Overview
Shaheen and colleagues collected 1,521 branded and unbranded soybean and palm oil samples from retail shops across all eight divisions of Bangladesh in 2021, pooled them into 44 composites, and measured arsenic, cadmium, chromium and lead by atomic absorption. Mercury was measured in the market composites and in 25 crude and refined refinery samples. Arsenic, cadmium and lead were low; mercury averages were in the milligram-per-kilogram range and exceeded the national limit in most composites.
Key numbers
- Soybean oil (n = 23 composites): lead 0.0228 (0.0102-0.0424) mg/kg, cadmium 0.0057 (0.0027-0.0083) mg/kg, arsenic 0.0078 (0.0051-0.0168) mg/kg, mercury “5.3000 (0.1300-44.300)” mg/kg (Table 2).
- Palm oil (n = 21 composites): lead 0.0238 (0.0106-0.0488) mg/kg, cadmium 0.0053 mg/kg, arsenic 0.0084 mg/kg, mercury 3.4000 (0.1400-23.200) mg/kg (Table 2).
- Refinery samples: mercury in crude vs refined soybean oil 2.4 vs 1.8 mg/kg; palm oil 1.5 crude vs 1.8 refined, no significant refining effect (Results text, p. 4).
Methods (brief)
Microwave digestion with nitric acid and hydrogen peroxide; graphite furnace AAS for cadmium, chromium and lead, hydride generation AAS for arsenic, cold-vapor AAS for mercury. Detection limits are given in micrograms per litre of digest. Recovery was checked against rice flour and nutritional formula reference materials because no oil reference material exists; recovery tables are in the supplement.
Evidence Fitness
A large, nationally representative retail sampling frame, but results are composites, so the 44 values hide individual-sample spread. Category medians and quality-control data sit in supplemental tables not included in the filed PDF. The mercury levels are unusually high for edible oil and the paper offers no independent confirmation. Soybean and palm oil are a proxy for rice-bran-oil: the paper does not measure rice bran oil, so it is not linked to that page.