Concentration by time product and gas penetration after marine container fumigation of table grapes with reduced doses of sulfur dioxide

Reduced doses of sulfur dioxide (SO2) were evaluated for the fumigation of marine containers with respect to the concentration x time (CT) product and gas penetration. Two commercial export containers were loaded at 32 degreesF (0 degreesC) with 20 metric pallets [40 x 48 inches (102.5 X 123.1 cm)] comprised of 72 expanded polystyrene foam boxes (12 tiers, 6 boxes/tier) of table grapes (Vitis vinifera) and fumigated with 1.0 and 0.5 lb (0.454 and 0.227 kg) SO2, respectively. A third marine container was loaded with 20 metric pallets comprised of 84 plastic boxes of table grapes (14 tiers, 6 boxes/tier) and fumigated with 0.25 lb (0.113 kg) SO2. The boxes contained 16 lb (7.3 kg) of table grapes distributed in nine polyethylene cluster bags enclosed in a perforated polyethylene box liner. Fumigations were performed through the bottom seal of the rear door from pre-weighed compressed SO, cylinders. CT product was calculated after taking samples of the atmosphere in the container every 5 to 10 min and measuring the ambient SO, concentration with a gas sampling pump and colorimetric dosimeter tubes. Pallet and box penetration of the gas was assessed by placing passive colorimetric SO2 dosimeters inside the cluster bags in boxes located in both the third and ninth center boxes from the top of pallets located in the front, center, and rear of the load. Fumigations with 1.0, 0.5, and 0.25 lb SO2, with calculated CT products at 32 OF of 925, 360, and 40 ppm-h (muL.L-1.h(-1)) respectively, were found to provide excessive, adequate, and insufficient SO2 doses.