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The effect of soil contamination with zinc on the count of selected taxonomic and physiologic groups of microorganisms has been studied in a laboratory experiment. Samples taken from brown soil originating from light clay with pHKCl 6.9 were contaminated with ZnSO₄ · 7H₂O in the following amounts (mg of Zn2+ · kg⁻¹ of soil; 0, 5, 500, 1000, 1500, 2000. The experiment was conducted for 120 days at 25oC, in two series: soil with cellulose (15,0 g · kg⁻¹ of dry soil) and without cellulose. The experiment showed that the count of oligotrophic, copiotrophic, ammonifying, cellulolytic and nitrogen immobilising bacteria as well as actinomyces and fungi were positively correlated with the zinc dose while the correlation was negative for Azotobacter spp.. The positive effect of zinc on nitrogen immobilising bacteria, actinomyces and fungi persisted throughout the experiment. ED₅₀ Zn⁺² (mg · kg⁻¹) equalled for: fungi – 240, oligotrophic bacteria – 584, ammonifying – 803, copiotrophic bacteria – 1016, nitrogen immobilising bacteria – 1620, cellulolytic bacteria – 2000 and actinomyces – 2000. When applied in the amount of 15 g · kg⁻¹ of soil, cellulose stimulated the bacteria multiplication in soil contaminated with zinc. It had the most positive effect on actinomyces and fungi.
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The paper gives a comprehensive insight into the role of zinc in the biosphere. It reviews numerous functions of this metal at various levels of the organisation of ecosystems. An attempt has ben made to assess its importance as a microelement, while not neglecting its toxicity due to excessive accumulation of zinc in the environment. Zinc is a natural component of the Earth's crust, but in many places it has accumulated in amounts near or above the safe levels. Currently, the use of this metal is very broad, and therefore attention should be drawn to possible consequences arising from elevated levels of zinc in the environment. Dispelling controversies surrounding heavy metals is a necessary step for gaining systematic and wider knowledge on these elements. This in turn will create an opportunity for the development of strategies and subsequent actions undertaken by everyone, from individuals to major international industrial corporations, aimed at achieving homeostasis in an environment polluted with heavy metals. Increased levels of zinc can adversely affect microbiological and biochemical processes occurring in the soil and the development of plants, which has a negative impact on the quantity and quality of crops. Therefore, low bioavailability of heavy metals, including zinc, in agricultural land is a key to the stability of ecosystems and food security.
Experiments were performed in the greenhouse of the University of Warmia and Mazury in Olsztyn, on soil taken from A-horizon. Under natural conditions it was leached brown soil developed from light loamy sand with pHKCl 5.8 and pHKCl 6.3. The tested metal was applied in the form of ZnCl2 or ZnS04 7H20, at the following doses: 0, 400, 800, 1,200, 1,600 mg Zn2+ kg-1 d.m. of soil (experiment 1); 0, 200, 400, 600, 800, 1,200, 1,600 mgZn+ kg-1 d.m. of soil (experiment 2). Prior to the establishment of the experiments, soil samples were mixed with mineral fertilizers and, in some treatments, with pine sawdust or finely ground barley straw in the amount of 0 and 5 g kg-1 d.m. of soil. Excessive zinc accumulation in soils modified the counts oligotrophic bacteria and copiotrophic bacteria. The effect of this metal was related not only to its dose and type of chemical compound, but also to crop species and organic fertilization.
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Remediation of soil contaminated with cadmium

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The search for the best solutions to restore soil balance is essential for attaining a stable and sustainable agricultural development worldwide. This research, which makes a contribution to these investigations, focuses on four substances (two innovative ones: basalt flour, brown algal extract, and two classic soil improvers: finely ground barley straw and compost) which can potentially alleviate the inhibitory effect of Cd2+ on the soil environment. The following were analyzed: the activity of acid phosphatase and alkaline phosphatase, counts of Pseudomonas sp., cellulolytic bacteria, copiotrophic bacteria and copiotrophic spore-forming bacteria, and the yield of spring barley. Cadmium (Cd2+) was applied as CdCl2 · 2.5H2O in the following doses: 0, 4, 40, 80, 120, 160, and 200 mg Cd2+ kg-1 of soil. For a more complete assessment of the soil, its biochemical properties and the counts of microorganisms were scrutinized with the following indices: RS – soil resistance, R:S – rhizosphere effect and EF – fertilization effect of the contamination alleviating substances. It was found that alkaline phosphatase is more sensitive to cadmium contamination of the soil than acid phosphatase. Cadmium did not exert any inhibitory effect on the number of microorganisms present or the yield of spring barley. Cellulolytic bacteria were the least sensitive to stress associated with the accumulation of high cadmium doses in the soil, whereas copiotrophic bacteria were the most sensitive microorganisms to the above stressor. The ability of cadmium-polluted soil to restore homeostasis depended on the type of a soil improver and the level of soil contamination. Negative consequences of cadmium pollution were effectively mitigated by straw, but less so by brown algal extract and basalt flour.
The effect of the herbicide Harpun 500 SC on the counts of soil microbes was determined in a laboratory experiment conducted at 25°C and 60% capillary water capacity of soil. The herbicide was applied at the following doses (mm3 • kg-1 d.m. of soil): 0, 0.83 (optimal), 41.5, 83, 124.5 and 166. The counts of soil microbes were determined on day 28, 56, 84 and 112. It was found that the herbicide did not disturb the microbiological equilibrium of soil when applied at the recommended dose, i.e. 0.83 mm3 • kg-1 d.m. of soil. Higher doses altered only faintly the counts of the tested soil microorganisms.
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Microbiological activity of zinc-contaminated soils

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Metale ciężkie, w tym także cynk, gdy dostaną się do gleby w nadmiernych ilościach, stanowią dość trwałe zanieczyszczenie, w przeciwieństwie do różnego rodzaju zanieczyszczeń organicznych, podatnych w większym lub mniejszym stopniu na degradację mikrobiologiczną. Mimo iż akumulacja metali ciężkich przez drobnoustroje jest procesem powszechnym, to nie do końca poznanym. Granice tolerancji nie są jednakowe i zależą od ich bioróżnorodności i czasu trwania imisji, a także właściwości fizykochemicznych gleby, jej struktury, zawartości materii organicznej, pH i pojemności kompleksu sorpcyjnego. Coraz częściej do oceny stanu zanieczyszczenia gleby wykorzystuje się metody biologiczne, w tym aktywność enzymów glebowych, i w nich należy upatrywać szybkiej diagnozy jakości gleb. Wskaźniki te mogą być jednak wykorzystywane tylko do oceny gleb zanieczyszczonych metalami ciężkimi, a są mało przydatne w ocenie jakości gleb zanieczyszczonych związkami organicznymi.
Two laboratory experiments were performed to determine the susceptibility of microorganisms to excessive amounts of zinc diffusing into artificial culture media. The effect of zinc on the growth of pure bacterial cultures in liquid media was determined in experiment 1, while the diameters of microbial growth inhibition zones in solid media were measured in experiment 2. Zinc was introduced into the media in the form of ZnCl2 and ZnS04 7H20 at the following doses: in mg Zn2+ dm-3 of medium: 0, 5, 100, 500, 1,000, 1,500, 2,000 (experiment 1), in µg Zn+2 disk-1 : 25, 50, 100, 200, 400, 800, 1,600 (experiment 2). It was found that this metal had a strongly toxic effect on all bacterial species analyzed in liquid media.
The aim of the study has been to determine the effect of soil contamination with zinc on the activity of soil enzymes. The study consisted of two laboratory experiments. Same, light loamy soil of pH 7.1, was used in both experiments. The variables in the first experiment were: a degree of soil contamination with zinc in mg Zn kg-1 d.m. of soil: 0, 5, 500, 1000, 1500 and 2000; dose of cellulose in g kg-1 d.m. of soil: 0, 15, and time of soil incubation (15 – 120 days). In the second experiment the following variables were tested: the degree of soil contamination with zinc in mg Zn kg-1 d.m. of soil: 0, 1000 and 2000; soil pH: 7.1, 6.4 and 5.5, and the time of soil incubation (15 – 120 days). The results of the experiments demonstrated that contamination of soil with zinc led to depressed activity of dehydrogenases, urease, acid phosphatase and alkaline phosphatase. Dehydrogenases and urease appeared to be more vulnerable to zinc contamination than phosphatases. The soil enzymes were adversely affected not only by zinc contamination but also by increasing soil acidity. According to their vulnerability to soil acidity the soil enzymes can be ordered as follows: dehydrogenases > urease > alkaline phosphatase > acid phosphatase. Cellulose added to soil (15 g kg-1) proved to be a good factor in the improvement of soil biochemical properties, although it did not limit the effects produced by zinc.
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