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Potentially toxic metals in small ruminant tissues: multivariate analysis and health risk assessment via Monte Carlo simulation

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Overview

Fathi-Beyranvand and colleagues measured essential and potentially toxic trace elements in breast muscle and liver of 80 small ruminants (sheep and goats, equal sex representation) slaughtered at the Golshan Slaughterhouse in Khorramabad, Lorestan Province, western Iran. Analytes included cadmium (Cd), nickel (Ni), lead (Pb), cobalt (Co), selenium (Se), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), and zinc (Zn). Analysis was by ICP-OES (Agilent 5110). Most metals were within concentrations consistent with international standards, but zinc values in both sheep and goat muscle exceeded FAO/WHO recommended levels (75.33-132.5 mg/kg vs MRL 50 mg/kg), and nickel muscle values (0.76-1.2 mg/kg) and lead muscle values (0.12-0.65 mg/kg) also exceeded FAO/WHO limits. Cadmium was not detected in muscle tissue but was detected in liver samples. Probabilistic Monte Carlo simulation for cancer risk (nickel) yielded lifetime cancer risk values in the moderate range.

Key numbers

  • Sample set: 80 total samples (sheep n = 40: 20 ewes, 20 rams x muscle and liver; goat n = 40: 20 female, 20 male x muscle and liver). Animals aged 2-4 years.
  • Analytical method: ICP-OES (Agilent 5110, USA). 0.5 g dried tissue digested with 5 mL 65% HNO3 + 2 mL 37% HCl + 1 mL 30% H2O2, heated to 140 degrees Celsius for 130 min in a high-pressure vessel (Parr Instrument Co., Model 4746).
  • LOD values (ppb, expressed in the source): lead 0.942, cobalt 0.160, copper 0.904, selenium 6.638, nickel 0.749, cadmium 0.127, iron 0.225, magnesium 1.0007, manganese 0.036, zinc 0.173.
  • Recovery range: 90.4% to 103% using NIST SRM 1577b (bovine liver) at concentrations 100, 500, and 1000 micrograms/L. Acceptable recovery defined as above 99%.
  • Cadmium concentrations (mean +/- SD, mg/kg): muscle - not detected (ND) in sheep ewes and rams, ND in goat female; goat male muscle 0.14 +/- 0.01. Liver: sheep ewes 0.15 +/- 0.01, sheep rams 0.12 +/- 0.01, goat female 0.41 +/- 0.04, goat male 0.23 +/- 0.01. MRL for Cd: muscle 0.05 mg/kg, liver 0.50 mg/kg (Codex Alimentarius / WHO). All liver Cd values below MRL.
  • Lead concentrations (mean +/- SD, mg/kg): sheep ewes muscle ND, sheep rams muscle ND, goat female muscle 0.65 +/- 0.02, goat male muscle 0.29 +/- 0.03. Liver: sheep ewes 0.12 +/- 0.02, sheep rams 0.57 +/- 0.02, goat female 0.52 +/- 0.02, goat male 0.52 +/- 0.02. MRL for Pb: muscle 0.10 mg/kg, liver 0.50 mg/kg. Goat female muscle Pb (0.65 mg/kg) exceeded MRL.
  • Nickel concentrations (mean +/- SD, mg/kg): sheep ewes muscle 0.83 +/- 0.07, sheep rams muscle 0.84 +/- 0.06, goat female muscle 1.21 +/- 0.27, goat male muscle 0.76 +/- 0.03. Sheep ewes liver 0.79 +/- 0.06, rams liver 0.84 +/- 0.07, goat female liver 0.83 +/- 0.05, goat male liver 0.78 +/- 0.03. MRL 0.5 mg/kg (FAO/WHO); all muscle values exceeded MRL.
  • Zinc (mg/kg): muscle values ranged 75.33-132.5 (MRL 50 mg/kg, all exceeded). Nickel 0.76-1.2 and lead 0.12-0.65 mg/kg in muscle exceeded FAO/WHO limits.
  • Health risk assessment: hazard index (HI) below 1 for all metals in all tissue types, indicating no significant non-carcinogenic risk. Lifetime cancer risk (ILCR) for nickel in meat: 0.380 (described by authors as “moderate carcinogenic risk”); for Pb: 0.0085; for Cd: 0.380.
  • Ingestion rates used: 2 g/day for liver, 3.14 kg/year for meat.
  • Multivariate analysis: Mn, Fe, Cu, and Cd were primarily associated with natural terrestrial sources; Ni, Pb, and Zn linked to anthropogenic inputs.

Methods (brief)

Sampling conducted from October to December 2023 at Khorramabad slaughterhouse (Lorestan Province, 33 degrees 34 minutes N, 48 degrees 24 minutes E), provincial capital with an estimated population of 1,760,649. 80 ruminant carcasses selected by systematic random sampling (one carcass per five), assessed by a licensed veterinarian. Breast muscle (20 rams, 20 ewes) and liver samples prepared: 50 g oven-dried at 60 degrees Celsius for 24 h, then ground using a mortar and pestle. 0.5 g of dried tissue subjected to acid digestion in a high-pressure vessel with 5 mL 65% HNO3 + 2 mL 37% HCl + 1 mL 30% H2O2, heated to 140 degrees Celsius for 130 min. Digests filtered through 0.45-micrometre membrane filter (Whatman, Merck), diluted to 25 mL with chromatography-grade water and stored in Falcon tubes. ICP-OES Agilent 5110 calibrated using multi-element standard solutions from certified 1000 mg/L stock solutions. SPSS version 27 used for statistical analysis; OriginPro 2025 for correlation and clustering. Monte Carlo simulation with 10,000 iterations using Crystal Ball (Oracle, Chicago) at 95% confidence level.

Implications

  • Certification (HMTc): Cadmium in liver samples from this population remained below Codex MRLs. Lead in goat female muscle exceeded the 0.10 mg/kg MRL. Nickel and zinc exceeded FAO/WHO limits in muscle across multiple tissue types. These findings are from a single provincial slaughterhouse in western Iran and reflect local environmental conditions; they should be treated as regional context rather than global small ruminant meat baselines.
  • Courses: Useful demonstration of organ-specific metal accumulation patterns (liver generally accumulates more cadmium than muscle, consistent with cadmium’s renal and hepatic tropism). Also illustrates multivariate clustering to distinguish natural versus anthropogenic metal source signatures.
  • App: Cadmium and lead concentration data from this source are specific to Lorestan Province, Iran. They should not be used to populate global meat contamination profiles without regional weighting.
  • Microbiome: No microbiome data.

Update history

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