The nitrate content of vegetables varies over a wide range (1 - 10,000 mg/kg) and depends on the type, origin, cultivation and storage conditions of the vegetables (JECFA, 1995). According to AESAN (2011), vegetables account for 80-85% of total daily nitrate intake.
Along with nitrates, by consuming vegetables, a certain amount of toxic heavy metals such as cadmium, lead, chromium, etc. can be introduced into the body.
The aim of the experiment was to determine the effect of the length of soaking lettuce in water with ZEOTEX zeolite relative to control (lettuce without soaking) and soaking the lettuce in pure water to reduce the concentration of nitrates and heavy metals in lettuce leaves.
The concentration of nitrates and heavy metals were determined in lettuce leaves control samples, soaking in water as well as in treated lettuce samples (soaked in water with ZEOTEX zeolite added) by prescribed methodology.
The experiment was carried out in three treatments with different times of soaking of lettuce in water with the addition of ZEOTEX zeolite (10, 20 and 30 min.). The experiment was conducted at the Faculty of Agrobiotechnical Sciences in Osijek, at the Department of Agroecology and Environmental Protection.
The nitrate concentration in the control sample of lettuce was 2265.07 mg NO3 -/kg of fresh lettuce, which is below the prescribed allowable nitrate concentration in leafy vegetables under EU Regulation 1881/2006 (4000 mg mg NO3 -/kg).
However, it is important to note that soaking lettuce in water containing zeoilt reduced the nitrate concentration in lettuce leaves in comparison to control and in lettuce soaking in clean water. Namely, rinsing lettuce in clean water is a common way of washing lettuce before consumption.
The obtained results show a decrease in the nitrate concentration in lettuce leaves:
- 41,72% after 30 min soaking in ZEOTEX zeolite solution.
Heavy metals concentrations
The term “heavy metals” has been very commonly used over the past few decades to refer to a group of metals and semi-metals (metalloids) that have been linked to contamination and potential toxic effects (Duffus, 2003).
The transfer of heavy metals from soil to plant and food is the basis for the entry of heavy metals into the food chain. The influence of man on the atmospheric deposition of heavy metals and the uptake of heavy metals in soil by agro-technical measures is quite large, and therefore agrotechnical measures and production processes should be directed towards reducing the bioavailability of toxic heavy metals, above all Cd and Pb.
The choice of growing site and type of vegetable is also very significant as it may be too high (above MDC) in vegetables produced in urban gardens. The lowest concentrations can be expected in fruit vegetables and the highest in root vegetables (Lončarić, 2015).
The results of the Co, Cr, Pb, and Cd heavy metals concentration in the lettuce leaf after soaking in ZEOTEX Zeolite solution indicate a decrease in the concentration of the heavy metals.
The decrease in concentration depending on the heavy metal was in the following order:
- 32,76 % after 30 min soaking in ZEOTEX zeolite solution.
- 22,75 % after 20 minutes soaking in ZEOTEX zeolite solution
- 19,04 % after 20 minutes soaking in ZEOTEX zeolite solution
- 42,59 % after 10 min soaking in ZEOTEX zeolite solution