Abstract:
Water and sediment are crucial for the survival of aquatic organisms, hence it is
imperative to determine the levels of contaminants in both systems. This research work was
conducted to evaluate the effects of seasonal variation on the physicochemical and microbial
properties of surface water and sediment samples collected from the two Ilaje communities in
Ondo State, Nigeria. The physicochemical and microbial analyses of water and sediment
samples were carried out using standard methods of analyses. Speciation of heavy metals in
the sediment samples was carried out using the sequential extraction method. Liquid-liquid
extraction and solid-liquid extraction methods were used for the extraction of organochlorine
and organophosphorus pesticide residues from water and sediment samples, respectively.
Analysis of the extracts was done using Gas Chromatography coupled with electron capture
detector. The results showed that most of the physicochemical parameters: turbidity
(42.55-49.85NTU); total hardness (622.00-2426.50mg/L); calcium hardness
(131.50-1478.50mg/L); alkalinity (121.50-152.00mg/L); chloride (1991.50-3533.50mg/L); and
electrical conductivity (521-2806.50μS/cm) of water samples from the two sampling locations
during the dry and rain seasons were above the WHO maximum permissible limits for
drinking water. The microbial analysis revealed the presence of oil tolerating bacteria and
fungi in the water and sediment samples collected from the two sampling sites. The mobility
and bioavailability of the heavy metals in the sediment samples for the two seasons were
observed to be in this order: Fe > Cr > Zn > Pb > Cu > Cd. The water and sediment samples
analyzed from both sites were contaminated with some levels of organophosphorus pesticide
residues. However, organochlorine pesticide residues were not detected in the water samples
from both locations but detected in the sediment samples from Ogogoro. In general, the water
samples from Abereke and Ogogoro are not suitable for domestic and other purposes. Also,
the sediment samples may endanger the survival of aquatic organisms in the investigated
