Relative developmental toxicities of reclaimed water to zebrafish embryos and the relationship with relevant water quality parameters

Reclaimed water recharging rivers is an important way to solve the problem of water shortage. However, reclaimed water contains some toxic contaminants, which will cause ecological and health risks. The objective of this study is to explore the relationship between developmental toxicities and relevant water quality parameters. Zebrafish embryos were exposed to secondary effluent, wastewater with advanced treatment (Tertiary treatment effluent) and blank (Aerated tap water). The samples taken in April showed higher biological toxicity to embryos, as the maximum value of mortality and malformation reached to 47.5 % for secondary effluent, 75 % for wastewater with advance treatment, while the blank was just 2 % at 120 hours post fertilization. The tested samples also showed significantly adverse effect on hatchability of zebrafish. The hatching rates of embryos exposed to secondary effluent and tertiary treatment effluent were much lower than blank. And significant delay in hatching time existed during the hatching period. The advanced treatment did not show beneficial effects for reducing acute toxicity. The main factor resulted in hatching inhibition may be ammonia especially the free ammonia, as it showed highest coefficient with hatching rate. The no observed effect concentration (NOEC) of ammonia for mortality and malformation were 5 ​mg/L and 10 ​mg/L respectively. The lowest observed effect concentration (LOEC) of ammonia for body length and hatchability were both 2 ​mg/L, while the concentration of free ammonia was 0.19 ​mg/L. Considering the biological toxicity of ammonia on aquatic organism, the discharge concentration of ammonia is advised to be controlled below 2 ​mg/L.