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Abstract 2,6-dichlorobenzoquinone (2,6-DCBQ), an emerging disinfection by-production, frequently occurs in reclaimed water and drinking water. However, limited information was available regarding its toxicity. To evaluate its impact, zebrafish at early life stage were exposed to 0, 10, 30, 60, 90, or 120 μg L−1 2,6-BDCQ for 72 h. Our results indicated that 2,6-BDCQ decreased zebrafish's survival rate to 65% and 44% at 90 and 120 μg L−1 treatments and increased its aberration rate to 11% and 26% at 90 μg L−1 and 120 μg L−1 treatments. Besides, 2,6-BDCQ had adverse effect on its oxidative stress (elevated superoxide dismutase activity), lipid peroxidation (increased malondialdehyde levels), DNA damage (increased 8-hydroxydeoxyguanosine contents) and apoptosis (increased caspase-3 activity). Although lower concentrations (≤60 μg L−1) of 2,6-BDCQ didn't exhibit significant effect on its survival development or lipid peroxidation of zebrafish, they induced obvious DNA damage and apoptosis occurrence. These results revealed 2,6-BDCQ caused genotoxicity and cytotoxicity to zebrafish. This study provides novel insight into 2,6-DCBQ-induced toxicity in zebrafish. Graphical abstract Image 1 Highlights • ≥ 90 μg L−1 2, 6-BDCQ significantly decreased survival rate and increased aberration rate. • 2,6-BDCQ significantly induced lipid peroxidation and disturbed fatty acid metabolism. • 2,6-BDCQ exert powerful genotoxicity, which can significantly cause DNA damage and influence DNA repair capacity, even at 10 μg L−1 treatment. • 2,6-BDCQ exert powerful cytotoxicity, which can obviously induce apoptosis, even at 10 μg L−1 treatment. 2,6-BDCQ caused genotoxicity and cytotoxicity to zebrafish at early life stage. [ABSTRACT FROM AUTHOR]

Arsenic (As) pollution in aquatic environment may adversely impact fish health by disrupting their thyroid hormone homeostasis. In this study, we explored the effect of short-term exposure of arsenite (AsIII) on thyroid endocrine system in zebrafish. We measured As concentrations, As speciation, and thyroid hormone thyroxine levels in whole zebrafish, oxidative stress (H 2 O 2 ) and damage (MDA) in the liver, and gene transcription in hypothalamic–pituitary–thyroid (HPT) axis in the brain and liver tissues of zebrafish after exposing to different AsIII concentrations for 48 h. Result indicated that exposure to AsIII increased inorganic As in zebrafish to 0.46–0.72 mg kg −1 , induced oxidative stress with H 2 O 2 being increased by 1.4–2.5 times and caused oxidative damage with MDA being augmented by 1.6 times. AsIII exposure increased thyroxine levels by 1.3–1.4 times and modulated gene transcription in HPT axis. Our study showed AsIII caused oxidative damage, affected thyroid endocrine system and altered gene transcription in HPT axis in zebrafish. [ABSTRACT FROM AUTHOR]

Arsenic (As) in the aquatic environment is a considerable environmental issue, previous studies have reported the toxic effects of low concentrations (≤ 150 μg/L) of As on fish. However, limited information is available regarding the impact of low levels of As on apoptosis. To evaluate this, zebrafish embryos were exposed to different concentrations (0, 25, 50, 75, and 150 μg/L) of As (arsenite [AsIII] and arsenate [AsV]) for 120 h. Our results indicated that low concentrations of AsIII exposure significantly inhibited the survival of zebrafish larvae, and significantly increased the transcription of Caspase-9 and Caspase-3 , the ratio of Bax/Bcl-2 transcription, and protein levels of Caspase-3. In contrast, AsV decreased the ratios of Bax/Bcl-2 transcription and protein levels, as well as protein levels of Caspase-3. Our data demonstrated that AsIII and AsV exert different toxic effects, AsIII induced apoptosis via the mitochondrial pathway and the extrinsic pathway, while AsV induced apoptosis only via the mitochondrial pathway. • Our study focused on the impact of low concentrations of arsenic on the apoptotic toxicity and manner of zebrafish larvae. • Low concentration of arsenite decreased the survival rate of zebrafish larvae, while low concentration arsenate had no effect on it. • Low concentration of arsenite can induce apoptosis of zebrafish larvae stage via the mitochondrial pathway and the extrinsic pathway. • Low concentration of arsenate can induce apoptosis of zebrafish larvae stage via the mitochondrial pathway. [ABSTRACT FROM AUTHOR]

Gill, as the organ of fish to contact most directly with xenobiotics, suffered more threat. To evaluate the impact of arsenite (AsIII) on the gill of fish, we measured the antioxidative responses (superoxide dismutase (SOD) and catalase (CAT) activities) and oxidative damage (malondialdehyde (MDA) content), histological changes and mRNA transcriptional responses of zebrafish gill, after exposure to AsIII (0, 10, 50, 100, and 150 μg L−1) solutions for 28 days. We found that AsIII increased the activities of CAT by 46%–87%, decreased the activities of SOD and the contents of MDA by 19% and 21%–32%. Furthermore, CuZnSOD and MnSOD mRNA transcription levels were also inhibited, decreasing by 62%–82% and 70%–77%. Besides, ≥ 100 μg L−1 AsIII also caused histological changes (a loss of mucus and desquamation in the surface of the epithelial cells) on zebrafish gill. These results showed that low concentrations of AsIII influenced biochemical and physiological performances of fish gill, which probably aggravates the toxic effect of AsIII on fish. Image 1 • Toxic effect of low level (≤150 μg L−1) of arsenite on zebrafish gill was studied. • Gill dealt with arsenite-induced toxicity by improving antioxidant capacity. • Exposure to low level of arsenite caused histopathological damage on gill tissues. • Cu/ZnSOD and MnSOD mRNA transcription levels of gill were significantly inhibited. [ABSTRACT FROM AUTHOR]

Lead bioavailability in contaminated soils varies considerably depending on Pb speciation and sources of contamination. However, little information is available on bioavailability of Pb associated with different fractions. In this study, the Tessier sequential extraction was used to fractionate Pb in 3 contaminated soils to exchangeable (F1), carbonate-bound (F2), Fe/Mn oxides-bound (F3), organic-bound (F4), and residual fractions (F5). In addition, soil residues after F1–F2 extraction (F 345), F1–F3 extraction (F 45), and F1–F4 extraction (F 5) were measured for Pb relative bioavailability (RBA) using a mouse kidney model. Based on the mouse model, Pb-RBA in the soils was 44–93%, which decreased to 43–89%, 28–75%, and 15–68% in the F 345 , F 45 , and F 5 fractions, respectively. Based on Pb-RBA in the soil residues, Pb-RBA in different fractions was calculated based on a mass balance. The data showed that Pb-RBA was the highest (∼100%) in the exchangeable and carbonate fraction, and the lowest (15–68%) in the residual fraction. In addition, Pb in the first three fractions (F1–F3) contributed most (83–89%) to bioavailable Pb in contaminated soils. Our study shed light on oral bioavailability of Pb in contaminated soils of different fractions based on sequential extraction and provide important information for soil remediation. Image 10800 • Pb-contaminated soils were fractionated via sequential extraction. • Relative bioavailability (RBA) of Pb in bulk and fractionated soils was measured. • The Pb-RBA in each fraction was calculated based on mass balance. • The Pb-RBA was highest (∼100%) in exchangeable and carbonate fraction. • The Pb-RBA was lowest (14–68%) in the residual fraction. Lead relative bioavailability in soil residues after each extraction was measured to assess Pb contribution in different fractions to bioavailable Pb in contaminated soils. [ABSTRACT FROM AUTHOR]

Arsenic (As) present in water is a nonignorable environmental issue, even at low concentrations (≤150 μg L−1). To evaluate the toxic effect of low concentrations of As, zebrafish at early life stage were exposed to 0, 25, 50, 75, or 150 μg L−1 AsIII for 120 h. Our results indicated that low concentration of AsIII decreased zebrafish larvae's survival rate to 85%, 89% and 86% at 50, 75 and 150 μg L−1. Furthermore, low concentrations of AsIII exposure caused oxidative stress (elevated superoxide dismutase (SOD) activity and influenced the mRNA transcriptional levels of Cu/ZnSOD and MnSOD) and damage (increased malondialdehyde levels). Meanwhile, zebrafish larvae regulated the mRNA transcription of metallothionein and heat shock protein 70 to alleviate toxicity caused by AsIII. These results revealed lower concentrations (≤150 μg L−1) of AsIII had a detriment effect on the survival of fish at early life stage, moreover, oxidative stress caused by AsIII posed potential risk for the zebrafish. This study provides novel insight into low concentration AsIII-induced toxicity in zebrafish. Image 10447 • Our study focused on the toxic effect of low concentrations of arsenite on the zebrafish at early life stage. • Low arsenite concentration decreased the survival rate of zebrafish at early life stage. • Low arsenite concentration caused oxidative stress and damage on zebrafish at early life stage. • Low arsenite concentration disturbed MT and HSP70 mRNA transcriptional levels of zebrafish at early life stage. Arsenite caused oxidative stress and damage to zebrafish at early life stage. [ABSTRACT FROM AUTHOR]