Son et al. 2021 - Nakdong River weir sediment metals

Son and colleagues measured Cu, Zn, and Pb in river sediments upstream of the Hapcheon-Changnyeong weir on the Nakdong River in South Korea. The study combines aqua regia extraction, Tessier five-step sequential extraction, and sediment-quality comparisons to evaluate whether the weir promotes metal accumulation. This is primary environmental sediment evidence, not food, ingredient, drinking-water, or consumer-product occurrence evidence.

Key numbers

Sampling frame and field conditions

Sediment samples were collected from two locations north of the weir: ND1 at 1 km from the weir and ND2 at 5 km from the weir. Sampling dates were 23 July 2019, 13 August 2019, and 19 September 2019. The top 2 cm of sediment from acrylic cores was dried, sieved to 0.5 mm, and analyzed in duplicate.

The Hapcheon-Changnyeong weir is 328 m long and 11.5 m high. Average retention times for the 28 days before sampling were 2.25 days in July, 2.31 days in August, and 2.75 days in September. Water-column pH ranged from 7.32 to 9.01 and dissolved oxygen stayed above 6 mg/L.

Table 2 field characteristics:

Aqua regia sediment concentrations

The study’s overall aqua regia concentration ranges were:

Concentrations were higher at ND1, closer to the weir, than at ND2. ND2/ND1 concentration ratios were:

The authors interpret the ND1 elevation as evidence that slower flow near the weir promotes sediment and metal accumulation.

Pre-weir comparison values cited in the paper

Table 3 summarizes earlier Nakdong River sediment values before the Hapcheon-Changnyeong weir construction:

The PDF labels the second-row lead entry as Pd; this page treats that as an apparent table typo because the surrounding text and column are Pb.

Sequential extraction and mobility

The Tessier five-step sequential extraction separated exchangeable, carbonate-bound, iron-manganese oxide-bound, sulfide/organic-bound, and residual fractions. Pb fraction results were not presented because some fractions were below detection limits.

For Cu and Zn, total concentrations across sequential fractions were:

Linear regression between aqua regia and sequential totals had slopes of 0.92 for Cu and 1.04 for Zn, with R2 values of 0.95 and 0.96, respectively.

Cu was concentrated mainly in the residual fraction:

Zn was concentrated mainly in the iron-manganese oxide fraction:

The authors caution that iron-manganese oxide-bound Zn may leach back to the water body under anaerobic conditions, especially in stagnant periods.

Risk and sediment-quality comparisons

The risk assessment code (RAC) classified Cu around the weir as medium risk. Zn was medium risk except for the August ND2 sample, which was high risk.

Against Korea NIER sediment criteria, Zn and Pb were grade 1, while Cu ranged from grade 1 to grade 2. Cu reached grade 2 in the July and September ND1 samples. Against Canadian sediment quality guidelines, all Cu concentrations exceeded the Lowest Effect Level, as did Zn in July and September at ND1 and Pb in September at ND1. Under US EPA comparisons, several Cu and Pb samples exceeded non-polluting standards.

Methods (brief)

Sediment cores were collected by an experienced diver using an acrylic core (5 cm diameter, 22 cm height), transported in an icebox at 4 degrees C, dried to constant weight (top 2 cm), and sieved through a 0.5 mm sieve (Section 2.2). In situ water-column pH and dissolved oxygen were measured with a multiparameter probe (YSI Professional Plus, USA). Total organic carbon of freeze-dried sediment was measured by elemental analyzer (EA 1110, FV Instruments, UK) after carbonate removal with 1.0 N HCl. Particle size was measured by laser diffraction (Mastersizer 2000, Malvern, UK) after organic and carbonate removal with 10% H2O2 and 0.1 N HCl (Section 2.3).

Aqua regia extraction (Section 2.4) used 1 g dried sediment with 10 mL aqua regia (HCl:HNO3, 3:1), heated first at 40 degrees C for 1 h and then at 140 degrees C for 4 h. Each sample was duplicated. Extracts were vacuum-filtered and diluted to 100 mL.

Sequential extraction used the modified Tessier method (Section 2.5): exchangeable ions in 1 M MgCl2 adjusted to pH 7 with CH3COOH for 1 h at room temperature; carbonates in 1 M CH3COONa adjusted to pH 5 with CH3COOH for 5 h at room temperature; iron-manganese oxides in 0.04 M NH2OH.HCl in 25% CH3COOH at 95 degrees C; sulfides and organics in 0.02 M HNO3 + 30% H2O2 at 85 degrees C followed by 3.2 M CH3COONH4 in 20% HNO3 at room temperature; residuals in 10 mL aqua regia at 40 degrees C for 1 h then 140 degrees C for 4 h. The fifth step used aqua regia rather than perchloric or hydrofluoric acid to enable direct comparison with the aqua regia totals. Effluents were filtered through Whatman 40 paper, diluted to 100 mL, and analyzed by the same ICP-OES instrument as the aqua regia totals.

Extracted Cu, Zn, and Pb were measured by inductively coupled plasma optical emission spectrometry (ICP-OES; ICP-5800, Agilent, USA) at the National Instrumentation Center for Environmental Management (NICEM), Seoul National University. Calibration used reference solution from Inorganic Ventures. Detection limits were 0.001 mg/L for Cu, 0.001 mg/L for Zn, and 0.003 mg/L for Pb; calibration R2 values were 0.999 for all three metals. The metals reported are total Cu, total Zn, and total Pb; no isotopic or oxidation-state speciation was performed.

The Risk Assessment Code (RAC, Section 2.6) was calculated as the ratio of (exchangeable + carbonate fractions) to total metal, expressed as percent; the five-class scheme defines no risk (RAC ⇐ 1), light risk (1 < RAC ⇐ 10), medium risk (10 < RAC ⇐ 30), high risk (30 < RAC ⇐ 50), and very high risk (RAC > 50).

Implications

Certification: Do not use this source in HMTc product or ingredient occurrence pools. It measures river sediment metals, not edible fish, foods, drinking water, or products.

App: Useful as environmental-pathway context for how weirs, retention time, sediment grain size, and organic carbon can influence metal accumulation and remobilization in river systems used for water resources.

Courses: Useful for teaching why total sediment concentration, sequential extraction fraction, RAC class, and aquatic-life sediment guideline status are different evidence types.

Wiki pages this source may touch

• Copper
• Lead
• Zinc
• Testing

Verification notes

This page was built from the full PDF, including the abstract, study-area description, sampling method, aqua regia extraction method, sequential extraction method, RAC definition, Tables 1-3, Figures 1-8, Results sections 3.1-3.5, Conclusions, and data-availability statement. Products and ingredients are intentionally empty because no food, crop, ingredient, product, fish, or drinking-water sample was analyzed. Lead fraction results are not transcribed because the paper states that Pb was below detection limits in some sequential-extraction fractions and therefore does not present those fraction results.

2026-06-03 merge-enhance pass: added access_url and raw_sha256 to frontmatter; expanded ## Methods (brief) with field instrument details (acrylic-core dimensions, YSI Professional Plus multiparameter probe, EA 1110 FV Instruments elemental analyzer for TOC, Mastersizer 2000 Malvern laser-diffraction particle sizer), the explicit Tessier-step reagent matrix, the Whatman 40 filtration step, ICP-OES instrument model and analytical lab (ICP-5800 Agilent at NICEM, Seoul National University), Inorganic Ventures calibration source, and an explicit note that the metals reported are total Cu/Zn/Pb with no isotopic or oxidation-state speciation. Vendor and instrument names are retained per the Part 12 brand-firewall Exception 2 (scientific-method vendor/material names, locked 2026-05-17). The RAC classification scheme thresholds were also moved from Section 2 into the Methods section so the RAC narrative in Key numbers is self-contained.

2026-06-03 audit application (subagent verdict REVISE, 2 findings applied, 0 rejected):

• Check 3 ⚠️ Tessier step-2 reagent. Audit subagent flagged that Methods (brief) said “carbonates in 1 M CH3COOH at pH 5 for 5 h”; the actual reagent is sodium acetate (CH3COONa). Verified independently by reading PDF p.4: the body text contains an apparent typo (“1 M CH3COOH adjusted to pH 5 with CH3COOH”, which is chemically impossible — pure 1 M acetic acid cannot be pH-adjusted to 5 with itself), but Figure 2 (the Tessier flow chart on p.4) unambiguously labels step 2 as “pH5 1M CH3COONa 8ml at room temperature.” Corrected step 2 to “1 M CH3COONa adjusted to pH 5 with CH3COOH for 5 h at room temperature.” While applying, also added the missing “adjusted to pH 7 with CH3COOH” detail to step 1 (paper p.4) and the missing “3.2 M” concentration prefix to CH3COONH4 in step 4 (paper p.4).

• Check 2 ⚠️ [[supply-chain/soil-to-plant-transfer]] overreach. Audit subagent flagged that this routing link overreaches the source’s scope because the paper measures river sediment only, not plant uptake, agricultural soils, or crop transfer. Verified by re-reading the abstract, introduction, methods, results, and conclusions: no plant, soil, crop, or transfer-coefficient measurement appears. Removed [[supply-chain/soil-to-plant-transfer]] from ## Wiki pages this source may touch. The remaining four entries (metals/copper, metals/lead, metals/zinc, testing/index) accurately reflect the paper’s metals scope and analytical-method relevance.

Findings retained as informational (not applied):

• Check 2 minor note that the matrices: array uses non-food descriptive slugs (river-sediment, weir-impounded-river, surface-water-quality, sequential-extraction, aqua-regia-extraction) outside the food-matrix controlled vocabulary. This is the same posture established for non-food environmental and remediation sources (e.g., Synthesis of Magnesium Modified Biochar for Removing Copper, Lead and Cadmium in Single and Binary Systems from Aqueous Solutions: Adsorption Mechanism, Biochars from Lignin-rich Residue of Furfural Manufacturing Process for Heavy Metal Ions Remediation); the routing-audit advisory row in routing_malformed.csv already records the empty products/ingredients arrays, which is the correct surfacing channel for this scope.

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.