Assessment of Embryotoxicity of Urban Highway Runoff in Manila Using the Zebrafish (Danio rerio) Embryo Toxicity (ZFET) Test

Urban highway runoff contains a complex mixture of contaminants which are known to be embryotoxic to the aquatic biota. While there have been a number of studies that focus on the inorganic contaminants found in urban highway runoff (e.g.. heavy metals), few have emphasized on the organic contaminants present in urban highway runoff. In this study, an assessment on the embryotoxicity was performed using the zebrafish embryotoxicity test (ZFET). Urban highway runoff samples were collected from five sample sites in Manila and were used as the test samples while 5% acetone and reconstituted water were used as positive and negative controls, respectively. Prior to chemical analysis, water chemistry parameters including pH, dissolved oxygen, total dissolved solids (TDS), conductivity, and salinity were measured. An identification of the possible organic toxicants was conducted using GC-MS analysis. One-way ANOVA with Dunnett's post-hoc analysis was conducted to compare mortality and abnormality rates with the positive and negative control. Only the urban highway runoff samples collected from Sites 1 and 5 were found to be highly embryotoxic and showed no significant difference (p>0.05) with that of the positive control (5% acetone). GC-MS results showed that Sites 1 and 5 were sources of chromone derivatives, dioxolane, and phthalates. Site 5 had the highest concentration of organic contaminants and consequently registered the highest mortality among the exposed zebrafish embryos. Pearson correlation analysis for toxicological indices and water chemistry parameters revealed no correlation while the presence of increasing concentrations of organic toxicants showed significant association with increased incidence of 24hpf coagulation and delayed hatching. Given these results, we support the claim that the presence of these organic toxicants impact embryo development in aquatic biota.