The Influence of Matrix Composition on Bioaccessible Zinc and Nickel in Residential Dust and Soil
Bibliographic record
Abstract
MS1-07 Abstract: Urban geochemical studies commonly report higher metal concentrations in settled dust samples compared with corresponding garden soil samples, particularly in residential neighborhoods that are not impacted by contaminated sites. The present study investigates the influence of matrix composition on indoor/outdoor ratios of nickel (Ni) and zinc (Zn) in the city of Ottawa, Canada, with particular attention to organic carbon content, metal speciation, and particle size distribution. Results from the analysis of the <150 μm size fraction show elevated organic carbon content in indoor vacuum dust samples (median, 28%; range, 16–37%; n = 58) compared with corresponding garden soil samples (median, 5%; range, 1–36%; n = 66). Determination of total Zn and Ni content in the same samples, using an aggressive acid digestion procedure, revealed elevated levels in indoor dust (median Zn = 626 μg/g; Ni = 41 μg/g) compared with garden soil (median Zn = 410 μg/g; Ni = 16 μg/g). These elevated indoor/outdoor ratios were enhanced when a simulated stomach acid extraction was used to determine bioaccessible metal concentrations. The median bioaccessible Zn content in dust was 410 μg/g compared with 18 μg/g in soil; the median bioaccessible Ni content in dust was 16 μg/g compared with 2.2 μg/g in soil. Zn speciation was investigated in 2 size fractions of dust (<36 μm and 80–150 μm) using synchrotron x-ray absorption spectroscopy (XAS). The dominant form is Zn hydroxyl carbonate (approximately 50% of total Zn) and the remainder is equally divided between Zn sulfide (ZnS) and Zn species associated with Fe hydroxide phases. Although both size fractions contain comparable Zn species, the fine fraction tends to have a higher proportion of ZnS than the coarse fraction (28% of total Zn as ZnS in fine fraction compared with 18% in coarse fraction). Particle size was found to be one of the most influential factors affecting metal bioaccessibility, and therefore it is critical that comparisons between dust and soil samples are made on the basis of equivalent size fractions. Organic carbon is another important factor: bioaccessible Zn and Ni concentrations tend to increase as the organic carbon content increases. Indoor/outdoor ratios appear to be enhanced by the ability of the organic-rich indoor dust matrix to accumulate certain metals (irrespective of source) to higher concentrations than are found in soil.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".