Toxicities of copper oxide nanomaterial and copper sulphate in early life stage zebrafish: Effects of pH and intermittent pulse exposure

Abstract

Effort has been made to standardise regulatory ecotoxicity tests for engineered nanomaterials (ENMs), but the environmental realism of altered water quality and/or pulse exposure to these pollutants should be considered. This study aimed to investigate the relative toxicity to early life-stage zebrafish of CuO ENMs at acid pH and then under pulse exposure conditions, all compared to CuSO 4 . At all pH values, CuSO 4 was more toxic to zebrafish than CuO ENMs. Additions of H + were protective of CuSO 4 toxicity, with median lethal concentrations LC 50 (with 95% confidence intervals) of: 0.36 (0.33-0.40), 0.22 (0.20-0.24) and 0.27 (0.25-0.29) mg L −1 at pH 5, pH 6 and pH 7, respectively. In contrast, the toxicity of CuO ENMs increased with acidity; LC 50 values were: 6.6 (4.5-8.5), 19.4 (11.6-27.2) and >100 mg L −1 at pH 5, pH 6 and pH 7, respectively. The increased toxicity of the CuO ENMs in acid water corresponded with greater dissolution of dissolved Cu from the particles at low pH, suggesting free Cu 2+ ion delivery to the zebrafish was responsible for the pH-effect. In continuous 96 h exposures to the substances at the LC 10 values and at pH 6, both CuSO 4 and CuO ENMs caused Cu accumulation, inhibition of Na + /K + -ATPase and depletions in total glutathione in zebrafish. However, two 24 h pulses of CuSO 4 or CuO ENMs at the same peak concentration caused similar effects to the continuous 96 h exposure, despite the shorter exposure durations of the former; suggesting that the pulses were more hazardous than the continuous exposure. In conclusion, the current water quality correction for pH with respect to Cu toxicity to freshwater fish should not be applied to the nano form. Crucially, CuO ENMs are more toxic in pulse than continuous exposure and new corrections for both water pH and the Cu exposure profile are needed for environmental risk assessment.

Influence of calcium and EDTA on copper ion bioavailability in copper nanoparticle toxicity tests improves understanding of nano-specific effects

“…When comparing the 96-h LC 50 values of Cu-NPs and Cu 2þ , it was found that the toxicity of Cu-NPs was less than that of Cu 2þ . This outcome was in accordance with previous works on the toxicities of soluble Cu ions, CuO-NPs, and Cu-NPs (Bai and Tang, 2020;Boyle et al, 2020;Griffitt et al, 2007;Lanone et al, 2009;Thit et al, 2017). This study hypothesized that the differences between toxicity of Cu-NPs and Cu 2þ to larval zebrafish should be due to the physicochemical properties of Cu-NPs.…”

“…Toxicity of Cu-NPs at 0.01 and 0.05 mg/L showed no significant difference from Cu(II) at the corresponding concentrations (0.006 and 0.03 mg/L), but 0.1 mg/L Cu-NPs had a greater toxicity than 0.06 mg/L Cu(II) in zebrafish embryos (Bai et al, 2010). The acute toxicity of nano-Cu and CuO-NPs was reported in zebrafish, showing a decrease in gill Na þ /K þ -ATPase activity (Boyle et al, 2020;Griffitt et al, 2007) and a depletion of total glutathione (Boyle et al, 2020). In zebrafish exposed to nano-Cu, real-time polymerase chain reaction (RT-PCR) results revealed higher levels of changes in global gene expression compared to CuSO 4exposed fish.…”

Nanotechnology‐based wastewater treatment

“…Since the application comes in water management, extra care has to be taken to ensure the safety and efficiency during its implementation. As said before most of the nanomaterials are toxic substances (Baek et al ., 2020; Boyle et al ., 2020, Renzi and Blaskovic, 2019), so there is a possibility of wide erratic outcomes, if they were to be implemented without a proper or elaborative studies. Though the current nanotechnology methodologies for wastewater treatment look promising, more in‐depth research is required to prove their safety.…”

Developmental exposure window influences silver toxicity but does not affect the susceptibility to subsequent exposures in zebrafish embryos

“…Alterations in tolerance, whether due to physiological or molecular differences, can improve plasticity and have been hypothesised to lead to genetic assimilation (Badyaev 2005 ). Repeated exposures to copper, an essential metal, showed that two pulsed 24 h exposures at 24 and 72 hpf caused the same effects as a continuous 96 h exposure in zebrafish embryos, despite the shorter total exposure duration (Boyle et al 2020 ), whereas pre-exposures to carbon tetrachloride increased tolerance to normally lethal doses in rats (Dambrauskas and Cornish 1970 ). Adult fish have shown increased tolerance to copper following a period of acclimation (Anadu et al 1989 ), and this has been attributed to increased metallothionein expression (Bradley et al 1985 ).…”

“…When exposed to 17α-ethinyloestradiol during the first 48 h of development, zebrafish show increased sensitivity to subsequent oestrogen exposures later in development (Green et al 2018 ), and similar results were observed following intermittent exposures to 17α-ethinyloestradiol in roach (Lange et al 2009 ). Higher concentrations of fenvalerate were recorded in intermittently exposed trout as opposed to those continuously exposed (Curtis et al 1985 ), and pulsed exposures to copper during early development were also shown to be more toxic than a continuous exposure at the same concentration (Boyle et al 2020 ). However, if adult fish were given time to acclimate to near lethal copper concentrations, an increase in tolerance was observed (Anadu et al 1989 ), usually attributed to increased metallothionein expression (Bradley et al 1985 ).…”