Does washing, peeling or boiling remove pesticide residues? Measured results
Rinsing under running water, peeling, boiling: how much each reduces residues, from measurements
In short
They do decrease, but washing alone has limits. In Akita Prefecture's measurements on store-bought produce, washing reduced residues by about 50% at most, and never by 80–90% or more.
Boiling reduced residues in spinach by 70–80%. On the other hand, pesticides taken up through the roots or leaves and carried inside the crop (systemic pesticides, such as the neonicotinoids) did not decrease with washing. Washing apples with baking soda did not reduce residues either.
Akita Prefecture's measurements (store-bought produce)
| Food | Method | Result (share remaining, etc.) |
|---|---|---|
| Spinach | Rinse under running water for 30 seconds | 68.7% of cyazofamid remained (100% after 5 seconds). Imidacloprid, which is taken up from the roots and ends up inside the plant, and tefluthrin, which is applied to the soil, did not decrease with rinsing |
| Spinach | Boil | 31.3% of cyazofamid and 22.8% of imidacloprid remained (70–80% reduction). Stir-frying reduced residues by about 30% |
| Cherry tomatoes | Rinse under running water / peel by blanching | Rinsing reduced boscalid by about 20–30% and cyazofamid by about 40–50%. Most of the acetamiprid was inside the fruit, and even peeling by blanching did not significantly reduce it in the flesh |
| Strawberries | Rinse under running water | 69.6% (5 seconds) and 60.9% (30 seconds) of azoxystrobin remained. Making jam left 45.7–54.9% |
| Apples | Rinse under running water / wash with baking soda | Neither reduced residues significantly (the report suggests the pesticides are taken into the waxy substances on the surface). Making jam, baking and drying reduced all four pesticides |
| Brown rice | Wash the rice / polish it | Washing left 84.4–91.7% (about 10% reduction). Polishing left 37.5% of fthalide and 63.3% of ferimzone. Dinotefuran barely changed |
Akita Prefectural Research Center for Public Health and Environment, Annual Report No. 18 (2022). The report infers that the decrease with heating was mainly due to evaporation (volatilization) rather than breakdown by heat. Residues also tended to remain more in parts that are not eaten, such as the calyx.
What research reviews (meta-analyses) found
- With boiling, blanching, canning, frying, juicing, peeling and washing, residues decreased on average, and the ratio after processing to before processing was 0.10–0.82 (Keikotlhaile et al., 2010). However, for baking, boiling, canning and juicing, some studies found increases.
- Washing or soaking often reduces residues only “to some extent”; peeling and blanching have larger effects. How residues change depends on the properties of the pesticide (whether it dissolves more easily in water or in oil) and the type of processing (Chung, 2018).
What you can do at home
- Rinse carefully under running water: in the Akita study, cyazofamid on spinach did not decrease after 5 seconds, but fell by about 30% after 30 seconds.
- Remove outer leaves, peel and calyx: pesticides tend to remain on the surface and in parts that are not eaten. Antifungal agents on citrus also concentrate in the peel (→ Postharvest pesticides).
- Boil leafy vegetables: with spinach, boiling reduced residues much more than rinsing.
- Know that some pesticides do not wash off: pesticides that enter the crop are hard to reduce by rinsing or peeling. If this concerns you, one option is to choose produce grown with fewer pesticides (organic JAS and specially cultivated produce).
The share of domestic produce exceeding the maximum residue limit in national inspections was 0.001% (MHLW, fiscal 2024) → How maximum residue limits are set
Sources
- Akita Prefectural Research Center for Public Health and Environment, Annual Report No. 18 (2022), “Distribution of pesticide residues in different parts of produce and changes caused by cooking,” pp. 39–42 (Japanese)
- Keikotlhaile BM, et al. Food Chem Toxicol 2010;48(1):1-6 (PMID 19879312)
- Chung SW. J Sci Food Agric 2018;98(8):2857-2870 (PMID 29222908)
- MHLW, “Results of Inspections for Pesticide Residues in Food, Fiscal 2024” (Japanese)
- MHLW Health and Labour Sciences Research, fiscal 2021 sub-study report (National Institute of Health Sciences; processing factors) (Japanese)
Last checked 2026-10-01. Systems and figures change over time. This page is a translation of our Japanese page; if they differ, the Japanese page is the reference.