Agricultural land soil pollutant testing is the systematic analysis of farmland soil to identify and quantify heavy metals, pesticide residues, petroleum hydrocarbons, and other contaminants that threaten crop safety, food quality, and sustainable land use. Accredited third-party laboratories perform these analyses in accordance with GB 15618-2018, ISO, ASTM, and HJ standards, delivering defensible data for risk screening, land classification, remediation, and regulatory compliance. This article provides a complete technical guide covering sample types, testing items, analytical methods, quality control, and practical applications.
Technical Overview
Agricultural land soil pollutant testing is a fundamental component of farmland environmental management and food safety assurance. Long-term application of fertilizers and pesticides, irrigation with polluted water, atmospheric deposition, and the historical presence of industry or mining near cultivation areas can introduce persistent contaminants into agricultural soil. Once accumulated, substances such as cadmium, arsenic, lead, and organochlorine pesticides can transfer into crops and enter the food chain, making reliable laboratory analysis essential for risk identification and control.
The principal regulatory benchmark in China is GB 15618-2018, the Soil Environmental Quality Standard for Risk Control of Soil Contamination of Agricultural Land. This standard defines risk screening values and risk control values for eight basic indicators, namely cadmium, mercury, arsenic, lead, chromium, copper, nickel, and zinc, with thresholds that vary according to soil pH and land use type, distinguishing paddy fields from other categories of agricultural land. Exceedance of a screening value triggers the need for detailed investigation, while exceedance of a control value indicates a high probability of unacceptable risk to agricultural products and the need for strict control or remediation measures.
Under the Soil Pollution Prevention and Control Law, which came into effect on January 1, 2019, agricultural land is managed through categorized classification into priority protection, safe utilization, and strict control categories. Soil pollutant testing provides the technical data foundation for this classification, supporting decisions on land use adjustment, remediation technology selection, and the verification of remediation outcomes.
- Risk screening and compliance assessment against GB 15618-2018 limit values
- Detailed investigation of plots where screening values are exceeded
- Baseline surveys prior to land transfer, leasing, or agricultural investment
- Verification of remediation effectiveness through before-and-after comparison
- Support for safe utilization measures such as passivation, soil dressing, and crop substitution
Testing Samples
Representative sampling is critical because soil contamination is typically heterogeneous. Sampling plans are designed according to the objectives of the survey, land use history, suspected pollution sources, and the requirements of HJ/T 166-2004, NY/T 395-2012, and the ISO 10381 series on soil sampling.
Plow-Layer Soil Samples
The plow layer, generally 0 to 20 centimeters deep for cultivated field crops and 0 to 40 centimeters for orchards and vineyards, is the primary sampling zone because it is the root-active horizon where contaminants interact with crops. Grid-based sampling is applied, with composite samples prepared by mixing subsamples collected at 3 to 20 points arranged in five-point, S-shaped, chessboard, or diagonal patterns within each sampling unit. Approximately 1 to 2 kilograms of soil is retained per composite sample after quartering.
Deep Profile Soil Samples
Profile samples are collected from excavated pits or drilled boreholes to depths of 1.0 to 2.0 meters, with subsamples taken by genetic horizon. Deep profiling is used to evaluate the vertical migration of leachable contaminants such as cadmium, arsenic, and petroleum hydrocarbons, particularly in detailed investigations near former industrial sites, landfills, mining areas, or wastewater irrigation channels.
Greenhouse and Facility Agriculture Soil
Intensive protected cultivation systems often show accumulated pesticide residues, plasticizer contamination, secondary salinization, and acidification. Greenhouse soil testing combines pollutant screening with salinity and pH assessment to characterize the distinctive contamination profile of facility agriculture.
Reference, Background, and Special-Purpose Samples
Background samples from uncontaminated areas with similar soil parent material are collected for comparison. Rhizosphere soil samples support crop uptake studies, and paired samples of irrigation water or adjacent ditch sediment may be collected to trace pollution sources. For paddy fields, sampling under representative moisture conditions is documented to ensure comparability.
Testing Items
Testing portfolios are configured according to the intended land use, suspected contamination sources, and the applicable standard. A typical farmland assessment panel combines inorganic pollutants, organic pollutants, and soil physicochemical parameters.
Heavy Metals and Metalloids
- The eight basic indicators of GB 15618-2018: cadmium, mercury, arsenic, lead, chromium, copper, nickel, and zinc
- Supplementary metals: hexavalent chromium, selenium, antimony, vanadium, cobalt, thallium, beryllium, molybdenum, and manganese
- Fluoride and other inorganic anions where regional geological backgrounds warrant attention
Organic Pollutants
- Organochlorine pesticides: hexachlorocyclohexane isomers, DDT and its metabolites DDE and DDD, aldrin, dieldrin, endrin, and heptachlor
- Polycyclic aromatic hydrocarbons, including the sixteen priority compounds such as benzo[a]pyrene
- Polychlorinated biphenyls, reported as indicator congeners and total content
- Total petroleum hydrocarbons in the C10-C40 carbon range
- Volatile and semi-volatile organic compounds, including benzene series, chlorinated solvents, phenols, nitroaromatics, and phthalate esters
Emerging Contaminants
- Per- and polyfluoroalkyl substances, including PFOA and PFOS, analyzed by isotope-dilution liquid chromatography-tandem mass spectrometry
- Veterinary antibiotic residues and their degradation products linked to manure and sludge application
- Microplastics and nonylphenol-type endocrine disrupting compounds
Physicochemical Properties and Nutrients
- pH, which is mandatory because GB 15618-2018 screening values are pH-dependent
- Organic matter and organic carbon, cation exchange capacity, and electrical conductivity
- Total nitrogen, available phosphorus, and available potassium for integrated fertility evaluation
- Soil moisture, particle size distribution, and texture classification
Testing Methods
Accredited third-party laboratories apply standardized national and international methods covering the complete analytical chain from field sampling to data reporting, ensuring that results are scientifically valid and legally defensible.
Sampling and Sample Preparation
Field sampling follows HJ/T 166-2004, NY/T 395-2012, and the ISO 10381 series. Stainless steel, wooden, or nylon tools are used to avoid cross-contamination with target metals. In the laboratory, samples for metal analysis are air-dried at room temperature, crushed with agate or nylon equipment, and sieved to 2 millimeters for general tests, 0.25 millimeters for organic matter, and 0.149 millimeters for elemental analysis, following ISO 11464. Samples for volatile organic compounds are refrigerated and analyzed without drying. Subsampling is performed by coning and quartering, and moisture content is determined in parallel for dry-weight correction.
Digestion and Extraction
For heavy metals, two digestion strategies are applied. Aqua regia extraction in accordance with HJ 803-2013 and ISO 11466 recovers the environmentally relevant acid-soluble fraction of twelve metallic elements. Total digestion with hydrofluoric acid based systems following HJ 832-2013 or HJ 680-2013 dissolves silicates and yields total elemental content. For organic pollutants, extraction is performed by accelerated solvent extraction, microwave-assisted extraction, or ultrasonic extraction, followed by cleanup through silica gel, alumina, florisil, or solid-phase extraction cartridges to remove matrix interferences.
Instrumental Analysis for Heavy Metals
Inductively coupled plasma mass spectrometry is the preferred multi-element technique for cadmium, lead, nickel, copper, zinc, and trace metals, following HJ 680-2013 and ISO 17294-2. Inductively coupled plasma optical emission spectrometry following HJ 803-2013 is used for higher-concentration elements. Graphite furnace atomic absorption spectrometry in accordance with GB/T 17141-1997 and ISO 11047 provides sensitive determination of lead and cadmium. Arsenic, mercury, and selenium are quantified by atomic fluorescence spectrometry following GB/T 22105.1-2008, with cold vapor techniques available for mercury confirmation. Hexavalent chromium is determined after alkaline digestion using colorimetric or ion chromatographic detection.
Instrumental Analysis for Organic Pollutants
Gas chromatography-mass spectrometry is the core platform for organic contaminants: HJ 835-2017 for organochlorine pesticides, HJ 805-2016 and ISO 18287 for polycyclic aromatic hydrocarbons, HJ 743-2015 for polychlorinated biphenyls, HJ 834-2017 for semi-volatile organic compounds, and HJ 642-2013 for volatile organic compounds by headspace analysis. Gas chromatography with electron capture detection in accordance with ISO 10382 offers a complementary technique for organochlorine pesticides. Total petroleum hydrocarbons C10-C40 are quantified by gas chromatography with flame ionization detection following HJ 1051-2019.
Physicochemical Testing
Soil pH is measured potentiometrically in a soil-water suspension following HJ 962-2018, ISO 10390, and ASTM D4972. Organic matter is determined by potassium dichromate oxidation according to the NY/T 1121 series, with organic carbon alternatively measured by elemental or combustion analysis in line with ISO 10694. Cation exchange capacity is determined following NY/T 1121.5 and ISO 11260. Nutrients are analyzed by flow injection analysis, spectrophotometry, and flame atomic absorption. Moisture content is determined gravimetrically following ASTM D2216.
Quality Assurance and Quality Control
Testing is performed in laboratories accredited to ISO/IEC 17025 with CMA metrology accreditation for regulatory reporting. Quality control measures include method blanks, laboratory duplicates at a minimum frequency of ten percent with relative deviation limits typically within thirty percent, matrix spike recoveries within the 70 to 130 percent range, certified reference materials for accuracy verification, multipoint calibrations with correlation coefficients of at least 0.995, and continuing calibration verification. Reporting limits are maintained below the lowest applicable GB 15618-2018 screening values so that compliance decisions remain statistically supported.
Applications
Test data from agricultural soil pollutant analysis directly support regulatory, commercial, and scientific decision-making across the agricultural lifecycle.
- Farmland soil environmental quality assessment and classification against GB 15618-2018 screening and control values
- Detailed investigation supporting safe utilization plans, including passivation agent application, soil dressing, deep plowing, and cultivation of low-accumulation crop varieties
- Verification of remediation effectiveness through statistically designed before-and-after comparison sampling
- Acceptance testing for high-standard farmland construction and integrated soil fertility and pollution surveys
- Origin environment assessment for green food, organic certification, and geographical indication agricultural products
- Environmental due diligence for land transfer, leasing, and agricultural investment transactions
- Traceability investigation of food safety incidents by pairing soil data with crop testing under GB 2762 food contaminant limits
- Long-term soil quality monitoring networks, academic research, and pollution source apportionment studies
FAQ
What is the difference between risk screening values and risk control values?
Risk screening values in GB 15618-2018 define the concentration threshold below which soil contamination risk is generally considered negligible and land can be used normally. Exceedance of a screening value indicates the need for a detailed investigation and enhanced monitoring. Risk control values represent concentrations above which contamination is likely to pose an unacceptable risk to agricultural products, requiring strict control measures, restricted planting, or remediation.
How many sampling points are required for a farmland survey?
Point density depends on the survey objective. General status surveys commonly use grid units or a defined area per composite sample, while detailed investigations for risk delineation or remediation design require denser grids defined by HJ/T 166-2004 and the relevant remediation technical specifications. Accredited third-party laboratories design statistically valid sampling plans based on plot size, heterogeneity, and data quality objectives.
How should soil samples be collected, stored, and transported?
Sampling should avoid fertilization and pesticide application periods and recent rainfall. Composite samples of 1 to 2 kilograms are collected using non-contaminating tools, with debris and foreign matter removed. Samples for metal and nutrient analysis are air-dried, while samples for volatile and semi-volatile organics are stored in pre-cleaned amber glass containers at 4 degrees Celsius or below and extracted within the standard holding period, typically seven to fourteen days.
How long does agricultural soil testing take?
Standard heavy metal panels with pH are usually completed within 7 to 10 working days after laboratory receipt. Comprehensive suites including organochlorine pesticides, PAHs, PCBs, and petroleum hydrocarbons generally require 10 to 15 working days due to extended extraction and cleanup procedures. Expedited services can be arranged for time-critical projects.
Are the test reports valid for government filing and regulatory use?
Yes. Reports issued by laboratories holding CMA accreditation and operating under ISO/IEC 17025 management systems are accepted by environmental and agricultural authorities for filing, categorized land management, remediation acceptance, and dispute resolution, provided the sampling process and analytical methods meet the applicable technical specifications.
Should crops be tested together with the soil?
Paired testing is strongly recommended when screening values are exceeded. Crop analysis against the contaminant limits in GB 2762 establishes whether soil contamination is actually transferring into agricultural products, which is decisive for selecting safe utilization pathways such as variety substitution or land use adjustment.