الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Exposure experiments were conducted to evaluate the influence of dissolved organic matter (DOM) on the toxicity of ZnO-NPs (10-30 nm) and dissolved Zn (from ZnCl2) at sub-lethal doses (50 ppm and 5 ppm, respectively) to zebrafish (Danio rerio). Humic acid, alginic acid, bovine serum albumin and various natural DOM isolated from USA rivers as Milwaukee River-WI (NOMW), Yukon River-AK (NOMA) and Suwannee River-GA DOM (NOMS) were used to represent humic substances (HA), carbohydrates (CHO), proteins (PTN), and natural organic matter (NOM), respectively.
To the best of our knowledge, there are few studies that have focused on the effects of different DOM quality and quantity on the toxicity of ZnO-NPs to zebrafish embryos. DOM with different functionalities and at different concentrations had the ability to mitigate the endpoints of ZnO-NPs toxicity, resulting in delayed hatching rates, mortality and malformations.
The impact of DOM mitigation on the hatching rate in ZnO-NPs exposures at 72 hpf followed the order of: NOMS > HA > NOMW > NOMA > CHO > PTN. However, that order changed to HA > CHO ≥ NOMS > NOMW ≥ NOMA > PTN in treatment with dissolved Zn. DOM also promoted bacterial survivorship in embryos exposed to ZnO-NPs although PTN had little influence on this phenotype, likely due to its high aggregative nature and because it is easily precipitated.
We moved beyond hatching rate analysis to investigate the consequences of ZnO-NPs exposure on the nervous and vascular systems in developing zebrafish. Zebrafish exposed to ZnO-NPs (1-100 ppm) exhibited an array of cellular phenotypes including: abnormal secondary motoneuron (SMN) axonal projections, abnormal dorsal root ganglion development and abnormal blood vessel development. Dissolved Zn (<10 kDa) exposure also caused abnormal SMN axonal projections, but to a lesser extent than the ZnO-NPs exposure.
The ZnO-NPs-induced abnormal phenotypes were reversed in embryos concurrently exposed with various types of DOM. In these acute mitigation exposure experiments, humic acid (HA) and carbohydrate (CHO), along with natural organic matter (NOM) obtained from the Suwannee River in Georgia were the best mitigators of ZnO-NPs-induced motoneuron toxicity. Further experiments were performed to determine if the ZnO-NPs-induced, abnormal axonal phenotypes and the DOM mitigated axonal phenotypes could persist across generations.
DOM of River Nile water sample seems to have a normal size distribution pattern with the 0.3-5 kDa DOM fraction in the summit during photodegradation. River Nile water has the ability to mitigate the toxicity of ZnO-NPs on zebrafish embryos.