Environmental Risk Assessment, Principal Component Analysis, Tracking the Source of Toxic Heavy Metals of Solid Gold Mine Waste Tailings, South Africa
Bibliographic record
Abstract
This study collected 21 soil samples from 30 to 120 cm depth, from 9 solid gold mine waste dumps in the Witwatersrand basin, South Africa. The samples were analysed using ICP-OES method to determine the concentrations of heavy metals. Principal component analysis (PCA) was performed to track sources of heavy metals, migration passages, their distributions and spatial variations at the study sites. The results of this study showed that the soil screening values (mg/kg) ranged from 2.20–7,070.00 Pb, 0.20–11.00 As, 0.06–2,630.00 Hg, 1.00–69.00 U, 0.02 − 4.20 Cd, and exceeded the background concentrations of the continental crust. The study results further showed that the average concentrations (mg/kg) of Pb (432.08), U (13.75), Tl (4.41), Ag (1.07), Cd (0.34) were highest at Durban Deep. Arsenic (59.86) and Sn (2.03) were highest at Krugersdorp, Kagiso, New Canada, and Shaft 17. The average values of Hg (625.56 µg/kg) and Au (17.67 µg/kg) were highest at Mogale City, Fleurhof, Krugersdorp, Shaft 17, and Davidsonville. These values reflected moderate to extreme contamination, supported by geoaccumulation index (Igeo), pollution load index (PLI), and contamination factor (Cfi) values. According to PCA, F1 was responsible for heavy metal generations from the local gold processing and waste dumping facilities. The F1 loading for Cd and Pb was 0.845 and 0.835, respectively, whereas F1 and F2 contribution of the variable % were greater than 0.70 for Ag, As, Au, Cd, Pb, Sn, Tl, and U, suggesting that they were generated from the waste dumps, transported by rain water and subsequently deposited in downstream soil. The heavy metal concentrations were traced upstream at the dumps where the highest averages were recorded, whereas the lowest values were measured from downstream samples. Thus, the gold mine tailing dumps are considered the primary sources of the high measured values of the heavy metals in the study sites. The ecological risk values were ranked in the order of As > Cd > Hg > Pb and exceeded the permissible health risk value suggested by the South African and global standards. Excessive Hg concentration with 160 ≤ Er i< 320 was recorded at Krugersdorp, whilst Pb with 320 ≤ Eri was recorded at Durban Deep. Thus, the estimated high Er i values insinuate higher ecological risk of heavy metals that can accumulate in the human body through absorption, inhalation and ingestion of dust, or ingestion of food grown from the contaminated soil.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".