Toxic metals soil pollution measures heavy metal contamination of topsoil, analysing seven elements of particular environmental and health significance: Arsenic (As), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb). The indicator 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 platform presents this KPI through multiple UI elements: a gauge showing the overall exceedance index, a site-versus-control comparison chart, and a set of 16 map layers (7 metals x 2 threshold categories + 2 total layers). Two threshold categories are used: AT (Agricultural Thresholds) for food-safety limits and HHET (Human Health and Ecological Thresholds) for health and ecosystem protection limits.
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.
Processing pipeline:
Formula: Exceedance Index = Measured Concentration / Reference Threshold
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Hou et al. (2025) Global Soil Toxic Metals (WRD_SLPOL_25) | Science Journal | Global | Point data, interpolated to ~1.1 km grid | Static dataset (2025) |
Gauge. A semicircular arc chart (CaRoiChart) displaying the site's toxic metals exceedance index for the selected metal and threshold, with a comparison to the control area.
Purpose: To show at a glance whether the site's soil is contaminated by toxic metals beyond acceptable thresholds, and how it compares to the surrounding control area.
Description: The card header shows the topic badge "E3", sub-topic "Pollution", and an info tooltip icon. Below the header, two dropdown selectors allow the user to choose the specific metal (Total, Arsenic, Cadmium, Cobalt, Chromium, Copper, Nickel, Lead) and threshold category (AT or HHET). The gauge arc is divided into five colored segments from green (low exceedance) to red (high exceedance), with separate needles for the site (ROI) and the control area (CA). The current exceedance index value is displayed numerically.
How it's calculated: The value shown is the mean threshold exceedance index for the selected metal and threshold type within the site polygon. A value of 0 indicates no contamination above detection level; a value of 0.5 means the concentration is at 50% of the reference threshold; a value at or above 1 means the threshold is exceeded. The control area value is calculated the same way for the surrounding reference polygon.
Note: This indicator is inverted -- lower values indicate better conditions.
Legend:
| Level | Index Range | Color | Meaning |
|---|---|---|---|
| A | 0 -- 0.2 | ■ #00A67A | Absent or negligible contamination |
| B | 0.2 -- 0.4 | ■ #00DF80 | Very low contamination; within safety limits |
| C | 0.4 -- 0.6 | ■ #FFD21E | Moderate contamination |
| D | 0.6 -- 0.8 | ■ #FF8B16 | Significant contamination; risk for biodiversity and agriculture |
| E | > 0.8 | ■ #FF367F | Severe contamination; health risk threshold approached or exceeded |
Interpretation example: If the gauge shows an index of 0.28 for Total AT, it means the combined concentration of all seven metals is at 28% of the agricultural safety threshold -- the soil is within safe limits (grade B), though some metal accumulation is present.
Bubble Chart. A site-versus-control comparison chart showing the toxic metals exceedance index for both the monitored site (ROI) and the surrounding control area (CA).
Purpose: To allow the user to compare the site's contamination level against the broader landscape and determine whether the site is more or less contaminated than its surroundings.
Description: The chart displays paired values for the site and the control area under the selected metal and threshold combination. The selected metal and threshold are controlled by the dropdowns on the gauge card above.
How it's calculated: Each bar or point represents the mean exceedance index for the respective polygon (site or control). The site polygon is the monitored area; the control area is a larger reference polygon around it. Both use the same interpolation and threshold methodology.
Note: This indicator is inverted -- lower values indicate better conditions.
Interpretation example: If the site shows 0.28 and the control area shows 0.35 for Total HHET, the monitored site has slightly lower overall contamination than its surroundings -- a positive signal, though both areas have detectable metal presence.
Map Layer. An interactive map overlay showing the spatial distribution of the threshold exceedance index for the selected metal and threshold category, using a coolwarm colour gradient.
Purpose: To show exactly where within and around the site metals are concentrated above or below the reference threshold.
Description: The map displays a raster overlay covering the site polygon and a 25 km buffer. The user selects the specific metal (Total, As, Cd, Co, Cr, Cu, Ni, Pb) and threshold (AT or HHET) from dropdowns. Blue tones indicate low exceedance (clean soil), transitioning through white to red tones indicating high exceedance (contaminated soil). The map includes an opacity slider, a download button, and a layer-specific tooltip describing the selected combination.
How it's calculated: The raster is generated by interpolating the Hou et al. (2025) point samples onto a regular grid, masking areas far from any sample point (> 0.1 degrees), and normalising to the selected threshold. One generation request produces all 16 layers simultaneously: 7 metals x 2 thresholds + Total x 2.
Note: This indicator is inverted -- lower values indicate better conditions.
Legend: Coolwarm colour gradient normalised from 0 to 1:
Interpretation example: If the map shows mostly blue tones for Cadmium AT with a small red patch in the north-east, it means most of the site has cadmium levels well below agricultural limits, but a localised area may have elevated concentrations requiring further investigation.
Highlights Table Row. A row in the multi-KPI comparison highlights table showing the toxic metals exceedance index for the selected site and its control area.
Purpose: To allow quick comparison of soil metal contamination across sites in a single summary view.
Description: A labelled row showing the total exceedance index value for the site (ROI) and the control area (CA), colour-coded by quality grade (A-E). The row label reads "Toxic Metals Soil Pollution".
How it's calculated: Same computation as the gauge element. The displayed value is the mean Total exceedance index (typically AT or HHET depending on platform configuration).
Note: This indicator is inverted -- lower values indicate better conditions.
Interpretation example: If the site shows 0.62 (grade D, orange) and the control area shows 0.28 (grade B, green), the site has significantly higher metal contamination than its surrounding landscape -- a potential concern for agricultural use and ecosystem health.
Assessment Sidebar Row. A grade row in the E3 Pollution section of the assessment sidebar, showing the toxic metals soil pollution grade for the site.
Purpose: To provide a quick letter-grade summary of soil metal contamination within the broader environmental risk assessment.
Description: A single row labelled "Toxic Metals Soil Pollution" with a coloured grade badge (A-E). Grade A (green) indicates absent or negligible contamination; grade E (pink-red) indicates severe contamination.
How it's calculated: The letter grade is derived from the mean Total exceedance index mapped to the A-E scale: A = 0-0.2, B = 0.2-0.4, C = 0.4-0.6, D = 0.6-0.8, E = > 0.8.
Note: This indicator is inverted -- lower values indicate better conditions.
Interpretation example: A grade B means the site's combined metal contamination is between 20% and 40% of the reference threshold -- low overall contamination, well within safety limits for most uses.
Map Layer. An interactive map layer in the Maps tool showing the toxic metals exceedance index for the selected metal and threshold category.
Purpose: To provide a standalone, full-screen map view of soil metal contamination, with selectable metals and threshold types.
Description: Accessible from the Maps section under the Pollution category, this layer displays the same raster data as the assessment map layer but in the dedicated Maps tool. The user selects the metal type from a menu (Total, Arsenic, Cadmium, Cobalt, Chromium, Copper, Nickel, Lead) and the threshold category (AT: Agriculture Thresholds, or HHET: Human Health and Ecological Thresholds). The map shows a coolwarm colour gradient. Each combination has its own tooltip explanation describing what the specific metal and threshold measure.
How it's calculated: Identical to the assessment map layer -- interpolated exceedance index for the selected metal and threshold, with 25 km buffer and masking beyond 0.1 degrees from the nearest sample point.
Note: This indicator is inverted -- lower values indicate better conditions.
Legend: Coolwarm colour gradient normalised from 0 to 1:
Interpretation example: If viewing Lead (Pb) HHET and the map is uniformly blue with values near 0.03-0.09, lead concentrations are far below the human health threshold (200 mg/kg) across the entire area -- no health concern for this metal.
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.adr5214
European Environment Agency (2022). "Progress in management of contaminated sites". EEA Indicator Assessment. Available at: https://www.eea.europa.eu
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| See Calculation Methodology | Various | Global | Varies | Varies |
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.