The Toxic Effects of Xylene

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The Toxic Effects of Xylene

• Rebecca E. Compton
• ENVS 531
• 11-9-02

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Outline

• Sources of Xylene
• Industrial Uses
• Physical Properties
• Fate in Environment
• Routes of Entry
• Transport in Body
• Toxicity
• Toxic Effects

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Sources of Xylene

• Natural
• Produced in forest fires
• Found in petroleum and coal tar
• Anthropogenic
• Produced as a by-product of petroleum industry

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Industrial Uses

• Solvent in paint, leather, rubber, and printing
  industries
• Utilized in plastics, synthetic fibers, and
  coating industries
• Used as an additive in gasoline to increase
  octane rating

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Physical Properties

• Colorless, flammable liquid
• Practically insoluble in water
• 0.013g/100 L water
• Octanol-Water Partition Coeffecient
• Log Kow 2.77 to 3.20
• Indicates lipid solubility
• Vapor pressure 10 mmHg near room temperature

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Fate in Environment

• Volatilization is the primary process that
  determines environmental behavior
• 98.66 of environmental releases end up in the
  atmosphere
• Transformed in atmosphere via photo-oxidation
  within 0.5 to 1 day

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Fate in Environment

• Release to soil
• Volatilization from soil surface
• Photo-oxidation with 24 hour half-life
• Some biodegradation
• Possible percolation through soil to groundwater

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Fate in Environment

• Release to water
• Vapor pressure and low density result in
  volatilization from surface waters
• Biodegradation in water around 10 days
• Groundwater contamination has longer half-life
• No volatilization
• Lack of other aromatics for cometabolism

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Routes of Entry

• Inhalation (main route)
• Volatility of chemical allows for easy inhalation
  of xylene vapors
• Workplace inhalation most common source
• 60 absorption

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Routes of Entry

• Ingestion
• Accidental ingestion of household products
  containing xylene
• Ingestion of contaminated groundwater
• 90 absorption

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Routes of Entry

• Dermal
• Much less common route
• Either liquid or gaseous exposure can cause
  dermal absorption
• 0.1 to 2 absorption

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Transport in Body

• Biotransformation by oxidation of side-chain
  methyl group
• Microsomal enzymes from oxidase group
• Conjugation with glycine
• Excretion into urine
• This pathway accounts for 90 of elimination

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Transport in Body

• Other elimination pathways (10)
• Unchanged compound in urine
• Exhalation
• Oxidation of aromatic carbon and excretion of
  xylenol in urine
• Elimination as methylbenzyl alcohol
• Conjugation via glucoronidation

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Main Metabolic Pathway

• C6H4(CH3)2 ? C6H4 (CH3)(CH2OH) ?
• (xylene) (methylbenzylalcohol)
• C6H4 (CH3)(COOH) ?
• (methylbenzoic acid)
• ? C6H4 (CH3)(CONHCH2COOH) excreted in urine
• (methylhippuric acid)

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Rates of Elimination

• From muscle tissue
• Half-life 1 hour
• From adipose tissue
• Half-life 20 hours
• From parenchymal organs
• Too rapid to measure

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Toxicity

• Actual mechanism of toxicity is unknown
• Theories
• Liposolubility in neuronal membrane disrupts
  normal function
• Metabolic intermediates responsible for toxic
  effects

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Toxicity

• Inhibition of microsomal enzymes has been
  observed
• Interactions with other chemicals can increase
  toxicity

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Toxic Effects

• Impairment of lung and respiratory functions
• Memory impairment
• Kidney and liver damage
• Lack of muscle coordination
• Dizziness
• Possibly reproductive effects
• Extreme cases death

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References

• Xylenes. Eco-USA. Available Online
  http//www.eco-usa.net/toxics/xylene.shtml.
  October 7, 2002.
• Office of Air Quality Planning and Standards
  Office of Air and Radiation. Locating and
  Estimating Air Emissions from Sources of Xylene.
  United States Environmental Protection Agency.
  March 1994.
• Ney, Ronald E., Fate and Transport of Organic
  Chemicals in the Environment A Practical Guide.
  3rd Edition.
• Clement Internation Corporation. Toxicological
  Profile for Xylene. Prepared for the United
  States Department of Health and Human Services.
  October 1993.
• Klaassen, Curtis D., Casarett and Doulls
  Toxicology The Basic Science of Poisons. 6th
  Edition. McGraw-Hill Publishing, 2002.

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