Environmental risk assessments of uses cyanide in gold extraction on water quality parameters and its effect on rhodanese activities in selected organs of coptodon zillii in igun reservoir, Southwestern, Nigeria

Abstract

This study was conducted to investigate the effect of cyanide on the pattern of rhodanese activity distribution in selected organs of Coptodon zillii and water quality of Igun reservoir. Fish and water samples were collected monthly for period of a year to cover both seasons. The physical parameters such as air and water temperature, conductivity, TDS, pH, depth, and transparency were determined. Air temperature and water temperature were determined in situ with a mercury-in-glass thermometer, pH and TDS were determined by calibrated pH meter (PCE-PHD Version 1.1 Model Q656697). Selected organs such as gill, fillet, and liver were used for rhodanese activity analysis while physico-chemical parameters were analyzed based on APHA (2012) standard methods. The pH concentration recorded in this study ranged from 7.1 - 8.1 with a mean of 7.48 ± 0.47 while highest pH mean concentration was observed in dry season (7.61 ± 0.5) compared with the rainy season (7.36 ± 0.24). The mean cyanide concentration was high during the rainy season (0.09 ± 0.03 mg/L) compared with dry season (0.07 ± 0.04 mg/L). The results of rhodanese activity recorded in the gills, fillet, and liver of Coptodon zillii (3.66 ± 3.19 RU/mg, 3.73 ± 2.58 RU/mg, and 3.73 ± 2.68 RU/mg) respectively. Water temperature, pH, and depth showed a positive correlation with rhodanese activity in the gills while a negative correlation was observed between water temperature and rhodanese in the fillet and liver of Coptodon zilllii. Based on the cyanide concentration recorded in this study shown that Igun reservoir is polluted which can be can harmful to humans and other organisms could due to archaic gold mining method using by local miner around the reservoir. Coptodon zillii inhabiting the reservoir showed a high concentration of rhodanese in the different tissues that could serve as the detoxifying mechanism. However, further biochemical analysis of others fish tissue should be examined to determine the effects of mining pollutants on aquatic biota.