Enamorado-Montes et al. 2021 - Total mercury accumulation in rice grown in La Mojana-region soil, Colombia

This controlled greenhouse study evaluated total mercury (tHg) accumulation in roots, husks, and grains of three commercial Oryza sativa L. cultivar codes (FA473, FA2000, FAM) cultivated in soil from La Mojana, Colombia. The control soil already contained 130 ug/kg Hg; the authors also spiked soil to 800 and 1500 ug/kg Hg. Across all cultivar/treatment combinations, Hg partitioned strongly into roots (overall mean 739.04 ug/kg tHg), with lower concentrations in husks (74.18 ug/kg) and grains (17.02 ug/kg), and translocation factors from root to grain were below 0.13 in all cases. The highest reported grain concentration, 26.15 +/- 3.23 ug/kg in FA473 at 1500 ug/kg soil Hg, exceeded the source-cited EU 10 ug/kg and China 20 ug/kg rice comparators, while all hazard quotients remained below 1.

Key numbers

Grain tHg by cultivar code and soil treatment (ug/kg dry weight):

Root tHg: Overall mean 739.04 ug/kg; highest value 1950.70 ± 347.15 ug/kg (FA2000, 1500 ug/kg soil treatment).

Husk tHg: Overall mean 74.18 ug/kg; FA2000 at the intermediate soil level reached 105.32 ± 3.51 ug/kg.

Grain tHg overall mean: 17.02 ug/kg across all treatments and cultivar codes.

Translocation factor (root→grain): <1 in all cases; highest was FA2000 at ambient soil Hg, 0.129.

Regulatory reference points: EU Commission Regulation (EU) 2018/73 sets an MRL for mercury compounds expressed as mercury of 0.01 mg/kg in cereals, including rice, equivalent to 10 ug/kg (eu-reg-2018-73-mercury-compounds-mrls). China GB 2762-2017 sets 20 ug/kg for total mercury in rice. The ambient-soil control concentration (130 ug/kg Hg) is below the agricultural-soil maximum-allowable-concentration ranges cited by the authors (500-5000 ug/kg Hg) but above the crustal/world-soil average of approximately 70 ug/kg Hg.

Health risk: Hazard quotients (HQ) were calculated using a La Mojana-specific weekly rice intake of 1218 g/week, 70 kg body weight, and the JECFA PTWI of 4 ug Hg/kg body weight/week. HQ ranged up to 0.350 (FA473, 1500 ug/kg soil Hg), below the HQ = 1 threshold.

Biomass: Highest dry biomass at 1500 ug/kg soil Hg was FA473 (308.76 ± 108.26 g); lowest was FAM (140.02 ± 2.36 g). Weight per 1000 grains ranged 17.64-20.62 g, with an overall mean of 19.16 g; it was significantly lower at 800 ug/kg soil Hg for all three cultivar codes.

Methods (brief)

Greenhouse pot experiment at the University of Cordoba, Colombia (October 2014-February 2015). The design was a 3 x 3 factorial experiment: three commercial rice cultivar codes x three soil Hg levels, three replicates, and 27 experimental units total. Surface soil (0-30 cm) from a La Mojana rice-growing site was homogenized, sieved (4 mm), and spiked to target concentrations using Hg(NO3)2 solution; soils were stabilized for 15 days before planting. Water management was aerobic rather than flooded.

Hg in roots, husks, and grains was analyzed by Direct Mercury Analyzer (DMA-80 TRICELL, Milestone) via thermal decomposition and amalgamation per EPA method 7473. The method was validated with certified tomato leaves CRM 1753a (34 ug/kg), with 97%-102% recovery, 5.35% RSD, a 0.01 ng total-Hg per sample LOD, and calibration-curve R2 values above 0.9995. Two-way ANOVA with Tukey contrasts was conducted in SAS Plus 4.1.

Speciation and methods caveats

• The study measures total mercury only. It does not distinguish methylmercury from inorganic mercury in rice grain, husk, or root.
• This is a controlled greenhouse pot study under aerobic water management. Aerobic conditions can reduce methylmercury formation relative to flooded paddy conditions, so the results should not be generalized directly to flooded-field rice without additional evidence.
• The 800 and 1500 ug/kg soil treatments are experimental spike levels; the 130 ug/kg control soil represents the native La Mojana-region soil concentration used by the authors.
• The three cultivar codes are Colombian commercial cultivars, so the cultivar-specific findings do not directly generalize to all rice varieties or rice markets.

Implications

Standards work: This paper contributes mechanistic source-route evidence for total mercury transfer from mining-impacted soil into rice grain. It is best used as experimental context for rice-bulk-grain sourcing from mining-adjacent regions, not as a broad market-occurrence distribution.

Courses: The study illustrates the root-as-barrier mechanism limiting tHg translocation to grain, the role of cultivar differences in contaminated-soil regions, and the importance of water management regime when interpreting mercury speciation and bioaccumulation in rice.

App: Display this source as experimental, dry-weight, total-mercury evidence for rice grown in La Mojana-region soil. It should be labeled as a greenhouse/spiked-soil study rather than a retail-market survey.

Microbiome: Not directly addressed in this paper.

Wiki pages this source may touch

• rice
• rice-bulk-grain
• mercury-total
• eu-reg-2018-73-mercury-compounds-mrls
• china-gb-2762-2017-contaminants-superseded

Verification notes

• Merge-enhanced 2026-05-18 from the full manual-fetch PDF path and SHA-256 recorded in frontmatter.
• Replaced product-empty and non-vocabulary matrix routing with products/rice-bulk-grain and broad matrices rice and soil.
• Replaced certification-threshold language with source-only implications.
• Created eu-reg-2018-73-mercury-compounds-mrls because the source uses EU Regulation 2018/73 as the 10 ug/kg rice comparator.
• Strict brand-firewall check: sampled commercial cultivar names are reduced to source codes (FA473, FA2000, FAM); instrument/software/vendor names are retained only as Methods details under the Part 12 scientific-method exception.

Page history

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