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, transported at 4 degrees C, dried, and sieved. Aqua regia extraction used 1 g dried sediment with 10 mL aqua regia, heated first at 40 degrees C for 1 h and then at 140 degrees C for 4 h. Extracts were vacuum-filtered and diluted to 100 mL.

Sequential extraction used the modified Tessier method: exchangeable ions, carbonates, iron-manganese oxides, sulfides/organics, and residuals. The fifth step used aqua regia rather than perchloric or hydrofluoric acid. Extracted Cu, Zn, and Pb were measured by ICP-OES. 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.

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
• index
• soil-to-plant-transfer

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.

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.