Soil Environmental Quality Testing: Standards, Sample Types, Analytical Methods, and Applications

Soil environmental quality testing is the scientific process of collecting and analyzing soil samples to determine the concentrations of heavy metals, organic pollutants, pesticides, and other contaminants that may threaten human health and ecosystems. Guided by national standards such as GB 36600-2018 and GB 15618-2018, together with internationally recognized ISO, ASTM, and US EPA methods, accredited third-party laboratories deliver defensible data for land development, agricultural safety, and soil remediation decision-making. This article provides a comprehensive overview of soil quality inspection, covering sample types, testing items, analytical techniques, quality assurance, and typical applications.

Technical Overview

Soil is a non-renewable environmental resource that connects the atmosphere, hydrosphere, and biosphere, directly influencing the safety of agricultural products, groundwater, and human living environments. Soil environmental quality testing refers to the systematic sampling, physical and chemical analysis, and standards-based evaluation of soil to determine whether contaminant levels pose ecological or human health risks. Typical drivers include land-use change, industrial site redevelopment, farmland protection, environmental impact assessment, and post-remediation verification.

In China, the core regulatory and technical framework consists of the Soil Pollution Prevention and Control Law (effective 2019), GB 36600-2018 (Soil Environmental Quality - Risk Control Standard for Soil Contamination of Development Land), GB 15618-2018 (Soil Environmental Quality - Risk Control Standard for Soil Contamination of Agricultural Land), HJ/T 166-2004 (Technical Specification for Soil Environmental Monitoring), and the HJ 25.1 to HJ 25.5 series covering site investigation, monitoring, risk assessment, and remediation. These standards define risk screening values and risk intervention (control) values for heavy metals, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and other priority pollutants. Internationally, ISO 10381 (sampling), ISO 11464 (pretreatment), and US EPA analytical methods such as 6010D, 6020B, 8260D, and 8270E are widely used as equivalent or supplementary procedures.

An accredited third-party laboratory performing soil testing should hold CMA (China Metrology Accreditation) and/or CNAS accreditation for the specific methods reported, ensuring that sampling, analysis, quality control, and reporting all meet regulatory acceptance requirements.

Testing Samples

Agricultural Land Soil

Collected from cultivated land, vegetable bases, orchards, tea plantations, and paddy fields, generally from the plow layer at 0 to 20 cm depth (or deeper for rooted crops). Testing focuses on heavy metals such as cadmium, lead, arsenic, mercury, and chromium, combined with nutrient indicators, to support the classification of farmland into priority protection, safe utilization, and strict control categories under GB 15618-2018.

Development (Construction) Land Soil

For residential, commercial, industrial, and public-management land parcels, sampling is designed according to the land-use sensitivity classes defined in GB 36600-2018. Class I land covers sensitive uses such as residential areas, schools, kindergartens, hospitals, and elderly care facilities, while Class II land covers industrial, commercial, and municipal uses; the two classes are evaluated against different risk screening values.

Contaminated Site and Brownfield Soil

Soil from former gasworks, electroplating plants, pesticide and chemical manufacturing facilities, smelters, fuel stations, and oil depots often contains complex mixtures of VOCs, SVOCs, petroleum hydrocarbons, PCBs, and heavy metals. Stratified core sampling from the surface down to the groundwater table or undisturbed strata is required to characterize the vertical extent of contamination.

Special-Purpose Soil Samples

These include soils from mining areas and tailings surroundings, landfills and their perimeters, industrial parks, roadside and urban green spaces, as well as soil gas samples for vapor intrusion assessment and adjacent sediments, all of which can be evaluated using the same technical framework.

Testing Items

Depending on the applicable standard and project objective, a soil testing program typically combines the following groups of parameters:

• Physical and chemical properties: pH (HJ 962-2018), moisture content, organic matter, cation exchange capacity, particle size distribution, bulk density, and electrical conductivity.
• Nutrient indicators: total nitrogen, available phosphorus, available potassium, and total phosphorus and potassium for soil fertility evaluation.
• Heavy metals and inorganic pollutants: arsenic, cadmium, mercury, lead, chromium, hexavalent chromium, copper, nickel, zinc, beryllium, barium, cobalt, manganese, molybdenum, antimony, selenium, thallium, vanadium, and silver.
• Volatile organic compounds (VOCs): benzene, toluene, ethylbenzene, and xylenes (BTEX), chlorinated solvents such as trichloroethylene, tetrachloroethylene, and vinyl chloride, chlorobenzenes, and other regulated volatile substances.
• Semi-volatile organic compounds (SVOCs): nitrobenzene compounds, aniline and chloroanilines, chlorophenols, polycyclic aromatic hydrocarbons (PAHs), and phthalate esters.
• Persistent organic pollutants: organochlorine pesticides (HCH, DDT), polychlorinated biphenyls (PCBs), and dioxins and furans (PCDD/Fs).
• Petroleum hydrocarbons: total petroleum hydrocarbon fractions C10 to C40, and light fractions C6 to C9 where required.
• Other indicators: cyanide, fluoride, soluble salts, and soil gas VOC concentrations.

Testing Methods

Sampling and Sample Pretreatment

Sampling follows HJ/T 166-2004, HJ 25.1 and HJ 25.2, or ISO 10381, using systematic grid layouts (commonly 40 m by 40 m for smaller sites and 64 m by 64 m for larger sites during preliminary investigations), stratified sampling, and judgmental placement near potential contamination sources. Samples are collected with stainless-steel or PTFE-coated tools to avoid cross contamination; VOC samples are transferred immediately into pre-weighed vials containing methanol or sodium bisulfate preservative and transported under cold-chain conditions at 0 to 4 degrees Celsius. In the laboratory, inorganic samples are air-dried at room temperature, ground, sieved (2 mm, 0.25 mm, or 0.149 mm depending on the analytical requirement), and reduced by quartering in accordance with ISO 11464 and HJ/T 166.

Heavy Metal Analysis

Elements are brought into solution by aqua-regia extraction (HJ 803-2016) or by total digestion using hydrofluoric-acid-based acid mixtures and microwave systems (US EPA 3052). Quantification is performed using inductively coupled plasma mass spectrometry (ICP-MS, HJ 680-2013), inductively coupled plasma optical emission spectrometry (ICP-OES, US EPA 6010D), graphite furnace atomic absorption spectrometry (GB/T 17141-1997 for lead and cadmium), and atomic fluorescence spectrometry (GB/T 22105.1-2008 for mercury and arsenic). Hexavalent chromium is determined separately by alkaline extraction followed by colorimetric analysis. X-ray fluorescence spectrometry (HJ 491-2019, US EPA 6200) is used for rapid on-site screening.

Organic Contaminant Analysis

VOCs are determined by purge-and-trap or headspace GC-MS (HJ 605-2011, US EPA 8260D). SVOCs, PAHs, and phthalate esters are extracted by Soxhlet extraction, ultrasonic extraction, or accelerated solvent extraction (US EPA 3540C, 3550C, 3545A) and analyzed by GC-MS (HJ 834-2017, US EPA 8270E). Organochlorine pesticides are measured by gas chromatography with electron capture detection (GB/T 14550-2003), petroleum hydrocarbons C10 to C40 by gas chromatography (HJ 1021-2019), and dioxins and furans by high-resolution GC-MS (HJ 77.4-2008).

Quality Assurance and Quality Control

Reliable data require full-method quality control, including field and trip blanks, duplicate samples (typically at a frequency of at least 10 percent), matrix spikes, certified reference materials such as GBW series soil standards, continuing calibration verification, and method detection limit studies. All results are compared with the applicable GB 36600 or GB 15618 screening and control values to produce clear conclusions of compliance, exceedance, or need for further assessment in CMA-stamped test reports.

Applications

Soil environmental quality testing data support a wide range of regulatory and commercial purposes:

• Classifying agricultural land and implementing safe-utilization or strict-control measures for contaminated farmland.
• Preliminary and detailed site investigations for brownfield redevelopment, land transfer, and change-of-land-use approvals.
• Human health and ecological risk assessments under the HJ 25.3 framework.
• Remediation target setting, process control, and post-remediation acceptance testing.
• Environmental impact assessment and completion acceptance for construction projects.
• Routine supervision and monitoring of industrial parks, mining areas, and waste disposal sites.
• Soil fertility evaluation and production base certification for green-food or organic farming.
• Technical evidence for environmental disputes, insurance claims, and judicial proceedings.

FAQ

Which standard applies to my project: GB 36600-2018 or GB 15618-2018?

GB 15618-2018 applies to agricultural land such as cultivated land, orchards, and pastures, while GB 36600-2018 applies to development land such as residential, commercial, industrial, and public-management parcels. A site changing from industrial to residential use is assessed against the Class I screening values of GB 36600-2018.

What is the difference between risk screening values and risk control (intervention) values?

Risk screening values identify contaminant levels below which health risks are generally acceptable, so the soil can normally continue in use without further action. Risk control or intervention values indicate levels at which potential health risks exist, requiring detailed risk assessment or remediation. Results falling between the two thresholds trigger further investigation and site-specific assessment.

How many soil samples and sampling points are required?

The number depends on the standard and the investigation stage. For site investigations, HJ 25.1 recommends systematic grids such as 40 m by 40 m supplemented by judgmental points near suspected sources, while agricultural monitoring follows the minimum point densities in HJ/T 166 based on land area and heterogeneity. A qualified sampling plan should always be prepared by experienced personnel before fieldwork begins.

At what depths should soil samples be collected?

Agricultural topsoil is typically collected at 0 to 20 cm, with a subsoil sample at 20 to 40 cm where needed. For development land, surface soil (0 to 0.5 m), shallow soil (0.5 to 1.5 m), deep soil (1.5 to 3 m), and deeper strata are sampled progressively until uncontaminated soil or the groundwater table is reached, so that the vertical extent of contamination can be defined.

How long does soil environmental quality testing take?

Routine heavy metal analysis generally takes about 5 to 10 working days after samples arrive at the laboratory. Full GB 36600 basic item suites including VOCs and SVOCs, or special analyses such as dioxins, may require 10 to 20 working days. Complete site investigation projects including sampling and reporting usually span several weeks.

Can on-site XRF screening replace laboratory testing?

No. Field XRF and photoionization detector instruments are excellent screening tools that guide sampling locations and reduce costs, but regulatory conclusions must be confirmed by accredited laboratory methods such as ICP-MS or GC-MS, because portable instruments carry wider measurement uncertainty and cannot fully replace validated analytical procedures.