Silver is a non-essential, toxic metal widespread in freshwaters and capable of causing adverse effects to wildlife. Its toxic effects have been studied in detail but less is known about how sensitivity varies during development and whether pre-exposures affect tolerance upon re-exposure. We address these knowledge gaps using the zebrafish embryo (Danio rerio) model to investigate whether exposures encompassing stages of development prior to mid-blastula transition, when chorion hardening and epigenetic reprogramming occur, result in greater toxicity compared to those initiated after this period. We conducted exposures to silver initiated at 0.5 h post fertilisation (hpf) and 4 hpf to determine if toxicity differed. In parallel, we exposed embryos to the methylation inhibitor 5-azacytidine as a positive control. Toxicity increased when exposures started from 0.5 hpf compared to 4 hpf and LC50 were significantly lower by 1.2 and 7.6 times for silver and 5-azacyitidine, respectively. We then investigated whether pre-exposure to silver during early development (from 0.5 or 4 hpf) affected the outcome of subsequent exposures during the larvae stage, and found no alterations in toxicity compared to naïve larvae. Together, these data demonstrate that during early development zebrafish embryos are more sensitive to silver when experiments are initiated at the one-cell stage, but that pre-exposures do not influence the outcome of subsequent exposures, suggesting that no long-lasting memory capable of influencing future susceptibility was maintained under our experimental conditions. The finding that toxicity is greater for exposures initiated at the one-cell stage has implications for designing testing systems to assess chemical toxicity.

银是一种非必需的有毒金属，广泛存在于淡水中，并且能够对野生生物造成不利影响。已经对其毒性作用进行了详细的研究，但对感光度在显影过程中如何变化以及预曝光是否会影响再曝光的耐受性知之甚少。我们使用斑马鱼胚胎（Danio rerio）模型进行研究，以了解当囊膜硬化和表观遗传重编程发生时，囊胚中部过渡之前包含发育阶段的暴露是否比该时期后引发的毒性更大。我们进行了受精后0.5 h（hpf）和4 hpf下开始的银暴露，以确定毒性是否不同。同时，我们将胚胎暴露于甲基化抑制剂5-氮杂胞苷作为阳性对照。当暴露量从0.5 hpf开始时，毒性增加，而4 hpf和LC50对于银和5-氮杂胞苷分别显着降低1.2和7.6倍。然后，我们调查了在早期发育期间（从0.5或4 hpf）预先暴露于银是否会影响幼虫阶段后续暴露的结果，与幼稚幼虫相比，毒性没有变化。总之，这些数据表明，在单细胞阶段启动实验时，斑马鱼胚胎在早期发育过程中对银更敏感，但是预暴露并不影响后续暴露的结果，这表明没有持久的记忆能够在我们的实验条件下，影响未来敏感性的因素得以保持。对于在单细胞阶段开始的暴露，毒性更大的发现对设计评估化学毒性的测试系统具有影响。这表明在我们的实验条件下，没有能够影响未来易感性的持久记忆得以维持。对于在单细胞阶段开始的暴露，毒性更大的发现对设计评估化学毒性的测试系统具有影响。这表明在我们的实验条件下，没有能够影响未来易感性的持久记忆得以维持。对于在单细胞阶段开始的暴露，毒性更大的发现对设计评估化学毒性的测试系统具有影响。