Common Heavy Metals Found in Soil and Their Sources

Heavy metals occur naturally in the Earth’s crust, but human activity has significantly elevated their concentrations in soils across the United States. For property developers, environmental consultants, and land managers, understanding which metals pose risks and where they come from is the first step toward effective site assessment and remediation.

Lead (Pb) is one of the most frequently encountered soil contaminants in urban and suburban environments. Historical sources include lead-based paint (used extensively in buildings constructed before 1978), leaded gasoline emissions that deposited along roadways for decades, and industrial operations such as smelting and battery manufacturing. Lead binds tightly to soil particles and can persist at elevated levels for centuries.

Arsenic (As) presents a dual challenge because it occurs both naturally in certain geological formations and as a result of human activity. In the southwestern United States, naturally elevated arsenic levels are common due to regional geology. Anthropogenic sources include historical pesticide applications (lead arsenate was widely used in orchards), mining operations, and wood treatment with chromated copper arsenate (CCA).

Mercury (Hg) enters soil through atmospheric deposition from coal-fired power plants, historical mining operations (particularly gold and silver extraction), and improper disposal of mercury-containing equipment.

Cadmium (Cd) contamination is associated with battery manufacturing, phosphate fertilizers, metal plating operations, and plastic stabilizer production. Agricultural soils may accumulate cadmium through long-term fertilizer application, making this metal a concern during land use transitions.

Chromium (Cr) is linked to leather tanning, metal finishing, and wood preservation. While trivalent chromium (Cr III) is relatively stable, hexavalent chromium (Cr VI) is highly toxic and mobile in soil, requiring careful analytical differentiation.

One of the defining characteristics of heavy metal contamination is persistence. Unlike organic pollutants that can break down over time, metals do not degrade. They may change chemical form or move between soil layers, but they remain in the environment indefinitely. This persistence is precisely why heavy metals screening is a fundamental component of environmental site investigations.

EPA Regional Screening Levels and State-Specific Standards

The U.S. Environmental Protection Agency (EPA) publishes Regional Screening Levels (RSLs) that serve as the primary benchmarks for evaluating soil contamination. These risk-based concentrations help environmental professionals determine whether detected levels of heavy metals warrant further investigation or remedial action.

RSLs are calculated using standardized exposure assumptions, toxicity values, and risk targets — typically a cancer risk of 1 x 10^-6 for carcinogens and a hazard quotient of 1.0 for non-carcinogens. Two sets of RSLs are published for soil:

• Residential RSLs assume long-term exposure including direct soil contact, incidental ingestion, and inhalation of dust, with children considered the most sensitive receptors
• Industrial/Commercial RSLs assume adult-only exposure during working hours with less direct soil contact

The difference between residential and commercial thresholds can be substantial. For example, the EPA residential screening level for arsenic in soil is 0.68 mg/kg (based on cancer risk), while the commercial/industrial level is 3.0 mg/kg. For lead, the residential screening level is 400 mg/kg, while commercial sites may reference higher action levels depending on state guidance. These differences directly affect project feasibility and remediation costs.

In Arizona, the Arizona Department of Environmental Quality (ADEQ) administers soil remediation standards through its Water Quality Assurance Revolving Fund (WQARF) program and the Voluntary Remediation Program. ADEQ has established soil remediation levels (SRLs) that may differ from federal RSLs based on Arizona-specific exposure factors and site conditions. Additionally, Arizona’s naturally elevated background concentrations of certain metals, particularly arsenic, must be considered when interpreting analytical results.

When analytical results exceed applicable screening levels, the response depends on the magnitude of exceedance and the intended land use. Options may include:

• Additional delineation sampling to define the extent of contamination
• Risk assessment to evaluate actual exposure pathways
• Development of a remedial action plan
• Institutional or engineering controls to limit exposure
• Soil removal and off-site disposal

When Heavy Metals Soil Testing Is Required

Numerous regulatory and transactional scenarios trigger the need for heavy metals analysis in soil. Understanding when testing is required helps property owners, developers, and consultants plan effectively and avoid costly delays.

Phase II Environmental Site Assessments (ESAs) are the most common driver of heavy metals soil testing. When a Phase I ESA identifies recognized environmental conditions (RECs) such as historical industrial use, underground storage tanks, or evidence of contamination, a Phase II investigation is conducted to collect and analyze soil and groundwater samples. Heavy metals are typically included in the analytical suite based on the site’s history and suspected contaminant sources.

Brownfield redevelopment projects almost always require comprehensive heavy metals testing. Brownfields are properties where expansion, redevelopment, or reuse may be complicated by the presence or potential presence of hazardous substances. Federal and state brownfield programs provide funding and liability protections, but they require thorough characterization of soil conditions, including metals analysis.

Real estate transactions increasingly involve environmental due diligence beyond the standard Phase I ESA. Lenders, investors, and buyers may require Phase II sampling to confirm that a property is free from contamination before closing. This is particularly common for properties with prior industrial, agricultural, or commercial uses.

Construction and excavation permits may require soil testing when projects disturb potentially contaminated land. Municipalities and counties may impose testing requirements for excavated soil to determine appropriate disposal methods. Soil classified as hazardous waste due to elevated metals concentrations requires special handling and disposal at permitted facilities.

School and daycare site assessments are subject to heightened scrutiny due to the vulnerability of children to heavy metal exposure. Many states require environmental assessments before new schools or childcare facilities can be constructed, with soil testing for metals being a standard component. Lead and arsenic are of particular concern in these settings.

Agricultural land use changes trigger testing when farmland is being converted to residential or commercial development. Long-term agricultural practices may have introduced arsenic (from pesticides), cadmium (from fertilizers), and lead (from historical orchard treatments) into the soil.

Voluntary cleanup programs allow property owners to proactively investigate and remediate contamination under state regulatory oversight. In Arizona, the ADEQ Voluntary Remediation Program provides a framework for obtaining closure on environmental issues, with metals testing forming a core part of the investigation process.

How to Collect Soil Samples for Accurate Heavy Metals Analysis

The reliability of laboratory results depends on the quality of sample collection. Improper techniques can produce misleading data, leading to unnecessary remediation costs or undetected contamination. Here is how to collect soil samples that yield defensible, accurate results.

Sampling Design: Grid vs. Composite Approaches

Two primary sampling strategies are used for heavy metals investigations. Systematic grid sampling places sample locations at regular intervals across a site, providing comprehensive spatial coverage and the ability to map contaminant distribution. This approach is preferred for large sites and regulatory investigations. Composite sampling combines soil from multiple locations into a single sample, reducing analytical costs while providing an average concentration for a defined area. Composite sampling is useful for screening purposes but may dilute localized hot spots.

Depth Requirements

Sample depth depends on the investigation objectives and regulatory requirements. Surface samples (0 to 6 inches or 0 to 2 inches for lead) evaluate direct contact exposure risk. Subsurface samples at various depth intervals assess the vertical extent of contamination and potential impacts to groundwater. Most residential risk assessments focus on the top two feet of soil, while commercial and industrial assessments may require deeper sampling.

Sample Handling and Preservation

Proper sample handling is essential for data quality:

• Use laboratory-supplied, certified-clean glass or plastic containers appropriate for metals analysis
• Avoid using galvanized or metal sampling tools that could introduce contamination
• Cool samples to 4 degrees Celsius immediately after collection
• Keep samples in dark conditions during transport
• Deliver samples to the laboratory within prescribed holding times (typically 180 days for most metals in soil, though shorter for mercury)

Chain of Custody Documentation

Every sample must be accompanied by a complete chain of custody (COC) form that records sample identification, collection date and time, preservatives used, analyses requested, and the names of everyone who handles the samples. This documentation is critical for data defensibility in regulatory and legal contexts.

Number of Samples

The appropriate number of samples depends on site size, suspected contamination patterns, and regulatory requirements. General guidance suggests a minimum of one sample per 2,500 to 10,000 square feet for initial screening, with additional samples collected in areas of suspected contamination. Your environmental consultant can determine the optimal sampling density based on site-specific conditions and applicable regulatory guidance.

How AATLS Supports Environmental Consultants and Developers

AATLS provides environmental lab services designed to support the full lifecycle of property development and remediation projects. As an ISO 17025 accredited laboratory, we perform heavy metals analysis using EPA-approved methods including EPA Method 6010 (ICP-OES) and EPA Method 6020 (ICP-MS), delivering accurate, defensible results. Our team works directly with environmental consultants to ensure proper sample submission, appropriate method selection, and clear reporting that meets regulatory requirements.

We offer expedited turnaround options and maintain open communication throughout the analytical process. Whether you need screening-level analysis for a preliminary assessment or full quantitative results for regulatory closure, AATLS delivers the data you need to move your project forward.

Need heavy metals soil testing for your project? AATLS provides EPA-method analysis with fast turnaround and comprehensive reporting. Call (928) 985-9399 or request a quote to get started.