Islam et al. (2007) review phytotoxic effects and bioaccumulation of heavy metals (Cd, Zn, Cu, Pb, Cr) in selected Asian vegetables — Chinese cabbage (Brassica chinensis), winter greens (B. rosularis), pakchoi, and celery — and derive soil heavy metal threshold values for potential dietary toxicity. The paper integrates primary pot and greenhouse experiment data from Zhejiang University with a literature review to answer: at what soil concentration does edible plant tissue metal concentration cross the food safety threshold? Soil extractable Cd threshold for safe vegetable production was estimated at 0.489–0.869 mg/kg soil depending on vegetable species. The paper also covers the bioavailability of soil metals (DTPA-extractable Zn, Cu fractionation) and agronomic factors (pH, organic matter, fertilizer) affecting uptake.
Key numbers
Cd in vegetable shoots and roots (pot experiment, Table 5; soil extractable Cd range 0.15–2.30 mg/kg; mg/kg fresh weight):
- Chinese cabbage (shoot, increasing Cd): 0.010 → 0.049 → 0.076 → 0.086 → 0.151 mg/kg FW
- Winter greens (shoot): 0.022 → 0.038 → 0.103 → 0.119 → 0.166 mg/kg FW
- Celery (leaf): 0.020 → 0.040 → 0.072 → 0.082 → 0.253 mg/kg FW
- Celery (stem): 0.020 → 0.085 → 0.113 → 0.204 → 0.241 mg/kg FW
- Celery accumulated highest Cd in edible parts among the three vegetable crops.
Soil Cd thresholds for potential dietary toxicity (limit: 0.05 mg/kg FW per Chinese standard GB N238-84):
- Chinese cabbage: soil extractable Cd threshold 0.869 mg/kg
- Winter greens: 0.730 mg/kg
- Celery: 0.489 mg/kg (most sensitive — lowest threshold)
Soil Zn thresholds for potential dietary toxicity (limit: 20 mg/kg per Chinese standard):
- Total soil Zn: 122–413 mg/kg depending on crop and tissue
- Available (DTPA) Zn: 74.9–175.6 mg/kg for shoot tissue
Soil Cu thresholds for potential dietary toxicity (limit: 10 mg/kg):
- Total soil Cu: 429.93–835.56 mg/kg; available Cu: 269.14–338.98 mg/kg
Pb food safety limit referenced: 0.2 mg/kg for edible parts of crops (Chinese Department of Preventive Medicine, 1994). Soil Pb thresholds for safe vegetable production described as “not available” at time of writing.
Al toxicity: Al-based coagulants at tested concentrations inhibited seed germination of Brassica chinensis; root elongation inhibited in acidic conditions; tissue uptake at pH 4.5 confirmed.
Methods (brief)
Combination of primary data (pot experiments, greenhouse, nutrient solution cultures at Zhejiang University using AAS, ICP-MS) and literature review. Primary data uses Chinese cabbages (B. chinensis cv. Zao-Shu 5), winter greens, pakchoi, and celery grown in Chinese garden soil. Soil extractable Cd measured by DTPA extraction. Soil Zn, Cu fractionation methods per Shuman 1991 and Kuo 1983 frameworks. Food safety standards reference Chinese GB standards (0.05 mg/kg Cd, 0.2 mg/kg Pb, 20 mg/kg Zn). Limitation: 2007 data; Chinese garden soil context; may not represent commercial supply chain soils; Chinese food standards differ from EU and Codex limits.
Implications
Certification: The soil Cd threshold work (0.489–0.869 mg/kg extractable Cd) provides useful reference values for agricultural soil certification criteria. The finding that celery is the most sensitive accumulator (lowest threshold for dietary toxicity) suggests celery and related crops deserve specific attention in soil-based certification tiers. The literature is dated but foundational for soil-to-crop Cd transfer reasoning.
Courses: Excellent mechanistic background on soil-to-plant metal transfer for Asian leafy vegetables. The dose-response tables for Cd, Zn, and Cu bioaccumulation in vegetables are useful for illustrating the linear relationship between soil contamination and crop contamination.
App: The vegetable crop species data (celery, Chinese cabbage, pakchoi) provides Cd bioaccumulation coefficients that can inform ingredient-level risk estimates for Asian leafy vegetables. Primary Chinese garden soil context limits direct applicability to global commercial supply chains.