Toxic Metals Soil Pollution

Risksv04.00 credits/per_km2

Responsible:Niccolò Calandri

Toxic Metals Soil Pollution

Overview

Toxic metals soil pollution measures heavy metal contamination of soil, analysing seven elements of particular environmental and health significance: Arsenic (As), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb). The KPI is based on the global dataset published by Hou et al. (2025) in Science, which integrates over 115,000 soil samples collected worldwide to produce interpolated contamination maps.

Exposure to heavy metals in soil poses a direct threat to agricultural productivity, ecosystem health, and human health through the food chain and direct soil contact. Contamination can originate from industrial activities, use of fertilisers and pesticides, vehicle traffic, and atmospheric deposition. The KPI is inverted: a lower contamination value indicates healthier soil and better environmental quality.

Calculation Methodology

The reference dataset is Hou et al. (2025) ("Global soil pollution by toxic metals threatens agriculture and human health", Science 388, 316–321), which produced global distribution maps of 7 toxic metal concentrations in topsoil.

Technical pipeline:

Source data — the dataset is stored on S3 in GeoParquet format, partitioned by H3 cell (resolution 3)
Interpolation — spatial concentrations interpolated via scipy.interpolate.griddata (linear method)
Masking — pixels more than 0.1° (~11 km) from the nearest sample are masked to avoid inaccurate extrapolations
Reference thresholds — two categories of thresholds are applied:
- AT (Agricultural Thresholds): safety thresholds for agricultural land use
- HHET (Human Health and Ecological Thresholds): thresholds for human and ecological health protection
Layer generation — each request produces 16 separate layers: 7 metals × 2 thresholds (AT + HHET) + 2 total layers (Total AT + Total HHET)
Value calculation — the final value is a threshold exceedance index: 0 = not contaminated, > 1 = threshold exceeded
Analysis buffer — 25 km around the study polygon

Value interpretation:

Value	Interpretation
0	Concentration below threshold: uncontaminated soil
0.2	Slight exceedance (20% of threshold)
0.6	Moderate exceedance (60% of threshold)
≥ 1	Threshold exceeded: significant contamination

Unit: dimensionless index (concentration/threshold ratio)

Data Sources

Code	Name	Provider	Resolution	Availability
`WRD_SLPOL_25`	Hou et al. 2025 Global Soil Pollution	Science Journal / Global dataset	variable	Static dataset (2025)

Quality Range and Levels

Indicator	Unit	Range	Inverted
`toxic_metals_soil_pollution`	—	[0, 0.2, 0.4, 0.6, 0.8, 1]	Yes

Inverted = Yes: a lower value indicates less contaminated soil and better environmental quality.

Level	Index	Interpretation
A (Excellent)	0 – 0.2	Absent or negligible contamination; healthy soil
B (Good)	0.2 – 0.4	Very low contamination; within safety limits
C (Moderate)	0.4 – 0.6	Moderate contamination; possible impact on sensitive ecosystems
D (Poor)	0.6 – 0.8	Significant contamination; risk for biodiversity and agriculture
E (Critical)	> 0.8	Severe contamination; human and ecological health risk threshold approached or exceeded

Metals Analysed and Thresholds

Metal	Symbol	Main contamination source
Arsenic	As	Pesticides, mining, natural processes
Cadmium	Cd	Phosphate fertilisers, industry
Cobalt	Co	Mining industry, atmospheric deposition
Chromium	Cr	Tanning industry, natural processes
Copper	Cu	Agricultural fungicides (bordeaux mixture), copper industry
Nickel	Ni	Metallurgical industry, natural processes
Lead	Pb	Vehicle traffic (leaded petrol), industry

Technical Notes

A single request generates 16 separate layers: 7 metals × 2 thresholds (AT + HHET) + Total × 2 thresholds
25 km analysis buffer around the polygon
Pixels beyond 0.1° (~11 km) from the nearest sample are masked to avoid inaccurate extrapolations
Static dataset (published 2025): does not reflect recent temporal variations
Natural background concentration varies significantly with local geology

References

Hou, D., O'Connor, D., Nathanail, P., Toth, G., Mack, L., Ma, Y., ..., Rinklebe, J. (2025). "Global soil pollution by toxic metals threatens agriculture and human health". Science, 388, 316–321. DOI: 10.1126/science.adp5994
European Environment Agency (2022). "Progress in management of contaminated sites". EEA Indicator Assessment.

Quality Ranges and Levels

toxic_metals_soil_pollution

ACritical

BLow

CModerate

DGood

EExcellent

0 → 0.19

0.2 → 0.39

0.4 → 0.59

0.6 → 0.79

0.8 → 1

Critical0 – 0.19

Low0.2 – 0.39

Moderate0.4 – 0.59

Good0.6 – 0.79

Excellent0.8 – 1

Data Sources & References

Sources

WRD_SLPOL_25

Methodology

Dataset: Hou et al. (2025) "Global soil pollution by toxic metals" (Science 388, 316–321). Integrates over 115,000 global soil samples. Seven metals analysed: As, Cd, Co, Cr, Cu, Ni, Pb. Two threshold categories: AT (Agricultural Thresholds) and HHET (Human Health and Ecological Thresholds). Data stored on S3 in GeoParquet partitioned by H3 cell (resolution 3). Interpolation: scipy.interpolate.griddata (linear method). Pixels beyond 0.1° (~11 km) from nearest sample are masked. Each request generates 16 layers: 7 metals × 2 thresholds + Total × 2 thresholds. Value = threshold exceedance index (0 = not contaminated, >1 = threshold exceeded). 25 km buffer. Inverted indicator.