Nanoscale colloids induce metabolic disturbance of zebrafish at environmentally relevant concentrations†
Nanoscale colloids are widely distributed in surface water, although the specific properties of nanoscale colloids and their effects on aquatic organisms remain largely unknown. Using a modified cross-flow filtration method combined with dialysis, the present work found that the concentrations of nanoscale colloids ranged from 3.62 to 7.66 mg L−1 in real surface water, which is thousands of times greater than that of reported and predicted engineered nanomaterials in the environment. Compared with expected sphere nanoparticles, the nanoscale colloids exhibited a nanodisc shape with diameters of approximately 11–20 nm and average heights of 3.5 ± 0.7 nm. The nanoscale colloids were composed of metallic elements (e.g., Mn, Mg, Cr, Cd and Pb) and natural organic matter (e.g., humic acid-like substances). Experiments on metal release suggested that nanoscale colloids are stable in aquatic environments. Nanoscale colloids triggered developmental and phenotypic deformities, oxidative stress and metabolic disturbance (especially for the downregulation of amino acids) in zebrafish at environment relevant concentrations. The specific metabolic pathway disturbance induced by nanoscale colloids in zebrafish was mapped. Given the high concentrations and observed toxicity, the environmental impacts of nanoscale colloids deserve reconsideration in environmentally relevant matrices (e.g., surface water, underground water, sea water, soil and even food).