ISO 12782-5:2012

Overview

ISO 12782-5:2012 - "Soil quality - Parameters for geochemical modelling of leaching and speciation of constituents in soils and materials - Part 5" - specifies a laboratory procedure to extract and quantify humic substances from aqueous samples. Applicable to natural waters and eluates produced by leaching tests on soils, wastes and other materials, the method produces input parameters (humic acid, fulvic acid, hydrophilic and hydrophobic organic carbon fractions) used in geochemical modelling of metal speciation, mobility and bioavailability.

Key technical topics and requirements

• Scope and purpose: Determines concentrations of humic substances in aqueous samples for use in geochemical models and environmental risk assessment.
• Principle: Fractionation based on solubility and adsorption:
  • Humic acids (HA) precipitated by acidifying to pH ~1.
  • Fulvic acids (FA) and hydrophobic neutral organics (HON) adsorbed on DAX-8 resin.
  • Hydrophilic organic carbon (Hy) remains in solution after resin treatment.
  • Dissolved organic carbon (DOC) is measured after each step to calculate fractions.
• Apparatus & reagents: Laboratory glassware/plastics, calibrated pH meter, end-over-end shaker, filtration/Büchner apparatus, DAX-8 resin and reagents compliant with ISO reagent/water quality standards.
• Sampling and sample handling: Guidance for laboratory sample, test sample and test portion definitions; requirements for eluate treatment and storage to avoid contamination or loss of organics.
• Procedure highlights:
  • Preparation of DAX-8 resin prior to adsorption steps.
  • Sequential fractionation with DOC measurement at each stage.
  • Blank tests and calculation of concentration using correction factors.
• Quality and reporting: Includes requirements for blank tests, expression of results, test report contents and performance characteristics (validation and annex guidance such as centrifugation conditions and schematic fractionation).

Practical applications and who uses this standard

ISO 12782-5:2012 is used by:

• Environmental and soil-testing laboratories performing leachate analysis.
• Geochemists and modelers requiring reliable humic/fulvic input parameters for speciation and mobility models of metals and contaminants.
• Waste management specialists assessing leaching behavior of by-products and recycled materials.
• Regulators, consultants, and remediation professionals conducting risk assessments or compliance testing. Practical uses include improving accuracy of geochemical speciation models, interpreting leaching test results (pH-dependent or percolation tests), and supporting decisions on material reuse, disposal or site remediation.

Related standards (selection)

• ISO 12782 series (Parts 1–4) - extraction of reactive mineral and organic surfaces
• ISO 3696 - water for laboratory use
• ISO 5667-3 - sampling preservation and handling
• ISO 8245 - determination of TOC and DOC

Keywords: ISO 12782-5:2012, humic substances extraction, soil quality, geochemical modelling, humic acid, fulvic acid, DOC, DAX-8 resin, leachates, aqueous samples.