Soil Environmental Monitoring and Analysis: Technical Standards, Testing Methods, and Applications

Soil environmental monitoring and analysis is a systematic process of sampling, testing, and evaluating soil quality to identify contamination levels, assess ecological and human health risks, and ensure regulatory compliance. Accredited third-party laboratories apply internationally recognized standards such as GB 36600, GB 15618, ISO, and ASTM methods to deliver accurate and legally defensible soil testing data. This article provides a comprehensive technical overview of soil sampling procedures, testing parameters, analytical methods, and practical applications across agricultural, industrial, and urban land uses.

Technical Overview

Soil environmental monitoring and analysis refers to the structured collection and laboratory examination of soil samples to determine the presence and concentration of physical, chemical, and biological contaminants. Soil serves as both a sink and a source of pollutants, accumulating heavy metals, persistent organic pollutants, petroleum hydrocarbons, and agrochemical residues over time. These contaminants can migrate into groundwater, enter the food chain through crops, and pose direct exposure risks to humans through ingestion, inhalation of dust, and dermal contact.

The technical framework for soil monitoring is governed by a hierarchy of national and international standards. In China, GB 36600-2018 establishes risk screening values and risk control values for soil contamination of development land, covering 85 basic items and 40 additional items. GB 15618-2018 provides risk control standards for agricultural land, focusing on cadmium, mercury, arsenic, lead, chromium, copper, nickel, and zinc. HJ/T 166-2004 defines the technical specifications for soil environmental monitoring, including sampling point layout, sample collection, transportation, preservation, and quality assurance requirements. Internationally, the ISO 10381 series addresses soil sampling design, while ASTM and ISO methods specify analytical procedures for individual parameters.

A complete soil monitoring program typically consists of four stages: investigation design and sampling plan development, field sampling and sample pretreatment, laboratory analysis, and data evaluation against applicable screening or intervention values. Robust quality assurance and quality control (QA/QC) protocols, including field duplicates, blanks, spike recoveries, and certified reference materials, are essential to ensure data validity and legal defensibility.

Testing Samples

Agricultural Soil

Agricultural soil samples are collected from cultivated land, orchards, vegetable plots, and greenhouse operations. Surface samples are generally taken from the 0 to 20 cm plow layer for fertility and contamination assessment, with deeper 20 to 40 cm samples collected where vertical migration is suspected. Monitoring focuses on heavy metals, pesticide residues, and nutrient balance to ensure food safety and sustainable production.

Construction and Development Land

Soil from residential, commercial, and industrial redevelopment sites is tested in accordance with GB 36600-2018 and the HJ 25.1 investigation guidelines. Samples are collected using systematic grid layouts, typically at depths of 0 to 0.5 m, 0.5 to 1.5 m, and 1.5 to 3 m, depending on the suspected contamination depth. This category supports land transactions, redevelopment approvals, and pollution liability evaluations.

Industrial and Contaminated Site Soil

Soil from active or abandoned industrial facilities, such as chemical plants, smelters, gas stations, electroplating workshops, and landfills, requires detailed site investigation. Sampling density is increased in areas of known spills, storage tanks, or process discharges. Target analytes include volatile organic compounds, semi-volatile organic compounds, petroleum hydrocarbons, heavy metals, and cyanides.

Forest, Grassland, and Background Soil

Background and ecological soil samples establish natural baseline concentrations and support long-term environmental trend monitoring. These samples are collected from areas remote from anthropogenic emission sources and are analyzed primarily for heavy metals and basic physicochemical properties to distinguish geogenic from anthropogenic contamination.

Testing Items

Soil testing programs are structured around several categories of parameters, selected according to land use, site history, and regulatory requirements:

• Basic physicochemical properties: pH value, moisture content, organic matter, cation exchange capacity (CEC), particle size distribution, soil texture, electrical conductivity, and redox potential.

• Heavy metals and inorganic pollutants: cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), zinc (Zn), beryllium (Be), antimony (Sb), thallium (Tl), cobalt (Co), vanadium (V), manganese (Mn), fluoride, and cyanide.

• Volatile organic compounds (VOCs): benzene, toluene, ethylbenzene, xylenes (BTEX), chlorinated solvents such as trichloroethylene and tetrachloroethylene, chloroform, carbon tetrachloride, and vinyl chloride.

• Semi-volatile organic compounds (SVOCs): phenols, nitroaromatics, anilines, phthalate esters, and chlorinated aromatics.

• Polycyclic aromatic hydrocarbons (PAHs): naphthalene, benzo[a]pyrene, benzo[a]anthracene, and other priority PAHs derived from combustion and petroleum sources.

• Pesticide residues: organochlorine pesticides such as DDT and hexachlorocyclohexane (HCH), organophosphorus pesticides, and pyrethroid compounds.

• Petroleum hydrocarbons: total petroleum hydrocarbons (TPH), mineral oil, and fractional analysis of aliphatic and aromatic hydrocarbon ranges.

• Polychlorinated biphenyls (PCBs) and dioxins and furans (PCDD/Fs) at sites with electrical equipment, transformer, or chemical manufacturing histories.

• Nutrient indicators: total nitrogen, available phosphorus, available potassium, ammonium nitrogen, nitrate nitrogen, and available micronutrients for agricultural assessment.

Testing Methods

Analytical methods are selected based on target analytes, required detection limits, and applicable regulatory standards. Samples are typically air-dried or frozen, ground, sieved through 2 mm or 0.149 mm meshes, and homogenized before extraction and instrumental analysis.

• Heavy metals: Acid digestion using nitric acid, hydrochloric acid, hydrofluoric acid, and hydrogen peroxide, followed by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES). Graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS) are used for specific elements, while atomic fluorescence spectrometry (AFS) is the preferred method for mercury and arsenic.

• VOCs: Purge-and-trap extraction combined with gas chromatography-mass spectrometry (GC-MS), following procedures equivalent to HJ 605 and EPA Method 8260. Headspace GC-MS is applied as an alternative for specific applications.

• SVOCs and PAHs: Ultrasonic or accelerated solvent extraction with dichloromethane or hexane-acetone solvents, followed by GC-MS analysis in accordance with HJ 834 and EPA Method 8270. High-performance liquid chromatography (HPLC) with fluorescence or UV detection is used for PAH confirmation.

• Organochlorine pesticides: Extraction and cleanup through florisil columns, followed by gas chromatography with electron capture detection (GC-ECD) or GC-MS in accordance with GB/T 14550.

• Petroleum hydrocarbons: Soxhlet or ultrasonic extraction with GC-FID quantification against certified hydrocarbon standards.

• pH and organic matter: Potentiometric measurement in water or calcium chloride suspension (ISO 10390) and potassium dichromate oxidation-spectrophotometric titration, respectively.

• On-site screening: Portable X-ray fluorescence (XRF) spectrometry and photoionization detectors (PID) provide rapid preliminary screening of metals and VOCs prior to confirmatory laboratory analysis.

All analytical procedures incorporate method blanks, laboratory control samples, matrix spikes, calibration verification standards, and duplicate analyses. Reporting limits are established below applicable GB 36600 and GB 15618 screening values to ensure regulatory interpretability of results.

Applications

Soil environmental monitoring and analysis data support a wide range of environmental management and regulatory decision-making scenarios:

• Environmental site investigations and due diligence for land acquisition, transfer, and redevelopment projects.

• Contaminated site remediation, including baseline assessment, remediation target verification, and post-remediation acceptance testing.

• Environmental impact assessments (EIA) for new industrial construction and expansion projects.

• Agricultural soil quality surveys, farmland pollution prevention, and safe utilization category management of cultivated land.

• Compliance monitoring for industrial enterprises under soil pollution prevention regulations, including key monitored enterprises.

• Accident and spill response investigations requiring rapid contaminant delineation.

• Scientific research, background surveys, and long-term national soil quality monitoring networks.

FAQ

What is the difference between GB 36600 and GB 15618 standards?

GB 36600-2018 applies to development land, including residential, commercial, and industrial uses, and establishes risk screening values based on human health exposure pathways. GB 15618-2018 applies to agricultural land and sets risk screening and control values oriented toward food safety and crop protection. The applicable standard depends on the current or planned land use of the sampling site.

How deep should soil samples be collected?

Surface samples from 0 to 20 cm are standard for agricultural monitoring. For construction land investigations, samples are typically collected at 0 to 0.5 m, 0.5 to 1.5 m, and 1.5 to 3 m intervals, extending deeper if contamination, fill material, or high water tables are encountered. Sampling depth must always extend below any visually or instrumentally identified contamination zone.

How are soil samples preserved and transported?

Samples for VOC analysis are collected with minimal disturbance in methanol-preserved vials or enCore-type samplers and transported at 4 degrees Celsius with same-day or next-day analysis. Metal and general chemistry samples are stored in polyethylene or glass containers at 4 degrees Celsius, while SVOC samples are held in amber glass jars. A complete chain-of-custody record must accompany all samples to the laboratory.

How long does a complete soil monitoring project take?

A typical project schedule includes one to two weeks for site investigation and sampling plan design, several days for field sampling, and ten to twenty working days for laboratory analysis and reporting, depending on the number of parameters and samples. Rapid screening with portable XRF instruments can provide preliminary results within one or two field days.

What happens if soil concentrations exceed the screening values?

Exceedance of a risk screening value does not automatically require remediation, but it triggers a detailed risk assessment to evaluate exposure pathways and calculate site-specific contaminant levels. If concentrations exceed risk control values, risk management or remediation measures such as source removal, barrier installation, or soil replacement are generally required before the land can be safely used.