Cadmium(II) Loading Exacerbates the Negative Effects of Nanobiochar on <i>Daphnia magna</i> : Evidence from Toxicity Test and Multiomics Analysis

Micro- (M-BC) and nanobiochar (N-BC) particles exhibit strong environmental mobility and superior adsorption capacity for heavy metals. This raises concerns regarding their ecological risks to aquatic ecosystems. However, systematic studies on the toxicity of contaminant-laden M-BC and N-BC to aquatic biota remain scarce. Here, we prepared the cadmium (Cd(II))-loaded complexes (M-BC-Cd and N-BC-Cd), identified the acute toxicity of M-BC-Cd and N-BC-Cd on zooplankton Daphnia magna, and emphasized the response in D. magna induced by N-BC and N-BC-Cd. The results indicated that N-BC alone induced minimal adverse effects on D. magna . N-BC demonstrated a higher Cd(II) adsorption capacity than M-BC, leading to a lower LC 50 level for N-BC-Cd. In chronic toxicity tests, exposure to N-BC-Cd resulted in a 30% reduction in the survival of D. magna compared to that of N-BC. The particles of N-BC-Cd caused more severe impairment in growth, reproduction, and oxidative stress responses. While N-BC primarily affected predation efficiency and disrupted metabolic pathways, the amplified toxicity of N-BC-Cd was attributed to a synergistic effect of prey limitation, metabolic dysregulation, oxidative stress, inhibition of signal transduction, and down-regulation of lysosomal proteins. This finding provides novel insights into assessing the environmental risks of biochar particles in aquatic ecosystems.