Effects of box liner perforation area on methyl bromide diffusion into table grape packages during fumigation

• Grape packages with plastic liners with perforated areas of 0.3, 0.6, or 0.9% were fumigated with methyl bromide (MB).
• MB fumigation at 4.4 or 6.0 °C employed dosages of 64 mg L−1 or 56 mg L−1 at 26.7 °C.
• MB diffusion was similar and rapid among all of the packages regardless of perforated areas.
• After fumigation, MB residue depuration at 2 °C was rapid and often below detection with 48 h.

Plastic liners are used inside boxes of table grapes to retard moisture loss from the grapes and to contain sulfur dioxide gas released inside the packages to control postharvest decay. However, to control organisms of quarantine concern, regulators specify exported packages must be fumigated with methyl bromide (MB), and to enable adequate diffusion of the fumigant into the packages they specify the liners must be perforated. The percentage of the area of the liner that is perforated, formerly stipulated to be not less than 0.3%, was recently increased to not less than 0.9%. Two MB fumigation schedules specified for control of the Chilean mite, Brevipalpus chilensis, were applied to grape packages with a high-density polyethylene liners with perforated areas of 0.9% or with a SO2-releasing liners with perforated areas of 0.3, 0.6, or 0.9%. Package and chamber concentrations were measured repeatedly for up to three hours during MB fumigation at 4.4 or 6.0 °C with a dosage 64 mg L−1 or at 26.7 °C with a dosage 56 mg L−1. Diffusion was similar and rapid into the packages among all perforated areas. MB concentrations inside the packages were not less than 95% of those of the chamber atmosphere within 15 min. After fumigation with an MB dosage 64 mg L−1 at 4.4 °C and subsequent storage at 2.0 °C, mean MB residue content in grapes from most packages 48 h after MB fumigation was below the limit of quantitation of 0.002 mg kg−1. After fumigation with an MB dosage 56 mg L−1 at 26.7 °C and subsequent storage at 2.0 °C, mean MB residue content in grapes from most packages 24 h after MB fumigation was below the limit of quantitation.