Overview
Hlyan and Chanpiwat bought 120 lettuces of three salad types (red coral, green oak and coral lettuce) in Bangkok markets in mid 2021 and measured total arsenic, cadmium and lead by ICP-MS. Each type was split into soil-grown and hydroponic samples. Soil-grown lettuce had higher means than hydroponic lettuce for most metal and type pairs, and cadmium drove the hazard index.
Key numbers
- Soil-grown red coral: cadmium mean 0.26 mg/kg (range 0.03 to 2.49), lead mean 0.19 mg/kg, arsenic mean 0.06 mg/kg (Table 3).
- Hydroponic red coral: cadmium mean 0.12 mg/kg, lead 0.09 mg/kg, arsenic 0.04 mg/kg (Table 3).
- Soil-grown green oak: lead maximum 0.53 mg/kg, the highest lead value in the study (Table 3).
Methods (brief)
Washed edible parts were oven-dried at 60 C, ground, digested in nitric acid and hydrogen peroxide, and analyzed by ICP-MS. Accuracy was checked with NIST tomato-leaf and water reference materials (arsenic and cadmium recoveries reported; no lead recovery). Table 3 reports minimum, maximum, mean, median and standard error per type and cultivation method.
Evidence Fitness
The journal is a Thai engineering journal; the PDF prints no received or accepted dates, so peer review is unverified. The basis (dry or fresh weight) of Table 3 is not stated, and the split of the 40 samples per type between soil and hydroponic is not given. The abstract ranges and some text statements do not match Table 3. The paper measures lettuce, not collard greens: it is a proxy for collard-greens, which is not linked.