Khe concentration of nitrate in vegetables varies in a very wide range from 1 to 10,000 mg/kg and depends on the type, variety, method of cultivation, and storage conditions of vegetables (JECFA, 1995). According to AESAN (2011), 80-85% of the total intake of nitrates in the human diet is consumed by vegetables. Furthermore, by consuming vegetables, in addition to nitrates, a certain amount of toxic heavy metals such as cadmium, lead, chromium, and others is introduced into the human diet, and the amount of their intake primarily depends on the type, origin, and method of growing vegetables. The concentration of toxic heavy metals in the soil/substrate in which vegetables are produced plays a key role in this.
The study aimed to determine the influence of the length of soaking vegetables in water with ZEOTEX zeolite in comparison with soaking vegetables in pure water to ascertain reduction of nitrate and toxic heavy metals in lettuce leaves. The salad was chosen as a representative of vegetables because of its pronounced accumulation capacity, both nitrate and heavy metals, and because of its fresh consumption.
oncentrations of nitrates and toxic heavy metals were determined in the lettuce leaf, in all treatments (water and water + ZEOTEX zeolite) according to the prescribed methodology following ISO Standards.
The study was conducted on three treatments with different duration of soaking the lettuce leaves:
1. Control - vegetables without soaking.
2. Water - soaking in water for 20 minutes
3. Water + ZEOTEX zeolite - soaking for 10, 20, and 30 min
The concentration of nitrate in the control - lettuce leaf was 2265.07 mg NO3 - / kg of fresh lettuce, which is below the limits prescribed by EU Regulation 1881/2006 which prescribes the maximum permissible concentrations of nitrate in fresh lettuce of 4000 mg NO3 - / kg. After conducting research, it was found that soaking lettuce in water with ZEOTEX zeolite resulted in an additional reduction in the concentration of nitrate in lettuce compared to soaking lettuce in clean water. Namely, soaking, ie washing the salad in clean water is a common way of treating the salad before consumption.
The results obtained in this way show a decrease in the concentration of nitrate in the lettuce leaf depending on the soaking time:
- 8.94% after 10 minutes of soaking in a solution with ZEOTEX zeolite
- 35.92% after 20 minutes of soaking in a solution with ZEOTEX zeolite
- 41.72% after 30 minutes of soaking in a solution with ZEOTEX zeolite
All results confirm the hypothesis that soaking vegetables in water with ZEOTEX zeolite leads to a decrease in nitrate concentration.
The research was conducted at the Faculty of Agrobiotechnical Sciences in Osijek, at the Department of Agroecology and Environmental Protection.
The term “heavy metals” has very often been used over the past few decades for a group of metals and semi-metals (metalloids) that have been linked to contamination and potential toxic effects (Duffus, 2003). The presence of heavy metals in the soil is a consequence of natural and anthropogenic processes.
There are natural pedogenetic processes by which the soil inherits heavy metals from the parent substrate, and anthropogenic processes include urbanization, industrialization, transport, but also agricultural production.
The transfer of heavy metals from the soil to the plant and food is the basis for the entry of heavy metals into the food chain. The human impact on the atmospheric deposition of heavy metals and the input of heavy metals into the soil by agrotechnical measures is considerable, so although primarily soil properties affect the bioavailability of heavy metals present in the soil, anthropogenic influences on the transfer of heavy metals into the food chain and agrotechnical measures and production processes should certainly be directed towards reducing the bioavailability of toxic heavy metals, primarily Cd and Pb.
The choice of growing place and type of vegetables also has a very significant effect on the intake of heavy metals in the human diet due to the possible excessive concentration of heavy metals (above the MPC) in vegetables produced in gardens in urban areas. The lowest concentrations can be expected in fruit vegetables, and the highest in root vegetables (Lončarić, 2015).
Reducing the concentration of heavy metals depending on the treatment is most effective in the following soaking period:
Co - 32.76% after 30 minutes of soaking in a solution with ZEOTEX zeolite
Cr - 22.75% after 20 minutes of soaking in a solution with ZEOTEX zeolite
Pb - 19.04% after 20 minutes of soaking in a solution with ZEOTEX zeolite
CD - 45.14% after 30 minutes of soaking in a solution with ZEOTEX zeolite
The obtained results indicate the justification of the hypothesis on the use of ZEOTEX Zeolite as a reducing agent of concentrations of nitrates and heavy metals in vegetables, but for more precise interpretations it is necessary to carry out additional research on different types of vegetables.