At 20 0C, ortho-xylene (o-xylene) is a liquid that floats on water and is low to
moderately volatile. Characterized by its low solubility, it will volatilize rapidly once dissolved
and adsorbs moderately to organic matter. During a spill, this compound will partially evaporate but
the majority of the product will enter into the soil or migrate into a waterway. Liquid 1,2-xylene
will form a film on the water surface which will promote its solubilization and volatilization. The
adsorbed 1,2-xylene in the vadose and saturated zones will take some time to disappear, liberating
contamination in either the gaseous (primarily) or dissolved state. The resulting gaseous or
dissolved (primarily) plumes will be relatively limited in size.
Xylene isomers (ortho-, meta-, and para-) are aromatic hydrocarbons naturally present
in crude petroleum and coal tar. Mixed xylene (a mixture of ethylbenzene and the three isomers of
xylene, where m-xylene predominates) is produced industrially in large amounts from petroleum or
coal tar. Approximately 70 % of mixed xylene is used in the production of ethylbenzene. The
remaining mixed xylene is primarily used as a solvent in the printing, rubber and leather
industries, in products such as paints and coatings, or blended into airplane fuels and
gasoline.
Xylene isomers are used primarily for internal industrial operations as solvents and
intermediates in synthetic reactions. o-Xylene is a chemical intermediate in the synthesis of
phthalic anhydride (for plasticizers), phthalonitrile, 4,4-(trifluoro-1-(trifluoromethyl)
ethylidene) diphthalic anhydride (for polyimide polymers), o-toluic acid, vitamins and
pharmaceuticals. m-Xylene is a chemical intermediate in the production of isophthalic acid and
isophthalonitrile; isophthalic acid, in turn, is used in the manufacture of polyesters. p-Xylene is
a chemical intermediate in the synthesis of terephthalic acid (for polyesters resins and fibers),
dimethyl tetrachloroterephthalate, vitamins and pharmaceuticals. Both o-xylene and p-xylene are used
as components of insecticides.
Because individual xylene isomers are used in large amounts in industrial settings, people who
work or live near these locations may receive a higher exposure to one xylene isomer compared to the
other isomers. However, since xylenes are present as a mixture in gasoline and in the solvent
components of commonly used commercial products (paint, coatings, etc.), exposure of the general
population is expected to be primarily to xylenes as a mixture, and not to the separate xylene
isomers. Xylenes may be introduced into groundwater by fuel oil, gasoline or solvent spills, leaking
underground petroleum storage tanks, or leaching from disposed wastes.
