The OECD 110 test is a reference method used in chemical regulation. It allows for the analysis of the particle size distribution of particles and fibers in water-insoluble substances. This test, although not widely known to the general public, plays a key role in the physicochemical characterization of materials, particularly those used in the chemical industry, composite materials, cosmetics, and packaging. Adopted several decades ago by the Organisation for Economic Co-operation and Development (OECD), the OECD 110 test provides critical data for risk assessment, regulatory classification, and the optimization of industrial formulations. To learn more about OECD standards, you can consult our article dedicated to the OECD Guidelines: a pillar of chemical safety and laboratory analysis.
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Context and challenges of particle size analysis
The size, shape, and distribution of solid particles are fundamental parameters in the study of a substance's physicochemical properties. These characteristics influence a compound's solubility, dispersion, reactivity, bioavailability, and toxicity. When a substance is insoluble in water, its behavior in the environment and its impact on living organisms are determined by its particle size and morphology.
In an increasingly stringent regulatory environment, manufacturers must provide reliable data on the particle size present in their products. The OECD 110 test meets this requirement. It offers two complementary approaches depending on the nature of the material being tested: a method for particles (fibrous or non-fibrous) and a specific method for materials likely to be in the form of fibers.
This is why carrying out a particle size analysis is an essential step to accurately characterize these properties.
An internationally recognized standard-setting tool
OECD Test 110 is one of the official guidelines published by the OECD for the evaluation of chemical substances. These guidelines are widely recognized by regulatory authorities worldwide, notably within the framework of the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals) in Europe, and in registration procedures in the United States, Japan, and Canada.
The OECD 110 test is a reference for measuring particle size distribution and characterizing fibers. It is used upstream in many toxicological and ecotoxicological studies and constitutes an essential basis for any chemical or environmental risk assessment.
What is the OECD 110 test?
A guideline stemming from the work of the OECD
OECD Test 110, officially titled “ Particle Size Distribution / Fiber Length and Diameter Distributions”, belongs to Section 1 of the OECD Guidelines for the Physicochemical Properties of Substances. Adopted in May 1981, it remains in force with widespread applications across various industrial sectors subject to requirements for characterizing raw materials or finished products.
This guideline is used in regulatory submissions, particularly for compliance with the requirements of the REACH Regulation, the CLP Regulation (Classification, Labelling and Packaging of Substances and Mixtures), and the recommendations of the OCSPP (Office of Chemical Safety and Pollution Prevention) in the United States. It is also incorporated into international regulations on the transport of dangerous goods and into certain protocols for the characterization of nanomaterials.
Main objective of the OECD 110 test
The objective of this test is to quantitatively determine the size distribution of particles or fibers within a solid sample, under controlled and reproducible conditions. This information is essential for predicting the behavior of the substance in different environments (air, water, living organisms) and for assessing potential risks to human health or the environment.
Depending on the morphology of the material being tested, two methods are planned:
- Method A applies to substances in the form of particles, whether spherical, irregular, or even fibrous.
- Method B is specifically designed for fibrous materials, i.e., materials capable of forming elongated filaments with a high length/diameter ratio.
Each method is based on different analytical principles, using specific tools (optical or electron microscopy, sedimentation, centrifugation, etc.), but pursues the same objective: to establish a complete and scientifically robust dimensional characterization of the substance studied.
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To which substances does the OECD 110 test apply?
Substances insoluble in water
The OECD 110 test is exclusively applicable to substances with a water solubility of less than 10⁻⁶ g/L. This means that the tested material does not dissolve significantly in water, even at very low concentrations. This physicochemical characteristic has direct implications for the substance's environmental and toxicological behavior, particularly regarding its persistence, dispersion, and interaction with living organisms.
For soluble substances, other OECD tests would be more appropriate, such as those relating to the octanol/water partition coefficient (OECD 117 or OECD 123), pH, or dissociation. However, for inert, powdered, or poorly dispersible solid materials in water, the OECD 110 test is an essential reference.
Examples of materials concerned
Many types of industrial substances can be included in OECD 110 testing. Some of the most common include:
- Metallic powders used in the alloys, pigments or technical inks industry.
- Mineral oxides such as titanium dioxide , zinc oxide or silica, often found in paints, cosmetics or plastics.
- Mineral fibers ( rock wool, glass fibers, aluminosilicates), used in insulation materials or industrial filters.
- Some nanomaterials or submicron particles are incorporated into advanced formulations, such as self-cleaning coatings or technical additives.
- Intermediate products from fine chemistry or green chemistry, intended to be encapsulated or mixed in polymer matrices.
A preliminary step to further assessments
Determining particle size distribution is often a preliminary step in a toxicological or ecotoxicological assessment program. It allows, among other things, for the adaptation of exposure conditions during in vitro or in vivo tests, the prediction of aerodynamic behavior upon inhalation, and the evaluation of the possibility of transmembrane passage in certain organisms. For example, in the case of fine particles present in a food additive, this analysis makes it possible to assess their ability to cross the intestinal barrier.
To which substances does the OECD 110 test apply?
Substances insoluble in water
As previously mentioned, OECD 110 testing applies only to substances with a water solubility of less than 10⁻⁶ g/L. This means that the tested material does not dissolve significantly in water, even at very low concentrations. This physicochemical characteristic has direct implications for the substance's environmental and toxicological behavior, particularly regarding its persistence, dispersion, and interaction with living organisms. For example, titanium dioxide powder used in cosmetics remains in particulate form in the aquatic environment, necessitating a specific assessment of its impact on aquatic organisms.
For soluble substances, other OECD tests would be more appropriate, such as those relating to the octanol/water partition coefficient (OECD 117 or OECD 123), pH, or dissociation. However, for inert, powdered, or poorly dispersible solid materials in water, the OECD 110 test is an essential reference.
Examples of materials concerned
Many types of industrial substances can be included in OECD 110 testing. Some of the most common include:
- Metallic powders used in the alloys, pigments or technical inks industry.
- Mineral oxides such as titanium dioxide, zinc oxide or silica, often found in paints, cosmetics or plastics.
- Mineral fibers ( rock wool, glass fibers, aluminosilicates), used in insulation materials or industrial filters.
- Some nanomaterials or submicron particles are incorporated into advanced formulations, such as self-cleaning coatings or technical additives.
- Intermediate products from fine chemistry or green chemistry, intended to be encapsulated or mixed in polymer matrices.
A preliminary step to further assessments
Determining particle size distribution is often a preliminary step in a toxicological or ecotoxicological assessment program. It allows, among other things, for adapting exposure conditions during in vitro or in vivo tests, anticipating aerodynamic behavior in case of inhalation, or assessing the possibility of transmembrane passage in certain organisms.
Method A: Particle size distribution
General principle of the method
Method A relies on characterizing the effective hydrodynamic radius (Rs) of particles. This parameter corresponds to the apparent size of a particle as it moves through a fluid, and it is influenced by the particle's density, shape, and surface area. The method is applicable for particles with an Rs between 2 µm and 100 µm . Below or above this range, measurement accuracy is no longer guaranteed.
The analysis begins with microscopic observation of the sample under visible light . This step allows verification of the nature of the particles and the elimination of any impurities, aggregates, or agglomerations. Next, standardized techniques are implemented to evaluate the size distribution according to three main classes:
- Particles larger than 200 µm.
- Particles between 2 and 200 µm.
- Particles smaller than 2 µm.
These three intervals allow for a sufficiently precise particle size evaluation for a wide range of industrial products.
Analytical techniques used
Several approaches can be used to determine particle size according to method A, depending on the physical properties of the sample. The most common techniques are:
- Sedimentation : this method relies on the settling rate of particles in a liquid. It is suitable for dense and poorly dispersible substances.
- Centrifugation : it accelerates the sedimentation process by applying a centrifugal force, which improves accuracy and allows working with smaller volumes.
- The Coulter counter : this instrument measures the changes in conductivity caused by the passage of particles through a calibrated aperture. It is particularly useful for aqueous or electrolytic suspensions.
Each technique must be carefully chosen according to the chemical and physical nature of the substance, the shape of the particles, and the experimental conditions. It is essential to ensure proper dispersion of the sample before analysis to avoid any measurement errors related to aggregation.
Applications of Method A
Method A is widely used in regulatory assessments, quality control, and formulation projects. For example, it allows for:
- Check the particle size distribution of a pigment or additive before incorporating it into a plastic or cosmetic matrix.
- Evaluate the stability of a product in powder or suspension form.
- Identify the risks associated with inhaling fine particles in a professional context.
Thanks to its flexibility and the variety of techniques that can be used, method A constitutes a reliable and versatile analytical tool for the dimensional characterization of solid particles.
Method B: Fiber length and diameter distribution
When to apply method B
Method B applies exclusively to fibrous substances, that is, materials whose constituent units can adopt a filamentous form. These fibers are characterized by a high length-to-diameter ratio , which implies specific aerodynamic and toxicological behavior. This type of morphology is often found in:
- Artificial mineral fibers ( rock wool, glass fibers).
- Refractory ceramic fibers .
- Some elongated nanomaterials or fibrous composites .
The value of this method lies in the need to better assess the potential toxicity of fibers in the event of inhalation exposure. Long, thin, insoluble, and biopersistent fibers can indeed pose risks to the respiratory system, as studies on asbestos fibers have shown. This is why regulators require precise characterization of these parameters before any product is placed on the market or integrated into industrial processes.
Measured parameters and defined thresholds
Method B is based on the measurement of two essential morphological parameters:
- The length (l) of the fibers, which must be greater than or equal to 5 µm .
- The diameter (d) , which must be greater than or equal to 0.1 µm .
These thresholds are set to exclude fragments that are too short or too thin, which are irrelevant for toxicological analysis. The measurement is carried out using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), depending on the type of fiber and the required precision.
At least distinct fibers two histograms :
- A histogram of length distribution.
- A histogram of diameter distribution.
These graphs make it possible to identify the majority classes, to observe the homogeneity of the sample, and to detect any anomalies or subpopulations of fibers.
Technical constraints and best practices
Method B requires a high level of technical expertise. Sample preparation must avoid any alteration of the fibers or creation of artifacts. The analysis must be conducted in a clean environment, with calibrated equipment and complete traceability. Laboratories that perform this type of testing generally have staff specializing in analytical microscopy and dimensional metrology.
The use of Method B is infrequent but essential in certain regulatory cases, particularly when registering new industrial fibers or re-evaluating existing substances. It plays a central role in preventing occupational risks and in complying with European directives on hazardous substances.
Why is the OECD 110 test important?
A regulatory decision-making support tool
The results obtained with the OECD 110 test are used in numerous regulatory files. In particular, they allow for:
- Demonstrate the conformity of substances under the REACH regulation , which requires full characterization for substances produced or imported in quantities exceeding one tonne per year.
- Contribute to the classification of a product according to the CLP (Classification, Labelling and Packaging) regulation , particularly in the event of a risk of inhalation of fine particles or fibers.
- Meeting the requirements of health and environmental protection authorities, such as ECHA in Europe, EPA in the United States, or Canadian and Japanese authorities .
This data can also be integrated into risk modelling systems (exposure, transport, pulmonary deposition) and into reports submitted via the IUCLID , a central tool for the regulatory registration of chemical substances.
A direct influence on toxicity and exposure
The particle size and shape directly influence the toxicological behavior of a substance. For example:
- Small particles (less than 10 µm) can reach the pulmonary alveoli and remain trapped there.
- Long, thin, biopersistent fibers can cause chronic inflammatory reactions or serious respiratory pathologies, as is the case with some ceramic fibers.
- A heterogeneous or bimodal size distribution may indicate product instability or poor dispersion, increasing the risk of accidental exposure.
This is why precise knowledge of size distribution is an essential prerequisite for interpreting the results of toxicological tests, choosing the right exposure methods (inhalation, ingestion, skin contact), and establishing appropriate prevention measures .
A link with other OECD trials
The OECD 110 test can be used in conjunction with other physicochemical tests, including:
- OECD 109 on the density of liquids and solids, useful for modeling sedimentation.
- OECD 114 on viscosity, relevant for suspensions containing particles.
- OECD 125 , specific to nanomaterials, also analyzes particle size distribution with more sensitive techniques.
- OECD 124 on specific surface area by volume, which can be correlated to the particle size measured by the OECD 110 test.
Integrating this data into a comprehensive assessment dossier allows for better prediction of environmental behavior and refinement of exposure scenarios , particularly for substances classified as hazardous or subject to restriction.
Have an OECD 110 test done with YesWeLab: a turnkey solution
A network of accredited laboratories
YesWeLab relies on a network of over 200 partner laboratories located throughout France and Europe. These laboratories are selected for their high level of technical expertise and their ability to meet the most stringent regulatory requirements. Depending on your needs, OECD 110 tests can be performed:
- Under ISO 17025 accreditation , to guarantee the reliability of methods and the validation of results.
- Under GLP (Good Laboratory Practice) conditions , to ensure regulatory recognition of data, particularly in REACH, OCSPP or UN dossiers.
The partner laboratories are also able to comply with international regulatory standards, such as:
- Regulation (EC) No 440/2008 for test methods applicable to REACH.
- The CLP Regulation (EC No. 1272/2008) concerning the classification and labelling of substances.
- OECD guidelines and OCSPP standards (United States).
A digital platform to simplify your procedures
YesWeLab has developed a unique digital platform , designed for industry professionals, that centralizes all analytical processes. This platform allows users to:
- Quickly search for an analysis from a catalogue of more than 10,000 services.
- Get a quote in just a few clicks , with or without GLP requirements.
- Track the shipment and receipt of samples in real time.
- Securely access validated results and reports
This smooth operation reduces processing times, decreases administrative errors, and offers complete traceability of tests, from order to validation of the final report.
Expert and personalized support
Beyond technical services, YesWeLab offers customized support to each client. A dedicated expert will help you to:
- Choose the correct method (A or B) depending on the nature of your substance.
- Determine the optimal analysis conditions , taking into account regulatory constraints and material properties.
- Validate the report's compliance with IUCLID requirements or international standards.
- Anticipate additional needs , such as toxicological tests or multi-method analyses (OECD 109, 114, 125).
YesWeLab thus acts as a strategic partner in your compliance process, offering you easy access to high-quality tests, while guaranteeing the responsiveness and transparency of the service.
