ISO 7303:2025

Overview

ISO 7303:2025 - "Simplified method for prediction of the oral bioaccessibility of metals and metalloids in soils" specifies a rapid, one‑step chemical extraction to predict the oral bioaccessibility of arsenic (As), cadmium (Cd) and lead (Pb) in contaminated soils. The method uses a dilute hydrochloric acid (HCl) extraction designed as a first‑tier screening tool that produces results representative of the validated Unified Bioaccessibility Method (UBM, ISO 17924). ISO 7303:2025 provides protocols, quality controls, and the linear regression equations and prediction intervals needed to convert HCl‑extractable concentrations into predicted gastric and gastrointestinal bioaccessibility.

Key technical topics and requirements

• Test principle: Single‑step extraction with HCl 0.65 % (≈0.078 mol·L‑1), pH 1.2, at 37 °C for 1 hour (includes an ultrasonication pre‑step in the illustrated protocol).
• Liquid/solid (L/S) ratio: 830:1 (ml/g) - chosen to approximate possible stomach conditions for incidental soil ingestion.
• Sample preparation:
  • Air‑dry < 40 °C and sieve to ≤ 250 µm (no milling).
  • Use at least 100 g starting material to obtain representative sieved fraction.
  • Typical test sample mass: 30 mg soil with 25 ml HCl (protocol diagram).
• Filtration and analysis: Filter extracts through 0.45 µm and quantify As, Cd, Pb using suitable analytical techniques.
• Data interpretation: Apply the document’s linear regression models and prediction intervals to convert HCl extractable concentrations into predicted gastric and gastrointestinal bioaccessibility values.
• Scope limits: Validated concentration ranges - As: 2–2 600 mg/kg; Cd: 0.2–480 mg/kg; Pb: 4–50 000 mg/kg.
• Quality assurance: Annexes provide method performance characteristics, regression model details and interlaboratory trial results.

Practical applications and users

ISO 7303:2025 is intended for:

• Environmental testing laboratories performing high‑throughput screening for soil contamination.
• Site managers and remediation consultants who need rapid prioritization of samples.
• Human health risk assessors and regulatory agencies seeking a cost‑effective first‑tier estimate of exposure via incidental soil ingestion.
• Researchers comparing in vitro bioaccessibility screening approaches to ISO 17924 UBM.

Practical benefits:

• Faster and lower‑cost screening compared with full UBM testing.
• Supports screening of large sample sets and selection of a subset (e.g., ~10–30 %) for confirmatory UBM analysis.
• Reduces overestimation of exposure compared to using total metal concentrations alone.

Related standards

• ISO 17924 - Unified Bioaccessibility Method (UBM) for in‑vitro gastric/gastrointestinal bioaccessibility (reference method used for validation).
• Relevant annexes in ISO 7303 include regression models, prediction intervals and interlaboratory performance data to support robust application.

Keywords: ISO 7303:2025, bioaccessibility, HCl extraction, soil metals, arsenic, cadmium, lead, ISO 17924, first‑tier screening, environmental risk assessment.