Overview
EN ISO 23753-1:2019 (CEN adoption of ISO 23753-1:2019) specifies a standardized laboratory method for measuring dehydrogenase activity in soils using 2,3,5‑triphenyltetrazolium chloride (TTC). Dehydrogenases are intracellular microbial enzymes linked to respiratory activity; their activity is used as an indicator of viable, physiologically active soil microbial communities and overall soil quality.
Key topics and technical requirements
- Principle: TTC is added to a soil sample; microbially mediated reduction produces triphenylformazan (TPF), which is extracted with ethanol and quantified by spectrophotometry at 485 nm.
- Core conditions:
- Incubation at 25 °C ± 1 °C for 6 h.
- Substrate (TTC) prepared in Tris buffer (100 mmol/l, pH 7.6); recommended TTC concentration in the procedure is noted (e.g., 300 mmol/l preparation, 10%).
- Extraction solvent: analytical grade ethanol (96 %) is specified; other solvents (e.g., acetone) are noted as alternatives.
- Reagents and calibration:
- Preparation of Tris buffer (100 mmol/l, pH 7.6), TTC substrate solution, and TPF stock/working solutions for standard curves.
- Establishment of a TPF standard curve for quantification and validity checks.
- Sampling and handling:
- Follow ISO 18400‑206 for soil collection and handling.
- If sieved fresh samples cannot be analysed immediately, storage up to 7 days at 4 °C ± 2 °C is acceptable.
- Dry matter determination per ISO 11465.
- Limitations and validity:
- Abiotic reducers (e.g., Fe(II), sulfides), coal or carbonaceous materials, or very organic-rich substrates can bias results; mitigation checks (spiking with TPF and recovery) are recommended.
- Storage time affects enzyme activity - samples with different storage times should not be compared.
Applications and users
This TTC-based soil enzyme assay is used for:
- Environmental and agricultural soil quality monitoring
- Research on soil microbial activity, biogeochemical cycles and soil management impacts
- Assessing effects of contamination, remediation and land-use changes
Primary users include environmental laboratories, academic researchers, agronomists, soil ecologists, and regulatory agencies involved in soil health and ecosystem assessments.
Related standards
- ISO 11465 - Determination of dry matter and water content (gravimetric)
- ISO 18400‑206 - Sampling: collection, handling and storage for microbiological assessment
- EN ISO 23753‑1:2019 supersedes the previous edition (EN ISO 23753‑1:2011)
Keywords: soil quality, dehydrogenase activity, TTC method, triphenyltetrazolium chloride, soil enzyme assay, ISO 23753-1, microbial activity assay.