Background: Environmental contamination by mercury is and will continue to be a serious risk for human health. Pollution of the terrestrial environment is particularly important as it is a place of human life and food production. This publication presents a review of the literature on issues related to mercury pollution of the terrestrial environment: soil and plants and their transformations. Results: Different forms of atmospheric Hg may be deposited on surfaces by way of wet and dry processes. These forms may be sequestered within terrestrial compartments or emitted back into the atmosphere, and the relative importance of these processes is dependent on the form of Hg, the surface chemistry, and the environmental conditions. On the land surface, Hg deposition mainly occurs in the oxidized form (Hg²⁺), and its transformations are associated primarily with the oxidation–reduction potential of the environment and the biological and chemical processes of methylation. The deposition of Hg pollutants on the ground with low vegetation is as 3–5 times lower than that in forests. The estimation of Hg emissions from soil and plants, which occur mainly in the Hg⁰ form, is very difficult. Generally, the largest amounts of Hg are emitted from tropical regions, followed by the temperate zone, and the lowest levels are from the polar regions. Areas with vegetation can be ranked according to the size of the emissions as follows: forests > other areas (tundra, savannas, and chaparral) > agricultural areas > grassland ecosystems; areas of land devoid of vegetation emit more Hg than those with plants. In areas with high pollution, such as areas near Hg mines, the Hg content in soil and plants is much higher than in other areas. Conclusions: Mercury is recognized as a toxic, persistent, and mobile contaminant; it does not degrade in the environment and becomes mobile because of the volatility of the element and several of its compounds. Atmospheric contamination by mercury continues to be one of the most important environmental problems in the modern world. The general conclusions were drawn from a review of the literature and presented in this paper.

Perennial ryegrass (Lolium perenne L.) belongs to the common cultivated grass species in Central and Western Europe. Despite being considered to be susceptible to drought, it is frequently used for forming the turf in urban green areas. In such areas, the water deficit in soil is recognized as one of the most important environmental factors, which can limit plant growth. The basic aim of this work was to explore the mechanisms standing behind the changes in the photosynthetic apparatus performance of two perennial ryegrass turf varieties grown under drought stress using comprehensive in vivo chlorophyll fluorescence signal analyses and plant gas exchange measurements. Drought was applied after eight weeks of sowing by controlling the humidity of the roots ground medium at the levels of 30, 50, and 70% of the field water capacity. Measurements were carried out at four times: 0, 120, and 240 h after drought application and after recovery (refilling water to 70%). We found that the difference between the two tested varieties’ response resulted from a particular re-reduction of P700⁺ (reaction certer of PSI) that was caused by slower electron donation from P680. The difference in the rate of electron flow from Photosystem II (PSII) to PSI was also detected. The application of the combined tools (plants’ photosynthetic efficiency analysis and plant gas exchange measurements) allowed exploring and explaining the specific variety response to drought stress.

Contamination with harmful chemical substances, including organic compounds of the BTEX and PAH groups, constitutes one of the major threats to the functioning of soil habitat. Excessive contents of the above substances can exert adverse effects on soil organisms, reduce biodiversity, and thus deteriorate soil quality. The threat to soil ecosystems within areas particularly exposed to contamination with accumulating chemical compounds was assessed using the Ecological Risk Assessment (ERA) with a multi-stage Triad (triage rapid initial assessment) procedure (taking into account the different lines of evidence). The article presents the results of chemical and ecotoxicological study of soils sampled at sites affected by contamination from petrochemical industry. The study results provided foundations for developing the site specific ERA framework for the area examined.

Key message: Some species synthesize larger amounts of polyprenols, which probably increase the plant’s ability to mitigate salt stress. Salt stress does not cause macronutrient deficiency in the leaves of urban trees. Ionic imbalance in the leaves caused by soil salinity worsens the health status of sensitive species. Street trees are exposed to relatively high stress levels, and the average lifespan of street trees is shortened compared to those of trees living under controlled natural conditions. Soil salinity adversely affects trees at all stages of growth and development. This study attempts to determine how the urban environment, with particular emphasis on salt stress, affects tree species with different levels of salinity sensitivity. The aim of this study was to identify the strategies of eight tree species for mitigating salt stress based on the determination of the chemical composition of the macroelements in the leaves, the ionic imbalance, and the ability of the trees to synthesize and accumulate polyprenols in the leaves. The obtained results suggest that individual species implemented different strategies in response to salt stress. The low sensitivity species:Q. rubra, R. pseudoacacia, G. triacanthosandA. campestre. blocked the uptake of Cl and Na to the leaves. The medium-sensitivity species:P. x hispanicablocked the uptake of Cl and Na andG. bilobamaintained very high contents of Cl and Na in its leaves without leaf damage and synthesized large amounts of polyprenols.G. triacanthos and A. campestresynthesized large amounts of polyprenols. The high-sensitivity species (T. x euchloraandA. platanoides) exhibited very high contents of Cl and Na in their leaves, which were significantly damaged and had a pronounced ionic imbalance. These effects were not compensated for by the increased synthesis of polyprenols. In conclusion, the accumulation of polyprenols in leaf tissue may be one of the strategies that increase the resistance of plants to salt stress. Plants have many other methods of mitigating salt stress.

Key message: Plants use multiple mechanisms to deal with salt stress. Salt stress increases the content of polyprenols inTilia’s leaves, which may mitigate stress. De-icing salt has been used on streets and pavements in most northern countries since the 1960s. Salt stress limits all vital functions of trees. Tilia × euchlora is planted in many cities given its unique decorative qualities. The aim of this study was to determine the tree strategy to mitigate salt stress due to the synthesis of polyprenols in leaves. Many years of observations have demonstrated that trees of the same species growing in the same street conditions may have extremely different health statuses. The study consisted of two experiments: a field experiment with urban street trees growing in saline soils and a controlled pot experiment with young trees exposed to increasing doses of salt. The differences between the young trees from the pot experiment and older trees from the field experiment were expressed in their ability to synthesize polyprenols. In urban conditions, the tree leaves with less damage contained significantly more polyprenols than did those with more damage. The salt stress mitigation strategy may be related to the ability to synthesize polyprenols. This ability can be acquired through adaptation by older trees. The mechanism involves limiting the transport of Cl⁻ and Na⁺ to leaves. In the pot experiment, the young trees did not exhibit this ability.