National Industrial Chemicals Notification and Assessment Scheme
Download 1.35 Mb.
|
- Navigate this page:
- 6.Methods of Detection and Analysis
- 6.2Biological monitoring
- 6.2.1Estimation of trichloroethylene
- 6.2.2Estimation of trichloroacetic acid and trichloroethanol
5.4Additives and impuritiesTrichloroethylene undergoes auto-oxidation in air at higher temperatures and on exposure to ultraviolet radiation. To prevent this, stabilisers and inhibitors are added to the commercial grades. Epichlorohydrin was one of the stabilisers used in the past but its use has been discontinued as it was found to be carcinogenic. Mixed amines are now used as stabilisers. Mixed amines and butylene oxide act as acid acceptors when solvent degradation leads to formation of hydrogen chloride. Trichloroethylene is available in a variety of commercial grades that are made up of approximately 99% trichloroethylene with impurities and stabilisers forming the remainder. Additives may include the following: Butanone
1,2-Butylene oxide Diisopropylamine Ethyl acetate Epoxybutane Glycidyl ether Isopropyl acetate 1-Methylpyrrole 2-Methyl-3-butin-2-ol Thymol Triethylamine Trimethyloxirane 2,2,4-trimethylpentene 2,4-di-tertbutylphenol
6.Methods of Detection and Analysis6.1Atmospheric monitoringThe most common analytical techniques for trichloroethylene in air are gas chromatography (GC) combined with either flame ionisation detection (FID), electron capture detection (ECD) or Hall’s electrolytic conductivity detection (HECD). Gas chromatography with mass spectrometry (MS) is used for identification of the chemical. Air samples are collected by adsorption on to activated charcoal or Tenax-GC. Trichloroethylene may be extracted either thermally or with a solvent such as carbon disulfide. In the standard NIOSH method, trichloroethylene is collected by adsorption on activated charcoal. It is then extracted with carbon disulfide and an aliquot is analysed by GC/FID. The estimated limit of detection for this method is 0.01 mg per sample (National Institute for Occupational Safety and Health (NIOSH), 1994). Table 4 gives details of commonly used analytical methods. 6.2Biological monitoringSeveral methods are available for measuring and testing for trichloroethylene in biological media. Samples may be analysed for the presence of trichloroethylene or its metabolites, trichloroethanol and trichloroacetic acid. Trichloroethylene may be estimated in exhaled air or blood while its metabolites are estimated in blood or urine. The main analytical method used is gas chromatography combined with electron capture detection (ECD). The headspace gas chromatographic method allows simultaneous measurements of trichloroethylene, trichloroacetic acid and trichloroethanol. In headspace analysis, the gaseous layer above the sample is injected in to a gas chromatograph either directly or following preconcentration prior to injection on to the GC column. 6.2.1Estimation of trichloroethyleneExpired air analyses 
Several methods have been described for analysis of trichloroethylene in expired air. Methods used include preconcentration on Tenax-GC cartridges followed by thermal desorption either directly onto the gas chromatograph column for separation and detection or to a cryogenic trap connected to the gas chromatograph. Results of studies in human volunteers indicate that the concentration of trichloroethylene in expired alveolar air collected during exposure is an indication of current atmospheric concentration, while estimation 16 h after the end of exposure reflects the average airborne exposure during the preceding day (Kimmerle & Eben, 1973; Stewart et al., 1974a; Fernandez et al., 1975; Monster et al., 1979). Measurements of trichloroacetic acid and trichloroethanol are non-specific indicators of exposure to trichloroethylene as they can be metabolites of other chlorine containing hydrocarbons. American Conference of Governmental Industrial Hygienists (ACGIH) has recommended monitoring of trichloroethylene in end-exhaled air as a confirmatory test when the origin of trichloroacetic acid and trichloroethanol is doubtful. Blood analyses The most common method used to analyse trichloroethylene in blood is headspace analysis, followed by GC or GC/MS. Sensitivity is in the low-ppb range (2-20 ppb) (ATSDR, 1993). 6.2.2Estimation of trichloroacetic acid and trichloroethanolUrine analyses Trichloroacetic acid in urine is an indicator of exposure by all routes. Measurements at the end of the shift and at the end of the work week are considered appropriate to measure recent exposure and cumulative effect, respectively. Trichloroethylene is converted to trichloroacetic acid and samples taken at the end of the shift reflect recent exposure. However, trichloroacetic acid is tightly and extensively bound to plasma proteins and has a half-life in blood of 70-100 h. Repeated exposure causes trichloroacetic acid to accumulate in blood with the metabolite being excreted very slowly. Trichloroacetic acid levels are not influenced by timing of exposure and sampling as very little fluctuation in concentration occurs because of the long elimination half-life. ACGIH recommends a biological exposure index (BEI) of 10 mg/g of creatinine. This provides the same degree of protection as a TLV of 50 ppm. There is a linear correlation between trichloroethylene levels in breathing zone air and urinary levels of the metabolites, total trichloro-compounds, trichloroethanol and trichloroacetic acid in men and women (Inoue et al., 1989). Measurements of trichloroacetic acid in urine may be much higher than indicated by atmospheric monitoring if dermal exposure to liquid trichloroethylene occurs. There are significant racial and ethnic differences in the production of trichloroacetic acid. Deficiency of alcohol dehydrogenase and aldehyde dehydrogenase is more common in non-Caucasians and can lead to an underestimation of exposure and an increase in risk to workers. Alcohol intake and disulfiram treatment also, partly inhibit production of trichloroacetic acid. Total trichloro-compounds (TTC) index in urine reflects the sum of trichloroacetic acid (TCA) and free and conjugated trichloroethanol expressed as trichloroacetic acid. Sampling time is critical for this index because of the short elimination half-life of trichloroethanol. ACGIH recommends collection at the end of the shift after 4 consecutive days of exposure. A TTC concentration of 300 mg/g of creatinine in urine provides the same degree of protection as inhalation exposure at the ACGIH TLV of 50 ppm.
Free trichloroethanol (TCOH) in blood index is an indicator of recent exposure (day of sampling). The sampling time is critical and a method without the hydrolysis of TCOH conjugates must be used as the BEI is for the free form. Hydrolysis would result in conversion of some conjugated trichloroethanol to the free form giving false results. The timing is critical as trichloroethanol in blood rises rapidly during exposure and starts declining shortly after exposure. A BEI of 4 mg/L (27 mol/L of SI units) of free TCOH is recommended by ACGIH for specimens collected at the end of the shift after at least 2 consecutive days exposure. Alcohol intake may result in lower trichloroethanol levels and lead to an underestimation of exposure. The test is nonspecific as trichloroethanol is a metabolite of other chlorine containing ethanes and ethylenes. Directory: data -> assets -> word doc -> 0017 word doc -> Rail safety news issue 6 – October 2011 word doc -> Review of Multiple Chemical Sensitivity: Identifying word doc -> Board Endorsed October 2009 amended 13-09-11 with extra units 0017 -> Rail Safety News Edition 8, December 2012 0017 -> Commonwealth of Australia 2010 0017 -> Real-Time License Plate Localisation on fpga 0017 -> Careers network bulletin issue 6 July 16 2012 0017 -> Wiser science: Finding References inspec for Physics and Engineering 0017 -> Part A: Depth Study: The globalising world Popular culture and public policy Download 1.35 Mb. Share with your friends:
|