A Decadal Baseline of Heavy Metal Bioaccumulation and Oxidative Stress in Cardisoma armatum: A Sentinel Assessment of the Western Lagos Lagoon

This study established a decadal baseline (2015) for heavy metal pollution in the Western Lagos Lagoon (Makoko and UNILAG Waterfront) using the rainbow land crab, Cardisoma armatum, as a sentinel biomonitor. Morphometric analysis revealed significantly large carapace dimensions, suggesting an advanced age-class or high nutrient loading (eutrophication) rather than environmental stability. While raw tissue concentrations for Lead (Pb) showed no significant spatial variance (p > 0.05), the Biota-Sediment Accumulation Factor for Pb was above the 1.0 threshold at both stations, identifying it as the primary toxicological threat. Conversely, Zinc (Zn) levels remained within safe BSAF limits, consistent with its role as a regulated essential micronutrient. Biochemical markers (CAT, GST, and MDA) indicated significant oxidative stress, particularly at the UNILAG site, suggesting a high pollution-induced metabolic burden. Histopathological examination corroborated these findings, showing a marked reduction in reserved inclusion cells (R-cells) across both populations, which is a clear signal of metabolic exhaustion as energy is diverted from somatic growth to detoxification. Physical evidence of organopathy was further observed via hemocyte plugs in the gills and tubular degradation in the hepatopancreas. These 2015 findings provide a critical reference point for future longitudinal studies and highlight the urgent need for integrated human health risk assessments, analysis of reproductive damage due to oxidative stress in the Lagos Lagoon ecosystem. Keywords- Bio-indicators, BSAF, Cardisoma armatum, Oxidative Stress Biomarkers, Metabolic Exhaustion.