Studies on Seasonal Variation and Effect of Heavy Metal Pollution on Microbial Load of Marine Sediment

Abstract

Sediment samples were collected from 15 stations at Onne Port, Rivers State, Nigeria, during the dry and rainy seasons of 2012 to determine the spatial distribution, seasonal and temporal variation and effect of different heavy metal contents on microbial load. The heavy metals; chromium, cadmium, copper, nickel, zinc, mercury, tin and arsenic were analyzed using atomic absorption spectrophotometer and compared with different standard and reference values of TELS (threshold effect levels) and PELS (probable effect levels). Total heterotrophic bacterial and fungal counts were evaluated using the spread plate technique. Heavy metals accumulated in the sediment during the dry season in the order As > Hg >Zn >Ni >Sn>Cr >Cd >Cu and in the wet season in the order As >Sn>Zn >Ni >Hg >Cr >Cd >Cu and ranged from 0.001 to 15.1 mg/kg and 0.001 to 13.2 mg/kg for dry and wet seasons respectively. The concentrations of heavy metals demonstrated a unique seasonal pattern with the highest concentration during the dry season and lowest during the wet season. The log count of total heterotrophic bacteria varied between 5.81 cfu/g and 5.37cfu/g for dry and wet season respectively and total fungal counts varied between 4.95cfu/g and 4.80cfu/g for dry and wet seasons respectively. There was no significant correlation between heavy metal concentration and microbial load. Although the levels of the heavy metals determined were within regulatory limits, destruction of wetland biomass will release the heavy metals into the environment with the risk of metals entering the food chain. To check the pollution in marine sediment, the anthropogenic sources of pollution should be at minimal level.