ISO 16751:2020

Overview

ISO 16751:2020 - "Soil quality - Environmental availability of non‑polar organic compounds" - specifies a laboratory extraction method to estimate the potentially bioavailable and non‑bioavailable fractions of non‑polar organic contaminants in soil and sediments. The standard uses a receiver phase (examples: Tenax® or cyclodextrin) as an “infinite sink” during a controlled water‑soil extraction to quantify the amount of contaminant that can desorb into the aqueous phase (environmental bioavailability). The method is applicable primarily to non‑polar compounds with aqueous solubility < 100 mg/L (theory extends to higher solubilities, but applicability is defined for <100 mg/L). The protocol defines a 20‑hour desorption period for determining the potential bioavailable fraction.

Key technical topics and requirements

• Scope and target analytes: Non‑polar organic compounds in soils, soil‑like materials and dredged sediments; mainly compounds with low aqueous solubility (Kow often > 3).
• Receiver phases: Two options described - cyclodextrin (complexing agent) and Tenax® (strong adsorbent). Tenax® is cited as an example and not endorsed by ISO.
• Principle: Receiver phase acts as a sink during a water‑soil extraction to capture rapidly desorbing (bioavailable) molecules; remaining contaminant is subsequently measured by a harsh/exhaustive extraction to obtain the non‑bioavailable fraction.
• Procedure elements:
  • Sample preparation (particle size <2 mm)
  • Determination of water content
  • Method A (cyclodextrin) and Method B (Tenax®): extraction, phase separation, extraction from receiver phase
  • Measurement, blank tests, calculations and expression of results
  • Validation, reporting and quality control
• Timeframe: Desorption measured over a defined period of 20 h for potential bioavailability.
• Calculations: Total concentration = bioavailable + non‑bioavailable fractions, with defined formulas and reporting requirements.

Practical applications

• Environmental risk assessment and site characterization - refining exposure estimates by distinguishing bioavailable vs. non‑bioavailable residues.
• Remediation planning and performance monitoring - assessing whether contaminated mass is accessible to biota or remediation agents.
• Regulatory compliance and decision support - providing measurable fractions that better reflect ecological risk than total concentration alone.
• Research and method development in soil chemistry, ecotoxicology, and environmental forensics.

Who would use this standard

• Environmental laboratories and contract testing facilities
• Soil scientists, environmental chemists and ecotoxicologists
• Remediation consultants and contaminated‑land regulators
• Research institutions studying contaminant bioavailability and fate

Related standards

• ISO 17402 (environmental bioavailability concepts)
• ISO 11074 (soil vocabulary)
• ISO 11465 (dry matter and water content)
• ISO 14507 (pretreatment of samples for organics)
• ISO 18512 (storage of soil samples)
• ISO 17924 (bioaccessibility context)

Keywords: ISO 16751:2020, soil quality, bioavailable fraction, non‑bioavailable fraction, Tenax, cyclodextrin, receiver phase, non‑polar organic compounds, soil contamination, environmental availability.