Are nitrate concentrations in leafy vegetables within safe limits?

Abstract

Leafy vegetables are an important source of nutrition in the human diet. Estimation of nitrate concentration in samples of leafy vegetables collected from the local markets of Delhi has revealed that a significant number of spinach and chenopodium samples contained nitrate in concentrations higher than the Acceptable Daily Intake (ADI) limit for an average 60 kg person (if consumed @ 100 g/day). However, nitrate concentration in fenugreek, coriander and sowa samples was well within the safe limits for consumption. On the basis of our findings with market samples, extensive studies were conducted in nine genotypes of spinach (Spinacia oleracea L.) grown under greenhouse conditions. The genotypes varied markedly in their nitrate concentration as well as nitrate reductase activity. At the threeweek stage of plant growth, one genotype, and at the six-week stage, six of the nine genotypes under investigation exceeded the ADI limit. Petioles possessed several times higher level of nitrate than the leaf laminae in market samples as well as in the genotypes. All the genotypes showed diurnal variation in nitrate accumulation with minimum concentration at noon. These findings warrant thorough investigation of nitrate levels in other leafy vegetables consumed regularly and the ways and means to control them.