Kinetics and metabolism :

About 50% of benzene is absorbed by inhalation  & absorption of it via skin is limited. The high lipophilicity and low water solubility of benzene favour its distribution to fat-rich tissues. Benzene distributed by blood accumulates in fat-rich tissues like adipose tissue bone marrow & liver.

Benzene is readily absorbed by the body during inhalation or ingestion and is rapidly distributed throughout the body, particularly in fatty tissues. Metabolism occurs primarily in liver and to less extent in the bone marrow, producing  intermediates, which account for the toxicity of benzene. In human, half-life of benzene is 1 - 2 days. Accumulation is not expected for benzene or its metabolites. Benzene is primarily exhaled through the lungs unchanged or excreted as metabolites in the urine.

Benzene is oxidized by cytochrome P-450- dependent mixed-function oxidase system. In humans voluntarily exposed to 100ppm (320 mg/m³) benzene for 5 hours, 61% absorbed benzene was metabolised to phenol, 6.4% to catechol & 2% to hydroquinoue while 26% was exhaled unmetabolized. The major part of the metabolites was excreted as sulfate or glucoronic acid conjugates.

Metabolites of benzene are responsible for haematotoxicity. The bio-transformation path ways are the formation of phenol via epoxide & catcehol via benzene dihydrodiol. Hydro-quinone, catechol and hydroxy hydroquinone are converted to p-benzosemiquinone and p- benzoquinone, to o-benzoquinone and to o- hydroy-p-benzosemiquinone and hydroxy – p – benzoquinone respectively. The copy of reactions is enclosed.