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Updated: Mar 9, 2026

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Dissipation Kinetics and Risk Assessment of Paclobutrazol in Onion.

Ravinder Singh1, Kousik Mandal2, Smriti Sharma1

  • 1Department of Entomology, Punjab Agricultural University, Ludhiana, 141004, India.

Bulletin of Environmental Contamination and Toxicology
|March 7, 2026
PubMed
Summary

Paclobutrazol residues in onions dissipate quickly, reaching below detectable levels within 10-15 days after application. This study confirms paclobutrazol is safe for consumption, with low dietary risk in onions.

Keywords:
Dissipation kineticsOnionPaclobutrazolRisk assessment

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Area of Science:

  • Agricultural Chemistry
  • Environmental Science
  • Food Safety

Background:

  • Paclobutrazol is a widely used fungicide and growth regulator in onion cultivation.
  • Concerns exist regarding paclobutrazol residue persistence, impacting food safety and environmental health.
  • Understanding its dissipation kinetics is crucial for safe agricultural practices.

Purpose of the Study:

  • To determine the residue levels and persistence of paclobutrazol in onion crops.
  • To assess the dissipation rate of paclobutrazol under field conditions.
  • To evaluate the dietary risk associated with paclobutrazol application in onions.

Main Methods:

  • Field study involving two foliar applications of paclobutrazol at recommended (X) and 1.25X doses.
  • Sample collection at various intervals post-application for residue analysis.
  • QuEChERS method for residue extraction, followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) for quantification.
  • First-order kinetics and half-life (T1/2) calculations for dissipation analysis.

Main Results:

  • Initial paclobutrazol residues were 0.29 mg kg⁻¹ (X dose) and 0.35 mg kg⁻¹ (1.25X dose).
  • Residues fell below the limit of quantification (LOQ) by day 10 (X dose) and day 15 (1.25X dose).
  • Half-life (T1/2) of paclobutrazol in green onion was calculated at 4.57 days (X dose) and 5.04 days (1.25X dose).
  • Residues were below LOQ in mature onions and soil at harvest.

Conclusions:

  • Paclobutrazol exhibits rapid dissipation in onion crops, with residues quickly falling below detectable limits.
  • The calculated half-life indicates a short persistence period in green onions.
  • Dietary risk assessment (Hazard Quotient < 1) suggests paclobutrazol is safe for consumption in onions at the tested doses for both adults and children.