Pesticides
Pesticides are chemical or biological substances that are used in various sectors and sometimes also at home to control pests. In agriculture and horticulture, pesticides are used to protect crops.

There are insecticides (against insects), herbicides (against weeds), fungicides (against fungi) and biocides (against various micro-organisms). Although these products are useful, they can also entail risks for the environment, humans and animals. This depends on the type of crop, the toxicity of the agent used, the concentration still present and the degree of (direct) exposure to it.

To minimize harmful effects, most countries have regulations in place. Certain hazardous pesticides have been banned for some time now. Sometimes residues of very slow-degrading pesticides can remain in the environment for a long time and be detectable.

Pesticides in substrate?
Pesticide residues can occur in potting soil and substrates if they are produced with renewable or circular raw materials that contain residue. Substrate raw materials often have a history from another chain. In that chain, pesticides (that were then still permitted) may have been used in the past.

The substrate raw material peat is free of residue, because no other activities have taken place in peat areas before. Most other raw materials do come from a chain with a history of possible pesticide use. For example, in the environment where the raw material originates or during a (previous) production process. A number of examples with a history are substrate raw materials such as compost, wood fibre and tree bark. GFT compost consists entirely of composted vegetable, fruit and garden waste. If pesticides have been used during gardening, this also ends up in the GFT waste and therefore in the compost. Wood fibre and tree bark are residual products from the wood industry, where pesticides can also be used. With the transition to increasing use of renewable raw materials, there is also a greater chance of pesticide residue in potting soil and substrates. Pesticide residues only partly disappear from the raw material through processing such as composting.

In order to gain more insight into the extent to which residues are absorbed by plants, RHP started a research project in 2022. For this purpose, raw materials are used in which residue has been found. These products are processed in a substrate on which plants are grown, which are also tested for residues themselves. Any absorption by the plant will partly depend on the type of agent and the concentrations (which are often low). The research project will run until the end of 2024, after which RHP, together with external bodies, wants to develop requirements for residues in raw materials. Any values ​​found in the plants can be tested against the existing maximum residue limits (MRL). MRL indicates how much residue of the active substances of pesticides may remain in vegetables, for example, without endangering health. These are officially established values ​​that apply to Europe. MRL values ​​cannot be adopted one-on-one for substrates, but MRL values ​​are a useful tool for determining the requirements for substrates based on plant uptake. Incidentally, RHP has been carrying out risk assessments at suppliers of substrate raw materials for years. Think of on-site inspections at sawmills and coconut fibre factories. Risks in the chain, such as the chance of residue, are reduced for RHP-certified raw materials.