Organic Solvents

Organic solvents Dr. Zhang Qiao Dep. of labor hygiene 09-11-2006

Learning Objectives 

 

Describe characteristics and identify sources of Benzene Discuss Health Effects of Benzene Determine actions for reducing exposures to Benzene

Benzene 

Benzene is an aromatic hydrocarbon that is produced by the burning of natural products.



It is a component of products derived from coal and petroleum and is found in gasoline and other fuels.

Benzene; C6H6 H H

H

H

H H

H

Examples of Aromatic Hydrocarbons

CH3

H

H

H

H

H

H

H

H

H Benzene

H

H

H

H

H

H H

H

H Toluene

Naphthalene

Resonance Formulation of Benzene The structure of benzene is a resonance hybrid of the two Lewis structures. Electrons are not localized in alternating single and double bonds, but are delocalized over all six ring carbons.

H

H

H

H

H

H

H

H

H

H

H

H

Circle-in-a-ring notation stands for resonance description of benzene (hybrid of two Kekulé structures)

Physical and chemical character  

 

Clear,colorless and volatile liquid sweet odor, evaporates quickly, highly flammable ℃ Boiling temperature=80 Variable amounts up to 50 ％ （ toluene ， xylene ）

Chance

of

expose

Benzene is used in the manufacture of plastics, detergents, pesticides, and other chemicals. The distillation of coal in the coking process As a solvent in oil refineries An additive in motor fuel

Chance

of

expose



Produced during the burning of gasoline, cigarettes, volcanoes, and forest fires



Used in plastics, resins, nylon, and synthetic fibers, some rubbers, lubricants, dyes, detergents, drugs, pesticides （ impregnant ， menstruum ， solvent ， thinner ， et,al)

In china, the highest incidence of benzene poisoning occurs in follow vocations ： Painting,

Shoemaking

Shoemaking

How Are We Exposed? 

Inhalation  





Ingestion 



Gasoline vapors Cigarette smoke (first and second hand) Vapors from contaminated steam during showering or cooking Contaminated groundwater

Skin Contact

Route of absorption 

Inhalation is the main way



Skin penetration is of little importance



The highest retention is in lipid-rich organs,adipose tissue and bone marrow(can reach a level 20 times higher than blood)

Elimination 





Mainly through the respiratory route(45-70%) The rest is excreted as urinary metabolites It can also be metabolized in the liver by the mixed-function microsomaloxidases

Results of expose 

High airborne concentrations of benzene results in:



CNS depression with acute, non-specific, narcotic effects.



It can even cause to death.

Acute Inhalation        

Drowsiness Dizziness Fast heart rate Headache Tremors Confusion Unconsciousness Death

Ingestion – High Level 

Food or water       

Nausea/vomiting Stomach irritation Dizziness Sleepiness Convulsions Fast heart rate Death

Health Effects: Skin Contact   

Redness Sores Eye irritation

Health Effects: Chronic      

Decreased blood production Cancer: Acute myeloid leukemia Inability to fight infection Low birth weight Delayed fetal bone formation Injury to reproductive organs leading to infertility and difficulty getting pregnant

Results of expose 

Chronic benzene poisoning can occur with much lower exposure levels.it can often cause severe bone marrow depression



Change in blood: anemia,leukopenia, throbocytopenia

Results of expose 

Leukemia secondary to benzene expose has been found,



and malignant transformation of the bone marrow has been noted years after cessation of expose.

Results of expose 

Chromosomal aberrations in lymphocytes were shown to persist even years after cessation of toxic exposure



(SCE: sister chromatid exchanges)



(MN :micronucleus)

micronucleus

cell

Chromatid exchange

Results of expose 

Carcinogenetic effects of benzene

benzene to be a carcinogen (cancer causing). With exposures from less than five years to more than 30 years, individuals have developed, and died from, leukemia.

Indication of Exposure 





Breath test – only useful shortly after exposure, cannot detect low levels Blood and bone marrow – only indicates recent exposures Urine for benzene breakdown products, such as phenol – may not be specific for benzene exposure

How to Reduce Risk  





Avoid breathing or ingesting vapors Wear protective respiratory equipment and gloves Ensure adequate ventilation where fumes are present If exposed at work  

Wash immediately and before going home Change clothes at work, launder separately

Policy 

EPA Maximum Contaminant Level  Water: 5 parts per billion (ppb)  Air: 0.4 ppb  Goal for both air and water: 0 ppb

Policy 



OSHA 8 hour day/40 hour week limit for air exposure is 1 part per million (ppm) with a short–term air exposure limit of 5 ppm NIOSH recommends use of special respiratory equipment when handling benzene

In Review 

What is benzene and how are we exposed to it



How does benzene effect our health



How can we reduce our exposure to benzene