Toxicity of lanthanum and yttrium oxide nanoparticles and bulk forms on Folsomia candida: a study of single versus mixture exposures.

The intensive use of rare earth elements (REEs) raises concerns about their effects on soil organisms, particularly under mixture exposure scenarios. This study evaluated the toxicity of lanthanum oxide (La2O3) and yttrium oxide (Y2O3) nanoparticles (NPs) and bulk forms on Folsomia candida. Single (0-2500 mg/kg) and dual mixture exposures were tested for effects on survival, reproduction, avoidance behavior, and biochemical markers. No effects on survival and avoidance behavior were observed. NPs were more toxic than bulk forms. La2O3 NPs reduced reproduction (≥ 1250 mg/kg) and acetylcholinesterase (AChE) activity (2500 mg/kg), whereas Y2O3 NPs exhibited greatest toxicity, reducing reproduction (≥ 313 mg/kg) and increasing catalase (CAT) (156 and 625 mg/kg) and glutathione reductase (GR) (625 and 2500 mg/kg) activities. Mixture exposures revealed complex interactions (synergism, antagonism, or no interaction), with toxicity depending on concentration, endpoint, and material form. Besides, higher number of biochemical endpoints were affected by mixture exposures, but dissimilar responses were observed with different concentrations: 2500 mg/kg Y2O3 NPs + 2500 mg/kg La2O3 NPs decreased reproduction and increased GR, glutathione S-transferases (GST) and AChE activities; 2500 mg/kg Y2O3 NPs + 625 mg/kg La2O3 NPs increased CAT, GR, GST and AChE activities; 625 mg/kg Y2O3 NPs + 625 mg/kg La2O3 NPs increased GR activity; 156 mg/kg Y2O3 NPs + 2500 mg/kg La2O3 NPs decreased AChE activity, increased GR activity and lipid peroxidation levels. This study highlights that REE exposures, particularly mixtures, can pose risks to soil organisms and emphasizes the need to include mixture interactions in risk assessments.