Study of bioremediation method for heavy metals in the marine environment

In different regions of the Persian Gulf, oil pollution along with other urban, agricultural and industrial pollution has destroyed this valuable ecosystem and the valuable aquatic resources in it have been exposed to the risk of various corruptions and have threatened the aquatic populations in it. (Pourrang, 2005). The Caspian Sea is one of the unique lakes in the world due to its biological resources (plants and animals) and supply of protein materials, sturgeon fishing, and caviar production (Bazrafshan, 1374). In recent years, the increasing development of human activities in the countries bordering the Caspian Sea has changed the ecology of this sea. The Caspian Sea has oil and gas refineries and oil reserves in oil fields and exploration and drilling activities by five common countries, especially Azerbaijan and Kazakhstan. And the discharge of sewage and industrial effluents has caused the pollution of the sea (Varedi, 2015). Some microorganisms are present in the contaminated site, but for more effective remediation, the growth of the microorganism must be stimulated. Biostimulation is the process of adding nutrients, electron acceptors, and oxygen to stimulate bacteria in bioremediation. This is the process of optimizing the environmental conditions of the place of correction. Additives are usually added to subsurface layers through injection wells. Subsurface characteristics such as groundwater velocity, subsurface hydraulic conductivity, and subsurface lithology are essential for the development of a biological stimulation system. The natural microorganisms in the soil are responsible for the decomposition of pollutants. But biostimulation can be improved with biological additives. The quality of life on earth depends on the quality of the environment. Large amounts of organic and inorganic substances are released into the environment every year as a result of human activities. Contaminated lands are generally the result of industrial activities, the use, and disposal of hazardous substances, and such. It is now widely recognized that contaminated land is a potential threat to human health, and its continued discovery over the past 13 years has led to international efforts to remediate many sites, or as a response to health hazards.or environmental effects caused by pollution or to activate this place for use, to be developed again. Bioremediation is a general concept that includes all those processes and actions that take place to transform an environment, which is currently changedby pollutants to its original state (Adhikari, 2004; Gunasekaran, 2003). Also, bioremediation means the process of cleaning hazardous waste with microorganisms or plants, and it is the safest method of cleaning soil pollution.So far, there have been several studies on biological indicators (various plant and animal species as biological monitors) of heavy metals in both aquatic and terrestrial environments, which we can mention here. The use of biological information and biological control programs for water pollution for the management of ecosystems started at the beginning of the 1920s in the United States and then in a more serious way since 1948 all over the world. Today, many researchers from international organizations, including the EPA and the World Health Organization (WHO), introduced these indicators as the most appropriate indicators for environmental assessment and ecosystem management (Freund, 2007). Hilsenhoff's research, which started in 1979 with periodic sampling of the end of aquatic habitats and measurement of physical and chemical parameters, and finally using the biological coefficient formula; is considered a turning point in the biological evaluations of the environment (Hilsenhoff, 1988).Also, by examining the management of drilling waste, which is one of the new biological methods being developed in Iran, we will deal with it. The wastes of drilling operations are mainly the result of the washing and cooling activities of drilling machines. These wastes are generally divided into two groups in terms of physical phase: solids and liquids. In the new method invented in this collection, these wastes are managed separately. Solids are recycled by biological methods (composting) and liquids are recycled by three chemical methods, biological absorbents, and evaporation-condensation, depending on their initial quality. This new method first recycles water with the help of flow management and mixing, and then with different chemical, physical, and sometimes biological methods.The results of various surveys show that by measuring different pollutants in the plants of the same region, it is possible to understand the state of pollution of various compounds, including heavy metals (Lehndorff, 2009). In 2010, Bonanno and Gaddis in South Phragmites examined reed aquatic plants in terms of the accumulation of heavy metals cadmium, chromium, copper, mercury, manganese, nickel, lead, and zinc in the root, rhizome, stem and leaf tissues and concluded They found that the mentioned plant can be a monitor to control water pollution (Bonanno, 2010). Wild oysters can also be used to monitor pollution. In 2011, Victoria et al. investigated the concentration of heavy metals in the soft tissue of a species of wild oysters from the Spanish North Atlantic coast and stated that wild oysters are a benchmark for international evaluation. Besada, 2011). Also, in 2015, Phillips et al. tested the concentration of four heavy metals cadmium, copper, lead, and zinc in the tissue of three aquatic plants, and based on the results of the research they have conducted, these species are suitable for use as indicators of the presence and level of pollutants. Heavy metals are introduced into estuary water places (Phillips, 2015). In Iran, many types of research have been conducted so far, by examining their results, the potential of different species in the direction of bioremediation can be achieved, and we are now mentioning some of them. In 2013, during research, Azami et al. investigated the amount of total mercury in different tissues of three of the most important waterfowl species in the north of the country, including the great cormorant, the mallard, and the green duck, and compared the results with the international standard of the American Environmental Protection Organization. Global health and domestic standards are compared and finally, while warning consumers of waterfowl, especially vulnerable people, the results of their research are an achievement for managers to control and monitor metal pollution in Gamishan and Anzali wetlands, which are one of the most important habitats. The wintering birds are listed (Aazami, 2012).

Although bioremediation is not the answer to all pollution, it provides a method of removing pollution by enhancing biological processes and natural biological decomposition. Also, its application in each place must be determined and depends on the local mineralogy, hydrology, geology, and chemistry of that place. Therefore, with the development and understanding of microbial communities and their response to the natural environment and pollutants, expanding the knowledge of microbial genetics to increase the ability to reduce pollutants, and conducting proper tests of new bioremediation techniques that are cost-effective, this technology is an efficient and cost-effective way to purify water, contaminated land, and soil. Therefore, this method is being developed and improved to be able to cover more areas of pollution.