Physiological Responses, Cadmium Partitioning, and Mineral Nutrient Disruption in Brassicaceae Crops Exposed to Cadmium Stress

Overview

This greenhouse pot experiment grew four Brassicaceae species (cress, watercress, broccoli (Brassica oleracea var. italica), and white cabbage (Brassica oleracea var. capitata)) in soil spiked with cadmium (CdCl2) at five levels (0, 5, 10, 20, and 50 mg cadmium (Cd) per kg soil) to characterize species-specific cadmium uptake, root-to-shoot translocation, and nutrient disruption. All cadmium concentrations applied exceed normal background agricultural soil levels (background typically 0.1 to 0.5 mg per kg; slightly contaminated soils approximately 1 to 3 mg per kg). This is a mechanistic context study, not a retail food survey. Values reported are on a dry weight basis from greenhouse plant material and cannot be used directly as fresh-weight food concentration data.

Key numbers

All cadmium concentrations are in mg per kg dry weight. Instrument: atomic absorption spectrometry (AAS). Certified reference material analyzed alongside samples with recoveries not reported. The study reports means plus/minus standard error (n = 3).

Broccoli shoot cadmium (dry weight, mg per kg):

Broccoli showed the strongest growth inhibition among the four species: shoot dry weight declined by up to 66.4% at 50 mg Cd per kg soil relative to the control. Root cadmium concentrations in broccoli were the highest of the four species at all treatment levels. Shoot cadmium was low and root-dominant at 0 to 20 mg per kg, but at 50 mg per kg a 185-fold increase in shoot cadmium relative to the control was observed as root retention capacity was exceeded.

White cabbage shoot cadmium (dry weight, mg per kg):

White cabbage showed the highest absolute shoot cadmium at 50 mg per kg (251.6 mg per kg DW), nearly 1.5-fold above broccoli at the same treatment level. It also exhibited the highest shoot cadmium distribution at moderate levels (5 mg per kg soil), indicating less effective root retention than broccoli at low to moderate contamination.

Cadmium toxicity threshold context: EFSA tolerable weekly intake is 2.5 µg Cd per kg body weight; JECFA provisional tolerable monthly intake is 25 µg Cd per kg body weight.

Soil cadmium at which root retention fails: The study identifies 20 to 50 mg per kg soil cadmium as the range where root retention declines and shoot translocation increases substantially for broccoli. At 5 mg per kg (representing slightly contaminated agricultural soil), broccoli shoot cadmium was 7.27 mg per kg DW.

Nutrient disruption: Cadmium exposure caused significant reductions in potassium, calcium, and zinc in plant tissues, particularly at high treatment levels, across all four species.

Methods (brief)

Controlled greenhouse pot experiment (4 kg soil per pot, three replicates per treatment level). Five cadmium treatment levels applied as CdCl2 (0, 5, 10, 20, 50 mg Cd per kg soil). Plants grown to harvest stage under controlled conditions. Cadmium and nutrient concentrations determined by AAS. Bio-concentration factor (BCF), translocation factor (TF), and total accumulation rate (TAR) calculated. DMRT used for post hoc comparison (p less than 0.05). No LOD, LOQ or certified reference material recovery data reported.

Implications

Pathways: Demonstrates that broccoli preferentially retains cadmium in roots under low to moderate soil contamination, limiting shoot (edible tissue) exposure. At high soil cadmium (above 20 mg per kg), root retention fails and shoot concentrations increase sharply. This root-retention mechanism is relevant to understanding how soil cadmium management affects edible tissue concentrations.

Courses: Case study for cadmium uptake physiology in Brassicaceae; illustrates the disconnect between agronomic tolerance (maintained growth) and food safety (cadmium accumulation in edible shoots even when plants appear healthy).

App: Values are from greenhouse spiked-soil experiments on a dry weight basis and represent extreme contamination scenarios. They should not be used as typical retail food concentration data.

Note: All cadmium concentrations in this study are dry weight from experimentally contaminated plants grown at soil cadmium levels well above normal agricultural fields. Direct comparison to fresh-weight retail vegetable data requires basis conversion and is not appropriate for typical supply-chain risk assessment.

Related evidence

• Cadmium
• Broccoli
• Brassica vegetables
• supply-chain/soil-cadmium-contamination

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