Effects of Heavy Metals on Microbial Function in Water and Sediment around Abonnema Island at Lower Sombriero River, Nigeria

Aims: The interrelationships between heavy metals Lead (Pb), Copper (Cu), Cadmium (Cd), Chromium (Cr) and Zinc (Zn) and microorganisms in sediment and overlying water along the shoreline of Abonnema Island were investigated by determining the levels of Carbon Dioxide (CO2), Ammonia (NH3), and Sulphate (SO42-).
Study Design: Water and sediment samples were collected from seven stations approximately 500 metres apart using plastic containers and Erkman grab sampler respectively. Glucose, palm oil, and cowbell powdered milk were separately added to each set of water and sediment samples and each inoculated with 0.05mg/l, 0.15mg/l and 0.5mg/l of copper, zinc, lead, chromium and cadmium and incubated for seven days at about 30ºC.
Place and Duration of Study: The study was undertaken in the Institute of Geosciences and Space Technology, University of Science and Technology, Port Harcourt, Nigeria between January 2007 and November 2008.
Methodology: Heavy metals were determined using Atomic Absorption Spectrophotometer. Carbon dioxide, Ammonia, Sulphate in water and sediment were determined by titration, phenate, turbidimetric and KH2PO4 extraction methods using Spectrophotometer. Total heterotrophic counts were carried out on Nutrient agar plates. Total coliform and Total faecal coliform counts were determined using the most probable number (MPN) technique using Mac – Conkey broth. Petroleum degrading bacteria was isolated in petroleum agar.
Results: The results showed that heavy metals had stimulatory effect on microbial functions in some cases and inhibitory effect in others. The stimulatory effect on CO2 respiration was more in the water than in the sediment while the stimulatory effect on NH3 respiration was more in the sediment than in the water. The stimulatory effect on SO42- respiration was more in the sediment than in the water. The inhibitory effects on NH3 and SO42- respiration were more in the water than in the sediment. The concentrations of CO2 and SO42- were within permissible limit while NH3 exceeded permissible limit.
Conclusion: The inhibitory effects of the heavy metals on the levels of CO2, NH3 and SO42- resulting from the biodegradation of carbohydrate (glucose) and protein (cowbell powdered milk) show that the rate of cycling of carbon, Nitrogen and Sulphur in the coastal waters is being affected by the heavy metals. Thus effluents should be treated before discharge into the river while direct discharge of other heavy metal containing wastes into the river should be discouraged.