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Toxicity & Mode of Entry in to human body

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A toxic effect is any reversible noxious effect on the body – any chemically induced tumor or any mutagenic or teratogenic effect or death – as a result of contact with a substance via the respiratory tract, skin, eye, mouth or any other route.


Toxicity Vs Hazard:

Toxicity is the ability of a substance to produce an unwanted effect when the chemical has reached a sufficient concentration at a certain site in the body. Hazard is regarded as the probability that this concentration in the body will occur.

Two liquid may pose same degree of toxic, but may pose different degree of hazard. One may be odorless and non irritating to the eyes and nose, whether the odor may produce a pungent or disagreeable odor at a harmless concentration. The material produce a pungent or disagreeable odor at a harmless concentration presents a lesser degree of hazard. Its presence can be detected in time to avert injury.


Inhalation: Most important and common type of entry into the body. The respiratory system is composed of two main areas, the upper respiratory tract airways and the alveoli. Only particles smaller than 5 micmetre in dia are likely to enter the alveolar sack. Inhalation depends upon concentration in air, duration of exposure, the pulmonary ventilation volume, which increases in higher work load. During inhalation exposure at a uniform level, the absorption of the compound into the blood reaches equilibrium with metabolism and elimination.

Skin absorption: Contact of skin with substance occurs in 4 ways. Substance can contact the skin and form local irritation on tissue destruction, the substance can produce skin sensitization or the substance can penetrate to the blood vessels under the skin and enter the blood stream. Some substance such as parathion the main mode of entry is through the skin in typical occupational exposure. For substance like aniline, nitrobenzene, phenol the amount absorbed through skin is equivalent to the amount of inhalation. The cutaneous absorption rate of some organic compound rises when temperature or perspiration increases. Absorption can occur in warm climate. Absorption depends upon factors such as pH of the skin and the chemical extent of ionization, aqueous and lipid soluabilities and molecular size. Human skin shows great difference in absorption at different anatomic regions.


Ingestion: Swallowed materials moves into the intestine and can be absorbed in the blood stream and therefore prone toxic. Intake can happen due to poor industrial hygiene of the workers e.g. not washing hands before taking food.


Injection: This can be directly done into the blood stream, the peritoneal cavity, or the pleural cavity. In industrial setup, injection is an infrequent type of exposure to toxic substances. Injection injuries with blood borne pathogens should be taken into account (Hepatitis B, C and HIV)

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