Assessment of heavy metal pollution sources and environmental capacity of typical farmland soils in northwestern Zhejiang based on the geological background of black rock series – Frontiers

Report on Soil Heavy Metal Pollution and Environmental Capacity in Changshan County with Emphasis on Sustainable Development Goals (SDGs)

Introduction

Soil, as a vital natural resource, underpins human survival and development. However, increasing population, industrial expansion, urbanization, and extensive agricultural chemical use have led to widespread soil heavy metal pollution, posing threats to ecosystems, human health, and agricultural product quality. Addressing this aligns closely with SDG 3 (Good Health and Well-being), SDG 6 (Clean Water and Sanitation), and SDG 15 (Life on Land).

Soil environmental capacity, defined as the maximum pollutant load soil can tolerate without environmental degradation or yield loss, is crucial for pollution prevention and sustainable land management (SDG 2: Zero Hunger). This study focuses on evaluating soil heavy metal environmental capacity in Changshan County, Zhejiang Province, integrating GIS, geostatistics, enrichment factor methods, and principal component analysis (PCA) to identify pollution sources and spatial distribution, thereby supporting sustainable agricultural practices and environmental protection.

Materials and Methods

Study Area

Changshan County, located in western Zhejiang Province, covers approximately 213.9 km² of cultivated land characterized by hilly terrain and diverse soil types, primarily paddy soils. The area’s hydrological and geological features, including the Cambrian and Ordovician strata rich in heavy metals, influence soil composition. This study area is significant for regional agriculture and environmental sustainability (SDG 2, SDG 15).

Sample Collection and Analysis

1. 1788 soil samples collected uniformly from 0–20 cm depth across cultivated lands.
2. Laboratory analysis measured heavy metals (Cd, Hg, As, Cu, Zn, Ni, Cr, Pb), soil pH, and SiO₂ using ICP-MS, XRF, and atomic fluorescence spectroscopy.
3. Quality control ensured compliance with national standards.

Measurement and Evaluation Methods

• Static and Existing Environmental Capacity: Calculated to assess maximum pollutant loads without degradation.
• Dynamic Environmental Capacity: Annual carrying capacity considering pollutant migration and self-purification.
• Comprehensive Index Method: Used for pollution assessment integrating multiple heavy metals.
• Enrichment Factor Method: Evaluated human impact on heavy metal accumulation.
• Data Analysis: Employed statistical tools including PCA, correlation analysis, and GIS mapping for spatial distribution and source identification.

Results

Heavy Metal Content Characteristics

• Average concentrations of Cd, Hg, As, Pb, Cr, Ni, Cu, and Zn exceeded regional soil background values, with Cd showing the highest exceedance and variability.
• Cd pollution was the most significant, with 32.77% of sampling points exceeding risk screening values.

Heavy Metal Enrichment

• Cd exhibited mild enrichment (average enrichment factor 2.30), while As, Hg, Zn, Cu, Ni, and Pb showed slight enrichment.
• Strong enrichment of Cd, As, and Cu was detected in localized areas, indicating potential pollution hotspots.

Source Analysis via Principal Component Analysis (PCA)

1. Factor 1 (32.62% variance): Cd, Ni, Cu, Zn linked to natural geological background and mining activities.
2. Factor 2 (18.63% variance): As, Pb, Zn associated with Cambrian strata and hydrothermal alterations (natural sources).
3. Factor 3 (15.08% variance): Cr, Ni influenced by both natural sources and industrial emissions.
4. Factor 4 (12.60% variance): Hg primarily from industrial sources including smelting and coal combustion.

Environmental Capacity of Soil Heavy Metals

Static and Existing Capacity

• Static environmental capacity ranking: Cr > Zn > Pb > Ni > Cu > As > Hg > Cd.
• Cd existing capacity was negative, indicating overloading and severe pollution risk.
• Significant reduction in existing capacity observed for Cd, As, and Pb, especially in paddy fields.

Dynamic Environmental Capacity

• Dynamic capacity decreased over time for all heavy metals, with Hg showing the highest cumulative reduction rate.
• Differences in dynamic capacity reduction between paddy fields and dry land were observed, notably for As.

Spatial Distribution and Pollution Risk

• High-risk areas with low or overloaded environmental capacity correspond to industrial parks, mining zones, and geological anomaly regions.
• Cd pollution hotspots align with black rock geological formations and intensive human activities.

Discussion

Source Attribution and Impact on SDGs

• Natural geological background significantly contributes to heavy metal presence, emphasizing the need for geologically informed land management (SDG 15).
• Industrial activities exacerbate pollution, particularly Hg and Cd, necessitating emission controls and sustainable industrial practices (SDG 9: Industry, Innovation and Infrastructure; SDG 12: Responsible Consumption and Production).
• Agricultural inputs, especially organic fertilizers, contribute to Cd and Cu accumulation, highlighting the importance of sustainable agriculture (SDG 2, SDG 12).

Environmental Capacity and Land Use

• Differences in environmental capacity between paddy fields and dry land suggest tailored management strategies to mitigate heavy metal risks.
• Soil pH and organic matter influence heavy metal mobility and accumulation, affecting pollution dynamics.

Recommendations for Pollution Prevention and Control

1. Implement targeted pollution control in high-risk areas, including industrial emission reduction and mine restoration (SDG 11: Sustainable Cities and Communities).
2. Promote green agricultural technologies to reduce fertilizer and pesticide use (SDG 2, SDG 12).
3. Enhance monitoring and remediation efforts in overloaded zones to protect soil health and food safety (SDG 3, SDG 15).

Limitations and Future Directions

• Study limited to farmland soils; broader land use types should be included for comprehensive risk assessment.
• Further research needed on heavy metal bioavailability, migration, and long-term ecological and health impacts.
• Consideration of climate change and soil chemistry effects on heavy metal dynamics is recommended.

Conclusion

This study reveals significant heavy metal pollution in Changshan County soils, with Cd as the primary pollutant exceeding environmental capacity, posing risks to agriculture and human health. The integration of geological background, industrial, and agricultural sources underscores the complexity of soil contamination. The findings support the implementation of sustainable land and pollution management practices aligned with multiple SDGs, particularly SDG 2 (Zero Hunger), SDG 3 (Good Health and Well-being), SDG 6 (Clean Water and Sanitation), SDG 9 (Industry, Innovation and Infrastructure), SDG 11 (Sustainable Cities and Communities), SDG 12 (Responsible Consumption and Production), and SDG 15 (Life on Land). Effective pollution control, monitoring, and remediation are essential to safeguard soil quality and ensure sustainable agricultural development in the region.

1. Relevant Sustainable Development Goals (SDGs)

1. SDG 2: Zero Hunger
   • The article addresses soil quality and pollution, which directly affect agricultural productivity and food safety.
2. SDG 3: Good Health and Well-being
   • Soil heavy metal pollution poses threats to human health through contaminated agricultural products.
3. SDG 6: Clean Water and Sanitation
   • Pollution from heavy metals can affect water bodies through runoff and sediment contamination.
4. SDG 12: Responsible Consumption and Production
   • The article highlights the impact of agricultural inputs such as fertilizers and sludge on soil pollution.
5. SDG 13: Climate Action
   • Although not directly discussed, the article mentions environmental factors and industrial emissions affecting soil quality.
6. SDG 15: Life on Land
   • The article focuses on soil pollution and ecosystem health, emphasizing sustainable land management and pollution control.

2. Specific Targets under the Identified SDGs

1. SDG 2: Zero Hunger
   • Target 2.4: By 2030, ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production, help maintain ecosystems, and strengthen capacity for adaptation to climate change, extreme weather, drought, flooding, and other disasters.
2. SDG 3: Good Health and Well-being
   • Target 3.9: By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water, and soil pollution and contamination.
3. SDG 6: Clean Water and Sanitation
   • Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials.
4. SDG 12: Responsible Consumption and Production
   • Target 12.4: By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle.
   • Target 12.5: By 2030, substantially reduce waste generation through prevention, reduction, recycling, and reuse.
5. SDG 15: Life on Land
   • Target 15.3: By 2030, combat desertification, restore degraded land and soil, including land affected by desertification, drought, and floods, and strive to achieve a land degradation-neutral world.

3. Indicators Mentioned or Implied in the Article

1. Soil Heavy Metal Concentrations
   • Measured concentrations of heavy metals such as Cd, Hg, As, Cu, Zn, Ni, Cr, and Pb in soil samples (mg·kg⁻¹).
   • Comparison with background values and risk screening values (e.g., GB 15618-2018 standards).
2. Enrichment Factor (EF)
   • Ratio of heavy metal concentration to reference element concentration (SiO₂) to assess human impact on soil heavy metal enrichment.
3. Environmental Capacity Indices
   • Static environmental capacity and existing environmental capacity of heavy metals in soil (kg·hm⁻²).
   • Dynamic environmental capacity over time to assess soil’s carrying capacity and pollution load.
   • Comprehensive environmental capacity index (PI) to evaluate overall pollution status.
4. Spatial Distribution Maps
   • GIS-based spatial distribution of heavy metal concentrations and environmental capacity indices to identify pollution hotspots and risk areas.
5. Source Apportionment Indicators
   • Principal Component Analysis (PCA) factor loadings to identify pollution sources (natural background, industrial, agricultural activities).

4. Summary Table of SDGs, Targets, and Indicators

SDGs	Targets	Indicators
SDG 2: Zero Hunger	2.4: Sustainable food production systems and resilient agricultural practices.	Soil heavy metal concentrations affecting agricultural productivity. Soil environmental capacity indices ensuring sustainable land use.
SDG 3: Good Health and Well-being	3.9: Reduce deaths and illnesses from hazardous chemicals and pollution.	Heavy metal contamination levels in soil and agricultural products. Risk screening values exceedance rates.
SDG 6: Clean Water and Sanitation	6.3: Improve water quality by reducing pollution and hazardous releases.	Heavy metal concentrations in soil affecting water bodies through runoff. Spatial distribution of pollution near water systems.
SDG 12: Responsible Consumption and Production	12.4: Environmentally sound management of chemicals and wastes. 12.5: Reduce waste generation through prevention and recycling.	Enrichment factor method to assess human impact on soil pollution. Monitoring of agricultural inputs (fertilizers, sludge) heavy metal content.
SDG 15: Life on Land	15.3: Combat desertification and restore degraded land and soil.	Environmental capacity indices indicating soil pollution and degradation. Spatial mapping of polluted and overloaded soil areas for targeted remediation.

Source: frontiersin.org