Seasonal changes in the heavy metal resistant bacterial population of the New Calabar River, Nigeria

Abstract

Seasonal changes and the contribution of industrial effluent discharges to the population of heavy metal – resistant bacteria (HMRB) in the river water and sediment of the New Calabar River, were examined. On exposure of river water microflora to 2µg of heavy metals, the HMRB population ranged from 55 to 78% in the rainy months and 100% in the dry months. The HMRB of the river water ranged from 0.4 to 0.8% and 11 to 21% in the rainy and dry months respectively, on exposure of river water microflora to 20µg of heavy metals. The HMRB in the sediment ranged from 86 to 100% and 20 to 43% in the dry months and 55 to 100% and 1.7 to 2.4% in the rainy months when sediment microflora were exposed to 2µg and 20µg of heavy metals respectively. Higher concentrations of heavy metals resulted in reduced populations of HMRB. The total aerobic heterotrophic bacterial (THB) count ranged from 1.0 x 107 to 5.8 x 108 cfu/ml and 2.2 x 106 to 5.3 x 107 cfu/ml for surface water, 5.5 x 106 to 7.4 x 108 cfu/ml and 1.4 x 105 to 4.0 x 106 cfu/ml for subsurface water and 1.0 x 105 to 1.1 x 109 and 2.5 x 105 to 6.8 x 107 cfu/g for sediment during the rainy and dry months respectively. Physicochemical parameters such as conductivity and BOD showed higher values in the rainy season than in the dry season. Dissolved oxygen and pH showed no significant difference between their rainy and dry season levels indicating the absence of seasonal variations with these parameters. Heavy metals levels of river water and sediment showed higher values in the dry season than in the rainy season. There was no significant difference between the heavy metal levels of industrial effluent discharges with those of the river water and sediment levels during the rainy season. During the dry season, the heavy metal levels of the industrial effluents were less than those of the river water and sediment. Thus their contribution to seasonal variation of these metals in the river water and sediment is negligible. Results also suggested that the percentage of heavy metal resistant bacteria and the heavy metal levels of the river water and sediments were higher in the dry season than in the rainy season.


Key words: Seasonal changes, effluent discharges, heavy metal resistant bacteria, New Calabar River.


(Global Journal of Pure and Applied Sciences: 2003 9(4): 425-434)