Air sampling for exposure to solvents (toluene, xylene and similar)

Exposure to solvents such as toluene, xylene or similar substances carries a risk of long term health problems if exposure is not properly controlled.  As occupational hygienists and qualified safety consultants we have many years experience of carrying out air sampling surveys to determine occupational exposure to many types of solvent used in paints, glues and mastics amongst other substances.

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If you would like to speak to one of our safety consultants or occupational hygienists about an air sampling survey for wood dusts please contact us on 01453 800100.

Xylene and toluene sampling methods

An activated charcoal badge type dosimeter was used, attached at the lapel. The badge was left exposed for a recorded period and later washed through with a solvent to extract the analyte which is then passed through a gas chromatography instrument to analyse the concentration of particular substances, in this case xylene and toluene were selected.


Xylene – Background Information

OCCUPATIONAL EXPOSURE STANDARDS

  • 8-HOUR TWA: 100 ppm
  • 15-MINUTE REF. PERIOD: 150 ppm
  • IDENTITY AND PROPERTIES
  • CAS No: 1330-20-7
  • EEC No: 601-022-00-9
  • Formula: C6H4(CH3)2
  • Synonyms: xylol, dimethylbenzene
  • Saturated vapour
  • concentration: about 8000 ppm at 20oC
  • Boiling point: 137-144 oC
  • Conversion factor: 1 ppm = 4.34 mg.m-3 at 25oC

Xylene is an aromatic hydrocarbon with a characteristic odour, perceptible at about 1 ppm. Commercial xylene is a mixture of the three xylene isomers and may contain some ethyl benzene. It is a clear, colourless, mobile, fairly volatile fluid, which is insoluble in water and miscible in other organic solvents. Xylene is classified under the CHIP 2 Regulations (1994) as harmful, to be labelled with risk (R) phrases:

  • R10: FLAMMABLE
  • R20/21: HARMFUL BY INHALATION AND IN CONTACT WITH SKIN
  • R38: IRRITATING TO SKIN

OCCURRENCE AND USE

Xylene is produced mainly from crude oil in the UK, but some also arises from coking processes. It is a component of petrol and hydrocarbon solvent mixtures; and is used in chemical manufacture and as a solvent. Individual isomers are raw materials for making terephthalic acid and phthalic anhydride. It is a carrier solvent for surface coatings (e.g. paints, adhesives, pesticides) supplied for commercial and domestic use.

EXPOSURE

Many thousands of workers may be potentially exposed to xylene, with more than 10 000 user-firms in the UK. Typically, exposures to xylene vapours are controlled to below 50 ppm where xylene is used as a chemical precursor and in the manufacture and use of formulated products. Higher exposures may occur in spray-painting large items, printing, and using xylene-containing products in confined spaces; in these circumstances respiratory protective equipment is worn. Short-term exposures up to 500 ppm have been reported in machine-cleaning operations.

MEASUREMENT

Long-term monitoring is performed by pumped sampling with solvent desorption or by diffusive sampling and thermal desorption {Methods for the determination of hazardous substances MDHS 66 (Rev) MIXED HYDROCARBONS (C5 TO C10) IN AIR – LABORATORY METHOD USING POROUS POLYMER DIFFUSION SAMPLERS, THERMAL DESORPTION AND GAS CHROMATOGRAPHY ISBN 0 7176 0867 0 HSE Books (1995)} and gas chromatographic determination. Measurement of the urinary metabolite methyl hippuric acid is a suitable biological indicator of uptake.

METABOLISM

Xylene vapour is rapidly absorbed through the respiratory tract. It is also absorbed by skin contact, and penetrates many materials used for protective clothing. Over 90% of the absorbed dose is metabolised and excreted in the urine as methyl hippuric acid. A small proportion (5%) is exhaled in the breath.

HEALTH EFFECTS

Animal studies

Exposure to high concentrations of xylene has been shown to cause hearing loss and enlargement of kidneys and liver, due to high metabolic demand. Toxicity to reproduction has been observed, but only at or near levels which are maternally toxic. Xylene gave negative results in carcinogenicity and various mutagenicity tests.

Human data

Minimal eye, nose and throat irritation has been reported at levels down to 100 ppm for 30 minutes, and this can also arise with brief exposures at slightly higher levels. The principal effects known in humans are on the central nervous system. Exposure at 300 ppm affected the sense of balance, caused visual disturbances and slowed reaction-times and some effects were seen at 200 ppm; but exposure to 160 ppm over 4 hours caused no significant adverse health effects. At around 700 ppm for up to 1 hour, headache, dizziness and nausea occur. The isomeric composition of xylene is not considered an important factor in its health effects.

BASIS FOR SETTING THE LIMIT

The critical health effects are irritation and central nervous system effects. The irritant effects reported at 100 ppm appear to be minimal and this was considered to be a no-effect level. In view of these irritancy effects an occupational exposure standard was set at 100 ppm (8-hour TWA). Since irritant effects can arise with even brief exposures at higher levels a short-term OES was set at 150 ppm (15-minute reference period). The limits apply to o-, m- or p- isomers of xylene, or mixtures thereof. A ‘Skin’ notation was considered appropriate to indicate the potential for absorption by this route.


Toluene – Background Information

OCCUPATIONAL EXPOSURE STANDARDS

  • 8-HOUR TWA: 50 ppm
  • 15-MINUTE REF. PERIOD: 150 ppm
  • NOTATION: SKIN
  • IDENTITY AND PROPERTIES
  • CAS No: 108-88-3
  • EEC No: 601-021-00-3
  • Formula: C6H5CH3
  • Synonyms: toluol, methyl benzene
  • Saturated vapour
  • concentration: about 30 000 ppm at 25oC
  • Boiling point: 110.6oC
  • Conversion factor: 1 ppm = 3.75 mg.m-3 at 25oC

Toluene is an aromatic hydrocarbon with the typical sweet/pungent odour of such substances and an odour threshold around 3 ppm. It is a clear, colourless, mobile, volatile liquid which is insoluble in water and miscible with most organic solvents. Toluene is classified under the CHIP 2 Regulations (1994) as highly flammable and harmful, to be labelled with risk (R) phrases:

  • R11: HIGHLY FLAMMABLE
  • R20: HARMFUL BY INHALATION
OCCURRENCE AND USE

Toluene occurs naturally in crude oils and is now produced by catalytic reforming of petroleum feedstocks. About 150 000 tonnes per annum are used in the UK. Toluene has widespread use in the production of a range of industrial chemicals, and as a solvent in adhesives, including rubber solutions, coatings and printing inks. It is a common component of many mixed petroleum hydrocarbon solvents.

EXPOSURE

A large number of workers are potentially exposed to toluene. Processes at which exposure to toluene is well-controlled are in the petrochemical sector; exposures are fairly well controlled in the footwear industry (adhesives), silk-screen printing, chemicals production, paint manufacture and decorating industries. In each case mean exposures are less than 15 ppm with more than 96 % of samples less than 100 ppm. Poorly controlled processes include rubber-coating, machine-cleaning, and general adhesives uses, where mean exposures range from 15 to 89 ppm with only around two thirds of samples less than 100 ppm. High short-term exposures can be experienced at liquid transfer points and during manual cleaning. There is a potential for domestic exposure from paint and adhesives.

MEASUREMENT

Short-term measurement can be performed by colorimetric detector tubes, and continuous monitoring is with meters, but these may not be selective for toluene. Long-term measurement is by pumped sampling onto charcoal with solvent desorption, {Methods for the determination of hazardous substances MDHS 36 (Rev) TOLUENE IN AIR – LABORATORY METHOD USING PUMPED CHARCOAL ADSORPTION TUBES, SOLVENT DESORPTION AND GAS CHROMATOGRAPHY ISBN 0 11 885960 9 HSE Books (1990)} or diffusive sampling with thermal or solvent desorption, {Methods for the determination of hazardous substances MDHS 40 (Rev) TOLUENE IN AIR – LABORATORY METHOD USING PUMPED POROUS POLYMER ADSORBENT TUBES, THERMAL DESORPTION AND GAS CHROMATOGRAPHY ISBN 0 11 885961 7 HSE Books (1990)} and gas chromatographic determination. Biological assessment of toluene exposure is by measuring blood-toluene at the shift-end.

METABOLISM

Toluene is readily absorbed by the respiratory tract, and is also absorbed through the skin. It is rapidly distributed, accumulating to some extent in fat and also the liver, brain and lung. Some toluene is exhaled: otherwise it is metabolised to hippuric acid and o-cresol, which are excreted in urine over an extended period.

HEALTH EFFECTS

Animal studies

Inhalation studies showed narcosis at 10 000 ppm, following central nervous system effects. In repeated studies at high exposures, kidney and liver damage occurred, with no effects at 200 ppm. It is difficult to form firm conclusions on findings that exposure to toluene may cause hearing or eyesight impairment.

IN VIVO and IN VITRO studies show toluene is unlikely to be carcinogenic or mutagenic. Toluene only showed teratogenic effects at high doses.

Human data

The principal effects are on the central nervous system with impaired reaction times and vigilance reported for exposures to 200 or 240 ppm for 3 to 7 hours, and dizziness, headache and fatigue reported following exposure at 50 to 100 ppm for 4 to 8 hours. Although longer term effects on the central nervous system have been claimed, there is no substantive evidence that they occur following repeated exposures between 50 and 200 ppm. Toluene vapour is irritating to the eyes and respiratory tract, with no effects being reported at 80 ppm. The liquid irritates the skin. There are no data on carcinogenic effects in humans.

BASIS FOR SETTING THE LIMIT

The critical health effect is upon the central nervous system. A level could be identified which was unlikely to be injurious to employees, and an occupational exposure standard was set at 50 ppm (8-hour TWA) on this basis. However, this implies a need to introduce improvements in control in some industry sectors. A short-term OES was set at 150 ppm (15-minute reference period) which would minimise short-term effects such as irritation. A ‘Skin’ notation was considered appropriate.