Tolerance of bacteria to toxicity of heavy metals in the New Calabar River

Abstract

The tolerance to salts of four heavy metals by pure and mixed cultures of four heavy metal–resistant bacteria, Bacillus, Proteus, Alcaligenes and Arthrobacter, isolated from the New Calabar River water was investigated. Heavy metal resistant bacteria were isolated from river water using nutrient agar supplemented with 20mg of salts of heavy metals per milliliter. Salts of heavy metals employed were CuCl­2.2H20, ZnS04.7H20, CdCl2.6H20 and Pb304. Bacillus was the most tolerant to the four heavy metal salts while Proteus showed the highest degree of sensitivity. The 24h LC50 of CuCl2.2H20 and ZnSO4.7H20 to Bacillus, Alcaligenes, Arthrobacter and Proteus were 100mg/L, 0.3mg/L, 0.5mg/L, 0.3mg/L, and 1.0mg/L, 0.4mg/L, 0.07mg/L, and 0.008mg/L, respectively. The 24h LC50 of CdCl2.6H20 and Pb304 to Bacillus, Alcaligenes, Arthrobacter and Proteus were 100mg/L, 100mg/L, 0.06mg/L, 0.07mg/L, 0.02mg/L, 0.2mg/L, 0.02mg/L and 0.07mg/L respectively. Hydrated Copper Chloride (CuCl2.2H20), CdCl2.6H20 and Pb304 were significantly less toxic to these organisms at 1% probability level, compared to ZnS04.7H20. Levels of heavy metals in river water ranged from <0.001 to 0.06mg/L for cadmium, 0.01 to 1.2mg/L for copper, 0.013 to 0.48mg/L for zinc, 0.007 to 0.44mg/L for iron. Vertical variation in the concentrations of heavy metals in the river water was significant at 1% probability level. River sediment concentrations of heavy metals were significantly greater than river water levels at 5% probability level. Dry season levels of heavy metals were significantly greater than rainy season levels at 5% probability level. Heavy metal concentrations of some industrial effluents discharged into the river ranged from 0.02 to 0.07mg/L for cadmium, 0.01 to 0.09mg/L for copper, 0.09 to 0.50mg/L for lead, 0.26 to 0.47mg/L for zinc and 0.42 to 2.31mg/L for iron. Results suggest that all the four heavy metal salts were toxic to river water micro flora. Hydrated zinc chloride (ZnCl2.7H20) was the most toxic to the bacteria while Pb304, CdCl2.6H20 and CuCl2.2H20 displayed similar levels of toxicity. Results also indicated that the heavy metal content of the industrial effluents sited along the New Calabar River water may pose toxicity problems especially to the abundance and diversity of the existing river water microflora.



Keywords: Tolerance, Sensitivity, Resistance, Toxicity, Concentration.

[Global Jnl Environ Sci Vol.2(2) 2003: 128-132]