Phytoremediation to recovery contaminated soil by metal(loid)s: possible interaction with soil bacteria and biochar

The industry development has improved living standards for much of the worldࢠs population. At the same time, this growth has created environmental problems in the world by producing large amount toxic compounds. The lack of controlling systems and appropriate laws to govern the waste management has produced worrisome problems for environment. Environmental pollution consists in three basic types of pollution: air, water and soil. Air pollution is cause by the injurious smokes, which contains namely sulphur dioxide, carbon monoxide and nitrogen oxides, emitted by cars, public transportation (buses, and taxi), trucks and factories. These gases have slowly changed the atmosphere and depleted the ozone layer leading to global warming. Water pollution caused industrial waste products released into lakes, rivers, and other water bodies, has made the life no hospitable with high risks associated to its application in agriculture and for the human activities. Soil pollution is a result of acid rain, polluted water, fertilizers etc., which lead to land fertility loss. Industrial activity has been the biggest contributor to the soil solution problem in the last century, especially since the amount of mining and manufacturing has increased. Also the house wastes are equally dangerous because of use of products such as cleaning detergents and products for the body. Moreover,-as result of globalization- an increase of demand and the quality of agricultural products were observed, with consequence of the increase of pesticides and fertilizers use. They are hazards because of chemical compounds presence that are not present in soil and can not be broken down by it. When the polluted are spilled in the environment, several dramatic effects could happen. All the ecosystems such as forests, wetlands, coral reefs, and rivers may be seriously impaired or destroyed by pollution. Moreover, because of the connection among the many types of vegetal and animal organisms that live in the ecosystems, environmental contamination may have far-reaching consequences that are not immediately obvious or easy to predict. In the environment, soil has important role, since it supports plant growth, it is a nutrient reservoir, moreover, it is a site for many biological processes involved in decomposition and recycling of plant and animal products. It has important effects on the interactions with environmental elements, influencing air quality (interacting with the atmosphere) and acting as purification medium for water. The pollutants deposition induce soil degradation, which in turn produces soil acidification (change in the chemical composition of soil), eutrophication (change in the chemical composition of water) and fertility loss. The human activities induce a soil degradation on nearly 40% of the worldࢠs agricultural land as a result of soil erosion, atmospheric pollution, extensive soil cultivation, over-grazing, land clearing, salinization, and desertification. Among the compounds that are released into the soil, damaging its quality because it changes its physical and chemical characteristics, the metal(loid)s represent a great danger. Metal(loid)s are highly hazardous since persisting for long time and can damage human health and environment. They are often present as natural components of soils. Several environmental causes, such as rocks erosion, volcanic eruption and continental dust determine their presence in the environment, although their prevalence has increased recently as the result of different human activities. They become dangerous for two reasons: they are produced, by anthropogenic activities, more rapid relative to natural ones, and the chemical form (species), in which a metal(loid)s are found in the environment, may render it more bioavailable. Metal(loid)s have adverse effects on human health and therefore their contamination of food chain , through soil contamination, deserves special attention. Recently there is an ever-increasing awareness of declining soil quality and its protection by metal(loid)s, is the duty and it is necessary for the survival of future generation. Therefore, new and effective remediation methods are necessary. The traditional physical and chemical methods for clean-up and restoration of metal(loid)s-contaminated soils have serious limitations like high cost, irreversible changes in soil properties, destruction of native soil microflora and creation of secondary pollution problems. Although during the years, they have been improved, most of them are environmentally not sustainable since involve unavoidably other negative consequences that destroys, soil structure. Therefore, within the framework of the European Strategy for Soil Protection, the need to develop new and viable technologies cost effective, efficient and environment friendly remediation methods for soil protection and remediation is becoming a priority. One such novel approach is phytoremediation which is considered as a green alternative solution to the problem of heavy metal pollution. The phytoremediation techniques are eco-friendly, gentle remediation techniques using different plant species. It can be included inside the Green Infrastructure (GI). GI is defined as a strategically planned network of natural and semi-natural areas with other environmental features designed and managed to deliver a wide range of ecosystem services. This definition includes three important aspects: the idea of a network of areas, the component of planning and management, and the concept of ecosystem services. They represent an innovative approach since plants are used to recreate a habitat in a land marred by human activities. These phytotechnologies, named as phytoremediation, makes use of natural processes where the plants alone or in combination with their microbial rhizosphere degrade and take up pollutants or to render them harmless. It is based on the idea of using landscape architecture to recover contaminated environment. Simultaneously these plants are able to reduce the dispersion of pollutants, as they are able to absorb them through their root system and accumulate them within their tissues. These methods have been widely studied and applied for several advantages, are generally considered to be less expensive and invasive (the fact that it is carried out in-situ), restorative of soil structure and aesthetically pleasant, compared to conventional, civil-engineering technologies. It has shown to be effective in cleaning-up of both organic and inorganic pollutants. The revolution concept associated to phytoremediation consists in the landscapes recovery using the same landscapes, conserving the biodiversity, soil quality, defending the ecosystem The plants used for the phytoremediation are called hyperaccumulator. Among them, the tree species have been identified as suitable for remediation of soil. The wood angiosperm plants, known as hardwood, that can process phytoextraction and they are frequently represented by willow, Populus, Acer, Atnus and Betula. In the 1990 have started the studies on Salicaceae useful for phytoremediation, which have involved various plant traits, such as pollutant uptake, accumulation and allocation in different organs, tolerance ability at root and leaf levels, including the physiological and biochemical mechanisms at the basis of these activities. The used of trees to phytoremediation is favoured by the possibility of long-term growth and high biomass for contaminants accumulation. This genus has specific features, such as the fast growth starting from whips and poles, the possibility of deep rooting at several metres of depth, over to be adapted to pollution environments that makes it suitable and a good candidate for the phytoremediation application. Moreover, they not only are able to grow in the presence of critical soil conditions, typical of the contaminated areas, but is also able to extract the metal(loid)s in the range of several parts per million of dry weight. However, the high metal(loid)s concentration in soils harmfully influence the plant growth, and consequently the yields of crops for the several cell damages caused, and disrupting the physiological process. For an efficient phytoremediation is important and fundamental an effective plant growth associated to a huge biomass production.