This paper evaluates hemp flakes, the dry solid residue remaining after CBD oil extraction from industrial hemp buds and seeds, as a potential food ingredient. It measures lead, arsenic, cadmium, cobalt, aluminum, and copper by ICP-OES and concludes that metal levels in both the by-product and three commercial hemp protein powder comparators are within FDA and EPA reference levels. The matrix is a dry solid hemp ingredient, not a finished liquid tincture or oil.
Key numbers
All values are on a dry-weight basis (mg/kg DW). Heavy metal results are presented in Fig. 3 (bar chart), which limits precise extraction of numerical values from text alone. Approximate values and direction from text are noted; exact values are from the figure.
Lead (Pb): Not detected in any of the four samples (hemp flakes H, and commercial products A, B, C).
Total arsenic (tAs): Not detected in any of the four samples.
Cadmium (Cd): “Insignificant amounts” recorded in all samples; exact values are below the detection threshold relevant to the FDA comparisons cited by the authors.
Cobalt (Co): “Insignificant amounts” recorded in all samples.
Aluminum (Al): Detected in all four samples. Order: A > H > C > B (p less than or equal to 0.05). The highest concentration was 0.71 mg/kg DW in commercial product A. Hemp flakes (H) were below A. Exact values for H, B, and C are readable only from Fig. 3.
Copper (Cu): Detected in all four samples. Order: A > C > H > B (p less than or equal to 0.05). Copper is classified by the authors as a trace element rather than a classic heavy metal, but its accumulation in hemp-derived materials warrants monitoring.
The paper states: “all the levels of heavy metals found in all samples were within the permissible levels according to the [EPA] and [FDA].” The specific regulatory benchmarks cited are EPA 10 ppm arsenic in drinking water and FDA food guidance; no formal US maximum level for lead, cadmium, or aluminum in hemp food ingredients is cited.
Methods (brief)
ICP-OES (PerkinElmer Optima 2100 DV); samples prepared by ashing followed by dissolution in 5% hydrochloric acid, heating to dryness, then dissolution in concentrated hydrochloric acid; filtered and diluted to 100 mL. Calibration standard: IV-STOCK-4 (1000 ppm 23-element ICP standard, Inorganic Ventures). Equipment recalibrated after every sample. Duplicate measurements for all metals. No certified reference material (CRM) recovery is reported and no LOD/LOQ values are stated in the paper.
Evidence fitness
The primary value of this paper for the cannabis-tinctures-oils row is as hemp-ingredient context: it shows that the dry solid by-product remaining after CBD oil extraction from hemp contained no detectable lead or arsenic, and only trace aluminum as the most prominent metal detected. This is not equivalent to measuring heavy metals in finished liquid tinctures or sublingual oils. Metal concentrations in a finished liquid tincture depend on extraction efficiency, solvent type, concentration steps, and dilution with carrier oil, none of which are addressed here.
The paper does not report LOD or LOQ values, which limits interpretation of non-detect findings. The absence of a CRM recovery check is a methodological gap that weakens confidence in the absolute accuracy of the aluminum and copper values. The sample size (n = 4 total, one hemp flake sample and three commercial hemp protein products) is very small. Commercial product identities are not disclosed. The geographic provenance of the commercial products (US, Canada, Italy) introduces soil and cultivation variability that is not characterized.
The paper is relevant as context for the material that feeds CBD oil production, particularly to establish that lead and total arsenic were below detection in one locally sourced hemp flake sample under the conditions tested.
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 |