Arsenic: A threatening environmental issue and role of cyanobacteria in toxicity mitigation

Industrialization has brought with it a host of technologies that employ chemicals such as cleaning agents, pesticides, fuels, paints and medicine, and many directly be used in industrial processes. The manufacture, use, and disposal of these chemicals often bring humans as well as plants, animals and the microbes of different niches into contact with them. Toxicity depends not only on exposure, but also on the dose of the toxic substance. Many chemicals containing heavy metals are hazardous at very low concentrations. Heavy metals may also be derived from the weathering of rocks, or, increasingly they may be introduced into the atmosphere and hydrosphere by human activities where they form stable persistent contaminants and sometimes non-biodegradable. Episodes of acute toxicity are easy to understand and are clearly preventable but long-term exposure to low levels of many of these metals it's the greatest challenge to our understanding. Arsenic (As) is a naturally occurring metallic element existing in various mineral forms and found in Earths crust, all type of soil and throughout the environment. Arsenic is considered to be very harmful or toxic to plants, humans, other living organisms and environment until of late and thisis a problem very pronounced in West Bengal and Bangladesh and a challenge to environmental lists. The toxicity of Arsenic is dependent on the route of entry into the cell and solubility of its compounds. Numerous studies have shown that microorganisms especially the cyanobacteria can interact with heavy metals. They also possess several detoxification mechanisms to counteract metals stress which include biosorption, bioaccumulation, exclusion of heavy metals, change in metal binding proteins, trapping of metals in bodies containing sulphoquinovocyl diglyceride, and compartmentalization into polyphosphate bodies.

This review attempts to bring forth the mechanisms involved in amelioration of Arsenic toxicity in general and rice fields in particular by cyanobacteria. This is very important in the light of the findings that most of these rice fields are irrigated with water containing good amounts of Arsenic that are present due to leaching of ground waters contaminated with Arsenic or from effluents containing As discharged into the waters bodies from where water is given to the fields.