Negligible effect of urea-formaldehyde as N fertilizer on the formaldehyde content and edible safety in leafy vegetables

【Objectives】 The residue of the formaldehyde accumulation (FA) and in leafy vegetables with urea-formaldehyde (UF) application is concerned by public. The safety of UF as N fertilizer applied on leafy vegetables was investigated in this paper.【Methods】The first pot experiment with three factors and four levels were conducted using lettuce and Chinese cabbage as materials. Three factors were 50%U + 50% UF activity index (AI) was 67%, UF1), 50%U + 50% UF (AI was 57%, UF2) and the U. Four levels were the N application as 0, 100, 200, 300 mg/kg soil. Each treatment was repeated 6 times and 12 treatments in total. The first pot experimental with four factors and three levels used lettuce as materials. Four factors were UF which the AI was 55% (UF3), 63% (UF4), and 72 %( UF5) and U (the nitrogen content was 46%). Three levels were the N application as 0, 200, 300 mg/kg soil. Each treatment was repeated 6 times and 12 treatments in total. The formaldehyde contents in the vegetables were measured by the Acetylacetone Spectrophotometric method after harvest.【Results】The formaldehyde was detected in vegetables on both treatments with and without N. The FA was 0.21 mg/pot and 0.35 mg/pot in the first lettuce and Chinese cabbage experiments and the formaldehyde content was 1.72 mg/kg of CK treatments. In the first lettuce experiment under N application level of 100 mg/kg soil, FA in U and U+UF treatment were about 2.7 to 2.8 times larger than in CK, however, there was no difference between U and U+UF treatments and when under N application levels of 200 and 300 mg/kg soil, FA in Urea treatment was 0.68 and 0.56 mg/pot, significantly higher than in U+UF treatment. The FA in U treatment was 26% and 33% higher than in UF1 + U and UF2 + U treatments respectively under N 200 mg/kg, and 30% and 24% higher than in UF1 + U and UF2 + U treatments under N 300 mg/kg. In the second lettuce experiment, the formaldehyde content of the U and UF5 treatments were the largest. There was no significant difference in formaldehyde content among treatments of CK, UF3 and UF4 under N 200 mg/kg. Also, no significant difference of formaldehyde content was tested between CK and UF3 treatments under N 300 mg/kg. But the formaldehyde content of UF4 was even significantly lower than that of CK treatment. The range of formaldehyde content of lettuce was from 4.97 to 5.36 mg/kg for both U and UF5 (AI=71.8%) and the formaldehyde content of UF3 and UF4 was decreased by 68% and 70% compared to that of UF5 respectively. The formaldehyde content of UF3 and UF4 was 69% and 71% lower than in U treatment respectively. The formaldehyde content and accumulation in leafy vegetables was not affected by amount of N application from N 100 to 300 mg/kg.【Conclusions】Compared with urea, whether application of urea-formaldehyde individually or mixed with urea, no matter the activity index of the urea-formaldehyde from 50% to 71.8% and whatever the N dosage from 100 to 300 mg per kilogram soil, the formaldehyde content in leafy vegetables will not be influenced and the formaldehyde residues in leafy vegetables is safe.