Isocyanates and Their Metabolites in Nutrient Solutions and Fruit and Leaf Vegetables in Soilless Crops On Rebounded Polyurethane Substrates

Tomato, cucumber, melon, and lamb's-lettuce soilless crops were grown on rebounded polyurethane foam substrates. Samples of the nutrient solutions, fruits, and vegetables were taken at the normal harvest time. In crop systems where the nutrient solution was continuously recirculated, the nutrient solution was sampled in its reservoir. In crop systems without nutrient solution recirculation, the nutrient solution was sampled after its passage through the polyurethane substrate. No residue of each of the polyurethane synthesis isocyanates (2,4- and 2,6-toluene diisocyanate, TDI, and 4,4'-diphenylmethane diisocyanate, MDI), nor of each of their immediate diamino derivatives (2,4- and 2,6-diaminotoluene, TDA, and 4,4'-methylenedianiline, MDA) were detected in the nutrient solutions or in the fruits and vegetables. The analytical limit of sensitivity for these compounds in the nutrient solutions was 0.002 mg/kg of solution; in the fruits and vegetables, it was 0.01 mg/kg fresh weight