The BPR includes biocidal substances generated in situ (Latin for “on site”): Products generating active substances during use . By in situ generation the generated active substance must have been approved by the EU or be under evaluation in the EU's review programme for active substances. This applies to the products even though they do not contain active substances at the time of placing them on the market.
The active substances may inter alia, be generated by a chemical reaction or through electrolysis.
The product generating active substances is not in itself covered by the rules concerning product authorisation. However, the substances contained in the product from which the biocidal active substances are generated are covered by these rules. According to EU terminology, the term "precursors" is used to describe them. Therefore, they require substance approval and authorisation as a biocidal product.
An example is disinfection of drinking water with the chemicals sodium sulphite and sodium hydrogen sulphite. Both substances are generated in situ by oxygenation of sodium hydrosulphite presented in the form of a stable powder. The latter is a "precursor" and will require substance approval and product authorisation. The same applies to the two chemicals generated by the oxygenation.
Even when no precursor is available approval may still be necessary.
An example of this could be an ozone generator. Ozone is the biocidal active substance for which active substance approval and product authorisation are prerequisites for placing the ozone generator on the market but the device, i.e. the generator, does not in itself require authorisation as a biocidal product. The item treated with ozone from the ozone generator will not be regarded as a treated article. Furthermore, an ozone generator contains no precursors, since the ozone is generated from oxygen in the air.