Physicochemical Characteristics Of Natural Colloids And Biological Effects On Aquatic Organisms

Nanoscale colloids are widely distributed in surface water,but the specific properties of nanoscale colloids and their effects on aquatic organisms remain largely unknown.Based on a modified cross-flow filtration method combined with a variety of analytical methods,including transmission electron microscopy with energydispersive X-ray spectroscopy,atomic force microscopy,Fourier transform infrared spectroscopy,excitation-emission matrices,thermo-gravimetric analysis and inductively coupled plasma mass spectrometry,the properties of nanoscale colloids were intensively investigated.The present work found that the concentrations of nanoscale colloids ranged from 3.62 to 7.66 mg/L in real surface water,thousands of times greater than that of reported and predicted engineered nanomaterials in the environment.Different from expected sphere nanoparticles in existing research,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.,Ca and Mg)and natural organic matter(e.g.,humic acid-like substances).Experiments on metal release suggested that nanoscale colloids were stable in aquatic environments.Meanwhile,there is very little information available on the potential toxicity of nanoscale colloids.To investigate the specific toxicological effects of nanoscale colloids on zebrafish(Danio rerio)and the molecular mechanisms,the zebrafish embryos were exposed to nanoscale colloids at concentrations of 0.45,4.5 and 45 mg/L in culture medium,and the regular analysis of biological endpoints and the metabolomics of zebrafish were analyzed.The results showed that nanoscale colloids triggered developmental and phenotypic deformities,oxidative stress and metabolic disturbance(especially for the down regulation of amino acids)of zebrafish at environment relevant concentrations.Compared with the control,abnormalities in the form of pericardial/yolk sac edema,uninflated swim bladder,tail flexure and spinal curvature were found in the treated embryos.In the altered metabolisms,the downregulation of amino acids such as proline and glycine was remarkable.Moreover,the disturbance of galactose metabolism and aminoacyl-t RNA biosynthesis were primarily induced by nanoscale colloids in zebrafish.The above studies elaborated the specific physicochemical properties of nanoscale colloids and the effects on aquatic organisms.Given their high concentrations and observed toxicity,the environmental impacts of nanoscale colloids deserve reconsideration in the future,compared with the well-known engineered nanoparticles and specific organic pollutants.