[en] Highlights: • Propiconazole initiates ROS-induced oxidative stress and damage in medaka fish. • Early life exposure to propiconazole increases incidence of hepatocarcionogensis in p53"−"/"− medaka. • Oxidative stress and CYP induction involved in p53 regulation are key events in propiconazole-induced hepatotumorigenesis. • Propiconazole-induced toxic response in medaka is compatible with that in rodents. - Abstract: Conazole pollution is an emerging concern to human health and environmental safety because of the broad use of conazole fungicides in agriculture and medicine and their frequent occurrence in aquifers. The agricultural pesticide propiconazole has received much regulatory interest because it is a known rodent carcinogen with evidence of multiple adverse effects in mammals and non-targeted organisms. However, the carcinogenic effect and associated mechanism of propiconazole in fish under microgram-per-liter levels of environmental-relevant exposure remains unclear. To explore whether early life of propiconzaole exposure would induce oxidative stress and latent carcinogenic effects in fish, we continuously exposed larvae of wild type or p53"−"/"− mutant of medaka fish (Oryzias latipes) to propiconazole (2.5–250 μg/L) for 3, 7, 14 or 28 days and assessed liver histopathology and/or the oxidative stress response and gene expression during exposure and throughout adulthood. Propiconazole dose-dependently induced reactive oxygen species (ROS) level, altered homeostasis of antioxidant superoxide dismutase, catalase and glutathione S-transferase and caused lipid and protein peroxidation during early life exposure in wild type medaka. Such exposure also significantly upregulated gene expression of the cytochrome P450 CYP1A, but marginally suppressed that of tumor suppressor p53 in adults. Furthermore, histopathology revealed that p53"−"/"− mutant medaka with early life exposure to propiconazole showed increased incidence of hepatocarcionogensis, as compared to the p53"−"/"− control group and wild type strain. We demonstrated that propiconazole can initiate ROS-mediated oxidative stress and induce hepatic tumorigenesis associated with CYP1A- and/or p53 -mediated pathways with the use of wild type and p53"−"/"− mutant of medaka fish. The toxic response of medaka to propiconazole is compatible with that observed in rodents.

[en] An acquisition of metal tolerance in cladocerans related to the historical exposure has been well documented for the genera Daphnia and Ceriodaphnia, which are frequently used in ecotoxicological studies. However, small-sized cladocerans are rarely investigated for the inter-clonal variation in metal sensitivity, whereas they often dominate zooplankton community in many lakes and ponds, and even in eutrophicated rivers. We investigated the influence of historical copper exposure on the copper sensitivity of Bosmina longirostris. Copper sensitivity was compared among three clones originating from a site (Lake Yanaka), which located at downstream of historically contaminated river (Watarase River) and clones from five different reservoirs. For reference, the background copper concentration (as Cu²⁺ activity) at each site and its toxicity to Daphnia magna were estimated by metal speciation and the biotic ligand model (BLM), respectively. Less copper-sensitive Bosmina clones were obtained only from Lake Yanaka, although the background copper concentrations were far below the lethal levels. The results suggested the variability in copper-sensitivity in B. longirostris and its association with historical copper contamination.

[en] The present study aimed to investigate the genotoxicity in erythrocytes induced after exposure of medaka (Oryzias latipes) to 4-nonylphenol (4-NP). Adult female medaka fish were exposed to 4-NP at three sublethal concentrations for 15 days to compare their sensitivity with that of catfish as an aquatic model. Comet assay and γ-H2AX were used as biomarkers to detect DNA damage in erythrocytes. Exposure to 4-NP resulted in an increase in the tail moment in a dose-dependent manner. The highest level of DNA damage was recorded after exposure to 100 μg/l 4-NP. The number of foci was increased after exposure to 4-NP, indicating damage to DNA. The present results confirmed the high level of morphological alterations and apoptosis of erythrocytes detected in the first part of this study. 4-NP induced genotoxic effects in medaka, which were found to be more sensitive than catfish after exposure to 4-nonylphenol.

[en] Highlights: • Acidic conditions enhanced the toxicity of silver to medaka embryogenesis. • Embryo-rearing medium alleviated the toxicity of silver in all tested forms. • Silver nanocolloid exposure significantly reduced medaka population growth rates. Fish embryo toxicology is important because embryos are more susceptible than adults to toxicants. In addition, the aquatic toxicity of chemicals depends on water quality. We examined the toxicities to medaka embryos of three types of silver—AgNO₃, silver nanocolloids (SNCs), and silver ions from silver nanoparticle plates (SNPPs)—under three pH conditions (4.0, 7.0, and 9.0) in embryo-rearing medium (ERM) or ultrapure water. Furthermore, we tested the later-life-stage effects of SNCs on medaka and their population growth. “Later-life-stage effects” were defined here as delayed toxic effects that occurred during the adult stage of organisms that had been exposed to toxicant during their early life stage only. AgNO₃, SNCs, and silver ions were less toxic in ERM than in ultrapure water. Release of silver ions from the SNPPs was pH dependent: in ERM, silver toxicity was decreased owing to the formation of silver chloro-complexes. SNC toxicity was higher at pH 4.0 than at 7.0 or 9.0. AgNO₃ was more toxic than SNCs. To observe later-life effects of SNCs, larvae hatched from embryos exposed to 0.01 mg/L SNCs in ultrapure water were incubated to maturity under clean conditions. The mature medaka were then allowed to reproduce for 21 days. Calculations using survival ratios and reproduction data indicated that the intrinsic population growth rate decreased after exposure of embryos to SNC. SNC exposure reduced the extinction time as a function of the medaka population-carrying capacity.

[en] Highlights: • Exposure of silver nanocolloids (SNC) induced serious deformities during medaka embryogenesis. • 5 glycan-related genes including human glycosylation diseases were employed. • SNC exposure changed the gene expressions and N-glycan syntheses in medaka. • The gene expressions were significant in the brain and essential for embryogenesis. • SNC may inhibit the skeletal formation of the head and eye through gene expression. Silver nanomaterials such as silver nanocolloids (SNC) contribute to environmental pollution and have adverse ecological effects on aquatic organisms. In particular, chemical exposure of fish during embryogenesis leads to deformities and puts the population at risk. Although glycans and glycosylation are known to be important for proper morphology in embryogenesis, little glycobiology-based research has examined morphological disorders caused by environmental pollutants. This study addressed the glycobiological effects of SNC exposure on medaka embryogenesis. After exposure of medaka embryos to SNC, deformities such as small heads and deformed eyes were observed. The expression of five glycan-related genes (alg2, gnsb, b4galt2, b3gat1a, and b3gat2) was significantly altered, with changes depending on the embryonic stage at exposure, with more severe deformities with exposure at earlier stages. In situ hybridization analyses indicated that the five genes were expressed mainly in the head region; exposure of SNC suppressed alg2 and gnsb and enhanced b4galt2 and b3gat1a expression relative to controls on day 7. Loss (siRNA)- and gain (RNA overexpression)-of-function experiments confirmed that alg2, gnsb, and b4galt2 are essential for embryogenesis. The effects of SNC exposure on glycan synthesis were estimated by glycan structure analysis. In the medaka embryo, high mannose–type glycans were dominant, and SNC exposure altered glycan synthesis. The alteration was more significant when exposure occurred at an early stage of medaka embryogenesis. Thus, SNC exposure causes embryonic deformities in medaka embryos through disordered glycosylation.