Overview
ISO 10390:2021 specifies an instrumental method for routine determination of pH in soil, treated biowaste and sludge. The method covers the pH range 2 to 12 using a glass electrode in a 1:5 (volume/volume) suspension of sample in either:
- water (pH in H2O),
- 1 mol·L−1 potassium chloride (pH in KCl), or
- 0.01 mol·L−1 calcium chloride (pH in CaCl2).
The standard is applicable to air‑dried soils and treated biowaste (and to liquid sludges measured directly). It consolidates earlier EN content (EN 15933) and includes validation and interlaboratory precision data.
Key topics and requirements
- Principle: prepare a 1:5 suspension (sample:liquid) and measure pH with a calibrated pH‑meter and glass or combined electrode.
- Sample preparation: use air‑dried or gently dried (<40 °C) material passed through a 2 mm sieve; liquid sludges can be measured directly. For untreated treated biowaste, use at least 60 mL sample to 300 mL liquid while maintaining 1:5 ratio.
- Reagents: low‑conductivity water, 1.0 mol·L−1 KCl, 0.01 mol·L−1 CaCl2, and standard buffer solutions (pH 4.00, 6.88, 9.22 at 20 °C) for calibration.
- Apparatus: pH‑meter with temperature compensation, glass/combined electrode (special electrode or pH 12 buffer recommended for pH >10), shaker/mixer, thermometer, sample bottles and a measuring spoon (≥5 mL).
- Procedure: shake suspension ~60 ± 10 min, wait 1–3 h (avoid air ingress), calibrate pH‑meter at 20 ± 2 °C, measure while stirring and report pH to two decimals (results typically reported to 0.1 pH unit).
- Quality and precision: Annex A provides repeatability and reproducibility from interlaboratory trials; statistical treatment follows ISO 5725 principles.
- Reporting: include ISO reference, sample ID, medium used, measured pH, any equilibration issues and deviations from the standard procedure.
Applications and users
ISO 10390:2021 is used for:
- Routine soil pH testing in agricultural and horticultural labs.
- Environmental monitoring (soil and sludge pH for contamination studies).
- Waste management and treated biowaste quality control.
- Research laboratories studying soil chemistry and amendment impacts.
Typical users: soil testing laboratories, environmental consultants, agronomists, waste treatment facilities, regulatory agencies and research institutions needing standardized, reproducible soil pH measurements.
Related standards (if applicable)
- ISO 11464 - sample pretreatment for soils (example).
- EN 16179, EN 15002 - sample pretreatment for biowaste and sludges (examples).
- EN 15933 - content merged into this edition.
- ISO 5725 series - precision and accuracy (used for repeatability/reproducibility calculations).
Keywords: ISO 10390:2021, soil pH determination, pH in soil, treated biowaste pH, sludge pH, glass electrode, 1:5 suspension, pH measurement standard.
