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Rare earth elements (REEs) are widely distributed in low concentrations in all parts of the biosphere. REEs are not at all rare, their concentration in the earth’s crust is close to 0.015%. REEs include the elements scandium, yttrium and the lanthanides from lanthanum to lutetium. REEs show similar physical and chemical properties. Today REEs are applied in industries and technologies, in agriculture as microfertilizers and feed additives and they are also used in medicine. REEs are dispersed especially as accessory minerals in pegmatites, granites and associated metamorphic volcanic rocks. Out of more than 250 kinds of minerals containing REEs, only bastnaesite and monazite are of economic importance. Their concentration in the soil varies widely and depends on their presence in parental materials, soil texture, organic matter content, pedogenetic processes and anthropogenic activities. REEs are found in small concentrations in surface stagnant and flowing waters as well as in underground waters. They are found in water in both suspended and dissolved form. REEs enter the atmosphere from various sources, largely owing to human activities. The majority of REEs in the atmosphere are carried by microscopic particles. The uptake and consequently accumulation of REEs in plants are affected by numerous biotic factors, such as plant species and genotype, and abiotic factors such as their concentration in the soil and some chemical and physical soil characteristics. They can enter plants via both root and foliage tissues. There are plant species called hyperaccumulators that are able to accumulate significant amounts of REEs without adverse consequences. RREs are not biogenic for higher plants or for other living organisms, but can influence their life processes. Experi­ments show that REEs can be beneficial for growth, yield and biochemical composition of cultivated plants. They can also alleviate some ecological stress in plants. It is not clear enough how they affect human and animal health. The wide-spread application of REEs in different industries as well as in agriculture lead to a constant increase of the concentrations of these elements in the environment. Therefore, studies on the uptake, accumulation, dis­tribution of REEs in cultivated plant species and their entrance into the food chain as well as their stimulating or toxic effect on living organisms, can be very significant in the future.

Rare earth elements (REEs) are a group of chemical elements that include lanthanides as well as scandium and yttrium. Today REEs are used in various industries, such as agriculture where they are used as micro fertilizers and feed additives, the latter being used in medicine as well. There is no indication that REEs might be essential for any form of life. At lower concentrations, they can favorably influence certain physiological processes of plants (enzyme activity, hormone content, photosynthesis, seed germination, plant growth, etc.). They may induce an increase in some antioxidant systems and thereby increase the tolerance of plants to environmental stressors caused by high concentrations of heavy metals, herbicides, lack of water and essential nutrients, UV radiation and oxidative stress. Thus, their favorable effect was documented regarding the yield of cultivated species as well as the effect of their chemical composition on the content of vitamin C, soluble sugars and essential elements, reduction of the concentration of toxic heavy metals, improvement of the quality of wheat kernel for different uses. REEs have been commonly used as feed additives in organic and inorganic forms in livestock production. The available literature on the use of REEs as feed additives in livestock suggests positive outcomes (affected various physiological processes, increase in milk, egg and meat production, promoted growth and reproductive performance), but further investigation and results are needed before extending their use to zootechnical purposes.

Nickel (Ni) is an essential microelement for higher plants and an important one for many other living organisms. It is present in every part of the biosphere. Higher plants have small requirements towards Ni for their optimal growth and development. That is why its latent and acute deficiencies in nature rarely occur. Soil and water pollution with Ni is a global issue. This is the reason special attention is paid to the effects of higher Ni concentrations on plants metabolism, their organic production, as well as on the possibility of using plants for phytoremediation of Ni contaminated habitats. Depending on the present concentrations, nickel may favourably, unfavourably or not affect the metabolic processes of plants at all (enzyme activity, photosynthesis, respiration, water regime, mineral nutrition, etc.), and thus the growth and development of plants. There are still many questions about the mechanism of Ni influence on the physiological and biochemical processes of plants. Therefore, we believe the presentation of the previous knowledge about the effect of Ni on plants' life processes can contribute to a better understanding of the biotechnical and ecological significance of Ni, and it can indicate further research directions in this field.

In the base, working of ventilation system can be analyzed in regular and incidental modes of operation. This paper concerns the specification of the longitudinal ventilation necessary to prevent upstream movement of combustion products in a tunnel fire. In this work the objective of the study is to analyze the road way tunnel ventilation system using CFD software to create comfort ventilation system in the tunnel. The comfort ventilation concept refers to the situation when air quality within the tunnel is reduced due to presence of polluted air in the tunnel. This paper is focused on ventilation system in a road traffic tunnel in moment of accident situation as fire. In this investigation numerical simulation of fire was carried out and determination of a critical air velocity depending on the power of the fire was conducted. The output results of the software developed for this purpose, which is also used in the realization of practical projects, are shown. [ABSTRACT FROM AUTHOR]