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.

The aim of the research was to compare the effects of various petroleum products, biodiesel, diesel oil, fuel oil and unleaded petrol on soil dehydrogenases, and to evaluate biostimulation with compost and urea in the restoration of homeostasis of the soil contaminated with these products. The obtained results allowed for defining the weight of dehydrogenases in monitoring of the environment subjected to pressure from petroleum hydrocarbons. The studies were carried out under laboratory conditions for 180 days, and loamy sand was the soil formation used in the experiment. The petroleum products were used in the following amounts: 0, 2, 4, 8 and 16 g kg−1 DM of soil. Indices of the influence of the petroleum product and the stimulating substance on the activity of dehydrogenases were calculated. It was proved that the petroleum products affect soil dehydrogenases in various ways. Biodiesel, diesel oil and fuel oil stimulate these enzymes, while petrol acts as an inhibitor. Among the substances tested regarding biostimulation of soils contaminated with petroleum products, compost is definitely more useful than urea, and therefore, the former should be used for the remediation of such soils. Stimulation of dehydrogenases by compost, both in contaminated and non-contaminated soils, proves that it may accelerate microbiological degradation of petroleum-derived contaminants.

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Soil Dehydrogenases as an Indicator of Contamination of the Environment with Petroleum Products.

The purpose of this research has been to identify relationships between soil moisture and the growth and development of microorganisms, their diversity and the activity of soil enzymes. Four soils with different texture were analysed. Air-dry soils were watered up to the moisture content corresponding to 20, 40 and 60% of the maximum water capacity (MWC) and subsequently were submitted to determinations of the counts of soil microorganisms, colony development index and ecophysiological diversity index for bacteria, actinomycetes and fungi. In addition, the response of seven soil enzymes to soil humidity was examined. It was found that the most optimum soil moisture for the development of organotrophic bacteria was the one at the level of 20% of MWC. For Azotobacter spp. bacteria and actinomycetes, the 40% MWC soil moisture level was optimum, while fungi developed the best at the soil moisture level of 60% of MWC. In turn, the activity of soil dehydrogenases, catalase, urease, acid phosphatase, alkaline phosphatase, β-glucosidase and arylsulfatase was the highest in soil with 20% of MWC. The principal component analysis showed that the soil moisture determined the microbial and biochemical soil activity to a much lesser degree than did the soil type.

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Soil moisture as a factor affecting the microbiological and biochemical activity of soil

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.

This study was undertaken to (1) determine the effects of petroleum pollution on changes in the biochemical properties of soil and (2) demonstrate whether the application of compost, bentonite, and calcium oxide is likely to restore biological balance. Petroleum soil pollution at a dose ranging from 2.5 to 10 cm(3)/kg disturbed the biochemical balance as evidenced by inhibition of the activities of soil dehydrogenases (SDH), urease (URE), and acid phosphatase (ACP). The greatest change was noted in the activity of SDH, whereas the least change occurred in URE. Petroleum significantly increased the activity of soil alkaline phosphatase (ALP) in soil used for spring rape, whereas in soil used for oat harvest there was decreased ALP activity. The application of compost, bentonite, and calcium oxide to soil proved effective in mitigating the adverse effects of petroleum on the activities of soil enzymes. Soil enrichment with compost, bentonite, and calcium oxide was found to stimulate the activities of URE and ALP and inhibit the activity of ACP. The influence of bentonite and calcium oxide was greater than that of compost. Calcium oxide and, to a lesser extent, compost were found to increase the activity of SDH, whereas bentonite exerted the opposite effect, especially in the case of the main crop, spring rape. The activities of SDH, URE, and ACP were higher in soil used for rape than that for oats. In contrast the activity of ALP was higher in soil used for oats. Data thus indicate that compost and especially bentonite and calcium oxide exerted a positive effect on activities of some enzymes in soil polluted with petroleum. Application of neutralizing additives to soil restored soil biological balance by counteracting the negative influence of petroleum on activities of URE and ALP.

Jadwiga Wyszkowska

Papers

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

Soil Dehydrogenases as an Indicator of Contamination of the Environment with Petroleum Products.

Soil moisture as a factor affecting the microbiological and biochemical activity of soil

Biochemical properties of soil contaminated by petrol.

Activity of soil dehydrogenases, urease, and acid and alkaline phosphatases in soil polluted with petroleum.