BS EN ISO 846:2019 pdf download – Plastics – Evaluation of the action of microorganisms
4.3 Method C: Resistance to bacteria
The action of bacteria on test specimens is assessed using an incomplete medium without a carbon source 1) . If there is no growth in the agar surrounding the specimen, then the specimen does not contain any nutritive components. If a material to be tested claims added functionality, such as a product with hygienic effects, the plastic material should be tested according to ISO 22196 which provides guidance for measuring the basic antibacterial performance of non-porous (plastic) materials that have been treated with a biocide with the intention of introducing antibacterial/hygienic properties into that material.
4.4 Method D: Resistance to microbially active soil (soil-burial test)
Test specimens are completely buried in natural soil with a known water-holding capacity and a specified moisture content (see Annex A). The soil-burial test has been included in this document because many plastics are used in permanent contact with soil and exposed to high humidities.
4.5 Choice of properties for assessment of biodeterioration
The choice of the properties to be determined depends on the aim of the test. A visual assessment of biological attack shall always be made as the first stage in assessing the resistance of the plastic. It is recommended that determinations be made of those properties which clearly indicate surface changes, such as surface gloss, flexural properties, impact resistance and hardness.
6.2.1.2 Sub-test series a (without biocide) and sub-test series b (with biocide).
If the test specimens contain biocides and the test is intended to show the biocidal efficacy of an active substance intended to protect the material from biodeterioration, then for test series I two sets of test specimens have to be tested: one without a biocide (sub-test series a) and one test series with the biocide (sub-test series b). Therefore, 10 test specimens in total need to be inoculated. Ideally, these test specimens should be identical except for their biocide content. This test set-up would allow the demonstration of the basic preservative efficacy for an active substance.
6.2.1.3 Sub-test series c (for Test A only): stainless steel coupons as negative controls (minimum 3 specimens).
These control specimens are comprised of non-corrodible stainless steel, which contains no nutrient source for fungi. They are inoculated, incubated and assessed (see Table 4) in the same way as the test specimens in test series I. Should growth occur on these inert surfaces this indicates that nutrients have been unintentionally transported onto the surface of the control specimen with the inoculum. Any growth on these negative control specimens shall be reported according to Table 4 as well as whether growth is more or less than on the other inoculated specimens in test series I.