Seasonal and spatial variations in water quality, heavy metal concentration in water, sediment and bioaccumulation in Pseudotolithus species from the Gulf of Guinea, Ondo state, Nigeria

The Ondo State coastal waters , face increasing heavy metal pollution from human activities, posing risks to ecosystems and public health. This study investigated seasonal and spatial variations of eight heavy metals: Lead (Pb), Cadmium (Cd), Chromium (Cr), Iron (Fe), Zinc (Zn), copper (Cu), Nickel (Ni), and Cobalt (Co) in water, sediment, and Pseudotolithus species from Awoye and Idi-Ogba. Metal levels were measured using Buck Scientific Atomic Absorption Spectrophotometer, with pollution indices and health risks evaluated. Most water quality parameters met USEPA standards, except turbidity, dissolved oxygen and nitrate. Significant seasonal metal peaks included Cd (0.19 mg/L, wet season, Awoye), Cr (0.10 mg/L, dry, Idi-Ogba), Fe (4.44 mg/L, dry, Idi-Ogba), and Pb (0.10 mg/L, wet, Awoye), with Pb exceeding WHO limits. Sediment metal levels were below Effect Range Low guidelines, indicating low ecological risk. Geo-accumulation Index showed unpolluted conditions at Awoye (wet: all metals negative; dry: Cd 0.42) and Idi-Ogba (all seasons negative). Enrichment Factor indicated extreme enrichment, especially Cd (Awoye dry season: 9330.67). Contamination Factor was moderate for Cd at Awoye dry season (2.00), others < 1. Nemerow Pollution Index revealed unpolluted status (Awoye: 0.05–0.21; Idi-Ogba: 0.03–0.04). In Pseudotolithus tissues, the liver and kidney accumulated the most metals, especially Fe and Pb in the two locations. At Awoye, Cd posed significant health risks (HQ: 12.62; cancer risk: 9.5 × 10⁻2), while Idi-Ogba showed minimal concern. These findings highlight the need for regular monitoring and mitigation efforts in the region.