Environmental Health Criteria, No 190
World Health Organization
ISBN-13    9789241571906 ISBN-10    924157190X
Order Number    11600190 Format    E-book collection (PDF)
Price    CHF    30.00 / US$    36.00 Developing countries:    CHF    21.00
English     1997        147   pages
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Evaluates the risks to human health and the environment posed by exposure to xylene and its three isomeric forms: ortho, meta, and para. Xylene is an aromatic hydrocarbon blended into petrol and used in a variety of solvent applications, mainly in the paint and printing industries.
The opening sections, on sources of exposure and behaviour in the environment, note that most xylene present in the environment results from its use as a solvent and its presence in motor vehicle exhaust. The majority of environmental xylene enters the atmosphere directly, where it is readily degraded via photooxidation. The report cites evidence that xylene is rapidly biodegraded in soil and water, though o-xylene is more persistent in soil than the other isomers. Limited evidence suggests low bioaccumulation by fish and invertebrates and low to moderate toxicity, supporting the conclusion that xylene is unlikely to endanger aquatic ecosystems except under the higher exposure conditions found in the vicinity of industrial discharges or following accidental spills.
A section on environmental levels and human exposure summarizes data on concentrations detected in various environmental media, in indoor air, near point sources, and in occupational settings where workers are exposed. Data on levels in food were judged inadequate for evaluation. Inhalation was determined to be the most important route of human exposure. Concerning kinetics and metabolism in laboratory animals and humans, the report cites abundant evidence that xylene is rapidly and efficiently metabolized, with more than 90% biotransformed to methylhippuric acid and excreted in urine.
A review of numerous studies conducted in laboratory animals and in vitro test systems cites evidence of chronic effects on the central nervous system following exposure at moderate concentrations. These findings support the limited data available on humans, where studies suggest that exposure to xylene may have an acute impairing effect on the sensory-motor and information-processing functions of the central nervous system. The report found no evidence that xylene is mutagenic or carcinogenic.