Overview
ISO 17126:2005 - "Soil quality - Determination of the effects of pollutants on soil flora - Screening test for emergence of lettuce seedlings (Lactuca sativa L.)" describes a standardized, rapid biological screening test to assess how contaminated soils or test substances affect seedling emergence. Designed as a cost‑effective complement to chemical analysis, the method uses lettuce (Lactuca sativa) seed emergence as an indicator of phytotoxicity in soils, composts, sludges and in chemical‑spiked growth media. Note: ISO 17126:2005 is not applicable to volatile contaminants.
Key topics and technical requirements
- Test organism: Lettuce seeds (Lactuca sativa L.); avoid pesticide‑coated (“dressed”) seeds and size the batch to reduce variability.
- Test media: Washed fine quartz sand (growth medium) and coarse quartz sand (cover material).
- Sample types: Contaminated soils, soil materials, compost, sludge and chemicals added to soil/growth medium.
- Preparation and dilution: Use a geometric dilution series of test material and growth medium (minimum 5 concentrations; dilution factor ≤ 2). Concentrations are calculated on a dry‑mass basis (g dry mass test material per g dry mass test mixture).
- Test setup: Typically 100 g dry mass per Petri dish (15 cm diameter) with 40 seeds per dish, three replicates per concentration and three controls. Sieve soils (preferably 2 mm) and determine water content, water‑holding capacity, pH and conductivity prior to testing (see referenced ISO methods).
- Environmental conditions: Incubate in controlled chamber - first 48 h in darkness, then a diurnal 16 h light / 8 h dark cycle with specified light intensity. Typical test duration is around 120 h (5 days) or until emergence is complete in controls.
- Moisture: Moisture adjusted to approximately 85% of water‑holding capacity; retain moisture by sealing dishes in polyethylene bags.
- Endpoints and metrics: Count emerged seedlings visible above cover material. Effects are expressed as ECx values (e.g., EC50) calculated relative to controls. Reference substances (e.g., 2‑chloroacetamide, boric acid) are recommended for quality control.
Applications and users
ISO 17126:2005 is used for:
- Rapid screening of soil phytotoxicity in environmental monitoring and risk assessment
- Comparing soil quality between sites or over time
- Evaluating remediation progress and efficacy of amendments
- Testing sludge, compost or materials for agricultural reuse suitability
- Laboratory validation when introducing new procedures (use of reference substances)
Primary users: environmental testing laboratories, remediation consultants, regulatory agencies, waste and compost producers, agronomists and academic researchers focused on soil ecotoxicology.
Related standards
Keywords: ISO 17126, soil quality testing, lettuce seedling emergence, Lactuca sativa, screening test, EC50, phytotoxicity, contaminated soil, sludge testing.