Determination of nitrates by a novel ion chromatographic method: occurrence in leafy vegetables (organic and conventional) and exposure assessment for Italian consumers

Abstract

A novel ion chromatographic method to detect nitrates in vegetables was developed, and the nitrate contents in green salad (a mixture of endive and prickly lettuce), lettuce, chicory, rocket and spinach were determined from Italian markets in 1996–2002. These leaf vegetables were included because they are currently supposed to provide most of the nitrate intake in the typical Italian diet. The highest content of nitrate was detected in chicory (6250 mg kg⁻¹) and rocket (6120 mg kg ⁻¹), which are consumed in large quantities in some regions of Italy. Green salad and lettuce contained less nitrate (highest values = 4200 and 3300 mg kg⁻¹, respectively), but because they are consumed more generally, they provided 60% of the total intake of nitrates. Only a few samples were above the legal limits, with seasonal variation. A significantly higher nitrate content was found in organically grown green salad and rocket than in those conventionally produced. These data indicate that the average intake of nitrates from leafy vegetables is below the acceptable daily intake, i.e. 3.7 mg nitrate ion kg⁻¹ body weight day⁻¹, but the total intake should be monitored to protect groups at risk, such as children and vegetarians.