Agricultural land pollutant analysis is a systematic laboratory testing process that identifies and quantifies heavy metals, pesticide residues, and organic contaminants in farmland soil, irrigation water, and agricultural products. By applying national and international standards such as GB 15618 and ISO soil quality methods, accredited third-party laboratories help growers, enterprises, and regulators determine whether agricultural land is safe for food production. This article explains the sample types, testing items, analytical methods, quality control requirements, and practical applications of agricultural land pollutant analysis.
Technical Overview
Agricultural land pollutant analysis refers to the comprehensive sampling, pretreatment, and laboratory determination of contaminants that accumulate in cultivated soil and can transfer into the food chain. The pollutants of greatest concern include heavy metals and metalloids such as cadmium, lead, mercury, arsenic, chromium, copper, nickel, and zinc, as well as persistent organic pollutants including organochlorine pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and total petroleum hydrocarbons. Emerging contaminants such as per- and polyfluoroalkyl substances (PFAS), veterinary antibiotics, and microplastics are receiving increasing attention in farmland monitoring programs.
In China, the core regulatory basis is GB 15618, the risk control standard for soil contamination of agricultural land, which defines risk screening values and risk control values for eight inorganic contaminants, differentiated by land use type (paddy field versus dryland) and soil pH range. Supporting standards include GB 5084 for irrigation water quality and GB 2762 for contaminant limits in food. At the international level, ISO soil quality standards such as ISO 10381 for sampling, ISO 11466 for aqua regia extraction, and ISO 11047 for metal determination by atomic absorption spectrometry are widely applied. Agricultural land pollutant analysis is typically performed by accredited third-party laboratories operating under ISO/IEC 17025 quality management systems.
The fundamental purpose of this analysis is to determine whether contaminant concentrations pose an unacceptable risk to crop safety and human health, to classify farmland into management categories such as priority protection, safe utilization, and strict control, and to provide a scientific basis for soil remediation, planting structure adjustment, and long-term monitoring.
Testing Samples
Farmland Surface Soil and Profile Samples
Surface soil from the plow layer (0–20 cm) is the primary matrix, because this horizon is where contaminants from atmospheric deposition, fertilizer inputs, and irrigation accumulate and where crop roots absorb them. For risk confirmation or vertical migration studies, subsoil samples from 20–40 cm and deeper genetic horizons are collected. Sampling is usually performed on a grid basis, with each composite sample combining 5–20 subsamples collected with stainless steel or plastic tools to avoid cross-contamination with target metals. Galvanized or brass implements must never be used when sampling for zinc, copper, or lead determination.
Paddy Field Soils
Paddy soils are analyzed as a distinct category because flooding and drainage cycles create alternating redox conditions that strongly influence the mobility and bioavailability of cadmium and arsenic. GB 15618 assigns different screening values to paddy land compared with other agricultural land, so accurate land use classification during sampling is essential for correct data interpretation.
Greenhouse and Intensive Horticultural Soils
Protected cultivation soils under plastic greenhouses and intensive vegetable production bases often receive elevated inputs of fertilizers, manure, and pesticides, leading to accumulation of heavy metals such as copper, zinc, and cadmium, nutrient excess, salinization, and pesticide residues. These samples are analyzed for metals, organics, pH, electrical conductivity, and nutrient status in combination.
Irrigation Water and Ditch Sediment
Irrigation water is a major pathway through which pollutants enter farmland, particularly in areas using treated wastewater or receiving upstream industrial discharge. Water samples are evaluated against GB 5084, covering pH, heavy metals, salinity, cyanide, fluoride, and organic indicators. Sediments from irrigation channels and drainage ditches are collected to assess historical pollutant deposition and secondary release risks.
Agricultural Products and Plant Tissues
Co-located crops such as rice grain, wheat grain, vegetables, and tea leaves are frequently tested alongside soil to establish soil–crop transfer relationships. Edible portions are compared against GB 2762 food contaminant limits, which is critical when soil concentrations fall between screening and control values and a site-specific risk judgment is required.
Fertilizers, Manure, and Soil Amendments
Phosphate fertilizers, livestock manure, compost, and biosolid-derived amendments are analyzed for heavy metals, antibiotics, and pathogen indicators before land application, because repeated amendment input is a well-documented source of cadmium, zinc, copper, and arsenic accumulation in agricultural soil.
Testing Items
Inorganic Pollutants
Inorganic analysis covers the eight heavy metals and metalloids regulated by GB 15618, together with supplementary elements of regional or crop-specific concern:
- Core regulated elements: cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn)
- Supplementary elements: selenium (Se), thallium (Tl), cobalt (Co), vanadium (V), beryllium (Be), manganese (Mn), and fluoride
- Speciation parameters where required, such as exchangeable cadmium or arsenic speciation for bioavailability assessment
Organic Pollutants
Organic analysis targets persistent and semi-volatile contaminants introduced by historical pesticide use, industrial deposition, and irrigation:
- Organochlorine pesticides: hexachlorocyclohexane (HCH) isomers, DDT and metabolites, endosulfan, aldrin, and dieldrin
- Organophosphorus, carbamate, pyrethroid, and amide pesticides in current agricultural use
- Polycyclic aromatic hydrocarbons (16 priority PAHs) and total petroleum hydrocarbons
- Polychlorinated biphenyls, chlorophenols, and phthalate esters
Emerging Contaminants
Monitoring programs increasingly include PFAS, veterinary antibiotics such as tetracyclines, sulfonamides, and fluoroquinolones derived from manure application, hormone residues, and microplastics, for which screening-level surveys are performed in areas near industrial sources or intensive livestock operations.
Physicochemical Parameters
Soil pH, organic matter, cation exchange capacity, texture, and moisture are measured together with pollutants, because pH and organic matter content directly determine which GB 15618 screening value applies and strongly influence metal mobility and crop uptake.
Testing Methods
Sampling and Sample Pretreatment
Sampling follows ISO 10381 and the corresponding national technical specifications, including grid layout, composite sampling, GPS positioning, and chain-of-custody documentation. Samples for metal analysis are air-dried at room temperature, ground, and sieved through 2 mm and 0.149 mm (100 mesh) nylon sieves in accordance with ISO 11464. Samples for organic analysis are transported in pre-baked amber glass jars at 4 °C and extracted within the specified holding time to prevent volatilization and biodegradation.
Heavy Metal Determination
For total metal content, soil is digested with aqua regia according to ISO 11466, or with hydrofluoric acid based total dissolution according to ISO 14869 when true total contents are required. Determination techniques are selected according to sensitivity and element behavior:
- Inductively coupled plasma mass spectrometry (ICP-MS) for multi-element ultra-trace determination, following ISO 17294-2
- Inductively coupled plasma optical emission spectrometry (ICP-OES) for higher-concentration elements, following ISO 11885
- Graphite furnace atomic absorption spectrometry for lead and cadmium, following GB/T 17141 and ISO 11047
- Atomic fluorescence spectrometry for mercury and arsenic, following GB/T 22105
- Cold vapor atomic absorption spectrometry for mercury, following GB/T 17136, or direct thermal decomposition analyzers for mercury screening
Organic Pollutant Determination
Organic contaminants are extracted by accelerated solvent extraction, Soxhlet extraction, or ultrasonic extraction, followed by cleanup through solid-phase extraction, florisil, or gel permeation chromatography. Instrumental determination employs gas chromatography with electron capture detection for organochlorine pesticides according to GB/T 14550, gas chromatography–mass spectrometry for PAHs according to ISO 18287 and for pesticide multi-residue screening, gas chromatography–tandem mass spectrometry for complex residues, and liquid chromatography–tandem mass spectrometry (LC-MS/MS) for polar pesticides, antibiotics, and PFAS.
Physicochemical and Support Analysis
Soil pH is measured potentiometrically according to ISO 10390 or ASTM D4972, organic carbon by sulfochromic oxidation according to ISO 14235, and cation exchange capacity by buffered extraction methods. These parameters are reported with every pollutant data set to enable correct regulatory comparison.
Rapid Field Screening
Portable X-ray fluorescence (XRF) analyzers are used for on-site screening of heavy metals prior to laboratory confirmation, allowing dense grid coverage and cost-effective identification of hotspots. Photoionization detectors support preliminary screening of volatile organic contamination. All screening results exceeding 50–80 percent of the applicable screening value are confirmed by laboratory analysis.
Quality Assurance and Quality Control
Accredited third-party laboratories apply ISO/IEC 17025 management requirements, including certified reference materials, method blanks, laboratory duplicates, matrix spikes, calibration verification, and rigorous detection limits that must be well below the applicable GB 15618 screening values. Measurement uncertainty is reported so that results can be statistically compared against regulatory thresholds, and proficiency testing participation validates laboratory competence.
Applications
Agricultural land pollutant analysis supports a wide range of regulatory, commercial, and scientific objectives:
- Farmland classification and management zoning into priority protection, safe utilization, and strict control categories based on GB 15618
- National and regional soil pollution status surveys and detailed investigations around industrial, mining, and peri-urban areas
- Design, implementation verification, and post-remediation effectiveness evaluation of soil remediation projects
- Food safety assurance through combined soil, irrigation water, and crop testing for grain, vegetable, fruit, and tea production bases
- Certification support for geographical indication products, green food, and organic production bases
- High-standard farmland construction, land improvement, and land transfer quality assessment
- Compliance evaluation for land application of fertilizers, manure, compost, and soil conditioners
- Pollution source identification and forensic tracing, including lead isotope fingerprinting where liability disputes arise
FAQ
Which standard defines acceptable pollutant levels in agricultural soil?
In China, GB 15618 establishes risk screening values and risk control values for eight inorganic contaminants in agricultural land, with thresholds varying by pH and by paddy versus dryland use. Irrigation water is governed by GB 5084, and contaminant limits in food are set by GB 2762. International projects commonly apply ISO soil quality standards or ASTM test methods as the analytical basis.
At what depth and density are soil samples collected?
The standard sampling depth is the plow layer at 0–20 cm, with 20–40 cm subsoil samples collected during risk confirmation. Sampling density follows grid-based survey specifications, and each composite sample typically integrates 5–20 subsample points to ensure representativeness across a management unit.
What is the difference between risk screening values and risk control values?
Screening values indicate the concentration below which soil contamination risk to agricultural products and human health is generally considered acceptable. Exceedance of a screening value signals possible risk and triggers enhanced investigation, crop co-testing, and monitoring. Exceedance of a control value indicates high risk and requires strict risk control measures, planting restrictions, or remediation.
Can soil, water, and crops be tested together?
Yes. An integrated soil–water–crop assessment is the recommended approach, because it directly demonstrates whether soil pollutant levels are translating into food chain contamination, and it provides the strongest basis for safe-utilization decisions such as varietal substitution or adjusted irrigation management.
How long does the analysis take and how should samples be preserved?
Heavy metal and physicochemical analysis typically requires 7–10 working days, while multi-residue organic analysis may require 10–15 working days. Metal samples are air-dried and stored in polyethylene containers, whereas organic samples must be chilled to 4 °C in amber glass jars and delivered promptly to the laboratory.
What happens if results exceed the screening values?
The land manager should commission a detailed investigation including denser sampling and crop testing, classify the plot into the appropriate management category, implement safe-utilization measures such as soil conditioning, passivation agents, or low-accumulation crop varieties, and establish periodic monitoring until concentrations fall within acceptable limits.