Soil Heavy Metal Testing to Chinese National Standards (GB): Framework, Methods, and Compliance

Soil heavy metal testing to Chinese national standards (GB) is the systematic sampling, chemical analysis, and compliance evaluation of soil for metallic contaminants such as cadmium, mercury, arsenic, lead, and chromium. The framework is anchored by GB 15618-2018 for agricultural land and GB 36600-2018 for development land, supported by a suite of GB/T and HJ reference methods for sample digestion and instrumental determination. This article explains the applicable standards, sample types, target elements, analytical techniques, and quality control requirements used by accredited third-party laboratories for GB-compliant soil heavy metal testing.

Technical Overview

Soil heavy metal testing under Chinese national standards (GB, or "Guobiao") refers to the full analytical chain of sampling, pretreatment, digestion, instrumental determination, and compliance evaluation of soil for metallic contaminants. The regulatory framework is defined by two complementary risk control standards: GB 15618-2018, which applies to agricultural land, and GB 36600-2018, which applies to development (construction) land. Both standards establish risk screening values and risk control (intervention) values that determine whether soil poses an unacceptable risk to human health or the agro-ecosystem.

Because these limit standards explicitly designate reference analytical methods, laboratories performing compliance testing must apply the cited GB/T and HJ method standards, operate under Chinese metrology accreditation (CMA) or CNAS accreditation, and follow the sampling and quality assurance requirements of HJ/T 166-2004, the technical specification for soil environmental monitoring, and HJ 25.2-2019, the technical guideline for soil environmental monitoring of contaminated sites. Key standards in this system include:

• GB 15618-2018 – Soil environmental quality: risk control standard for soil contamination of agricultural land
• GB 36600-2018 – Soil environmental quality: risk control standard for soil contamination of development land
• GB/T 17141-1997, GB/T 17138-1997, GB/T 17139-1997, GB/T 17136-1997 – Determination of lead, cadmium, copper, zinc, nickel, and mercury by atomic absorption spectrometry
• GB/T 22105 series – Determination of mercury, arsenic, and lead by atomic fluorescence spectrometry
• HJ 803-2016 – Determination of 12 metal elements in soil and sediment by aqua regia extraction and ICP-MS
• HJ 680-2013, HJ 702-2014 – Determination of mercury, arsenic, selenium, bismuth, and antimony by atomic fluorescence spectrometry
• HJ 491-2019 – Determination of copper, zinc, lead, nickel, and chromium by flame atomic absorption spectrometry
• HJ 832-2017 – Determination of metal elements in soil and sediment by microwave digestion
• HJ 1082-2019 – Determination of hexavalent chromium in soil and sediment
• GB 5085.3-2007 – Identification standards for hazardous wastes: identification for leaching toxicity

Testing Samples

Agricultural Land Soil

Surface soil from the plow layer (typically 0–20 cm) is collected from paddy fields, dry farmland, vegetable bases, orchards, and greenhouse operations. Because GB 15618-2018 sets pH-dependent screening values, soil pH (determined per HJ 962-2018) is measured alongside the metal suite. Sub-soil samples may be added where deep tillage, elevated groundwater, or suspected vertical migration is a concern.

Development Land Soil

Soil from current or former industrial sites, chemical plants, fuel stations, smelters, landfills, and parcels undergoing redevelopment is tested against GB 36600-2018. Sampling follows HJ 25.2-2019 with stratified cores, commonly at depth intervals such as 0–0.5 m, 0.5–1.5 m, and deeper intervals depending on the conceptual site model and stratigraphy.

Sediment, Sludge, and Solid Waste

River, lake, and ditch sediments, sewage sludge intended for land application, compost, biogas residue, and organic soil amendments can be analyzed using the same HJ soil and sediment method series. Waste rock, tailings, and process solids may additionally be evaluated for hazardous waste identification via leaching toxicity procedures (such as the sulfuric acid/nitric acid extraction of HJ/T 299) referenced in GB 5085.3-2007.

Adjacent Matrices

Fertilizers and soil conditioners, irrigation water, atmospheric deposition, and crop tissue samples are frequently tested in parallel with soil to trace contamination pathways and to support source apportionment under the soil pollution prevention regulatory framework.

Testing Items

The core compliance suite for agricultural land comprises the eight regulatory heavy metals: cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn). For development land, GB 36600-2018 covers basic screening items including arsenic, cadmium, hexavalent chromium, copper, lead, mercury, and nickel, with extended items such as antimony, beryllium, cobalt, thallium, vanadium, manganese, and selenium. Typical testing items include:

• Total cadmium, lead, chromium, copper, nickel, and zinc (aqua regia or total digestion)
• Total mercury and arsenic (aqua regia extraction with atomic fluorescence determination)
• Hexavalent chromium (alkaline digestion per HJ 1082-2019)
• Extended elements: manganese, molybdenum, cobalt, selenium, antimony, thallium, beryllium, vanadium, barium, silver, and tin
• Soil pH (HJ 962-2018) and organic matter as evaluation parameters
• Phyto-available fractions (for example, DTPA-extractable metals) for agronomic interpretation

Testing Methods

Sample Preparation

Field samples are air-dried at room temperature, crushed with non-metallic implements, homogenized by quartering, and sieved through nylon mesh (commonly 2 mm for pH and 0.149 mm, approximately 100 mesh, for metal analysis). Contact with galvanized tools, rubber stoppers, or metallic sieves is prohibited to prevent cross-contamination with zinc, copper, or lead.

Extraction and Digestion

Aqua regia extraction (hydrochloric acid and nitric acid at 3:1) is the reference route for the compliance values in GB 15618-2018 and GB 36600-2018, as specified in methods such as HJ 803-2016 and HJ 680-2013. Total digestion using hydrofluoric-acid-based four-acid systems or closed-vessel microwave digestion (HJ 832-2017) is applied when complete silicate dissolution and true total content are required, for example in geochemical baseline studies. Hexavalent chromium is determined separately by alkaline digestion to preserve its oxidation state.

Instrumental Determination

• ICP-MS (HJ 803-2016): simultaneous determination of up to 12 metal elements with sub-microgram-per-kilogram detection limits, using internal standards such as rhodium, indium, and rhenium
• ICP-OES: multi-element determination at higher concentration ranges with wide linear calibration
• Flame atomic absorption spectrometry (HJ 491-2019, GB/T 17138-1997, GB/T 17139-1997): copper, zinc, chromium, nickel, and manganese
• Graphite furnace atomic absorption spectrometry (GB/T 17141-1997): trace-level lead and cadmium
• Atomic fluorescence spectrometry (HJ 680-2013, HJ 702-2014, GB/T 22105 series): mercury, arsenic, selenium, antimony, and bismuth
• Cold vapor atomic absorption spectrometry (GB/T 17136-1997): total mercury
• Portable X-ray fluorescence (XRF): rapid field screening for project triage, always subject to confirmatory laboratory analysis

Quality Assurance and Quality Control

Accredited third-party laboratories apply a full QC regime for every batch: method blanks, laboratory duplicates with relative deviation control limits, matrix spike recoveries (typically 70–130 percent), calibration verification standards, certified reference materials such as the GBW07401 through GBW07408 soil series, and internal standards for ICP-MS runs. Results are validated against method detection limits and reported with CMA certification where the data are used for regulatory submission, land transaction due diligence, or judicial purposes.

Applications

Agricultural Land Safety Management

GB 15618-2018 test data support the classification of farmland into priority protection, safe utilization, and strict control categories, guiding planting adjustments, soil conditioning, and food-safety risk management for rice, vegetables, and other crops.

Contaminated Site Investigation and Remediation

GB 36600-2018 data underpin phase site investigations, risk assessment under HJ 25.3-2019, remediation target derivation, and post-remediation acceptance sampling for brownfield redevelopment and industrial land transfers.

Regulatory Compliance and Reporting

Enterprises subject to soil pollution prevention obligations use GB-compliant results for environmental impact assessment, soil pollution status investigations when key monitored enterprises change land use, discharge permit documentation, and government soil quality surveys.

Forensic, Insurance, and Dispute Resolution

CMA-certified GB-standard reports are accepted as evidence in judicial appraisal, pollution liability claims, neighbor disputes over farmland damage, and environmental incident investigations.

Research and Background Monitoring

Long-term monitoring networks, soil background studies, and academic research rely on the same HJ and GB/T reference methods to ensure comparability of total-element data across regions and time series.

FAQ

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

GB 15618-2018 applies to agricultural land including cultivated land, orchards, and pastures, while GB 36600-2018 applies to development land, with Class 1 covering residential, schools, medical, and other sensitive uses and Class 2 covering industrial and commercial uses. Selection is based on current or planned land use; for mixed or unclear future use, the more conservative Class 1 values are typically applied.

What is the difference between aqua regia extraction and total digestion?

Aqua regia extraction dissolves the environmentally reactive fraction of metals bound to sulfides, organic matter, and iron-manganese oxides, producing a "pseudo-total" concentration, and it is the basis of the reference methods cited in the GB risk control standards. Total digestion with hydrofluoric acid additionally dissolves the silicate lattice and yields the true total content, which is used for geochemical purposes rather than direct comparison with GB screening values.

Can handheld XRF results be used for compliance reporting?

No. Portable XRF is a rapid screening tool useful for delineating hotspots and optimizing laboratory sampling, consistent with the phased approach in HJ 25.2-2019. Regulatory conclusions and remediation decisions require confirmatory analysis by accredited third-party laboratories using the designated GB/T and HJ reference methods.

How are representative soil samples collected?

Sampling points are laid out on a grid or judgmental design based on the site conceptual model, and multiple subsamples (commonly 5 to 20) are composited into one sample. Samples are collected with stainless steel or wooden tools, placed in polyethylene or borosilicate containers, transported under chain of custody, and typically kept cool prior to air-drying, all in accordance with HJ/T 166-2004.

What do "risk screening value" and "risk control value" mean?

A risk screening value is a threshold below which soil contamination risk is generally considered acceptable; exceedance triggers detailed investigation or risk assessment. A risk control value is a threshold above which risk is unacceptable and strict control or remediation is required. For example, under GB 15618-2018 the cadmium screening value for paddy soil at pH of 5.5 or below is 0.3 mg/kg with a risk control value of 1.5 mg/kg, while under GB 36600-2018 the Class 1 screening values include 8 mg/kg for mercury and 400 mg/kg for lead.

How long does GB-standard soil heavy metal testing take?

A routine eight-metal suite typically requires 5 to 10 working days from sample receipt, covering air-drying, grinding and sieving, digestion, instrumental analysis, and QC validation. Turnaround depends on sample load, digestion method, and whether expedited service is requested, and data reports should be issued with CMA certification when used for regulatory purposes.