This paper combines a narrative review of the cannabis hyperaccumulation literature with a controlled hydroponic dose-response experiment exposing four medical cannabis cultivars to escalating cadmium, lead, cobalt, and nickel concentrations. It provides mechanistic context for why cannabis accumulates heavy metals from soil but does not supply finished-product occurrence data for the regulated or retail cannabis market.
Key numbers
Inflorescence concentrations at the 5 µM exposure (highest dose, figures 6 and 7; approximate from figures; mg/g DW):
- Cadmium in inflorescences: up to approximately 0.025 mg/g DW (Dov cultivar, highest)
- Lead in inflorescences: approximately 0.0010 to 0.0015 mg/g DW
Translocation factor ranking across cultivars: nickel > cadmium > cobalt > lead. Roots accumulated substantially more metal than inflorescences at all exposure levels. WHO 2007 herbal-medicine thresholds for cadmium and nickel were exceeded in inflorescences at the 5 µM dose in the most sensitive cultivar.
These values are from an artificial hydroponic exposure that is 100 to 10,000 times higher than typical soil metal concentrations in regulated agricultural settings. They should not be used as occurrence estimates for retail dried cannabis.
Methods (brief)
Controlled hydroponics; ICP-MS for cadmium (Cd), lead (Pb), Co, nickel (Ni); 4 cultivars, 3 dose levels (0, 1, 5 µM cocktail); multiple time points; dry-weight basis. Literature review covers phytoremediation, hyperaccumulation, soil-to-plant transfer factors, and interactions between metal stress and cannabinoid biosynthesis.
Evidence fitness
This paper is uptake-mechanism context, not occurrence evidence. Its inflorescence values are from an extreme experimental exposure not representative of field-grown cannabis. The review section synthesizes prior literature on how cannabis accumulates metals from contaminated soils, the relative translocation efficiency of different metals, and interactions between metal stress and terpene or cannabinoid production. These mechanistic insights are relevant for understanding why cannabis flower metal concentrations vary with geographic origin and soil quality but do not establish occurrence distributions.
Limitations
All quantitative values are from a controlled dose-response experiment, not from retail or field-grown cannabis. Doses are orders of magnitude higher than typical soil contamination. Values cannot be used for occurrence profiling or compliance comparisons.
Related evidence
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