Abstract:
The present study investigated the quality of sediments from Rapu-Rapu Island, Albay, Bicol and the aptness of contact assay using zebrafish (Danio rerid) embryos in assessing contamination levels in freshwater ecosystems. Chemical analysis of the sediment samples was done prior to the embryotoxicity test. In the assay, fertilized zebrafish eggs were exposed to sediments prepared from samples collected from Binosawan River and Mistika Creek in Rapu-Rapu Island. Artificial water and silica were used as negative controls and 2% ethanol was used as positive control. Mortality, abnormality, heart rate and hatching rate of zebrafish embryos were noted within 96-hour exposure in different media and these served as endpoints for the study. In both sites, background levels of cadmium and zinc were found but copper content exceeded the criterion. Also, sediments from both sites induced embryotoxic responses in zebrafish embryos. Mortality and abnormality rates significantly increased (especially in the undiluted sediment concentration) compared with the negative controls. Hatching success rates were decreased significantly in higher sediment concentrations taken from Binosawan River and Mistika Creek. There was a direct correlation between embryotoxic responses with that of the varying heavy metals concentration of the sediments. Sediments taken from both sites were shown to have different lethal and sublethal effects on zebrafish embryos. These suggest that the overall quality of sediments from both sites is contaminated. The study further confirms that the contact assay using zebrafish embryos is a practical and sensitive bioassay for assessing sediment quality of freshwater ecosystem of Rapu-Rapu Island.
