This paper is a controlled greenhouse experiment examining how zinc supply affects zinc bioaccumulation across plant organs and cannabinoid concentrations in drug-type medical cannabis. It provides mechanistic context for why excess zinc does not accumulate proportionally in cannabis inflorescences. It does not provide occurrence data for retail or finished hemp-derived products.
Key numbers
All organ concentrations are from ICP-OES analysis of dried tissue; units are mg/kg dry weight (DW). Values are presented in Fig. 6A and discussed in the text; exact numeric readings from figures are approximations.
Zinc concentrations in inflorescences increased with zinc supply but substantially less than in roots. Under the standard industry fertigation concentration (~0.35 mg/L Zn), the percentage of total plant zinc allocated to inflorescences was approximately 24%. Under severe zinc excess (4 mg/L, more than 10 times the industry standard), the inflorescence allocation dropped to approximately 5% while roots accumulated proportionally more.
Leaf zinc concentration at the highest treatment (4 mg/L Zn) reached 187.9 mg/kg DW, which is within the plant phytotoxicity range (100 to 300 mg/kg DW reported for other species), yet no severe toxicity symptoms were observed in the cannabis plants. The critical deficiency concentration for zinc in cannabis leaves was slightly above 20 mg/kg DW, based on observed yield reduction at leaf concentrations of 14.7 mg/kg DW (0.05 mg/L treatment) and 23.5 mg/kg DW (0.1 mg/L treatment).
No concentrations for lead, cadmium, arsenic, mercury, nickel, aluminum, chromium, or tin are reported; the study measured only zinc and other essential mineral nutrients (N, P, K, Ca, Mg, S, Fe, Mn, Cu) across plant organs.
Cannabinoid concentrations (THCA, CBDA, CBCA, THCA, CBD) were highest under 0.35 mg/L Zn and declined with both deficiency and excess. Total cannabinoid yield per plant was optimized at 0.35 mg/L Zn.
Methods (brief)
Drug-type cannabis (cultivar Annapurna) grown in soilless perlite culture under controlled conditions at the Volcani Institute, Israel. Five zinc levels (0.05, 0.1, 0.35, 1.0, 4.0 mg/L as Zn-EDTA) with 6 replicates per treatment. Zinc and other elements measured by ICP-OES (PlasmaQuant PQ9000) after acid digestion (HNO3/HClO4 for metals, H2SO4/H2O2 for N/P/K). Cannabinoids measured by HPLC after solvent extraction. Bioaccumulation coefficient factor (BCF) and translocation factor (TF) calculated from tissue and solution concentrations. No CRM recovery is reported for the ICP-OES analysis.
Evidence fitness
This paper provides mechanistic context for the zinc uptake pathway in drug-type medical cannabis, specifically:
- Medical cannabis uses a root-exclusion strategy for zinc: excess zinc accumulates predominantly in roots and is not proportionally translocated to inflorescences or other aerial organs.
- Even under extreme zinc supply (10 times the industry standard), zinc concentrations in inflorescences did not reach phytotoxic levels and the authors conclude there is no additional health risk to consumers from elevated zinc in growing media.
- Zinc supply affects cannabinoid concentrations bidirectionally: both deficiency and excess reduce total cannabinoids relative to the optimal 0.35 mg/L fertigation level.
This paper should NOT be used as an occurrence estimate for zinc in retail cannabis flower, cannabis extracts, tinctures, or oils. The experimental conditions (soilless culture, single cultivar, single geographic location, controlled fertigation) are not representative of the range of real-world cultivation conditions. The inflorescence concentrations reported here reflect a specific controlled dose-response design, not environmental occurrence distributions.
The paper mentions zinc toxicity via cannabis consumption (oral, inhalation) in the discussion section but does not calculate consumer exposures from observed inflorescence concentrations.
Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git.
| Commit | Date | Change | Description |
|---|---|---|---|
| c60295e768 | 2026-11-08 | major | 3 sections added; narrative text revised |