Sub-Chronic Toxicity Testing of Heavy Metals in Target Fresh Water Fish (Coptodon zillii) Histology

This histology-based toxicological study is aimed to advance the histopathological characteristics of fish gills exposed to some known crude oil spill heavy metals. Toxicity tests can measure lethal and/or sublethal effects. These effects are known as measurement endpoints: that is, they are ecological attributes that may be adversely affected by exposure to site contaminants and are readily measurable. Based on literature review on the environmental crude oil spill burdens of Niger Delta region of Nigeria, the following target chemicals (TC) were selected for the study: Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni) and Lead (Pb). The experimental type is a sub-chronicity fish exposure testing for twenty-eight (28) days duration. The experimental set-up involves twenty-two pieces (22) of twenty-liter (20l) tanks of four (4) replicate tanks per target chemical (TC) containing ten (10) juvenile study fish per tank in a semi-static tank testing system. TC exposure concentrations above the maximum allowable toxicant concentration (MATC) for freshwater were used for the study. Quality histological results showed alteration which was consistent with heavy metal exposure studies. Semi-quantitative assessment showed a significant difference between control and experimental gills organ histopathological indices. The study further validates MATC freshwater guideline use for toxicity certification in Cr, Cd and Ni exposure.