Mining activities can lead to the generation of large quantities of heavy metal laden wastes which are released in an uncontrolled manner, causing widespread contamination of the ecosystem Though some heavy metals classified as essential are important for normal life physiological processes, higher concentrations above stipulated levels have deleterious effects on human health and biota Bacteria able to withstand high concentrations of these heavy metals are found in the environment as a result of various inherent biochemical, physiological, and/or genetic mechanisms These mechanisms can serve as potential tools for bioremediation of heavy metal polluted sites This review focuses on the effects of heavy metal wastes generated from gold mining activities on the environment and the various mechanisms used by bacteria to counteract the effect of these heavy metals in their immediate environment

Heavy Metal Pollution from Gold Mines: Environmental Effects and Bacterial Strategies for Resistance.

Biological approaches to tackle heavy metal pollution: A survey of literature

Environmental problems have always received immense attention from scientists. Toxicants pollution is a critical environmental concern that has posed serious threats to human health and agricultural production. Heavy metals and pesticides are top of the list of environmental toxicants endangering nature. This review focuses on the toxic effect of heavy metals (cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn)) and pesticides (insecticides, herbicides, and fungicides) adversely influencing the agricultural ecosystem (plant and soil) and human health. Furthermore, heavy metals accumulation and pesticide residues in soils and plants have been discussed in detail. In addition, the characteristics of contaminated soil and plant physiological parameters have been reviewed. Moreover, human diseases caused by exposure to heavy metals and pesticides were also reported. The bioaccumulation, mechanism of action, and transmission pathways of both heavy metals and pesticides are emphasized. In addition, the bioavailability in soil and plant uptake of these contaminants has also been considered. Meanwhile, the synergistic and antagonistic interactions between heavy metals and pesticides and their combined toxic effects have been discussed. Previous relevant studies are included to cover all aspects of this review. The information in this review provides deep insights into the understanding of environmental toxicants and their hazardous effects.

Heavy Metals and Pesticides Toxicity in Agricultural Soil and Plants: Ecological Risks and Human Health Implications.

The most common laboratory procedure used for DHA determination is the method developed by Casida et al. (1964). According this method, specific dyes such as the triphenyltetrazolium chloride (TTC), that can specify the flow of electrons are useful indicators of electron transport system (ETS) activity. By the reduction of colorless, water soluble substrate (TTC) by dehydrogenases present in the soil environment, an insoluble product with red color (triphenylformazan-TPF) is formed. TPF can be easily quantified calorimetrically at the range of visible light (485 nm). This test however, reflected positive answer only at neutral range of pH and in presence of calcium carbonate for buffering soil system. Briefly, if the red colors of soil samples prepared for spectrophotometer analyses are more intensive, the measured level of DHA is higher. Consequently, soil samples without red colors or those with light red colors are characterized by lower DHA values.

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Dehydrogenase Activity in the Soil Environment

Trace Elements in Soils

Heavy metals when present in amounts equal to the geochemical background do not interfere with the soil metabolism, which is associated with the growth and development of soil microorganisms as well as the processes of synthesis and re-synthesis, governed by intraand extracellular enzymes. In the said concentrations, heavy metals do not cause undesirable changes in the development of plants. On the contrary, such elements as copper and zinc are essential constituents of physiological processes in all living organisms, including microorganisms and plants. Some soils suffer from zinc and copper deficits, which is why they are enriched with fertilizers containing copper or zinc to satisfy the nutritional requirements of crops. Cadmium is different in that its essential role in the proper functioning of living organisms has not been proven yet. In Poland, soils contaminated with heavy metals, including cadmium, copper and zinc, occur only locally. The purpose of this study has been to discuss the characteristics of these elements in terms of the chemical properties and the role in the natural environment, the effect they produce on plants when present in excessive concentrations in soil and the response of soil microbes and enzymes to such contaminants. Crops cultivated on soil with an elevated content of heavy metals typically present inhibited growth, reduced transpiration, chlorosis of leaves, limited germination of seeds and deformations of the root system. The effect induced by heavy metals is more pronounced in the early development of plants. Mobility and plant availability of heavy metals depend on a series of factors, for example the soil pH, content of organic matter, grainsize composition of soil, content of iron and manganese oxides, soil sorption capacity and the type of metal. Higher bioavailability of heavy metals is observed in soils with a low content of humic acids. As the soil pH increases (within 6.5-7.5), metals, especially zinc and – to a lesser degree – copper become less toxic to plants.

http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.agro-e1fd2c35-5b09-4442-9051-c70272c71ace/c/769-796.pdf

Effect of cadmium, copper and zinc on plants, soil microorganisms and soil enzymes.

In this experiment the effects of lead and lead-free petrol applied at the following doses of: 0, 2, 4 and 6 cm 3 • kg' 1 of soil on growth and development of triticale and biochemical properties of the soil were studied. For detoxication of petrol organic amendment with barley straw was applied. The experiment was performed in two experimental series with and without triticale cover. It was found that soil contamination by petrol adversely affected growth and development of tested crops. Barley straw appeared to be ineffective in detoxication of the contaminated soil. Lead and lead-free petrol (irrespective of plant cover and application of straw) adversely affected activity of soil dehydrogenases and urease. Straw application and growing of triticale positively affected biochemical properties of the soil. These positive effects were diminished by petrol, irrespective of the lead addition. Biochemical index of soil fertility calculated on the basis of enzymatic activity and carbon content was negatively correlated with the level of soil contamination by petrol and positively with triticale yield.

Biochemical properties of soil contaminated by petrol.

The use of fungicides in crop protection still effectively eliminates fungal pathogens of plants. However, fungicides may dissipate to various elements of the environment and cause irreversible changes. Considering this problem, the aim of the presented study was to evaluate changes in soil biological activity in response to contamination with azoxystrobin. The study was carried out in the laboratory on samples of sandy loam with a pH of 7.0 in 1 Mol KCl dm−3. Soil samples were treated with azoxystrobin in one of four doses: 0.075 (dose recommended by the manufacturer), 2.250, 11.25 and 22.50 mg kg−1 soil DM (dry matter of soil). The control soil sample did not contain fungicide. Bacteria were identified based on 16S rRNA gene sequencing, and fungi were identified by internal transcribed spacer (ITS) region sequencing. The study revealed that increased doses of azoxystrobin inhibited the growth of organotrophic bacteria, actinomycetes and fungi. The fungicide also caused changes in microbial biodiversity. The lowest values of the colony development (CD) index were recorded for fungi and the ecophysiological (EP) index for organotrophic bacteria. Azoxystrobin had an inhibitory effect on the activity of dehydrogenases, catalase, urease, acid phosphatase and alkaline phosphatase. Dehydrogenases were found to be most resistant to the effects of the fungicide, while alkaline phosphatase in the soil recovered the balance in the shortest time. Four species of bacteria from the genus Bacillus and two species of fungi from the genus Aphanoascus were isolated from the soil contaminated with the highest dose of azoxystrobin (22.50 mg kg−1).

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Microbial and enzymatic activity of soil contaminated with azoxystrobin

The aim of this study was to determine the effect of three active substances, diflufenican, mesosulfuron-methyl and iodosulfuron-methyl-sodium, applied in combination, on soil microbial counts, the structure of soil microbial communities, activity of soil enzymes and their resistance to the tested product, the biochemical indicator of soil fertility, and spring wheat yield. Soil samples with the granulometric composition of sandy loam with pHKCl 7.0 were used in a pot experiment. The herbicide was applied to soil at seven doses: 0.057 (dose recommended by the manufacturer), 1.140, 2.280, 4.560, 9.120, 18.240 and 36.480 mg kg−1 soil DM. Uncontaminated soil served as the control treatment. It was found that a mixture of the tested active substances increased the counts of total oligotrophic bacteria and spore-forming oligotrophic bacteria, organotrophic bacteria and actinomycetes, decreased the counts of Azotobacter and fungi, and modified the structure of soil microbial communities. The highest values of the colony development (CD) index and the ecophysiological (EP) index were observed in fungi and organotrophic bacteria, respectively. The herbicide applied in the recommended dose stimulated the activity of catalase, urease and acid phosphatase, but it had no effect on the activity of dehydrogenases, alkaline phosphatase, arylsulfatase and β-glucosidase. The highest dose of the analyzed substances (36.480 mg kg−1) significantly inhibited the activity of dehydrogenases, acid phosphatase, alkaline phosphatase and arylsulfatase. The values of the biochemical soil fertility indicator (BA21) decreased in response to high doses of the herbicide. Urease was most resistant and dehydrogenases were least resistant to soil contamination with a mixture of diflufenican + mesosulfuron-methyl + iodosulfuron-methyl-sodium. The analyzed herbicide had an adverse influence on spring wheat yield, and doses of 18.240 and 36.480 mg kg−1 led to eventual death of plants.

/pdf/microbial-and-enzymatic-activity-of-soil-contaminated-with-a-2a95awyl1f.pdf

Microbial and enzymatic activity of soil contaminated with a mixture of diflufenican + mesosulfuron-methyl + iodosulfuron-methyl-sodium.

The effect of soil contamination with copper on soil biochemical properties and oat yields was assessed in a pot experiment. Copper was applied alone or in combination with other heavy metals. The study was conducted on samples of brown soil consisting of heavy loamy sand and brown soil developed from light silty clay. On days 28 and 56 of the experiment the following were determined: activity of dehydrogenases, urease, acid phosphatase and alkaline phosphatase in soil as well as oat yields. Contamination of soil with copper, zinc, nickel, lead, cadmium and chromium in concentrations of 50 mg kg-1 was found to have a negative influence on the activity of dehydrogenases, urease, acid phosphatase, alkaline phosphatase and yield of oats. The soil enzymes can be arranged in terms of their sensitivity to heavy metals as follows: dehydrogenases > urease > alkaline phosphatase > acid phosphatase. Higher activity of dehydrogenases was determined in brown soil developed from heavy loamy sand, while urease, acid phosphatase and alkaline phosphatase were more active in brown soil formed from light silty clay. The contamination of copper with other heavy metals was inhibited in heavy loamy sand more than in light silty clay.

Jan Kucharski

Papers

Effect of cadmium, copper and zinc on plants, soil microorganisms and soil enzymes.

Biochemical properties of soil contaminated by petrol.

Microbial and enzymatic activity of soil contaminated with azoxystrobin

Microbial and enzymatic activity of soil contaminated with a mixture of diflufenican + mesosulfuron-methyl + iodosulfuron-methyl-sodium.

The effects of copper on soil biochemical properties and its interaction with other heavy metals