Cantoral et al. 2024 — Lead levels in the most consumed Mexican foods
This study reports the first systematic monitoring of lead (Pb) concentrations across 103 foods and beverages commonly consumed by the Mexican population, purchased from retail outlets in Mexico City. Samples were analyzed by graphite furnace atomic absorption spectrophotometry (GF-AAS) with a limit of quantification (LOQ) of 0.0025 mg/kg. Overall, 18% of samples had detectable Pb (above LOQ), with the highest single concentration found in infant rice cereal (1.005 mg/kg), followed by whole wheat bread (0.447 mg/kg), pre-cooked rice (0.276 mg/kg), black pepper (0.239 mg/kg), and turmeric (0.176 mg/kg). Four items exceeded FAO/WHO maximum limits (MLs) for Pb: infant rice cereal, whole wheat bread, pre-cooked rice, and soy infant formula. The baby foods group had the highest rate of ML exceedances (18%), followed by cereals (11%).
Key numbers
Baby foods (n = 11):
- Infant rice cereal (Brand 2): 1.005 (SD 0.042) mg/kg — exceeds FAO/WHO ML of 0.20 mg/kg for baby food cereals
- Soy infant formula (Brand 2): 0.035 (SD 0.008) mg/kg — exceeds FAO/WHO ML of 0.01 mg/kg for infant formula
- Infant formula whole milk (Brands 1, 2, 3): all <LOQ
- Infant formula soy (Brand 1): <LOQ
Cereals (n = 18):
- Pre-cooked rice: 0.276 (SD 0.017) mg/kg — exceeds ML of 0.20 mg/kg for cereal grains
- Whole wheat bread: 0.447 (SD 0.192) mg/kg — exceeds ML of 0.20 mg/kg
- Rice cake: 0.030 (SD 0.012) mg/kg
- Sweet bread: 0.123 (SD 0.020) mg/kg
- Wheat flour (Brand 1): 0.031 (SD 0.009) mg/kg
- Wheat flour (Brand 2): 0.070 (SD 0.007) mg/kg
- Rice flour, raw rice (3 brands), oats, cookies, crackers, tortillas: all <LOQ
Condiments and spices (n = 11); 45% detection rate:
- Black pepper: 0.239 (SD 0.007) mg/kg
- Turmeric: 0.176 (SD 0.032) mg/kg
- Paprika: 0.092 (SD 0.027) mg/kg
- Guajillo chili: 0.037 (SD 0.000) mg/kg
- Tea sachet: 0.021 (SD 0.003) mg/kg
- No FAO/WHO MLs established for turmeric, paprika, or black pepper
Meats (n = 7); 43% detection rate:
- Beef liver: 0.133 (SD 0.015) mg/kg
- Pork ham: 0.062 (SD 0.003) mg/kg
- Turkey sausages (Brand 2): 0.026 (SD 0.010) mg/kg
- All below their respective FAO/WHO MLs
Legumes (n = 6):
- Soybean: 0.029 (SD 0.013) mg/kg
Beverages, dairy products, seafood, fruits, fats/oils, soups, vegetables: all <LOQ
Detection summary: 19 of 103 food items with detectable Pb; 4 of these exceeded FAO/WHO MLs.
LOQ: 0.0025 mg/kg (applies to all solid samples; liquid samples analyzed in wet weight)
Method: Graphite furnace AAS (Perkin Elmer AAnalyst-600 with HGA-600 furnace and AS800 autosampler); acid digestion with HNO3; duplicate analysis per sample; CRM: bovine liver NIST 1577c (recovery 105.03 ± 9.01%); coefficient of variation 8.9% at LOQ, 4.8% at low level.
Methods (brief)
Samples purchased from retail outlets in three Mexico City counties (Iztapalapa, Benito Juárez, Álvaro Obregón), including the Central de Abastos and La Viga wholesale markets. Solid samples dehydrated at 80°C for 72 h; liquids processed in wet weight. All analyses reported in duplicate; method validated against CCAYAC-CR-03/0 repeatability protocol. Speciation was not performed; all values represent total Pb. Comparison against FAO/WHO Codex Alimentarius MLs and, for candy/snacks, US FDA candy guidance (0.1 mg/kg).
Implications
Certification: Infant rice cereal result (1.005 mg/kg = 1,005 ppb) is the highest Pb value reported for that matrix in this dataset and far exceeds both FAO/WHO ML (0.20 mg/kg = 200 ppb) and FDA Closer to Zero draft action level (20 ppb as-consumed, equivalent to approximately 140 ppb in powder at 1:7 reconstitution). This is a single-brand sample with high variance (SD 0.042 mg/kg); row-fit is exact for infant rice cereal. The soy infant formula exceedance (0.035 mg/kg = 35 ppb) also exceeds FAO/WHO ML (0.01 mg/kg = 10 ppb). This paper contributes to non-US occurrence data for both matrices. Mexico City represents urban retail sourcing; regional variation and contamination-source heterogeneity are acknowledged limitations.
Courses: First systematic food monitoring effort in Mexico. Useful case study for supply chain contamination pathways: atmospheric deposition implicated for rice and wheat grain; industrial processing implicated for soy. Pre-cooked and processed forms of rice (pre-cooked rice 0.276 mg/kg, rice cake 0.030 mg/kg) had detectable Pb while unprocessed raw rice brands did not.
App: Provides Mexico-jurisdiction Pb concentration data for infant rice cereal and soy infant formula. The infant rice cereal value is a high outlier by international standards and should be treated as a single-brand observation from a small n. Spice contamination data (turmeric, black pepper, paprika) also supports ingredient-level risk flagging.