Overview
This study measured 20 elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Hg, Mo, Pb) in 34 surface soil samples from the Al-Khassa Sub Basin, a 468 km² agricultural watershed in Kirkuk Province, northeastern Iraq. The basin is the agricultural catchment of the Al-Khassa dam (constructed 2010, increasing irrigated agriculture in the surrounding villages) and is described by the authors as suffering from increasing anthropogenic pollution from fertilizer overuse, pesticide application, and poor irrigation practice. The sampling design covers 32 villages including agricultural, pastoral, and cultivated land. Cd is not measured. Speciation is not reported for As or Hg, so reported values are read as total arsenic and total mercury. The paper is a soil-geochemistry study; no food crops, food products, or animal tissues are sampled. Two reported concentration ranges (Mo at 420–796 mg/kg and Hg at 1.9–5.0 mg/kg) sit far outside expected crustal/agricultural-soil envelopes and are flagged in ## Verification notes as data-integrity concerns the source itself does not address.
Key numbers
Table 3 — Trace and abundant element concentrations (mg/kg dry soil; n=34 surface soil samples):
| Element | Min | Max | Mean | World-soil reference (Vinogradov 1959) | Local-soil reference (Al-Saadi 2016, Lesser Zab) |
|---|---|---|---|---|---|
| Pb | 2.3 | 5.6 | 3.8 | 17 | 5.14 |
| tAs | 63 | 90 | 76 | 5 | (not reported) |
| tHg | 1.9 | 5.0 | 3.3 | 0.1 | (not reported) |
| Cr | 32 | 140 | 73.8 | 200 | 72 |
| Ni | 162 | 278 | 204.9 | 40 | 78 |
| Cu | 144 | 188 | 169.8 | 20 | 15 |
| Zn | 120 | 370 | 237.8 | 50 | 37 |
| Mn | 101 | 179 | 144.5 | 850 | 512 |
| Co | 21 | 48 | 35.4 | 8 | 10.7 |
| Mo | 420 | 796 | 593.7 | 2 | (not reported) |
| V | 19 | 66 | 35.7 | 100 | (not reported) |
| Al | 34,852 | 79,898 | 51,917.3 | 71,300 | 48,908 |
Soil physicochemical parameters (Table 1):
| Parameter | Min | Max | Mean |
|---|---|---|---|
| pH | 7.1 | 9.9 | 7.98 |
| Organic matter (%) | 0.55 | 2.1 | 1.28 |
| Loss on ignition (%) | 8.6 | 30 | 19.10 |
| Total organic carbon (%) | 0.9 | 4.1 | 2.65 |
| Cation exchange capacity (cmol/kg) | 31 | 65 | 42.64 |
| Total hydrocarbons (mg/kg) | 16 | 76 | 40.29 |
Enrichment Factor (EF) and Contamination Factor (Cf) findings:
- Aluminum used as reference element for EF normalization. Local geochemical background derived by iterative ±2SD trimming.
- Mg is the only element with significant enrichment (EF 5–20) at any site — site S25 (Sedan), attributed by the authors to heavy magnesium-sulfate fertilizer use.
- Pb shows EF < 2 (depletion to minimal enrichment) at most sites; no Pb contamination signal at the basin scale.
- Most other elements (Al, Mn, Co, Cu) classified as EF < 2 (no/minimal pollution) across all 34 samples.
- Mg Cf > 6 (very high contamination) at Mam Rash (S22) and Sedan (S25) per Table 5; Cf 3–6 (considerable) at Belgrad (S10), Gurgay Shammar (S11), and Obarick (S32). The paper’s prose section 5.3 reassigns Belgrad (S10) to the Cf > 6 group, which contradicts Table 5; the table reading is retained here as more internally consistent with the EF discussion (Sedan S25 is independently flagged for Mg fertilizer overuse). See
## Verification notes. - P Cf in the considerable range (3 < Cf < 6) at Heon (S7) and Ali Makaeel (S20) per Table 5; the authors attribute these to phosphate-fertilizer use combined with proximity to poultry farms. Most other sites fall in the moderate Cf range (1 < Cf < 3) for P.
- All four metals on the HMTc 10-analyte list that the study measured (Pb, tAs, Cr, Ni; plus tHg) are reported with Cf in the low-to-moderate range across all sample sites in the published Cf table (Table 5).
Per-sample values for the HMI-tracked metals (Table 2):
- Pb range across S1–S34: 2.3 (S26, S34) to 5.6 (S17). Mean 3.8 mg/kg.
- tAs range across S1–S34: 63 (S8, S24, S34) to 90 (S22). Mean 76 mg/kg.
- tHg range across S1–S34: 1.9 (S34) to 5.0 (S21, S22). Mean 3.3 mg/kg.
- Cr range across S1–S34: 32 (S5) to 140 (S18). Mean 73.8 mg/kg.
- Ni range across S1–S34: 162 (S33) to 278 (S29). Mean 204.9 mg/kg.
Evidence Fitness
EF-4 (Modeled or limited evidence — context only). This source supplies geographic-context occurrence values for surface soil in an irrigated agricultural sub-basin in northeastern Iraq. It does not support per-ingredient or per-product occurrence claims because no food crops, food products, or animal tissues are sampled. Two analyte ranges (Mo and Hg) sit outside physically plausible envelopes for agricultural soil and would not survive defensibility review if used as occurrence anchors; values are reported here as the source reports them but should not propagate into the wiki’s regional soil-context summaries without independent corroboration. Pb, Cr, Ni, and the Cd-absent gap are the values that can be cited as Kirkuk-region agricultural-soil context with the lowest defensibility risk.
Methods (brief)
- Sampling: 34 surface soil samples taken at 35–45 cm depth, density of one sample per 4 km² across the 468 km² Al-Khassa Sub Basin. Approximately 2–3 kg per sampling site collected in polyethylene bags. Sites geo-referenced with GPS (Garmin eTrex Vista).
- Sample preparation: All samples air-dried and sieved to <2 mm for chemical analysis. For elemental analysis 5.0 g of each sample was sieved to <2 mm and powdered to 0.063 mm.
- Analytical method: Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for major oxides and heavy metals, performed at ALS Environmental Lab, Mississauga, Canada, following the lab’s accredited procedures (referenced as approved in January 2021).
- Physicochemical parameters (pH, organic matter, loss on ignition, TOC, CEC, total hydrocarbons) also performed at ALS Environmental Lab.
- Statistical methods: Iterative ±2SD trimming to derive local geochemical background. Enrichment factor calculated with Al as the immobile reference element. Contamination factor calculated against derived local background.
- LODs, reference materials, QA/QC recoveries, replicate-sample structure, and digestion chemistry are not tabulated in the published text. Speciation for As (inorganic vs total) and Hg (methylmercury vs total) is not reported; values are read as total arsenic and total mercury.
Implications
- Certification: Provides Kirkuk-region geographic-context soil occurrence for Pb, As, Cr, Ni, Hg. Cd is not measured and remains a gap for this region. The Pb soil values are unusually low compared to world background, while As is elevated ~15× world background — both are signals worth retaining as Iraq-region context if corroborated by independent regional surveys.
- Courses: Useful illustration of enrichment-factor and contamination-factor methodology applied at the sub-basin scale, and of the role of phosphate fertilizers and irrigation practice in shifting soil trace-element burdens. Also a teaching example of how a published paper can carry analyte values outside physically plausible envelopes without being flagged by the authors.
- App: Does not support direct ingredient
contamination_profileupdates. Could feed an Iraq-region geographic-risk adjustment for soil-derived ingredients only after corroborating regional sources are ingested and the Mo/Hg data-integrity concerns are resolved. - Microbiome: Not addressed.
Related evidence
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