Background: Found on the priority organic pollutants list and mono substituted derivatives of phenol, 4-chloro and 4-nitrophenol compounds are organic-origin micropollutants with toxicologic research performed due to recalcitrant properties, endocrine disrupting and lipophilic character, and tendency for bioaccumulation. As both pollutants are used in many industrial and other applications (from paper, pesticides, dye, pharmaceutical and explosives industries to chlorination of drinking water), they rapidly accumulate at all trophic levels of the ecosystem and are known to cause negative effects on organisms in the ecosystem led by aquatic systems. As a result, there are many methods developed for toxicity research of these types of priority organic pollutants, though studying the small freshwater fish species of zebrafish (embryo and adult) is chosen due to some advantages compared to other methods. Aims: To our knowledge, there are no studies performed on the embryotoxic effects of 4-nitrophenol and 4-chlorophenol derivatives on fish species. With this aim, the lethal and teratogenic effects of the phenol derivatives on zebrafish (Danio rerio) were evaluated by means of FET (fish embryo toxicity) test. Materials and methods: According to FET test, embryos at 1.5 hpf (hour post-fertilization) were exposed to 4-nitrophenol and 4-chlorophenol solutions in concentrations 1.0, 2.0, 4.0, 8.0 and 16.0 mg/L during 96 h. Every 12 hours, the embryos were observed and scored for lethal and teratogenic effects. Also, LC50 values were calculated for 48 h. Results: 48 h LC50 values were 2.409 mg/L for 4-chlorophenol and 4.581 mg/L for 4-nitrophenol. With increasing phenol concentrations, lethality and malformations increased. Teratogenic malformations more frequently produced by phenol derivatives were: incomplete body, chorda deformity, tail curvature, lordosis, scoliosis, delayed development and hatching, weak or non-pigmentation. Conclusion: 4-chlorophenol was found to be more toxic than 4-nitrophenol. Results firstly showed that the phenol derivatives caused embryotoxicity in zebrafish. 

Keywords: 4-chlorophenol; 4-nitrophenol; Zebrafish; Embryotoxicity, LC50