ISO 11268 earthworm toxicity testing is the internationally recognized standard for evaluating the harmful effects of chemicals, contaminated soils, and waste materials on earthworms, which serve as key bioindicators of soil ecosystem health. This technical article provides a comprehensive overview of ISO 11268 Parts 1, 2, and 3, covering test organisms, applicable sample types, experimental methodology, measured endpoints, and regulatory applications. Whether you are supporting chemical registration, ecological risk assessment, or contaminated site evaluation, this guide explains how ISO 11268 testing generates reliable soil toxicity data for environmental decision-making.
Technical Overview
ISO 11268 is a series of international standards developed by the International Organization for Standardization (ISO) under Technical Committee 190 (Soil Quality). The series specifies standardized laboratory and field methods for determining the toxic effects of pollutants and contaminated media on earthworms. Because earthworms often constitute the largest proportion of soil invertebrate biomass in temperate regions and ingest large volumes of soil and organic debris, they are exposed to contaminants through both dermal contact and dietary uptake. This dual exposure pathway, combined with their critical ecological role in soil aeration, organic matter decomposition, and nutrient cycling, makes earthworms an ideal sentinel organism for terrestrial ecotoxicology.
The ISO 11268 series is structured into three complementary parts, each addressing a distinct level of biological organization:
- ISO 11268-1 – Determination of acute toxicity to Eisenia fetida/Eisenia andrei, assessing earthworm survival following a 14-day exposure period.
- ISO 11268-2 – Determination of effects on reproduction of Eisenia fetida/Eisenia andrei, assessing long-term impacts on juvenile production over an 8-week test cycle.
- ISO 11268-3 – Guidance on the determination of effects on earthworms in field situations, supporting assessment of natural populations at contaminated or treated sites.
The recommended test organisms are Eisenia fetida (Savigny, 1826) and Eisenia andrei (Bouché, 1972), collectively known as redworms or compost worms. These epigeic species are used worldwide because they are easy to culture in the laboratory, reproduce rapidly, have well-documented sensitivity to a broad range of chemicals, and allow consistent comparison of results across testing facilities and jurisdictions.
Testing Samples
Chemical Substances and Formulations
The standard is routinely applied to industrial chemicals, agrochemicals, pesticides, biocides, fertilizers, and formulated products. Test substances are typically mixed into a defined artificial soil substrate at a geometric series of concentrations to establish concentration-response relationships and derive toxicity thresholds such as LC50 and NOEC values.
Contaminated Soils and Site Materials
Soil samples collected from contaminated sites, industrial estates, former gasworks, mining areas, or agricultural land can be evaluated directly. This direct-soil approach captures the combined toxicity of contaminant mixtures, aging effects, and soil-specific bioavailability, making it valuable for site-specific ecological risk assessment.
Waste Materials, Composts, and Soil Amendments
Sewage sludge, dredged sediments, composted organic waste, biochar, digestates, and other materials intended for land application can be tested to verify that they do not pose unacceptable risks to soil organisms before environmental release or agricultural use.
Emerging Contaminants and Advanced Materials
Increasingly, ISO 11268 methods are adapted to evaluate nanomaterials, microplastics, biodegradable polymers, per- and polyfluoroalkyl substances (PFAS), pharmaceuticals, and veterinary drugs, supporting the environmental safety assessment of next-generation materials.
Testing Items
ISO 11268 testing covers a hierarchy of biological endpoints that progress from individual survival to population-level reproduction and community-level field effects:
- Acute mortality (survival rate) – the primary endpoint of ISO 11268-1, expressed as percent mortality and used to calculate the 14-day LC50.
- Growth and biomass change – body weight variation of adult worms during exposure, providing a sensitive sublethal indicator in the acute test.
- Reproductive output (juvenile production) – the key endpoint of ISO 11268-2, quantified as the number of surviving juveniles per replicate after eight weeks, from which ECx, NOEC, and LOEC values are derived.
- Behavioral and population-level effects – field observations under ISO 11268-3, including population density, species composition, and age structure of natural earthworm communities.
- Supporting parameters – soil pH, moisture content, water holding capacity, organic carbon content, and contaminant concentrations, which are measured for interpretation and quality assurance.
Testing Methods
Test Organism and Substrate Preparation
Adult earthworms with a well-developed clitellum and a fresh body weight of approximately 250 to 600 mg are selected, acclimated in culture substrate, and fasted briefly before test initiation. The standard exposure medium is artificial soil composed of 70% quartz sand, 20% kaolin clay, and 10% sphagnum peat by dry weight, with pH adjusted to 6.0 ± 0.5 using calcium carbonate and moisture maintained at 40–60% of the water holding capacity. Test vessels are incubated at 20 ± 2 °C under continuous illumination of approximately 400–800 lux to prevent worms from escaping the substrate.
Acute Toxicity Test Procedure (ISO 11268-1)
Ten adult worms are placed in each test vessel containing soil spiked with the test substance or contaminated sample at a range of concentrations, with a minimum of three to four replicates per treatment and appropriate controls. Mortality and clinical observations (such as behavioral abnormalities, paralysis, or weight loss) are recorded after 7 and 14 days of exposure. A worm is considered dead when it shows no response to gentle mechanical stimulation. The resulting mortality data are analyzed using probit or logistic regression to determine the LC50, while biomass changes are evaluated statistically against controls.
Reproduction Toxicity Test Procedure (ISO 11268-2)
In the chronic test, ten adult worms per replicate are exposed to treated soil for four weeks, after which the adults are removed, counted, and weighed. The cocoons and remaining soil are then incubated for an additional four weeks to allow juvenile development. At test termination, the number of juveniles in each replicate is counted by hand sorting or heat extraction. Reproduction data are analyzed by ANOVA-based or regression-based methods to derive the ECx, NOEC, and LOEC for juvenile production.
Field Assessment (ISO 11268-3)
The field guidance describes survey designs for evaluating earthworm communities at contaminated or treated sites relative to reference areas, using standardized extraction techniques such as hand sorting combined with chemical expulsion agents. This part supports real-world validation of laboratory findings and site-specific risk characterization.
Validity Criteria and Quality Control
For results to be acceptable, control mortality must not exceed 10%, adult worms must remain healthy, and reproduction in the controls must meet the minimum thresholds defined by the standard, typically at least 30 juveniles per replicate with variability among control replicates within the specified coefficient of variation limit. Reference toxicity tests with a validated control substance are performed periodically to confirm the sensitivity and health of the worm culture. Regulatory studies are generally conducted in compliance with Good Laboratory Practice (GLP) principles.
Applications
ISO 11268 earthworm toxicity data are widely used across regulatory, industrial, and scientific contexts:
- Chemical registration under REACH – fulfilling terrestrial toxicity data requirements for substances manufactured or imported into the European Union at high tonnage levels.
- Agrochemical and biocide authorization – evaluating risks of pesticides and plant protection products to non-target soil organisms as required by regulators worldwide.
- Contaminated land assessment – supporting site investigation, derivation of soil screening values, and tiered ecological risk assessment at polluted sites.
- Remediation verification – confirming that remediated soils no longer exhibit unacceptable toxicity before reuse or site closure.
- Waste and compost quality evaluation – demonstrating the environmental safety of organic waste streams destined for land application.
- Environmental research – investigating the terrestrial toxicity of nanomaterials, microplastics, industrial effluents, and climate-related soil stressors.
FAQ
Which earthworm species are used in ISO 11268 testing?
The standard specifies Eisenia fetida and Eisenia andrei as the recommended test species. Adult worms with a visible clitellum and a body weight of approximately 250–600 mg are used to ensure physiological maturity and test comparability.
What is the difference between ISO 11268-1 and ISO 11268-2?
ISO 11268-1 is an acute test measuring adult mortality over 14 days, while ISO 11268-2 is a chronic test measuring reproductive output, expressed as juvenile production, over a total duration of eight weeks. The reproduction test is generally more sensitive and is frequently required for long-term risk characterization.
What substrate is used for exposure?
Tests are typically performed in artificial soil containing 70% quartz sand, 20% kaolin clay, and 10% sphagnum peat, with pH adjusted to approximately 6.0 and moisture maintained at 40–60% of the water holding capacity. Natural soils may also be tested directly when assessing site-specific contamination.
How long does ISO 11268 testing take?
The acute test (Part 1) requires approximately 14 days of exposure plus organism acclimation, typically two to three weeks in total. The reproduction test (Part 2) requires eight weeks of incubation, with full study completion including culture preparation and statistical reporting generally achieved within ten to twelve weeks.
What statistical endpoints are reported?
Key results include the 14-day LC50 for mortality, the ECx (such as EC10 and EC50) for reproduction, and NOEC/LOEC values derived from hypothesis testing. These metrics feed directly into derivation of predicted no-effect concentrations (PNECs) for terrestrial risk assessment.
Can ISO 11268 tests support GLP regulatory submissions?
Yes. Contract testing laboratories routinely perform ISO 11268 studies in accordance with GLP standards, producing auditable reports that are accepted by regulatory authorities such as ECHA, EFSA, and the US EPA for chemical and pesticide evaluation programs.