Rueda-Saa and colleagues measured total metals in agricultural soils from 489 sites across 13 Colombian watersheds. Concentrations differed substantially by watershed, with the highest mean nickel concentration in Pescador. These are upstream soil measurements: the study did not measure harvested crops or establish soil-to-crop transfer factors.
Key numbers
The sample frame comprised 489 sites; 44% of samples came from sugarcane cultivation and 56% from other crops (p. 3). Laboratory analyses occurred in 2017–2019; collection dates and separate annual results are not stated. All concentrations below retain the paper’s mg/kg unit. The paper does not explicitly identify a dry- or wet-weight basis.
Overall soil summaries
Table 1, p. 4. Zeros and sub-detection values are source-reported entries, not proof of absence. The table footnote identifies starred values as below detection; the substitution rule used to calculate summaries is not stated.
| Analyte | Mean | Median | SD | Minimum | Maximum |
|---|---|---|---|---|---|
| tAs | 0.03 | 0.00 | 0.28 | 0.00 | 2.92 |
| tHg | 0.01 | 0.00 | 0.14 | 0.00 | 3.01 |
| Cd | 0.16 | 0.13 | 0.18 | 0.00 | 2.77 |
| Cr | 58.56 | 46.30 | 47.62 | 0.00 | 240.00 |
| Ni | 41.62 | 30.80 | 38.8 | 0.001 | 226.00 |
| Pb | 4.54 | 2.65 | 7.47 | 0.00 | 90.00 |
| Co | 17.17 | 14.55 | 10.89 | 0.00 | 72.60 |
Geographic breakdown
Mean concentrations by watershed, Table 2, pp. 6–7. RUT means Roldanillo–Unión–Toro. Every watershed is kept separate; no product concentration is inferred from these soil values.
| Watershed | n | tAs | tHg | Cd | Cr | Ni | Pb | Co |
|---|---|---|---|---|---|---|---|---|
| Arroyohondo | 7 | 0.00* | 0.00 | 0.01 | 50.31 | 44.74 | 5.49 | 22.47 |
| Guabas | 22 | 0.00 | 0.00 | 0.06 | 113.45 | 43.14 | 6.07 | 28.86 |
| Guachal | 159 | 0.00 | 0.00 | 0.16 | 26.49 | 21.65 | 2.14 | 9.54 |
| Guadalajara | 36 | 0.00 | 0.00 | 0.11 | 40.69 | 25.79 | 3.80 | 14.01 |
| Jamundí | 28 | 0.00 | 0.00 | 0.05 | 31.41 | 14.49 | 7.82 | 19.36 |
| Meléndez | 9 | 0.0 | 0.0 | 0.02 | 37.82 | 24.88 | 0.93 | 10.20 |
| Pescador | 41 | 0.39 | 0.09 | 0.11 | 98.49 | 111.40 | 3.61 | 33.81 |
| RUT | 53 | 0.00 | 0.00 | 0.22 | 80.00 | 46.08 | 7.37 | 18.39 |
| San Pedro | 41 | 0.00 | 0.00 | 0.25 | 48.18 | 34.51 | 7.59 | 15.18 |
| Sonso | 25 | 0.00 | 0.00 | 0.13 | 76.88 | 40.72 | 8.74 | 27.52 |
| Tuluá | 61 | 0.00 | 0.00 | 0.29 | 103.44 | 70.98 | 2.76 | 17.79 |
| Yumbo | 5 | 0.0 | 0.0 | 0.02 | 55.67 | 46.53 | 16.93 | 25.44 |
| Zona Industrial | 2 | 0.00 | 0.00 | 0.12 | 64.50 | 42.50 | 11.50 | 32.00 |
Table 2 additionally provides medians, minima and maxima for all seven analytes in every watershed. For example, Pescador nickel has median 121.00, minimum 23.00 and maximum 226.00 mg/kg; San Pedro cadmium has median 0.19, minimum 0.00 and maximum 2.77 mg/kg. All 364 watershed statistic cells, 63 overall statistic cells, 84 soil-order statistic cells and seven detection limits are preserved in the structured extraction.
Methods (brief)
The authors used simple random sampling across mapped agricultural areas. Disturbed composite soil samples were homogenized from approximately 3 cm thickness, 20 cm width and 30 cm depth. Methods lists HCl–HNO3 wet digestion and graphite-furnace atomic absorption for Cd, Ni, Pb and Co. It supplies a Cr detection limit but omits Cr from that method’s analyte enumeration, so a complete Cr method is not independently specified. As and Hg are described as hydride-generation atomic absorption measurements (p. 3); no arsenic, mercury or chromium speciation is reported.
Detection limits in mg/kg were Cd 0.02, Cr 1, Ni 1, Pb 0.75, Co 0.10, As 0.10 and Hg 0.10. The paper reports neither a clear moisture-basis statement nor a full recovery/reference-material quality-control record. Source comparisons to background ranges are literature comparisons, not verified regulatory instruments.
Implications
Evidence Fitness: EF-4 for product-occurrence use. The study directly supports geographic variation in agricultural-soil total metals and can inform investigations of upstream contamination. It cannot establish edible-crop concentrations, transfer factors, metal species concentrations, year-on-year trends, or attribution to a particular polluter. Missing crop measurements do not invalidate its supply-chain evidence.
Wiki pages this source may touch
- Soil-to-plant transfer of heavy metals
- Arsenic, Total
- Mercury, Total
- Cadmium
- Chromium
- Nickel
- Lead
- Cobalt
Verification notes
The byline, title, journal, year and DOI were checked against the primary PDF. The manifest identity agrees. SHA-256: f0907939e04c8f3c6f0af3433cbb71f85b4d7353a8ca8295c385eae02d2b04d3. Access: Library PDF preserved through the repository symlink; publisher identifier https://doi.org/10.22267/rcia.20254202.259. The PDF footer displays CC BY-NC symbols; it does not specify a license version.
Tables 1–3 and analytical detection limits were transcribed with source-native precision and visually checked. Table 3 labels inceptisol n = 128 and vertisol n = 90, while Methods reverses those sample sizes. The extraction preserves the table labels and flags the conflict; no soil-order inference depends on choosing a correction. Table 3 also prints Hg means of 0.00 for all three orders despite Table 1’s mean of 0.01 and an inceptisol maximum of 3.01. These discrepancies remain visible, without inventing corrected values.
No concentration was converted to a food basis. Total Cr does not represent Cr(VI); total As does not represent inorganic As; total Hg does not represent methylmercury. No annual split was reconstructed from the analysis-year range. The primary source’s statements of environmental safety or permissible ranges are not adopted as independently verified health or legal conclusions.
Update history
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