Overview
Normatov and colleagues monitored heavy-metal migration and sedimentation along the Syrdarya River in Tajikistan, with attention to the Kayrakkum Reservoir and irrigation-water relevance. This is upstream water-pathway evidence: it measures metals in river water and models mobility/sedimentation, not bottled or mineral-water products.
Key numbers
The study sampled five points along the Syrdarya River: 1 Akjar, 2 Bulok, 3 Kanibadam, 4 Kairakkum HPP, and 5 Kizilkishlak. The abstract states that water samples were analyzed for arsenic (As), cadmium (Cd), Cu, nickel (Ni), lead (Pb), and Zn, and later states that distribution results for Cd, Zn, As, Pb, Cu, and chromium (Cr) are presented.
Table 3 reports pH and expected metal forms by river segment. Akjar-Bulok was 23 km with pH 7.50 and listed Ni(OH)2 and As(OH)3. Bulok-Kanibadam was 43 km with pH 7.31 and listed Ni(OH)2 and Cd(OH)2. Kanibadam-Kairakkum HPP was 42 km with pH 7.57 and listed [Pb(OH)]+, [Cu(OH)3]-, Zn(OH)2, and As(OH)3. Kairakkum HPP-Kizilkishlak was 20 km with pH 7.60 and listed [Pb(OH)]+, [Cu(OH)3]-, and Ni(OH)2.
Figure 3 labels heavy-metal values as Ci - C average-on River, mg/l; these are deviations from the river-course average, not absolute concentrations. The figure labels Cd deviations at points 1-5 as 0.0038, 0.0058, -0.0092, -0.0032, and 0.0028 mg/l. Zn deviations are -0.007, -0.002, 0.004, -0.003, and 0.008 mg/l. As deviations are -0.004, -0.009, 0.02, -0.006, and -0.001 mg/l. Cr deviations are 0.0032, -0.0028, -0.0028, 0.0012, and -0.0038 mg/l.
Figure 3 also labels Pb and Cu deviations in a combined panel. Clearly legible Pb values are 0.0062 mg/l at point 1, -0.0048 mg/l at point 2, 0.0042 mg/l at point 3, and 0.0022 mg/l at point 4; the point-5 Pb label is cut off or not cleanly legible in the extracted figure image. Clearly legible Cu values are -0.0026 mg/l at point 1, 0.0034 mg/l at point 3, 0.0014 mg/l at point 4, and -0.0016 mg/l at point 5; the point-2 Cu label is not cleanly legible enough to transcribe.
Table 4 reports non-heavy-metal water chemistry for the same five sampling points: Ca2+ 68.24, 76.21, 72.14, 56.43, and 52.32 mg/l; Mg2+ 33.61, 38.42, 38.23, 26.44, and 28.79 mg/l; Cl- 39.68, 22.62, 34.98, 19.83, and 19.71 mg/l; SO4 341, 385, 387, 372, and 268 mg/l; NO3- 4.38, 3.13, 3.14, 0.43, and 0.98 mg/l; HCO3- 164.68, 207.39, 176.88, 134.23, and 137.89 mg/l; and dissolved O2 5.38, 4.06, 6.58, 6.27, and 6.57 mg/l.
The authors conclude that mobile heavy-metal complexes form mainly in acidic media, while increasing pH favors precipitation of heavy metals. They also state that Central Asian river waters are widely used for irrigation of agricultural lands, making planned and regular hydrochemical monitoring important.
Methods (brief)
Water sampling was carried out at five points along the Syrdarya River bed beginning at the Kyrgyzstan-Tajikistan border section. The authors measured heavy metals using an AAnalyst 800 atomic absorption spectrometer and discuss metal forms as a function of pH, complexation, adsorption, and sedimentation. The paper does not report As speciation, Cr(VI), or methylmercury; arsenic and chromium are treated here as total elemental As and total Cr.
Related evidence
- Irrigation water and soil amendments as anthropogenic inputs to cropland
- Source attribution and environmental burden apportionment
- Arsenic, Total
- Cadmium
- Copper
- Nickel
- Lead
- Zinc
- Chromium
Update history
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