Toxicity of mercuric chloride when combined with ionic and nanoparticulate silver on Artemia salina: growth, fatty acid composition, oxidative stress, and lipid peroxidation†

Abstract

This study assessed the individual and binary toxic effects of inorganic mercury (Hg) plus total dissolved Ag (Ag), or silver nanoparticles (Ag NPs), on the immobilization, fatty acid composition, and oxidative stress of Artemia salina nauplii as an aquatic animal model. Acute toxicity tests revealed that the immobilization of nauplii exposed to 5 × 10⁻⁹ M, 2.5 × 10⁻⁸ M, and 5 × 10⁻⁸ M of Hg as HgCl₂ decreased in the presence of 1 × 10⁻⁴ M of Ag NPs or dissolved Ag as AgNO₃. The median effective concentration (EC₅₀) of Hg increased from 4.5 × 10⁻⁸ M to 9 × 10⁻⁸ M (two-fold) in the presence of Ag (Hg + Ag). Both Ag NPs and Ag decreased the immobilization of nauplii and diminished the oxidative stress and lipid peroxidation induced by Hg. Total amounts of saturated fatty acids (∑SFA) in Hg and Hg + Ag increased compared with that in the control, but this increase was significantly (P < 0.05) lower in Hg + Ag than in Hg. Total amounts of monounsaturated (∑MUFA) and polyunsaturated (∑PUFA) and the ratio of unsaturated to saturated fatty acids (unsat./sat.) decreased compared with the control; however, this reduction was significantly (P < 0.05) smaller for ∑PUFA in Hg + Ag than in Hg. In Hg + Ag NP co-exposure, ∑SFA and the unsat./sat. ratio showed no significant (P < 0.05) change compared with the control. However, MUFAs exhibited a significantly (P < 0.05) increased response, while the amount of PUFAs decreased compared with that in the control, but it was significantly (P < 0.05) higher than that in Hg. A decline in superoxide dismutase (SOD) and catalase (CAT) activity in nauplii due to exposure to mercury alone was mitigated in the presence of Ag or Ag NPs. The thiobarbituric acid reactive substance also decreased in the Hg + Ag and Hg + Ag NP treatments. The toxicity effect of the treatments was in the order of Hg > Hg + Ag > Hg + Ag NPs, revealing the antagonistic effect of Ag or Ag NPs on Hg toxicity, with the highest amelioration observed in the presence of Ag NPs.