Assessment of Comprehensive Pollution, Trophic Transfer, Bioaccumulation Patterns and Human Health Risks of Heavy Metals from Sediments Through Seagrasses to Fish in Chukwani Bay, Zanzibar

Anthony OO, Rashid Juma Rashid and Salim Mohammed Salim

Published on: 2025-11-19

Abstract

This study assessed the comprehensive pollution status, trophic transfer, and human health risks associated with heavy metals through seagrasses in the marine ecosystem of Chukwani Bay, Zanzibar. Sediment, seagrass, and fish samples were collected and analyzed for selected heavy metals (Pb, As, Cu, Ti, Al, Mg, Mn, Fe, Hg, Cd, and Zn) using Agilent 5900 Inductively Coupled Plasma–Optical Emission Spectrometry (ICP–OES). The Comprehensive Pollution Index (CPI) was applied to evaluate overall metallic contamination in fish, while bioaccumulation and trophic transfer factors were used to trace metal movement from sediments through seagrasses to fish.

Among the eleven metals analyzed, sediment samples exhibited the highest mean concentrations from Fe: 121.45 ppm; Ti: 210.05 ppm; Mg: 188.37 ppm, etc., followed by seagrasses and fish tissues, indicating a distinct trophic transfer of metals across the benthic food web. Notably, Fe, Mn, and Zn demonstrated strong bioaccumulation tendencies, while elevated levels of Pb (up to 3.88 ppm) and As (up to 1.96 ppm) contributed to high CPI values ranging from 84.13 in Mugil cephalus to 157.04 in Kyphosus vaigiensis. These findings highlight a progressive enrichment pattern from sediments to higher trophic levels, underscoring potential toxicological risks to seagrass-associated fish species and, consequently, to human consumers.

Human health risk evaluation based on Estimated Daily Intake (EDI), Hazard Quotient (HQ) and Hazard Index (HI) revealed that while most EDI values were within WHO/FAO tolerable limits, Pb and As in Stegastes nigricans and K. vaigiensis slightly exceeded reference thresholds. The individual HQ values were found to be below 1, HI values ranges from 2.16 to 4.45 while Comprehensive Pollution Index (CPI) indicated potential chronic risks from long-term fish consumption.

Overall, these findings highlight the strong linkage between sediment contamination and heavy metal accumulation across trophic levels, emphasizing the need for continuous monitoring and pollution mitigation to safeguard marine ecosystem integrity and community health in Chukwani Bay and Zanzibar at large.