Mercury accumulation in vegetable Houttuynia cordata Thunb. from two different geological areas in southwest China and implications for human consumption

Overview

Wang et al. measured total mercury and methylmercury in edible Houttuynia cordata tissues from a mercury-mining area and a non-mining comparison area in Guizhou, China. The source is direct occurrence evidence for a consumed leafy/herbal vegetable, not for cereal bars despite the wishlist filename.

Key numbers

All concentration values below are dry-weight (DW) unless noted.

Composite underground vs aboveground tissue, Table 1:

Per-tissue breakdown, Danzhai mining area, Table 3:

Per-tissue breakdown, Zhijin comparison area, Table 3:

Roots carry the highest mercury burden: in the Danzhai mining area, root THg ranged up to 1295 ug/kg DW (mean 523 ug/kg DW) and root MeHg ranged up to 6.3 ug/kg DW. Bioaccumulation factors for roots reached 2.88 (THg) and 2.91 (MeHg) at maximum.

On a fresh-weight basis (Table 1, FW columns), every Danzhai sample exceeded the Chinese national vegetable guidance value of 10 ug/kg FW for total mercury: underground parts ranged 15-56 ug/kg FW (mean 26 +/- 13) and aboveground parts ranged 21-83 ug/kg FW (mean 38 +/- 18). In the Zhijin comparison area only a minority of samples exceeded the same limit.

Note on a source internal inconsistency: the paper’s narrative paragraph on page 5 states the DZ maxima as “272 ug/kg THg and 3.49 ug/kg MeHg in the aboveground parts, and 541 ug/kg THg and 1.39 ug/kg MeHg in the underground parts,” which is reversed from the paper’s own Table 1 (where DZ aboveground max = 541 THg / 1.39 MeHg and DZ underground max = 272 THg / 3.49 MeHg). The values reproduced above follow Table 1 and Table 3, which are the authoritative tabulations.

Methods (brief)

Plant tissues were separated into root, rhizome, aboveground stem, and leaf, dried at 50 C for approximately 5 days, ground, and passed through a 0.150-mm sieve. Total mercury was measured by direct mercury analysis (Milestone DMA-80 with AMA-254 software) following US EPA Method 7473, with thermal decomposition, gold amalgamation, and atomic absorption detection at 253.7 nm. Methylmercury was measured by gas chromatography coupled with cold-vapor atomic fluorescence spectrometry (Thermo Fisher TRACE 1300E GC and Tekran Model 2500 CVAFS) after potassium hydroxide and methanol/solvent extraction, ethylation, and purge-and-trap collection. Limits of detection were 0.01 ug/kg for THg and 0.002 ug/kg for MeHg, and the relative standard deviation of duplicate analyses was under 8 percent. Certified reference materials included GBW10020 (orange foliage) and TORT-2 (lobster hepatopancreas) for tissue THg and MeHg respectively, and GBW07405 and ERMCC580 for soil THg and MeHg. Recoveries for the tissue reference materials were 104.7 percent for THg and 101.6 percent for MeHg.

Implications

This source supports mercury occurrence context for leafy/herbal vegetables grown near mercury mining areas. It should remain geography- and contamination-source specific and should not be used as a general-market vegetable baseline. It also illustrates that edible tissue choice changes total mercury and methylmercury exposure.

Related evidence

• Leafy / Green Vegetables, Other
• Non-Root Vegetables
• Leafy Vegetables
• Vegetables
• Mercury
• Mercury, Total
• Methylmercury

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