Container fumigation with sulfuryl fluoride

Sulfuryl fluoride has been widely used as a pesticide and biocide since around the year 2000. It serves as a substitute for the ozone-depleting substance methyl bromide, whose use has been severely restricted worldwide by the Montreal Protocol. Unlike methyl bromide, emissions of sulfuryl fluoride do not have a damaging effect on the ozone layer. However, sulfuryl fluoride has a high global warming potential: according to Fifth Assessment Report of the Intergovernmental Panel on Climate Change, one tonne of sulfuryl fluoride emitted over 100 years is as harmful to the climate as 4,090 tons of CO₂. Based on atmospheric measurements, the decrease in the concentration of methyl bromide since around 2000 has been accompanied by a steady increase in the background concentration of the substitute substance sulfuryl fluoride.

Sulfuryl fluoride is used worldwide as a fumigant to control food and wood pests, for example in buildings such as churches or for foodstuffs such as dried fruit, nuts and cereals. In recent years, the increasing use for fumigating timber in overseas containers has caused a stir. Importing countries often require export timber to be fumigated prior to export as a prerequisite for import. This is intended to prevent ecosystems from being disturbed by the import of new species, such as bark beetles.

In accordance with standard fumigation practice, the containers are ventilated after fumigation by opening the doors. For this reason, it can be assumed that the entire amount of fumigation used escapes directly into the atmosphere. Due to the dry summers and the severe bark beetle infestation, the export of so-called calamity timber via European and German overseas ports such as Hamburg has increased significantly since 2018. This was reflected in significant sulfuryl fluoride emissions.

Sulfuryl fluoride is authorized for use as a biocide and plant protection product in the EU on the basis of EU Regulations No. 1107/2009 (Plant Protection Products Regulation) and No. 528/2012 (Biocidal Products Regulation). In compliance with the provisions of the German Plant Protection Act, manufacturers, distributors and importers are obliged to notify the Federal Office of Consumer Protection and Food Safety (BVL) annually of the quantities of sulfuryl fluoride for plant protection applications that are supplied and exported in Germany.

In Regulation (EU) 2024/573 on fluorinated greenhouse gases, which came into force on 11 March 2024, sulfuryl fluoride was included as a controlled substance in Annex II, Group 3. This is associated with a labeling obligation for containers containing sulfuryl fluoride (Article 12), which will apply from 1 January 2025, as well as reporting obligations for companies that produce, import, export, destroy or reclaim this gas from calendar year 2024 onwards (Article 26). According to Article 4 of the Regulation, there is also an obligation to avoid emissions: the deliberate release of fluorinated greenhouse gases into the atmosphere is prohibited unless this release is technically necessary for the intended use. In the case of fumigation with sulfuryl fluoride, operators must document the capture and collection measures or provide reasons why possible measures to prevent emissions were not technically or economically feasible.

In Germany, regulations on the use of acutely toxic fumigants for container fumigation are laid down in the 2021 Technical Instructions on Air Quality Control (TA-Luft). This administrative regulation governs the implementation of the Federal Immission Control Act (BImSchG) for approval and monitoring authorities. It stipulates the separation of sulfuryl fluoride from container exhaust air for the approval of new fumigation systems from 1 December 2021. Old systems must be retrofitted with appropriate technologies by 1 December 2026.

Due to the increasing international importance of sulfuryl fluoride as a greenhouse gas, Germany has been voluntarily reporting sulfuryl fluoride emissions in the National Inventory Report for the German Greenhouse Gas Inventory since 2021.

The fumigation of overseas containers with sulfuryl fluoride is internationally recognised as an effective method of preventing the import of pests. In Germany, sulfuryl fluoride is currently the only plant protection agent authorised for the protection of hardwoods and conifers.

A reduction in sulfuryl fluoride emissions is possible in two ways:

Firstly, through the development of gas separators that clean the exhaust air of sulfuryl fluoride after fumigation. However, no suitable gas separator is yet available on the market.

Secondly, through the approval of internationally recognised alternative processes. For example, the suitability and approval of alternative fumigants, such as the toxic and flammable gases monophosphane (PH₃) or ethanedinitrile (dicyan), as a substitute for sulfuryl difluoride is being tested. There are also processes that do not require the use of toxic gases at all, such as the thermal treatment of wood trunks in heat chambers. However, high energy consumption is to be expected here, and the greenhouse gas balance should also be included in an assessment. In general, however, the use of alternative processes depends above all on recognition by the importing countries.

The effectiveness of legal as well as alternative and climate-neutral plant protection measures for the import and export of round timber is currently being investigated in the "KLIMAtiv" research project. The project, which is funded by the Federal Ministry of Food and Agriculture as part of the Climate Protection Emergency Programme 2022, will run until the end of 2025.