Heavy Metal Hepatotoxicity and Public Health Risks of Tyre-Flame Processed Cow Hide (Ponmo) in West Africa: An In Vivo Toxicological Assessment

Abstract

Background: Cow hide (Ponmo) is widely consumed in West Africa as an affordable protein supplement. Traditional processing involves singeing with scrap tyre flames, which introduces toxic heavy metals and combustion by-products. However, no comprehensive in vivo toxicological assessment has been published.
Objective: To evaluate the hepatotoxicity, heavy metal bioaccumulation, and nutritional impact of tyre-flame processed (TFP) cow hide in a 28-day Wistar rat model.
Methods: Twenty-five male Wistar rats (80-100g) were randomized into five groups (n=5 per group) and fed diets containing 10%, 20%, or 30% TFP cow hide for 28 days. Control groups received razor-shaved processed (RSP) cow hide or normal rat chow. Endpoints included serum heavy metals (Pb, Cd, Cu, Zn, As, Ni) by atomic absorption spectrophotometry, liver function enzymes (AST, ALT, ALP), blinded histopathological examination of liver and kidney (H&E staining), GC-MS analysis of 17 priority PAHs in liver tissue, and body weight/organ weight changes. One-way ANOVA with Tukey's posthoc test was used (p<0.05).
Results: TFP cow hide consumption caused dose-dependent accumulation of lead (0.73-1.30 mg/L) and nickel (0.50-1.23 mg/L) in serum, exceeding permissible limits for meat products by 7-13 fold. Serum liver enzymes remained within normal ranges across all groups (AST: 115-130 U/L, ALT: 79-92 U/L, p>0.05). However, rats fed 30% TFP cow hide developed severe portal inflammation with interface hepatitis (piecemeal necrosis) – a lesion associated with chronic progressive liver injury. Kidney histology remained normal in all groups. No priority PAHs were detected in liver tissues (detection limit: 0.01 µg/kg). The RSP control group showed minimal weight gain (5.8g vs. 20.0g in normal controls, p<0.05), confirming poor nutritional quality of cow hide irrespective of processing method.
Conclusion: Tyre-flame processed cow hide is unsafe for human consumption due to dose-dependent heavy metal accumulation (particularly lead and nickel) and portal inflammation with interface hepatitis. Normal serum transaminases do not rule out liver injury from TFP cow hide consumption. Regulatory prohibition of tyre-flame processing is urgently recommended.