While hydrogen peroxide is widely known outside horticulture for bleaching hair, in horticulture, it has become an important agent in recent years for keeping irrigation systems clean and free of biofilm. In the Netherlands, however, concern has arisen because clear rules around its use appear to be lacking, and product approvals are lagging behind practical use. What is going on? What is still allowed, and what is not?
Authorization procedures
It's a complicated story, and to understand it, it's important to first look at the authorization procedures in the Netherlands and in Europe. Products used for disinfecting irrigation systems are classified as biocides in the Netherlands, according to EU regulations. Hydrogen peroxide as an active substance is authorized at the European level within the biocides regulation, including for disinfection purposes.
Thanks to that approval, manufacturers can apply for authorization in the Netherlands for a biocide containing hydrogen peroxide as the active substance. They do so via a reviewing body, such as the Dutch Ctgb (Board for the Authorization of Plant Protection Products and Biocides). After approval, the NVWA (Dutch Food and Consumer Product Safety Authority) enforces its use.
Hydrogen peroxide is used as a disinfectant due to its strong oxidizing properties. It is effective at killing bacteria, fungi, and other viruses, as well as preventing and controlling biofilm. After reacting, it breaks down into water and oxygen.
Biocide authorization
In the Netherlands, several suppliers offer hydrogen peroxide. It usually involves stabilized hydrogen peroxide, where an additive such as silver is included to prevent it from reacting too early or decomposing. These suppliers must have a biocide authorization before their products can be used in greenhouses.
However, unrest arose this summer: the NVWA warned that inspections on the use of biocides in greenhouse horticulture had revealed several violations, resulting in fines. The focus of these inspections was on the use of hydrogen peroxide, and according to the NVWA, particular attention was given to tomato growers. These inspections are part of a government-requested baseline measurement to assess biocide use in greenhouses. And violations were found.
"The biocides are not being applied according to the applicable instructions," said the NVWA, which will release a report early next year. A biocide is not simply authorized; it is only approved for use in a specific manner.
Continuous dosing
In horticulture, continuous dosing (also known as "inline dosing") has become common practice, where small amounts of hydrogen-peroxide-based product are added to irrigation water regularly. But this is not how the products are authorized for use. They are only approved for "shock dosing," where a higher dosage is applied to the system, followed by a reaction time, aeration, and rinsing.
Moreover, there turned out to be much uncertainty surrounding the regulations and the interpretation of product labels, leading to doubts about whether certain products were even authorized at all. Is the phrasing "for use in piping systems" sufficient, or must it specifically say "greenhouse horticulture," or even "food production horticulture"? Even the Ctgb itself seems to struggle with precisely interpreting the labels. At first, it appeared that only one product was authorized, but more emerged quickly. Again, only if the instructions for use are followed.
New regulation
A new European biocides regulation has been in effect for some time. (Since 2012, the BPR—the Biocidal Products Regulation—has been in force, with the goal of harmonizing regulations across Europe. As a regulation, all member states must follow these rules. Depending on where the active substance or product stands in the approval process, it may fall under transitional rules or must already comply with BPR requirements.)
This makes the situation even more complicated. In response, several suppliers have applied for re-registration with the Ctgb. These applications include re-registrations that "better match practical needs"—meaning approval for continuous dosing. For hydrogen-peroxide products that were already on the market, the deadline for submitting these adjusted applications was 2017. But many of these re-registrations have still not been processed. Dutch authorization procedures are complex and lengthy, and the Ctgb is facing a backlog. Efforts are being made to address this.
Getting the issue prioritized
In the meantime, the sector is trying to get this issue prioritized. The industry organization Glastuinbouw Nederland is also in discussions with government bodies. "Policy has overtaken practice. Thanks to the inspections, we now know that things are not going well. At the moment, there is a complete mismatch between current labels and actual use. That needs to be resolved quickly."
How sensitive the issue is becomes clear from an article published at the end of November on a major Dutch news website, in which the NVWA was interviewed. It referred to "possibly unsafe tomatoes," due to the use of continuous dosing of silver-stabilized hydrogen peroxide—which is not allowed. Organizations opposed to pesticide use called it a "scandal," and online the story fueled heated debate. The tomatoes in question were tested and found safe for consumption, but that information appeared several paragraphs below the sensational headline.
Whether authorization for continuous dosing will be granted in the near future remains uncertain. Until then, the use of certain products is allowed under previous European legislation and transitional rules (Huwa-San from Roam Technology and Hortixyl from Cindro). Intracare's Intra Hydropure has an authorization under the new European legislation. For all three products, the same rule applies: no continuous dosing—only use as indicated on the label. Dutch growers are advised to always check the Ctgb website, which lists authorized products and their instructions for use.
