Shellfish as Bio-indicators of Petroleum-related Pollution in a Tropical Oil-producing Estuarine Ecosystem of the Niger Delta, Nigeria

Abstract

Petroleum-producing estuaries of the Niger Delta support shellfish harvesting while receiving complex, spatially variable mixtures of hydrocarbons and other contaminants. Shellfish can integrate biologically accessible exposure, but their interpretation is complicated by differences in habitat, taxonomy, physiology and analytical practice. This critical narrative review evaluates the conditions under which shellfish provide reliable evidence of petroleum-related contamination, biological effects and potential dietary exposure. Search-engine-assisted scholarly retrieval, bibliographic verification and thematic appraisal covered literature published from 2000 to 30 July 2026, with emphasis on regional field investigations and experimentally supported mechanisms. The evidence supports sediment-associated periwinkles and locally verified mangrove oysters as complementary sentinel candidates, rather than interchangeable monitors. Niger Delta studies demonstrate hydrocarbon and metal occurrence, heterogeneous tissue burdens and biological disturbance, but frequently provide weaker evidence for source-specific attribution, causal injury or population-level consequences. Apparent disagreements among seafood risk assessments arise partly from different analyte panels, tissue-weight bases, consumption assumptions, treatment of non-detects and interpretation of screening values. Petroleum hydrocarbon totals, individual biochemical responses and tissue-to-sediment ratios cannot independently establish ecological impairment or consumer safety. Recent molecular and rapid-screening approaches improve investigative capacity, although local calibration and independent validation remain necessary. An integrated monitoring framework is proposed that combines taxonomically verified organisms, paired environmental chemistry, exposure and effect measurements, seasonally matched comparisons, and separately conducted dietary assessments. Its central requirement is to preserve distinctions between contaminant detection, source attribution, biological injury, ecological recovery and human exposure. Immediate priorities are harmonised regional sampling, reproducible analytical quality assurance, experimentally validated biomarker panels and transparent reassessment of published risk calculations. Shellfish are defensible bio-indicators when embedded within this chain of evidence; they are not self-sufficient forensic tools or substitutes for representative food-safety surveillance.