Keywords: 
• Cu²⁺ /
• Cd²⁺ /
• polystyrene microsphere /
• Artemia parthenogenetica /
• combined toxicity

Abstract: As a kind of important marine pollutants, microplastics (MPs) are potentially harmful to the marine ecosystem because of their stable and non-degradable properties. MPs can easily absorb heavy metals and other pollutants in the ocean due to their small particle size and large specific surface area, which would result in additional ecological risks. Therefore, it is of great significance to study the mixture toxicity of MPs and heavy metals for their ecological risk assessment. The individual and mixture acute toxicities of 10 μm polystyrene (PS) and Cu²⁺ and Cd²⁺ on nauplii of brine shrimp, Artemia parthenogenetica, were investigated. The concentrations of Cu²⁺ and Cd²⁺ in nauplii were measured by inductively coupled plasma mass spectrometry (ICP-MS), and then the effects of the presence of polystyrene particles on the accumulation of heavy metals in nauplii were explored. The results showed that the 24-h median lethal concentration (LC₅₀) of Cu²⁺ and Cd²⁺ were (1.26±0.15) mg·L^-1 and (164.5±27.3) mg·L^-1, respectively. In contrast, the 24 h-LC₅₀ of Cu²⁺ and Cd²⁺ combined with PS were (1.38±0.23) mg·L^-1 and (178.3±36.4) mg·L^-1, respectively. Furthermore, the time-dependent concentrations of heavy metals in nauplii showed that the presence of polystyrene microspheres significantly promoted the uptake and excretion rates of Cu²⁺ and Cd²⁺ by nauplii of A. parthenogenetica. However, this promotion did not affect the acute toxicities of Cu²⁺ and Cd²⁺ compared with the absence of MPs. Our results could provide a theoretical basis for ecological risk assessment of microplastics and heavy metals in the marine environment.