Highly potent toxicity of nickel in river water to daphnia lumholtzi

Trace metals are essential for aquatic organisms at low concentrations but become toxic at certain concentrations. This study aimed to evaluate the acute and chronic toxicity of Ni dissolved in natural water of Saigon River in Vietnam to the tropical micro-crustacean, Daphnia lumholtzi. Filtered field water was physical and chemical characterization prior to the acute and chronic experiments. In the acute test, D. lumholtzi was exposed to Ni at the concentrations from 50 – 1000 µg/L. In the chronic experiments, the animals were incubated in control (filtered field water only) or filtered field water with Ni addition (final concentrations of 5, 12, and 196 µg/L) over the period of 14 days. The results showed that the values of median lethal concentrations (48h-LC50) was 468 µg Ni/L (95% CI = 302 – 726 µg Ni/L). In chronic exposures, it was observed that Ni caused the strong survivorship decrease, maturation postponement, fecundity reduction and reproduction inhibition. The detrimental impacts of Ni on daphnids in natural water bodies would be more severe than those in the artificial medium in laboratory conditions. In addition, the Vietnam guideline values regarding Ni should be re-considered and adjusted to protect the aquatic ecosystem.