Extremely Elevated Total Mercury and Methylmercury in Forage

Overview

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families. The THg and MeHg concentrations in the forage plants varied widely and were in the range of 0.10 to 13 mg/kg and 0.19 to
23 μg/kg, respectively. Shoots of Aster ageratoides showed the highest average THg concentration of 12±1.1 mg/kg, while those of
Aster subulatus had the highest average MeHg concentrations of 7.4±6.1 μg/kg. Both the THg and MeHg concentrations in the
dietary exposure of 4 ng/g into account, grazing on 1.0 kg of forage (dry weight) by a 65 kg animal would mean that the daily intake
generated significant quantities of wastelands. THg concentrations as high as 4,400 mg/kg have been found in mine-waste calcines
of the Wanshan Hg mine, as high as 790 mg/kg Hg in soils from paddies, and 10,000 ng/L Hg in surface water (Horvat et al., 2003;
of magnitude higher than the ‘probable effect concentration’ of 1.06 mg/kg Hg, above which harmful effects on organisms are likely
µg/kg MeHg has been reported in calcines (Gray et al., 2006;). Owing to the extremely high Hg, particularly MeHg, mine-waste
(Chenopodium glaucum) and ferns (Pteris vittata L.) from the Wanshan Hg mining region reached 100 mg/kg (Wang et al., 2011;
Qian, 2020), which is 3–4 orders of magnitude higher than the limit of 0.05 mg/kg in edible plants set by the Ministry of Health of
elevation of 850 m. The annual average temperature is 13.4°C, and the mean annual precipitation is 1,400 mm/year. Cinnabar is the
methanol solution with 25% KOH was added. The samples were digested for 3 h in a water bath at 75°C, and then, 1.5 mL of
2 M acetate buffer, ethylation with 1% sodium tetraethylborate. The methylethylmercury was purged onto Tenax traps, from which it
red soil (GBW07405), and estuarine sediment (ERM-CC580), as further described below and in the Supplementary Material (Table S2).
0.475 ± 0.02 mg/kg (n = 5) was obtained for the lichen standard BCR-482, which was within the range of the certified value of 0.48 ±
0.02 mg/kg. For the soil, GBW07405 was used, and the measured concentration of 0.32 ± 0.02 mg/kg (n = 5) was within acceptable
range of the certified value of 0.29 ± 0.04 mg/kg.
For MeHg, the obtained value of 75.0 ± 3.1 µg/kg (n = 5) met the certified value of 75.5 ± 3.7 µg/kg for the ERMCC-580 soil standard.
In addition, the obtained value of 155 ± 25 µg/kg (n = 5) met the certified value of 152 ± 13 µg/kg for the TORT-2 plant standard. The
recovery of THg and MeHg in the solid samples was in the range of 95–109%, and 87–108%, respectively.
biomass, and the Asteraceae family accounted for 50.0% of them. Plants such as C. canadensis are amphibious plants, which have
69.2% of the total.
in disturbed environments and with a high Hg tolerance. The herbaceous Asteraceae species accounted for 40% of the total
THg exhibited a wide range of concentrations in the roots and shoots of the 22 species, ranging from 0.10 to 4.4 mg/kg and 0.19 to
13 mg/kg, respectively (Table 1; Fig. 2a). Compared with the average THg values among the different species, the shoots of A.
ageratoides showed the highest THg level, reaching 12 ± 1.1 mg/kg, followed by P. sikkimensis with 6.7 ± 1.2 mg/kg, while the lowest
THg level was in A. subulatus with 0.39 ± 0.055 mg/kg. The A. ageratoides roots also showed the highest THg level of 3.8 ± 0.69
mg/kg, on average, while the lowest THg level of 0.13 ± 0.052 mg/kg was in B. campestris. One-Way ANOVA tests showed no
significant differences in soil THg were observed between CJ and MZX (P = 0.0007), and between LFD and MZX (P = 0.0108) (Table 3;
The plants in the present study exhibited a comparable level of THg (9.9 mg/kg on average) to that recently reported from artisanal
Forage-plants showed broad ranges of MeHg concentrations in the roots and shoots, ranging from 0.19 to 23 µg/kg and 0.28 to 11
µg/kg, respectively (Table 2; Fig. 2b). The highest average MeHg concentration was found in the shoots of A. subulatus at 7.4 ± 6.1
µg/kg, followed by S. brachyotus with 3.5 ± 2.5 µg/kg, while the lowest was in B. camperstris with 0.49 ± 0.11 µg/kg. S. brachyotus
exhibited the highest average MeHg concentration in its roots with 13 ± 10 µg/kg, followed by A. subulatus at 9.4 ± 8.0 µg/kg, while
the lowest was in A. ageratoides at 1.1 ± 0.76 µg/kg. As expected, the root MeHg exhibited a significant positive correlation to the
levels of MeHg concentration (greater than 10 µg/kg on average) in both the shoots and roots, species S. brachyotus, C. edulis, and P.
oleracea also showed high MeHg concentrations, particularly in their roots, with a range of 6.3–19 µg/kg on average. Those values
THg (mg/kg) Minimum 14 0.56 0.61 24 0.19 0.19 16 0.1 0.24
MeHg(μg/kg) Minimum 0.74 0.56 0.61 1.2 0.94 0.81 0.75 0.19 0.28
Plants exhibited a wide range of BCFs for IHg and MeHg, ranging from 0.0023 to 0.16 and from 0.022 to 17, respectively. The BCFs
brachyotus with 3.8 ± 1.8, while the lowest value of 0.13 ± 0.049 was in I. batatas (Tables 1 & 2; Fig. 4). The extent of
value observed in I. batatas (Tables 1 & 2; Fig. 4). Five species, A. ageratoides, C. barometz, C. canadensis, I. batatas, and M.

Methods (brief)

Ninety-five wild forage plants (belonging to 22 species of 18 families) and their corresponding rhizosphere soil samples were
collected from wastelands of a world large-scale abandoned Hg mining region for total Hg (THg) and methylmercury (MeHg)
Ninety-five samples of dominant forage plants belonging to 22 species of 18 families, which are favored by grazing animals, were
collected from the wastelands. We preferentially sampled herbaceous plants rather than woody species. All of the plants were
During sampling, dominant forage samples were randomly taken from the wastelands, within a sampling grid of 5×5 m. For each
sample, three or more similarly sized individual plants of the same species were collected to ensure adequate amounts of tissue for
analysis. Plant samples were dug out of the ground with a shovel and separated in situ into aboveground parts (shoots) and roots. In
lab equipment was rinsed three times with ethanol cleansing to control cross-contamination among the samples. The fine powder
samples were stored in hermetic bags for analysis.
Corresponding rhizosphere soils were simultaneously collected with the plants. Approximately 0.5 kg of rhizosphere soil from the
roots of each individual plant was shaken onto a piece of paper, and then the total 1.5 kg of soil collected from the 3 individual plant
roots mentioned above was mixed as the final composite sample. The soils were stored in double polyethylene plastic bags to
prevent any cross-contamination. After collection, all of the soil samples were air-dried in the laboratory, thoroughly mixed, and
the plant samples preparation was applied to control cross-contamination among the samples. The fine powder samples were stored
For THg determination, approximately 0.1–0.2 g (accurate to 0.0001) samples were weighed into plastic tubes and digested with 5
they were digested for another 30 min. Finally, the digestion solution was brought to a fixed volume of 50 mL with DW. After leaving
the digestion for 24 h, 400 µL NH2OH·HCl was added, and 5.0 mL of the liquid supernatant was transferred to a bubble bottle. Then,
400 µL SnCl2 was added for Hg determination by atomic absorption spectroscopy (AAS, F732-V, Shanghai Huaguang, China) (Qiu et

Implications

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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
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised