Heavy metals levels in medicinal plants have attracted worldwide interest in recent years because these ele-

Overview

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tidis rhizoma) is commonly used to treat diarrhea, fever, and eczema1. To date, more than 30 alkaloid compounds
have been isolated from the rhizome of C. chinensis Franch2–4, including berberine, coptisine, and palmatine; all
mor activities-related attributes1,5. Because the rhizomes of C. chinensis Franch. contain high alkaloids levels, this
leading to a large number health problems6. Chromium (Cr)-induced plants and thus food safety has recently
gained substantial attention worldwide7–9. Cr uptake by vegetables and the accumulation of Cr in the edible parts
of plants can lead to numerous consumer health risks7,10. In humans, excessive Cr can induce clinical disorders
genotoxic and mutagenic health issues7. Cr is one of the most common heavy metals in soils, water, air, sediments,
animals, and plants11. Cr is generated by a number of natural and anthropogenic activities7,12, and significant
electroplating, and textile dyes as well as the production of paints and paper7,13,14. Cr is also released into the envi-
ronment from geological15 and other natural sources, such as dust from rocks and volcanic activity7.
College of Life Science, Northwest A&F University, Yangling, China. 2Institute of Soil and Water Conservation,
Chinese Academy of Sciences, Yangling, China. 3State Key Laboratory of Continental Dynamics, Department of
Geology, Northwest University, Xi’an, China. 4College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou,
Although Cr occurs in several oxidation states that range between −2 and +6, its trivalent (Cr(III)) and hex-
avalent chromate (Cr(VI)) forms are the most common and stable in natural12. Of these, Cr(III) is necessary for
lipid and sugar metabolism and is an essential trace element for human and animal health7,16. Cr, however, does
not have any known biological role in plant physiological and biochemical metabolism17. Compared with Cr(III),
Cr(VI) is more soluble and more toxic18. Cr phytotoxicity results in reduced growth and biomass production,
activities and triggering mutagenesis17,19–21. However, although plants can uptake both Cr(III) and Cr(VI), the
Cr uptake mechanism of plants remains unclear7. As it is not an element that is essential for plants, Cr is mostly
absorbed by specific carriers for essential ions in plant metabolism7,11, while Cr(III) uptake is a passive mech-
anism and does not require the input of any energy11. In contrast, Cr(VI) uptake is active21, generally utilizing
either phosphate or sulfate transporters because of their structural resemblance to one another22,23. Furthermore,
their ionic resemblance7,24.
To date, neither Chinese Pharmacopoeia (2015) nor Green Trade Standards of Importing & Exporting Medicinal
tration of this element in plants generally ranges between 0.05 mg kg−1 and 1 mg kg−1 25. However, we found that
the Cr levels between 2.48 mg kg−1 and 7.90 mg kg−1 in coptidis rhizoma (the rhizome) collected from three loca-
tions within Zhenping County in the city of Ankang, Shaanxi Province, China (Supplementary Table S1). These
Cr levels are much higher than is generally the case in plants. Similarly, there have been other previous reports26,27
in order to understand their accumulation and transportation mechanisms28,29 as these are regulated by various
and sequestration of metals in cell walls or vacuoles, xylem loading, and translocation from roots to shoots30.
plant by carrier ions19. Cr is principally transported through the xylem; and the reduction of Cr(VI) to Cr(III) can
occur in the root, within the rhizosphere31 or in the aerial parts of plants21,32. Several studies have explored the
(Trifolium brachycalycium)18, Lycopersicum esculentum Mill33, Gynura pseudochina (L.) DC34, Callitriche copho-
carpa Sendtn35, and Typha angustifolia36. However, the accumulation of this metal in medicinal plants, including
als in plants29. At the same time, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is
ples37; this second approach also has a lower detection limit (0.01 μg g−1) than XRF (0.1–1 μg g−1)38. In addition,
in vivo ligand environments of metals within plants39. We utilized these analytical approaches to generate basic
scanned cross-sections of root and rhizome are shown in Fig. 1 alongside sample micrographs. Our μ-XRF maps
of root cross-sections for the Cr10d group are presented in Fig. 1A; these results show that Cr is mainly localized
mapping of Cr10d group rhizome cross-sections reveal that the Cr distribution pattern of this region differed
(Fig. 1B); the main area of Cr accumulation in this case was the external layer (the periderm and some outer cor-

Methods (brief)

Laser Ablation ICP-MS
laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to spatially locate Cr, X-ray
mass spectrometry (ICP-MS) to detect Cr subcellular concentration. Micromapping results showed that
plant contain elemental chromium. ICP-MS data showed that Cr was primarily compartmentalized in
the Cr levels between 2.48 mg kg−1 and 7.90 mg kg−1 in coptidis rhizoma (the rhizome) collected from three loca-
als in plants29. At the same time, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is
in C. chinensis Franch. Specifically, we used SR-μXRF mapping and LA-ICP-MS imaging to spatially locate Cr in
tively coupled plasma mass spectrometry (ICP-MS) of different tissues to study the Cr subcellular distribution of
scanned cross-sections of root and rhizome are shown in Fig. 1 alongside sample micrographs. Our μ-XRF maps
in the central part of the root in these samples, a region that corresponds to the vascular cylinder. Similarly, maps
Spatial imaging of Cr and other elements in petioles using LA-ICP-MS. Because the leaves of
C. chinensis Franch. have low Cr concentrations (Supplementary Table S2), we utilized LA-ICP-MS for spatial
LA-ICP-MS (μg g−1) 0.98 ± 0.03 15,448 ± 22 1,355 ± 60 95.5 ± 0.4 3.7 ± 0.2
Table 1. Comparison of analyte concentrations in NIST SRM 1547 Peach Leaves measured using LA-ICP-MS
of roots and rhizomes, the left image is the scanned sample cross-sections (300-μm thick) of roots and rhizomes,
interest using LA-ICP-MS were also in agreement with certified values (Table 1).
by scanning cross-sections line-by-line using a focused laser beam and analyzing them with mass spectrometry.
P, Mn, and Cu) using LA-ICP-MS imaging (Fig. 2).

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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. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
3171d06	2026-08-02	major	1 section added
bc84bfc	2026-08-02	major	6 sections added; narrative text revised