Agricultural soil pollution analysis is a critical process for identifying and quantifying contaminants such as heavy metals, pesticide residues, and organic pollutants in farmland that directly affect crop safety and human health. This article provides a comprehensive overview of sampling procedures, regulated testing items, analytical methods, and evaluation criteria based on recognized standards such as GB 15618-2018, ISO, and ASTM. Whether you are conducting a detailed soil pollution survey, verifying remediation effectiveness, or supporting safe farmland utilization, understanding these technical requirements is essential for reliable, compliant results.
Technical Overview
Agricultural soil pollution analysis refers to the systematic sampling, chemical testing, and risk evaluation of soil used for crop cultivation, including paddy fields, dry farmland, vegetable bases, and orchards. Soil contamination in agricultural land arises from multiple sources, including industrial emissions and deposition, mining and smelting activities, wastewater irrigation, excessive or improper application of fertilizers and pesticides, livestock waste, and atmospheric transport of pollutants. Because contaminants in soil can transfer into the food chain through crops, groundwater, and dust inhalation, systematic analysis is fundamental to food safety, land management, and public health protection.
In China, the evaluation of agricultural soil quality is governed primarily by GB 15618-2018, the risk control standard for soil contamination of agricultural land. This standard defines risk screening values and risk intervention values for eight basic inorganic pollutants, differentiated by land use type (paddy field versus other agricultural land) and soil pH range. Soils with contaminant concentrations below the screening values are generally considered to present negligible pollution risk; concentrations between the screening and intervention values trigger the need for detailed investigation and combined monitoring of agricultural products; concentrations above the intervention values indicate serious pollution requiring strict control measures, which may include planting structure adjustment or risk remediation. Sampling and monitoring procedures are further supported by technical specifications such as HJ/T 166-2004, GB/T 36198-2018, and the international sampling guidance in the ISO 10381 series.
Testing Samples
Surface Soil from Cultivated Land
The most common sample type is surface soil collected from the plow layer, typically at a depth of 0–20 cm. Surface samples reflect the soil zone in active contact with crop roots and are the primary basis for comparison against the risk screening values of GB 15618-2018. Sampling points are usually arranged in a grid pattern, with multiple subsamples combined into one representative composite sample of at least 1 kg.
Paddy Field Soil
Paddy field soils are analyzed as a distinct category because redox conditions under flooded cultivation significantly influence the mobility and bioavailability of contaminants such as cadmium and arsenic. Paddy samples require separate evaluation against the paddy-specific screening values, and sampling should account for irrigation water quality and flooding history.
Vegetable Greenhouse and Orchard Soil
Greenhouse soils and orchard soils often receive intensive fertilizer and pesticide inputs over long periods, resulting in characteristic accumulation of heavy metals such as copper and zinc, pesticide residues, and soil acidification. These samples are tested with an expanded analyte list covering both regulated metals and persistent organic contaminants.
Soil Profile and Deep Layer Samples
To characterize vertical contaminant migration, profile samples may be collected at multiple depths, for example 0–20 cm, 20–40 cm, 40–60 cm, and deeper intervals. Profile analysis is essential in areas near industrial sites, mining zones, or where historical spills may have transported pollutants below the surface layer.
Auxiliary Environmental Samples
When source tracing is required, agricultural soil analysis is often combined with testing of irrigation water, atmospheric deposition, fertilizer and amendment products, and crop or grain samples, enabling a complete exposure pathway assessment from pollution source to agricultural product.
Testing Items
A typical agricultural soil pollution analysis program includes basic physicochemical parameters, regulated inorganic pollutants, and selected organic contaminants. The scope is tailored to land use history, surrounding pollution sources, and regulatory requirements.
- Basic properties: pH, organic matter, cation exchange capacity (CEC), soil texture and particle size distribution, moisture content, and electrical conductivity.
- Regulated heavy metals and metalloids (GB 15618-2018 basic items): cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn).
- Additional inorganic pollutants selected based on regional conditions: vanadium (V), antimony (Sb), thallium (Tl), cobalt (Co), manganese (Mn), molybdenum (Mo), selenium (Se), fluoride, and soluble salts.
- Organochlorine pesticides: hexachlorocyclohexane (HCH) isomers, dichlorodiphenyltrichloroethane (DDT) and its metabolites.
- Other pesticides: organophosphorus pesticides, pyrethroids, amide herbicides, triazines, and carbamates.
- Semi-volatile organic pollutants: polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), petroleum hydrocarbons (C10–C40), and phthalate esters.
- Emerging contaminants: per- and polyfluoroalkyl substances (PFAS), antibiotic residues, and microplastics where relevant to land use history.
Testing Methods
Sample Collection and Preparation
Sampling follows grid-based or judgment-based designs in accordance with HJ/T 166-2004, GB/T 36198-2018, and ISO 10381. To avoid cross-contamination with target metals, sampling tools made of bamboo, wood, stainless steel, or titanium are used, and plastic or metal containers are selected according to the target analytes. Composite samples are reduced by quartering, transported under chain-of-custody procedures, air-dried in a clean environment, and ground with non-contaminating equipment such as agate mills. Prepared samples are sieved through 2 mm and 0.149 mm (100 mesh) nylon sieves depending on the analytical method.
Heavy Metal and Metalloid Analysis
For total metal content, soils are digested with aqua regia according to ISO 11466 or by microwave-assisted acid digestion with hydrofluoric acid for true total content following ISO 14869-1. Quantification is performed using inductively coupled plasma mass spectrometry (ICP-MS) for ultra-trace elements such as cadmium and thallium, inductively coupled plasma optical emission spectrometry (ICP-OES) for multi-element screening, flame and graphite furnace atomic absorption spectrometry (FAAS/GFAAS) for elements such as lead, cadmium, copper, and zinc, and atomic fluorescence spectrometry (AFS) for mercury and arsenic. Corresponding method standards include HJ 680, HJ 766, GB/T 17141, GB/T 17138, and GB/T 22105. Cold vapor atomic absorption may also be applied for mercury. Available or extractable fractions can additionally be assessed using sequential extraction procedures and DTPA extraction to estimate bioavailability to crops.
Organic Contaminant Analysis
Organic pollutants are extracted from soils using accelerated solvent extraction, ultrasonic extraction, or Soxhlet extraction, followed by cleanup through silica gel, Florisil, or gel permeation chromatography. Organochlorine pesticides and PCBs are quantified by gas chromatography with electron capture detection (GC-ECD) or gas chromatography-mass spectrometry (GC-MS) in accordance with standards such as HJ 835 and HJ 834. PAHs are determined by GC-MS or high-performance liquid chromatography with fluorescence detection (HPLC-FLD) following HJ 805. Organophosphorus pesticides and modern pesticide formulations are analyzed by GC-MS/MS or liquid chromatography-tandem mass spectrometry (LC-MS/MS), and petroleum hydrocarbons are quantified by gas chromatography with flame ionization detection (GC-FID).
Physicochemical Property Analysis
Soil pH is determined potentiometrically according to ISO 10390 or HJ 962, organic matter by the potassium dichromate oxidation method, cation exchange capacity following ISO 13536 or NY/T 295, and particle size distribution by pipette or laser diffraction methods. These parameters are essential because pH and organic matter strongly govern contaminant mobility and the applicable screening thresholds.
Quality Assurance and Quality Control
Accredited third-party laboratories implement comprehensive QA/QC programs, including method blanks, laboratory control samples, matrix spikes with defined recovery limits, duplicate analyses, certified reference materials (CRMs), and calibration verification. Multi-point subsampling and splitting ensure representativeness, and all results are reported with detection limits, measurement uncertainty, and full chain-of-custody documentation to support regulatory acceptance.
Applications
- Detailed investigation of soil pollution in farmland where screening-level surveys indicate exceedance of GB 15618-2018 risk screening values.
- Classification of agricultural land into priority protection, safe utilization, and strict control categories to support land quality management files.
- Joint evaluation of soil and agricultural products to determine safe planting strategies for cadmium- or arsenic-affected farmland.
- Verification of remediation effectiveness after soil passivation, replacement, deep plowing, or phytoremediation projects.
- Assessment of soil quality for high-standard farmland construction, pollution-free and organic production bases, and geographical indication product origins.
- Environmental due diligence for land transfer, agricultural development projects, and compliance monitoring around industrial or mining pollution sources.
- Scientific research on contaminant migration, bioavailability, and the relationship between soil pollution and crop uptake.
FAQ
What is the difference between risk screening values and risk intervention values?
Risk screening values are concentration thresholds below which soil pollution risk to agricultural products and human health is generally considered negligible. Risk intervention values are higher thresholds above which soil poses a serious risk, requiring strict control measures such as planting restrictions or remediation. Concentrations between the two values require detailed investigation and combined soil-crop monitoring, as specified in GB 15618-2018.
At what depth should agricultural soil samples be collected?
For routine pollution assessment, surface soil from the cultivated layer at 0–20 cm depth is collected. For paddy fields with deeply plowed layers, sampling may extend to 25 cm. Deeper profile samples are collected when vertical migration assessment is needed near industrial or mining sources.
How many sampling points are required for a farmland plot?
Sampling density depends on the investigation stage and plot heterogeneity. Grid-based designs are standard, with finer grids applied during detailed investigation of confirmed polluted areas. Professional sampling plans also account for topography, crop type, irrigation patterns, and known pollution source locations.
How long does agricultural soil pollution analysis take?
Standard testing of basic heavy metals and physicochemical parameters is typically completed within 7–10 working days after sample receipt. Programs including organic contaminants, profile sampling, or expanded analyte lists generally require 10–20 working days depending on laboratory workload and QC requirements.
What should be done if test results exceed the screening values?
Exceedance does not automatically mean crops are unsafe, because contaminant bioavailability varies with soil properties. The recommended steps are a detailed investigation with increased sampling density, joint testing of soil and grown agricultural products, evaluation against food safety limits, and implementation of safe utilization measures such as pH adjustment, variety selection, or soil amendments under technical guidance.
Can the results be used for regulatory and compliance purposes?
Yes, provided the analysis is performed by accredited third-party laboratories using recognized method standards, documented QA/QC procedures, and traceable chain-of-custody records. Reports issued under formal accreditation schemes are accepted by environmental authorities for detailed investigations, remediation acceptance, and land management decisions.