也不同。PS-COOH形成微米级聚集体（Z-平均直径>1μm），在浓度高达50μg/ml时对微藻生长或浓度高达10μg/ml时对卤虫生长均无影响。然而，这些带负电荷的纳米颗粒被吸附在微藻上，并在卤虫中积累（和排泄），这表明存在从猎物到捕食者的潜在营养转移。相反，PS-NH形成纳米级聚集体（Z-平均直径<200nm），导致藻类生长受到抑制（半数有效浓度=12.97μg/ml），并在14天时导致卤虫死亡（半数致死浓度=0.83μg/ml）。此外，1μg/ml的PS-NH显著诱导clap和cstb基因表达，这解释了之前在48小时幼虫中观察到的生理变化（如蜕皮增加），也表明卤虫在暴露于PS-NH后，组织蛋白酶L样蛋白酶触发了凋亡途径。这些发现首次深入了解了纳米塑料对海洋浮游生物的长期毒性，强调了表面化学在决定PS纳米颗粒的行为和影响方面的作用，包括吸附、生长抑制、积累、基因调节和死亡率。长期终点的使用已被确定为评估纳米塑料对海洋浮游生物物种影响的有价值工具，对于风险评估目的的实际暴露情况更具预测性。
