Combined toxic effects of La,Ce,Pr,and Nd on biofilm extracellular enzymes
The aquatic ecological toxicity of rare earth elements(REEs),considered emerging pollutants,has garnered significant attention.Existing toxicological research has primarily focused on the individual toxic effects of REEs,with a lack of comprehensive investigations into the impacts of mixtures of these elements on aquatic organisms.We conducted single-factor toxicity,factorial design combined toxicity,and binary mixture toxicity experiments to investigate the toxic effects of La,Ce,Pr,and Nd on the β-glucosidase(BETA)activity in biofilms.Results showed that the impact of individual elements on BETA activity exhibited a'low-stimulation,high-inhibition'pattern in the range of 0.5-10 mg/L,with Pr demonstrating the strongest toxic effect at 5 mg/L.Analysis of variance and multiple linear regressions indicated that Nd had a negative effect on combined toxicity,whereas La had a negative effect on combined stimulation.The contribution of ternary and quaternary interactions to combined toxicity was not significant.A binary mixed validation experiment demonstrated that the La*Ce combination had a promoting effect at both high and low levels,whereas Ce*Pr,Ce*Nd,and Pr*Nd exhibited low promoting and high inhibiting effects.The binary combinations of low La*Ce,Ce*Pr,and Pr*Nd concentrations displayed synergistic effects,while high concentrations showed antagonistic effects.The Ce*Nd interaction was unaffected by concentration and exhibited antagonistic effects.In conclusion,the combined toxic effects and interaction modes of rare earths are influenced by both elemental properties and concentration combinations.Investigating the antagonistic effects of Ce*Pr,Ce*Nd,and Pr*Nd is crucial for mitigating the collective toxicity of rare earths.This research is of considerable importance for reducing rare earth composite pollution.
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