Yongjie Wang1,, Fei Dang2,, R. Douglas Evans1,3, Huan Zhong1,4, Jiating Zhao5

Overview

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Key numbers

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(maximally 73%). In contrast, foliar fertilization with Se enhanced plant Se levels (3–12 folds) without
Table 1. Characteristics of the Low-Se and High-Se soils in this study. Values are given as means ± SD
ambient Se concentrations (0.91 ± 0.10 and 10.55 ± 0.17 mg Se kg–1, respectively, Table 1). The resulting soil Se
tions in the Low-Se soil decreased by 37–87% on day 20, 21–55% on day 80 and 10–44% on day 140 (Fig. 1A).
MeHg levels decreased by 13–46% on day 20 and were less variable on day 125 (Fig. 1B), with Se dose having a
Figure 1. MeHg concentrations (means ± SD, n = 3) in soils under soil amendment with various levels
given as means ± SD (n = 3). Different letters indicate significant differences among treatments within the same
High-Se soil. Data are given as means ± SD (n = 3). ND: not detected. Different letters indicate significant
Se. Concentrations of MeHg decreased by 3–44% in root, 3–44% in straw, 7–73% in brown rice and 8–72% in
case of High-Se soil, soil fertilization of Se resulted in 0.2–55%, 3–38%, or 5–21% decrease of MeHg levels in root,
Methylmercury concentrated in rice grain within plants in Low-Se soil (85–92%, SI Fig. S5A) and MeHg
accounted for 83% and 76% of the total mercury in brown rice and white rice, respectively (SI Fig. S6). Distribution
of MeHg (%MeHg) in root and straw was significantly affected by soil fertilization with Se (SI Fig. S5A).
p ≤ 0.002), but decreased distribution in grain (85–92% in Se-amended treatments compared to 92% in the con-
Table 2. Amended Se species/doses and crop yields (means ± SD, n = 3) following soil or foliar
(e.g., to selenide, elemental Se and/or organic Se5,29,30), considering that Se(IV) represents only 9–16% of total
Figure 6. (A) Changes in MeHg concentrations in soil (Δ MeHgsoil, %) and brown rice (Δ MeHgbrown rice, %) as
included. Data are given as means ± SD (n = 3).
residual Se, with an extremely low proportion as mobile Se (i.e., 2–3% as water-soluble and ligand-exchangeable
(11–71%, SI Fig. S8) ultimately result in reduction in grain MeHg concentrations (Fig. 5B,D). Therefore, the
soil (decrease of 34–38%, p < 0.01) is unlikely to be derived mainly from the accumulated Se within plant but
distribution among the tissues following that of Se; however, the majority of MeHg is found in the grain (85–92%)
not be completely ruled out, as indicated by the significant changes in MeHg distribution (up to ~8%, compared
to averagely 29% decrease in soil MeHg levels) under soil fertilization with Se; the addition of Se resulted in a
range between Se deficiency and toxicity to plants. The highest Se level measured in the straw was 2.3 mg Se kg–1
(6.0Se(VI) in Low-Se soil), which did not reduce crop yield (Table 2) and was within the toxicity threshold for
Low-Se soil only, were conducted (Table 2). In ‘soil fertilization’ experiments, sodium selenite (Se(IV)) or selenate
(Se(VI)) (40 mg Se L–1; Sigma Aldrich) was mixed thoroughly with the soils to reach a range of environmentally
peat soil (Se 0.56 ± 0.06 mg/kg THg; 93.4 ± 10.5 μ g/kg; MeHg 0.10 ± 0.05 μ g/kg), vermiculite and perlite (3:2:1,
0.45 μ m polyethersulfone filter capsules (Anpel, China). Porewater was preserved with 0.4% HCl (v/v) and stored,
(AtmosBag, Sigma Aldrich) filled with high-purity N2 (99.999%) unless otherwise specified.
those used in the pot experiment (i.e., 2.0 mg Hg kg–1 and 3.0 mg Se(IV) or Se(VI) kg–1, Table 2), was flooded with
to 5.5 (Table 1), the tubes were sealed, incubated in the dark at 28 oC and mixed by turning the tubes end-over-end
Se(IV) analysis, subsamples of overlying water were preserved with 0.4% HCl (v/v) and stored at –20 oC whereas
for total Se determination, subsamples were preserved with 2% HNO3 (v/v) and stored at 4 oC. Soil samples were

Methods (brief)

a downward trend in brown rice MeHg levels with increasing soil Se levels in field-collected samples from a
a key first step in determining concentrations and bioaccumulation of MeHg20. Unfortunately, in field-collected
samples from mercury mining areas, the potential negative effect of Se on soil MeHg levels may be masked.
Figure 4. Hg LIII XANES spectra of the soil sample (100 mg Hg kg–1 and 150 mg Se kg–1) and the reference
highly consistent of the XANES spectrum of soil sample with that of HgSe compound.
absorption near edge structure (XANES). The Hg LIII-edge XANES spectrum of the sample was very similar
MeHg contents in digested straw samples were generally lower than 0.1 pg per 0.1 mL (maximum sample volume
in the nanoparticles was also close to 1:1, the Hg LIII-edge XANES spectrum of the sample exhibited the typical
ent Se in soil on grain MeHg levels has been reported recently in field-collected samples16. However in our study,
mercury-mining area (from which the High-Se soil was sampled) is mainly in the form of sulfide-bound Se and
Surface soils (1–11 cm) were sampled on day 20 (initial seedling transplants) and day 125 (harvest) for
soil. All soil samples were vacuum-packed immediately, placed in an ice box and transferred to the laboratory
within 3 h of sampling. Porewater was collected by centrifuging soil subsamples at 2000 × g and filtering through
together with the soil samples, at –20 oC, until MeHg analysis. Sample preparation was conducted in a glove bag
manually from grain (brown rice) and subsamples were milled using a benchtop rice polisher to produce ‘white
rice’, freeze-dried and ground into ≤ 0.15 mm powder. All plant tissue samples were kept at –80 oC until further
time-point). Moreover, conducting these batch experiments precluded the need to intensively sample soil from
meters (HACH, USA), samples were centrifuged (2000 × g) to separate soil and overlying water. For MeHg and

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

Yongjie Wang1,*, Fei Dang2,*, R. Douglas Evans1,3, Huan Zhong1,4, Jiating Zhao5