of course dear Neethu Hydrogen peroxide is a xenobiotic

Hydrogen peroxide (H2O2), is a nonplanar molecule.

 Hydrogen peroxide is a strong oxidizer and is used as a bleaching agent and disinfectant. Concentrated hydrogen peroxide, or 'high-test peroxide' is a reactive oxygen species and has been used as a propellant in rocketry.Organisms naturally produce trace quantities of hydrogen peroxide, most notably by a respiratory burst as part of the immune response

it is very toxic and induces cancer

that's all you can see also oxidative stress and H2O2

best regards

Thank you Rachid for your information!

Neethu,

A xenobiotic is a substance foreign to life. “Xeno” refers to foreign. It is a molecule (as a drug, pesticide, or carcinogen) that is foreign to a living organism. Xenobiotics are chemical compounds to which an organism is exposed, and these molecules are extrinsic to the normal metabolism of that organism.

Hydrogen peroxide is a well-known, essential component of aerobic living cells. It is critical in host defense and oxidative biosynthetic reactions. In addition, accumulating evidence shows that at low levels, hydrogen peroxide also functions as a cell signaling agent in higher organisms.

Hydrogen peroxide is an endogenous molecule generated in mammalian cells from molecular oxygen during cellular respiration in the organelle, mitochondrion. Hydrogen peroxide is a two-electron reduction product of molecular oxygen. Molecular oxygen has two unpaired electrons of opposite spins in its outer shell, and is therefore a free radical. During cellular respiration, molecular oxygen accepts one electron, and becomes superoxide radical, which by accepting another electron is converted to hydrogen peroxide. Hydrogen peroxide is further converted to water. Hydrogen peroxide formed in the mitochondria is converted into water and oxygen by the enzyme, catalase. Hydrogen peroxide is produced during normal metabolism by enzymes such as monoamine oxidase and D-amino acid oxidase. It is also produced in peroxisomes.

Peroxisomes are so named because they usually contain one or more enzymes that use molecular oxygen in order to remove hydrogen atoms from specific organic substrates in an oxidative reaction that produces hydrogen peroxide. The enzyme, catalase, in peroxisomes, employs the hydrogen peroxide generated by other enzymes in the organelle to oxidize a variety of other substrates, including phenols, formic acid, formaldehyde, and ethanol (alcohol) by the “peroxidative” reaction to produce an oxidized product and water. This type of oxidative reaction is particularly important in liver and kidney cells, where peroxisomes detoxify various toxic molecules that enter the bloodstream. About 25% of the ethanol one consumes is oxidized to acetaldehyde in this fashion. When hydrogen peroxide accumulation is excessive in the cell, catalase converts it into water.

Thank you Chithan ...

Please see my above response. Hydrogen peroxide is normally produced in mammalian cells (endogenously) during the course of cellular respiration and metabolism. It is not a xenobiotic in mammalian cells.

Hydrogen peroxide is not a xenobiotic to onion. This compound is found in different locations in the onion root zone, and is primarily localized in cell walls of epidermal cells and other cells.

Chithan,

Will it be xenobiotic to onion, when  root zone is  contaminated with exogenous Hydrogen peroxide?

Neethu:

Good question! I see your point.

Genotoxicity studies, in general, use non-physiological or pharmacologic concentrations of the potential toxicant to be evaluated, particularly in in vitro studies, and tests such as the micronucleus assay. In such a situation, excessive exogenous hydrogen peroxide employed may not be at physiological concentrations, and may simulate the action of a xenobiotic. Hydrogen peroxide production and physiological levels in cells are tightly controlled. Cellular hydrogen peroxide in onion roots can be efficiently removed by catalase and other enzymic defense systems such as ascorbate peroxidase and other peroxidases.

Dear Neethu,

H2O2 is produced in trace amounts in cells (especially where oxygen consumption is higher) and is one of the active players in free radical biology. It is formed as a byproduct of SOD reaction where highly toxic superoxide anion is converted to comparatively less toxic H2O2. H2O2 will be scavenged to water and oxygen by catalase. Since it is an endogeneous molecule it cannot be considered as a xenobiotic.

Please see the article below

http://www.scirp.org/journal/PaperInformation.aspx?paperID=41356#.VIf5NzGUeyI

It is very toxic, kind (ROS) reactive oxigen species and induces cancer.   

Hydrogen peroxide is formed in human and animal organisms as a short-lived product in biochemical processes and is toxic to cells. The toxicity is due to oxidation.

Also, hydrogen peroxide occurs in surface water, groundwater and in the atmosphere. It forms upon illumination or natural catalytic action by substances containing in water.