Isoprothiolane イソプロチオラン
Fungicides for rice blast and other rice diseases: Used against rice blast, sheath blight and other rice diseases (some stop melanin synthesis, some strengthen the rice plant's own resistance).
In Japan
- Registration
- Registered as a pesticide (first registered July 17, 1974). 15 formulated products contain it.
- Main registered crops
- rice (paddy), Western lawn grass, turfgrass, apple, Japanese pear, cherry and others (15 crop names in the registered uses)
- Toxicity class
- Active ingredient: Ordinary substanceClasses of the 15 formulated products (diluted products sold): ordinary substance 15Classes under Japan's Poisonous and Deleterious Substances Control Act.
- ADI (acceptable daily intake)
- 0.1 mg per kg of body weight per day
- ARfD (acute reference dose)
- 0.5（一般の集団） ／ 0.12（妊婦又は妊娠している可能性のある女性） mg per kg of body weight
- Evaluation
- Food Safety Commission of Japan, September 11, 2025
ADI: the amount considered to have no effect on health even if eaten every day for a lifetime. ARfD: the amount considered to have no effect on health when eaten at one time (within 24 hours). Both are set by the Food Safety Commission of Japan, mainly from animal studies.
In Japan's national residue testing (fiscal 2024)
| Produce | Detected / tested | Detection rate | Over the limit |
|---|---|---|---|
| Domestic | 3 / 4,438 | 0.1% | 0 |
| Imported | 0 / 3,159 | 0.0% | 0 |
Found in domestic foods: mikan (mandarin orange), rice (brown rice) (max. 0.35 ppm)
Tests are counted as pesticide × sample. Any detection counts as “detected” — it does not mean the limit was exceeded. For pesticides outside the top 20, figures are summed from the food-by-food tables of the full report.
Evaluations abroad
- WHO acute toxicity class
- II (Moderately hazardous), LD50 ≥300 mg/kgBased on the toxicity of the undiluted active ingredient given once, mainly to rats by mouth (LD50 = the dose that kills half; the smaller, the stronger the acute toxicity). It is not an assessment of the safety of residues in food.
- EU
- Not approved in the EUEU ADI: Not Applicable; ARfD: Not Applicable
- IARC (carcinogenicity)
- No matching entry in the IARC list (not evaluated or out of scope, including Group 3)
Related explainers
Sources
- FAMIC (Food and Agricultural Materials Inspection Center), pesticide registration information (as of Sept. 30, 2026) (Japanese)
- Food Safety Commission of Japan, risk assessment report on Isoprothiolane (September 11, 2025) (Japanese)
- MHLW, results of pesticide residue testing in foods, fiscal 2024 (Japanese)
- WHO Recommended Classification of Pesticides by Hazard 2019
- EU Pesticides Database (Isoprothiolane)
Last checked 2026-10-01. Registrations and evaluations change over time. This page is a translation of our Japanese page; if they differ, the Japanese page is the reference.