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A survey of nitrate-ion concentrations in plant-factory-cultured leafy vegetables was conducted. 344 samples of twenty-one varieties of raw leafy vegetables were examined using HPLC. The nitrate-ion concentrations in plant-factory-cultured leafy vegetables were found to be LOD-6,800 mg/ kg. Furthermore, the average concentration values varied among different leafy vegetables. The average values for plant-factory-cultured leafy vegetables were higher than those of open-cultured leafy vegetables reported in previous studies, such as the values listed in the Standard Tables of Food Composition in Japan-2015 -Seventh revised edition . For some plant-factory-cultured leafy vegetables, such as salad spinach, the average values were above the maximum permissible levels of nitrate concentration in EC No 1258/2011; however, even when these plant-factory-cultured vegetables were routinely eaten, the intake of nitrate ions in humans did not exceed the ADI.

Heavy metals are ubiquitous in the environment and nature, and even in trace amounts, chronic exposure to them can have negative health effects on humans. It is known that rice, in particular, easily accumulate cadmium (Cd). Cd can accumulate in the human body and affect human health. In Japan, rice is a staple food and a main leading source of Cd poisoning. The Tokyo Metropolitan Government has been investigating the Cd content in brown rice sold in Tokyo since 1973 in order to prevent Cd poisoning in humans. A survey result from 2010 to 2018 stated that there was no sample that exceeded the maximum limit (0.4 ppm). Moreover, compared with past survey reports in Tokyo, the Cd content in brown rice has obviously decreased. In this survey, cadmium intake from brown rice was not particularly problematic in terms of food hygiene.

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