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Nitrate in Leafy Vegetables
Comparing Conventional and Organic Lettuce and Spinach in California

 

Abstract: The potential health hazards of human nitrate intake are well studied. Since leafy vegetables are the main source of dietary nitrate, the European Union established maximum limits for nitrate content in lettuce and spinach in 1997. No regulations have yet been introduced in the US. To assess their relative safety based on EU limits, we measured nitrate levels in winter and summer samples of organic and conventionally-produced Iceberg lettuce, Romaine lettuce and spinach (n=120, each) from various markets in Santa Cruz, California. To demonstrate effects of farming practices on nitrate content in those leafy vegetables, farmer's field survey (n=5) and a field experiment were also conducted. Market sampling survey showed that nitrate levels in lettuce samples never exceeded EU limits; however, 29% of our spinach sample exceeded EU limits. Conventional spinach nitrate levels exceeded EU limits much more often than organic spinach. Measured nitrate levels are compared with data reported previously in the US and other countries. Farmer's field survey and the field experiment suggested that not only farming practices but also environmental factors strongly affected nitrate content in lettuce and spinach.

 

Full Report: Comparison of Nitrate Content in Leafy Vegetables from Organic and Conventional Farms in California (64 pages). leafnitrate.pdf


Supported by: Organic Farming Research Foundation Research Grant, 1997: Comparison of Nitrate Content in Leafy Vegetables from Organic and Conventional Farms in California.