Heavy metal trophic transfer and human health risks in the Northern Benguela current ecosystem: a review with a focus on cape hake species (Merluccius capensis and M. paradoxus)

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The Benguela Current Large Marine Ecosystem (BCLME), renowned for its high productivity, sustains vital fisheries, including the ecologically and economically crucial Cape hake ( Merluccius capensis and M. paradoxus ). This system faces threats from anthropogenic heavy metal (HM) pollution, primarily from industrial and mining activities, which jeopardizes ecosystem integrity and seafood safety. This review synthesizes current knowledge on trophic interactions and heavy metal (HM) transfer in the BCLME, focusing on Cape hake ( Merluccius capensis and M. paradoxus ) and their crustacean prey. Using a PRISMA structured systematic literature review of published literature, the review evaluates patterns of HM bioaccumulation and trophic transfer across marine food webs. Evidence indicates that mercury (Hg) is the most extensively studied and bioaccumulative metal, with concentrations generally increasing with trophic position marine organisms. Spatial variability in HM concentrations is influenced by environmental drivers such as upwelling intensity, sediment interactions, and coastal inputs, which affect metal bioavailability. However, important gaps remain, including limited data on non-mercury metals, seasonal variability, and multi-trophic level analyses within the BCLME. In addition, the application of trophic ecology tools, such as stable isotope analysis (SIA) and Bayesian mixing models (MixSIAR), remains underutilized in assessing contaminant pathways. These limitations constrain a comprehensive understanding of HM dynamics in the region. The review highlights the implications of HM bioaccumulation for ecosystem functioning, fisheries sustainability, and seafood safety in Namibia. Evidence from the reviewed studies indicates that mercury concentrations in most marine organisms generally remain below established food safety thresholds, suggesting a low immediate risk to consumers. Strengthening region-specific monitoring and integrating ecological and human health assessments will be essential for improving management under increasing environmental and anthropogenic pressures.

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