Heavy metal bioaccumulation in liver, kidney, and muscle tissues of free-ranging sheep grazing near informal electronic waste recycling sites in the Greater Accra region, Ghana

Introduction

An estimated 53.6 million metric tonnes of electronic waste were generated globally in 2019, with projections suggesting this figure will reach 74.7 million tonnes by 2030. A disproportionate share of this waste stream flows to low-and middle-income countries in West Africa, where informal recycling operations extract valuable metals through open burning of cables, acid leaching of circuit boards, and manual dismantling of components-processes that release heavy metals into the surrounding environment with minimal containment. The Agbogbloshie scrapyard in central Accra, Ghana, has become internationally recognised as one of the largest and most heavily contaminated informal e-waste processing sites in the world. Previous environmental surveys have documented extremely elevated concentrations of lead, cadmium, mercury, and other toxic metals in soils, surface water, and airborne particulates at and around the site. Human health effects among e-waste workers and nearby residents-including elevated blood lead levels, respiratory illness, and developmental neurotoxicity in children-have been the subject of considerable research attention and public health concern.

What has received far less attention is the livestock dimension of this contamination. Hundreds of sheep, goats, and cattle graze freely on and around the Agbogbloshie site, feeding on contaminated vegetation and drinking from polluted water sources. These animals are subsequently sold and slaughtered for human consumption at local markets, creating a pathway for heavy metal transfer from e-waste to the human food chain that bypasses the occupational exposure route entirely. A consumer eating offal (liver, kidney) from a sheep that has grazed at Agbogbloshie may unknowingly ingest heavy metals at concentrations far exceeding international food safety limits-yet the magnitude of this risk has not been systematically quantified. This research was designed to fill that gap by measuring five priority heavy metals in three edible tissue types across a distance gradient from the Agbogbloshie site, establishing dose-response relationships between environmental contamination and tissue bioaccumulation, and evaluating the results against Codex Alimentarius maximum residue limits to assess the food safety implications.

Materials and Methods Materials

Forty-eight West African Dwarf sheep (adult females, estimated age 2-4 years based on dentition) were purchased from three zones defined by distance from the centre of the Agbogbloshie e-waste processing area: Zone A (0-1 km, n = 16) comprised animals that had grazed continuously on or immediately adjacent to the scrapyard for at least 12 months, as confirmed by interviews with their owners; Zone B (1-3 km, n = 16) comprised animals grazing in the Agbogbloshie neighbourhood but not on the scrapyard itself; Zone C (reference,>15 km, n = 16) comprised animals from Dodowa, a semi-rural area in the Greater Accra Region with no known industrial contamination. All animals were transported to the Accra Abattoir and slaughtered following standard Ghanaian Veterinary Services protocols. Within 30 minutes of slaughter, approximately 200 g samples of liver (right lobe), kidney (cortex), and longissimus dorsi muscle were collected using stainless steel instruments, sealed in acid-washed polyethylene bags, and stored on ice for transport to the laboratory, where they were frozen at-20 degrees C until analysis. Soil samples (0-15 cm depth, composite of five subsamples per site) and forage samples (composite of dominant grass species) were collected from 12 locations across the three zones on the same days as animal purchases. All sampling was conducted between March and August 2023.

Methods

Tissue samples (approximately 2 g wet weight) were digested in a closed-vessel microwave digestion system (MARS 6, CEM Corporation, Matthews, NC, USA) using 7 mL concentrated HNO 3 (trace metal grade) and 1 mL H2O2 (30%). Digests were diluted to 50 mL with ultrapure water (18.2 megaohms-cm). Soil and forage samples were dried at 105 degrees C for 24 hours, ground, sieved through 2 mm mesh, and digested using the same protocol. Concentrations of Pb, Cd, Cr, and As were determined by inductively coupled plasma mass spectrometry (ICP-MS; Agilent 7900, Santa Clara, CA, USA) and Hg by cold vapour atomic absorption spectrometry (CV-AAS; Milestone DMA-80, Sorisole, Italy). Quality assurance included certified reference materials (NIST SRM 1577c Bovine Liver and NIST SRM 2711a Montana Soil), reagent blanks, and duplicate analyses. Recoveries for all metals were 92-107%. Results were expressed as mg/kg wet weight for tissues and mg/kg dry weight for soils. Statistical analyses were performed in R v4.

Discussion

The most alarming finding of this research is the sheer magnitude of the food safety exceedances. Kidney Pb in Zone A sheep averaged 6.14 mg/kg-more than twelve times the Codex MRL of 0.5 mg/kg and among the highest values reported for any livestock species in the published literature.

Conclusion

This research establishes that free-ranging sheep grazing within 3 km of the Agbogbloshie e-waste recycling site in Accra accumulate lead and cadmium in edible tissues at concentrations that exceed international food safety limits by factors of 3 to 12. The contamination is not confined to the scrapyard itself: Zone B animals grazing 1-3 km away still had kidney and liver metal levels significantly above Codex MRLs, indicating a broader contamination footprint than has been previously recognised. Two practical implications follow. First, livestock grazing should be prohibited within at least a 3 km radius of Agbogbloshie and similar e-waste processing sites, and animals currently grazing in these areas should be excluded from the food chain through a publicly funded buyout programme rather than simply redirected to market, where they would continue to expose consumers to unacceptable metal burdens. Second, the strong soil-tissue correlations identified here suggest that routine soil monitoring could serve as an early warning system for identifying livestock contamination risk in areas near known pollution sources, enabling intervention before contaminated animal products reach consumers.

Acknowledgement

Acknowledgements

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