Single and mixture toxicity of gold nanoparticles and gold(III) to Enchytraeus buchholzi (Oligochaeta)

•Toxicity of Au-NPs, Au(III) and Au-NPs/Au(III) assessed in the Enchytraeus buchholzi.•No significant effect of Au-NPs on survival and reproduction of E. buchholzi.•No effect of Au(III) on survival but on reproduction.•14-day EC50Au(III) = 35.5 mg/kg estimated for reproduction.•Au-NPs/Au(III) mixtures as deleterious as Au(III) with one exception.

The ecotoxicity of gold nanoparticles (Au-NPs), gold(III) and their mixtures was assessed in the potworm Enchytraeus buchholzi after 14-day bioassays. The worms were exposed at 20 °C in OECD artificial soil to 0, 9.37, 18.7, 28.1 and 37.5 mg/kg Au-NPs or Au(III) and 0, 9.37 + 9.37, 18.7 + 18.7, 28.1 + 28.1, 37.5 + 37.5 mg Au-NPs + Au(III)/kg. The results indicated that the range of Au-NPs concentrations used in the present study was not deleterious to the survival and reproduction of E. buchholzi. Au(III) showed no significant effect on survival but was significantly deleterious to reproduction in the highest treatment (p ≤ 0.01). A 14-day EC50Au(III) = 35.5 mg/kg was estimated for effects on reproduction. Au-NPs/Au(III) mixtures essentially caused the same effects as Au(III) except for 18.7 mg Au(III)/kg vs. 18.7 + 18.7 mg Au-NPs + Au(III)/kg where the mixture treatment was significantly more toxic to reproduction (p < 0.02). Mixture results suggested a seemingly additive effect between Au-NPs and Au(III), although the conventional toxic unit approach could not be used to ascertain this conclusively because of the lack of Au-NPs toxicity. The order of toxicity between Au-NPs, Au(III) and their mixtures was Au-NPs = Au(III) = Au-NPs/Au(III) for survival and Au-NPs < Au(III) ≤ Au-NPs/Au(III) for reproduction.