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ISO 846 Microbial Testing for Plastics
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Summary
ISO 846 testing is done to evaluate the resistance of plastics to microbial growth and biodeterioration under controlled laboratory conditions. This test helps plastic manufacturers understand material durability, surface contamination risks, and long-term performance in real-use environments. MIS lab performs ISO 846 testing to deliver reproducible data to support microbial resistance and material durability claims for compliance and product decisions.
Quick understanding about test
ISO 846: 2019 – Evaluation of the action of microorganisms on plastics
Applicable to a wide range of plastic products that are used in construction, medical, and agricultural industries.
- Aspergillus niger (ATCC 6275)
- Penicillium pinophilum (ATCC 36839)
- Paecilomyces variotii (ATCC 18502)
- Trichoderma virens (ATCC 9645)
- Method A: Fungal-growth test
- Method B: Determination of fungistatic effects
- Method C: Resistance to bacteria
- Method D: Resistance to microbially active soil (soil-burial test)
- Help manufacturers in optimizing plastic formulations.
- Ensures compliance with industry standards .
Results
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What Is ISO 846?
ISO 846 is an internationally recognised standard and plays an important role in ensuring regulatory adherence for plastics products/ materials claims for durability and microbial resistance. It specifies test conditions and requirements for the measurement of the resistance of plastics to microbial attack, specifically fungi, bacteria, and other soil microorganisms. While plastics are generally highly durable but they can still be damaged by microbial growth Therefore, evaluating their resistance to microbial attack is crucial to ensure their durability.
The deterioration of plastic materials by microorganisms (bacteria and fungus) is affected by two processes –
- Direct action – Plastics act as a nutrient medium for the growth of microorganisms. This subsequently results in the deterioration of plastic.
- Indirect action – Metabolic products of microorganisms cause the deterioration of plastic.
It’s important to note that this standard does not test the biodegradability of plastics. The standard specifically tests the resistivity of plastics to microbial attack.
Plastic Products Tested Using ISO 846
ISO 846 applies to solid, non-porous plastics and polymer-based materials commonly used in high humidity and soil-rich environments.
- Construction
- Agriculture
- Healthcare
- Consumer goods
- Electronics
Out of Scope
ISO 846 does not apply to:
- Porous materials (foams, textiles, fibrous substrates)
- Biodegradability assessment
Mandatory and Optional Test Microorganisms
- Bacteria: Pseudomonas aeruginosa (ATCC 15442)
- Fungi: Aspergillus niger (ATCC 6275), Penicillium pinophilum (ATCC 36839), Paecilomyces variotii (ATCC 18502), Trichoderma virens (ATCC 9645) and Chaetomium globosum (ATCC 6205)
Test Conditions and Environmental Parameters
Parameter | Typical Value (Methods A, B, C) |
Temperature | 29 °C ± 1 °C (incubation) for fungal/bacterial tests. |
Relative Humidity | 95 % ± 5 % (very high humidity to promote growth). |
Duration of Exposure | Minimum 4 weeks (unless a longer period is agreed). |
Media | Method A : Incomplete nutrient Medium Method B : Complete nutrient Medium Method C : Incomplete nutrient Medium |
Specimen Preparation | 50 mm ± 1 mm, thickness 0.5–2 mm |
ISO 846 test methods
Method A: Fungal-growth test
In this method, plastic test specimens treated with antimicrobial treatments are exposed to a mixed suspension of fungal spores with insufficient nutritive medium (no carbon source) under conditions of ≥95% relative humidity. The fungi grow only if the plastic acts as a nutrient source. Negative controls, stainless steel coupons, confirm that any growth observed is due to the plastic itself. Suppose the material does not contain nutritive components; the fungal mycelium does not develop, preventing plastic degradation. The test is applicable for comparing the inherent resistance of plastics to attack by fungi in the absence of other organic materials.
Method B: Determination of fungistatic effects
Method C: Resistance to bacteria
In this method, the resistance of plastics to bacterial action is evaluated by placing test specimens on an incomplete medium which lacks a carbon source. If no bacterial growth is observed in the agar surrounding the specimen, it implies that the material does not contain nutritive components to support bacterial growth. This method is typically applied to assess the inherent microbial resistance of plastics.
However, if the material claims added antibacterial or hygienic functionality, it should also be tested according to ISO 22196, which specifically measures the antibacterial performance of non-porous plastics by treating them with biocides.
Results Interpretation and Passing Criteria
Results are interpreted qualitatively by observing the microbial growth effects such as surface colonization or discoloration using a standardized visual rating scale. Lower growth ratings indicate stronger resistance to microbial attack. ISO 846 does not define a universal “pass or fail” limit; acceptance criteria are usually defined based on the intended use of the product, applicable standards, or regulatory expectations.
ISO 846 vs Other Standards
Criterion | ISO 846 | ISO 22196 | ASTM G21 |
Purpose | To assess microbial ( (fungi & bacteria) deterioration of plastics | To evaluate antibacterial activity of treated plastics. | To assess antifungal resistance of synthetic plastics and polymers |
Test microorganisms | Aspergillus brasiliensis (niger), Penicillium funiculosum, Paecilomyces variotii, Chaetomium globosum, Trichoderma virens | Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 8739) | Aspergillus brasiliensis, Penicillium funiculosum, Chaetomium globosum, Trichoderma virens, Aureobasidium pullulans |
Scope of products | Plastics with even, cleanable surfaces (excludes porous foams) | Antibacterial-treated plastic products (non-porous surfaces) | Plastics and other synthetic polymeric materials (films, sheets, molded parts). |
Result interpretation | Qualitative : Deterioration of treated samples vs controls | Quantitative: Bacterial reduction on treated samples vs controls | Qualitative: Visual growth rating (0-4 fungal growth scale) |
Importance of ISO 846 Test
The ISO 846 test is essential as it:
- Evaluates the long-term performance of plastics when exposed to environments prone to microbial growth.
- Replicates real-world usage conditions to assess microbial resistance of plastic materials.
- Critical test for sectors where plastic degradation can compromise safety, functionality, and service life.
- Test involves both visual inspections and measurements of physical properties to determine material impact.
- Ensures plastics meet durability and performance standards in microbial-rich environments.
Why choose MIS
At Microbe Investigations Switzerland (MIS), we offer comprehensive antimicrobial testing services for products claiming microbial protection, including plastics, coatings, textiles and disinfectants. Our advanced microbiology testing facility enables precise evaluation of antimicrobial efficacy, ensuring compliance with international standards.
In addition to ISO 846 microbial testing for plastics, MIS performs other testing methods such as ISO 22196, JIS Z 2801, ASTM G21 and ISO 21702 to check the antimicrobial efficacy of treated plastic materials.
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Frequently Asked Questions
DR. Martinoz Scholtz
ISO 846 assesses long-term resistance of plastics to microbial growth and deterioration, while ISO 22196 measures short-term antibacterial effectiveness on surfaces. In simple words, ISO 846 testing focuses on material durability and ISO 22196 assesses antimicrobial efficacy.
ISO 846 indicates a plastic’s resistance to microbial attack under accelerated laboratory conditions but does not by itself predict long-term outdoor durability. Outdoor performance is also influenced by UV exposure, temperature cycling, and weathering, and must be evaluated separately.
It takes approximately 28 days to complete the test, depending on the test organisms.
Yes. ISO 846 testing can be applied to plastics containing antimicrobial additives.
Results are assessed visually using a standardized growth rating, with lower ratings indicating better microbial resistance. ISO 846 has no fixed pass/fail limit, and acceptance criteria depend on the intended use and applicable requirements.
Industries that commonly rely on ISO 846 include plastics manufacturing, construction materials, electrical and electronic components, automotive interiors, packaging, textiles, medical devices (non-implant), and consumer goods where microbial resistance and material longevity are important.
Yes. ISO 846 Method D (soil-burial test) specifically evaluates the effect of soil microorganisms by exposing plastic specimens to controlled soil conditions, allowing detection of biodegradation or deterioration caused by naturally occurring microbial populations.
The standard specifies representative fungal species and bacteria commonly found in indoor, outdoor, and soil environments to ensure a realistic and reproducible challenge.
A high resistance rating would suggest that the material possesses great durability to microbial growth, promoting longer product life and ensuring that regulatory requirements are adequately met.
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