Li et al. 2017 — Total mercury in vegetables, grains, and soils near two Chinese coal-fired power plants
Li and colleagues measured total mercury concentrations in soil and in the edible parts of three leafy vegetables (lettuce, amaranth, water spinach), five fruit vegetables (tomato, eggplant, pepper, cucumber, cowpea), and two grains (rice, maize) collected from six open-field locations within 10 km of two Chinese coal-fired power plants in 2015, compared to control samples from a grocery store >55 km from any power plant. 79% of vegetable samples and 67% of grain samples exceeded China’s GB 2762-2012 maximum levels for Hg (10 µg/kg FW vegetables; 20 µg/kg FW grains). Soil Hg was negatively correlated with distance from the power plants (R² = 0.82, P<0.001).
Key numbers
- Two coal-fired power plants in operation 3 and 4 years at sampling; mercury in coal used in the area averaged 120 µg/kg.
- Soil Hg means at sampling sites (µg/kg ± SD): A1 (1 km from PPA) 305.10 ± 47.97; A2 (3 km from PPA) 157.81 ± 20.52; B1 (1 km from PPB) 383.23 ± 32.59; B2 (3 km from PPB) 294.91 ± 15.67; B3 (5 km from PPB) 179.14 ± 13.53; B4 (10 km from both PPA and PPB) 124.58 ± 6.14. Control farmland soil (>55 km from any power plant) 32.01 ± 1.30 µg/kg. China background soil Hg ~37 µg/kg (Fig. 2).
- Soil Hg vs. distance from power plant: R² = 0.82, P<0.001 (Supplemental Fig. 1).
- Vegetable and grain Hg (µg/kg fresh weight; Table 2) at the six sampling locations and control:
- Lettuce: A1 39.04 ± 4.41; A2 22.70 ± 1.81; B1 21.03 ± 0.16; B2 19.41 ± 1.16; B3 9.17 ± 0.52; B4 7.23 ± 0.57; control 0.35 ± 0.10.
- Amaranth: A1 46.40 ± 2.33; A2 27.76 ± 1.13; B1 29.29 ± 5.06; B2 7.50 ± 0.21; B3 5.52 ± 0.86; B4 3.64 ± 0.37; control 0.28 ± 0.21.
- Water spinach: A1 86.69 ± 2.16; A2 69.02 ± 5.17; B1 54.46 ± 4.55; B2 49.19 ± 0.28; B3 38.97 ± 3.43; B4 23.88 ± 1.28; control 0.85 ± 0.22.
- Tomato (fruit): A1 71.80 ± 11.95; A2 29.80 ± 3.03; B1 76.33 ± 5.47; B2 57.09 ± 8.33; B3 29.07 ± 1.45; B4 9.79 ± 0.43; control 0.73 ± 0.36.
- Eggplant (fruit): A1 42.37 ± 4.24; A2 13.07 ± 1.73; B1 43.36 ± 1.71; B2 25.02 ± 1.80; B3 14.61 ± 2.95; B4 3.25 ± 0.41; control 0.43 ± 0.39.
- Pepper (fruit): A1 49.66 ± 1.40; A2 14.65 ± 1.63; B1 62.09 ± 3.22; B2 30.89 ± 2.19; B3 15.75 ± 1.27; B4 4.69 ± 0.13; control 0.93 ± 0.84.
- Cucumber (fruit): A1 38.45 ± 1.40; A2 9.87 ± 0.11; B1 18.21 ± 1.19; B2 16.94 ± 0.66; B3 10.09 ± 0.40; B4 2.18 ± 0.34; control 0.87 ± 0.24.
- Cowpea: A1 56.31 ± 4.03; A2 11.63 ± 1.36; B1 57.30 ± 9.24; B2 21.75 ± 1.55; B3 18.46 ± 0.61; B4 11.20 ± 0.95; control 0.93 ± 0.13.
- Rice (grain): A1 62.95 ± 3.88; A2 29.24 ± 2.04; B1 59.21 ± 4.36; B2 43.30 ± 2.19; B3 37.15 ± 2.39; B4 24.99 ± 1.99; control 0.55 ± 0.48.
- Maize (grain): A1 21.02 ± 1.98; A2 6.68 ± 1.002; B1 21.18 ± 0.67; B2 4.68 ± 0.707; B3 1.06 ± 0.08; B4 0.55 ± 0.63; control 0.72 ± 0.19.
- 79% of vegetable samples and 67% of grain samples exceeded China’s GB 2762-2012 maximum allowed Hg (10 µg/kg FW vegetables; 20 µg/kg FW grains).
- Highest vegetable concentration (water spinach at A1, 86.69 µg/kg) = 8.67× the 10 µg/kg vegetable limit; highest grain (rice at A1, 62.95 µg/kg) = 3.15× the 20 µg/kg grain limit.
- Tomato organ Hg at location B3 (µg/kg FW): leaves 116.17 ± 14.69; fruit 29.07 ± 1.45; stem 18.35 ± 0.83; root 13.64 ± 1.37.
- Water-rinse effect on leaf Hg (Table 4, µg/kg FW): Lettuce reduced 35.70 → 21.03 (B1); 33.94 → 19.41 (B2); 23.02 → 9.17 (B3); 13.15 → 7.24 (B4). Amaranth reduced 56.06 → 29.29 (B1); 20.5 → 7.50 (B2); 14.91 → 5.52 (B3); 4.47 → 3.64 (B4). Reductions of 19–63% reported.
- 95th-percentile concentrations used for PWI calculation: vegetables 70.83 ng/g FW; rice 62.02 ng/g FW.
- Probable weekly Hg intake (PWI; µg/kg bw/week) assuming all produce from local farmland: vegetables 2.67; grains 1.69; total 4.36 — vs. WHO PTWI 1 µg/kg bw/week.
- Annual vegetable consumption 301.1 g/person/day; grain 217.6 g/person/day; adult body weight 55.9 kg (China).
Methods (brief)
Vegetables, grains, and soil (0–15 cm depth) were collected in 2015 from six open-field locations within 10 km of two coal-fired power plants. Plant samples were rinsed with tap water for 10 min and washed three times with Milli-Q water (except samples specifically tested for fly-ash effect, which were not washed); separated into root, stem, leaf, and seed/fruit; dried at 55 °C; ground; and digested in 10 mL HNO3 in Teflon vessels using a Microwave Sample Preparation System (Milestone ETHOS One) per EPA Method 7473. Soil samples were air-dried, sieved (0.18 mm), and digested in 9 mL HCl + 3 mL HNO3. Mercury was determined by atomic fluorescence spectrophotometry (AFS-230E; HG, Shaanxi, China) after pre-concentration and dilution. Each sampled location was pooled from ~20 individual plants of the same type, with parallel pooled samples measured. Control vegetable and grain samples were purchased from a grocery store >55 km from any power plant. The paper reports total mercury concentrations; speciation (Hg(0), Hg(II), organic Hg) was not performed on these samples. The paper notes that aquatic plants generally contain more methyl mercury than terrestrial plants but does not measure MeHg in this study.
Implications
- Certification (HMTc): Adds tHg occurrence data for ten vegetable and grain species near two Chinese coal-fired power plants on fresh-weight basis. Demonstrates a distance-from-source gradient (R²=0.82) for soil Hg with corresponding plant uptake. The leafy-vegetable Hg accumulation pattern (water spinach > amaranth ≈ lettuce) is informative for sourcing-lever discussions on the Hg-in-vegetables ingredient pages. The rice-vs-maize differential (rice >> maize for Hg in this region) supports the rice discussion of paddy-cultivar mercury accumulation.
- Courses: Suitable case study on point-source atmospheric Hg deposition as a route into food crops; relevant to QA, supply-chain, and regulatory-affairs audiences. The water-rinse effect (19–63% leaf Hg reduction) is teachable for processing-lever discussions.
- App: Contributes tHg occurrence rows on fresh-weight basis to lettuce, tomato, cucumber, green-bell-pepper, rice, maize, and the broader leafy-greens / vegetables categories.
Wiki pages this source may touch
- lettuce
- tomato
- cucumber
- green-bell-pepper
- leafy-greens
- vegetables
- rice
- maize
- legumes
- cereals
- mercury-total
- mercury
Page history
The five most recent substantive edits to this page. 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.