National Industrial Chemicals Notification and Assessment Scheme
Occupational Risk Characterisation
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- 13.2Critical health effects
- 13.2.2Effects due to repeated exposure
- 13.3Occupational health and safety risks of trichloroethylene
- 13.3.2Margin of exposure
- 13.3.3Uncertainties in risk characterisation
- 13.3.4Uncertainties in risk characterisation of trichloroethylene
- 13.3.5Risk during formulation
- 13.3.6Risk during vapour degreasing
- 13.3.7Risk during cold cleaning
- 13.3.8Risk during use of trichloroethylene products
13.Occupational Risk CharacterisationOccupational risk characterisation combines the results of the hazard and occupational exposure assessments to determine the potential risks of adverse health effects in workers exposed to trichloroethylene. 13.1MethodologyThe methodology used to characterise risk to human health from exposure to trichloroethylene in this report is the margin of exposure approach. This approach is commonly used in international assessments (OECD, 1993; UK Government, 1993, July; European Commission, 1994) The following steps are used for risk characterisation of critical effects caused by repeated or prolonged exposure: 1. Identification of the critical health effect(s). 2. If appropriate and available, then identification of the most reliable NOAEL for the critical effect(s). 3. Estimation of the human dose (EHD) 4. Comparison of the NOAEL with the estimated human dose to give a
estimated human dose (EHD) 5. Characterisation of risk by judging whether the margin of exposure indicates a concern. Margin of exposure (MOE) is an indication of the magnitude by which the NOAEL exceeds estimated human exposure (EHD). Characterisation of risk requires consideration of a number of parameters such as the completeness and quality of the database (including exposure data), nature and severity of the effects, interspecies and intraspecies variability and characteristics of the human population exposed when judging whether the MOE indicates that exposure to the substance is of concern. For acute effects, the risk characterisation process considers likely exposure patterns to assess whether single exposures are high enough to indicate a health concern.
13.2.1Acute effectsThe main adverse effect observed following acute exposure to trichloroethylene is CNS depression. The NOAEL for CNS depression in humans is about 300 ppm for exposure of about 8 h. Exposure to high doses causes narcosis and recovery is generally complete. Symptoms of CNS depression such as lightheadedness, dizziness and lethargy have been reported in workers. Trichloroethylene is considered to be a skin and eye irritant. 13.2.2Effects due to repeated exposureSevere renal tubular damage and tubular-glomerular damage have been observed in workers with long-term occupational exposure to trichloroethylene. However, the data is insufficient to identify a NOAEL as exposures were not known. The toxic effects identified from repeated inhalational exposure to trichloroethylene in animal studies were liver, kidneys, CNS, lungs and hearing effects. The kidneys appear to be the most sensitive organs in animals hence the critical effect is kidney toxicity. In a 2-year inhalation study using rats, meganucleocytosis of the renal tubules was reported at 300 ppm (LOAEL) with no effects being seen at 100 ppm (NOAEL). Five rats in the highest exposure group (600 ppm) had renal tubular adenocarcinomas (Maltoni et al., 1986). Long term carcinogenicity studies in animals by the inhalation and oral routes indicate that trichloroethylene is carcinogenic in rats and mice. The principal tumour sites are the liver and the lungs in mice and the kidneys in rats. Renal adenocarcinomas have been reported in rats following gavage and inhalation exposure. Rat kidney tumours are thought to be due to persistent cytotoxicity and regeneration. Epidemiological studies, one cohort and one case control, have indicated an association between prolonged occupational exposure to high levels of trichloroethylene and kidney tumours. The main route of exposure is inhalation, with dermal exposure occurring to a lesser extent. There is no dermal NOAEL available. The inhalation NOAEL chosen for risk characterisation is the NOAEL for kidney effects in rats of 100 ppm (546 mg/m3). Assuming 100% absorption, an average rat weight of 215g and a respiratory rate of 0.16 m3/day, this represents an absorbed dose of :
0.215 x 24 h 13.3Occupational health and safety risks of trichloroethylene13.3.1Risks from physicochemical hazardsTrichloroethylene is non-flammable and non-explosive under normal conditions of use. Its flammability limits in air are 8.0 to 10.5 and the chemical is flammable when exposed to a high energy source. At workplaces using old degreaser tanks with inadequate engineering controls, vapours may accumulate increasing the risk of flammability. Trichloroethylene is relatively stable but at high temperatures may decompose to hydrochloric acid, phosgene and other compounds. Such conditions are seen in the vicinity of arc welding and degreasing operations. In the presence of strong alkalis like sodium hydroxide, dichloroacetylene is formed which is explosive and flammable.
estimated human dose (EHD) in mg/kg/day The EHD for each scenario is given in Appendix 1, with the summary in Chapter 8. The NOAEL for the critical effect, renal toxicity, is 118 mg/kg/day (100 ppm) based on a 2-year inhalation rat study. The estimated MOE for each scenario is given in Table 30. 
13.3.3Uncertainties in risk characterisationIn any risk assessment process, uncertainties arise due to assumptions made during the process because of inadequate information. Uncertainties inherent in the assessment of health risk of a chemical are listed in Table 31. Table 31 – Uncertainties in risk characterisation
These uncertainties need to be considered when discussing the implications of any margin of exposure, and in particular when deciding if an estimated exposure is of concern. 13.3.4Uncertainties in risk characterisation of trichloroethyleneFor the critical effect, renal toxicity, an inhalational NOAEL of 100 ppm was identified from the animal data with the LOAEL being 300 ppm. Renal adenocarcinomas were observed at 600 ppm. The actual NOAEL may be anywhere between 100 and 300 ppm. Renal effects are thought to be related to the metabolism of trichloroethylene by the reductive pathway. In humans, as in rats, the mercapturates formed are only minor excretory products but are excreted slowly from the kidney. These metabolites have been identified in human urine even at low levels of exposure. The ratio of the two isomers N-acetyl-S-(dichlorovinyl) -L-cysteine excreted in urine is different in rats and humans. In humans the proportion of the two isomers are the same. However, in rats excretion of 2,2 isomer is 3 to 4 fold higher than the 1,2 isomer. Uncertainty exists as to whether small amounts of these metabolites are sufficient to cause renal toxicity or the metabolites need to exceed a certain threshold for appearance of renal toxicity. The skin absorption rate used to estimate dermal exposure introduces an element of uncertainty in the assessment as no data on the skin permeability rate for trichloroethylene in humans was available in the open literature. The skin absorption rate used (0.32 mg/cm2/h) was derived from experiments in hairless guinea pigs. The dermal absorption rate in mice was reported as 0.47 mg/cm2/h in one study while the theoretical model of Fiserova-Bergerova predicts that for dermal absorption of trichloroethylene, the predicted flux is 0.27 mg/cm2/h (Fiserova-Bergerova & Pierce, 1989). The skin absorption rate in guinea pigs was used to estimate dermal exposure as the rate in guinea pigs in general is closer to the rate in humans compared to mice. These above uncertainties are likely to have a similar impact on MOE for all scenarios. Uncertainties such as lack of exposure data (inhalational and dermal) and extent and duration of skin absorption will have varying degrees of impact on the risk assessment. These will be discussed for each scenario. 13.3.5Risk during formulationAcute effects No atmospheric monitoring data were available for formulation of products containing trichloroethylene. There is a range of processes, with some being open and others closed. Certain stages of the formulation process such as manual filling of the mixing vessels from drums or bulk storage sites and emptying of the tank into containers could result in high peak inhalation exposures and dermal contact. In a well-controlled, enclosed process, acute exposures are likely to be low. There is a risk of irritant effects during formulation when mixing in open systems, during maintenance work or during clean-up of spills.
No atmospheric monitoring data were available for formulation of products containing trichloroethylene. According to the data provided for assessment, formulation is a batch process occurring approximately 1 to 2 h a day for 1 to 60 days a year and this has been taken into account in the formulae used to estimate exposure. The MOE for inhalation exposure was estimated for 3 atmospheric concentrations, 10, 30 and 50 ppm and were found to be 474, 158 and 95 respectively. For combined exposure (inhalation and dermal) during formulation of a product containing 90% trichloroethylene the MOE for the 3 scenarios were 456, 156 and 94. In estimating dermal exposure, contact with liquid trichloroethylene was assumed to be incidental as skin contact is expected to be infrequent during formulation. The MOE calculated indicate that the risk of kidney effects is considered to be minimal during formulation.
The atmospheric monitoring data available for assessment consisted of short- term measurements or instantaneous readings indicating peak concentrations of trichloroethylene, with all readings well below the NOAEL of 300 ppm for CNS effects. If it is assumed that the results are representative of vapour degreasing in Australia, then the risk of CNS effects is low. However a reading of 145 ppm was reported 15 cms above a degreaser, indicating that a worker involved in manually lowering or lifting workloads from the degreaser could be exposed to high vapour concentrations with some risk of CNS effects. As trichloroethylene vapour is irritant to the eyes, exposure to vapours during degreasing operations may lead to a risk of eye irritation. Trichloroethylene liquid is a skin and eye irritant, so any splashes or spills present a risk of irritation.
The atmospheric monitoring data provided by end-users during assessment were inadequate as most of the data was limited and consisted of grab samples and not TWA measurements. However, there is sufficient UK monitoring data available for vapour degreasing. The mode of use of trichloroethylene in vapour degreasing in the U.K. is similar to that in Australia and the U.K. monitoring data was used to estimate worker exposure. Monitoring by HSE inspectors between 1984 and 1994 showed that of 25 personal samples (8 h TWAs), 96% were <30 ppm and all were less than 50 ppm (United Kingdom, 1996). Based on this data exposure was estimated for 3 scenarios, 10, 30 and 50 ppm. The combined MOE for both inhalation and dermal exposure for the three scenarios were 34, 12 and 7 respectively. The severity of the renal toxicity, with higher doses causing tumours in animals, suggests the need for a high margin of safety. The MOE at all the levels calculated for vapour degreasing are of concern. Inhalational values may be overestimated to some extent as most workers are involved in other activities in addition to vapour degreasing. However in some workplaces workers are involved in only operating the degreasers. Poor work practices and working conditions such as poor ventilation or lack of proper protective equipment may lead to increased exposure. Some of the commonly reported examples of poor work practice in the literature included workers ignoring the recommended speed for lowering and raising workloads from the degreaser and not holding the workload in the freeboard zone for a sufficient time. Exposure during vapour degreasing is mainly to vapours. Dermal absorption of trichloroethylene vapour is negligible resulting in minimal absorption through the skin. Dermal exposure to the liquid during vapour degreasing is considered to be incidental and may occur during activities such as filling degreaser with trichloroethylene or handling of the degreased parts containing trapped liquid chemical. More frequent dermal exposure will lower the MOE. 13.3.7Risk during cold cleaningInformation obtained from industry indicates that 29% of the respondents use trichloroethylene in cold cleaning of metal parts. Common types of cleaning include immersion in tubs or tanks along with spraying or brushing of the metal parts. Manual wipe cleaning was another common method. Atmospheric monitoring has not been carried out at workplaces using trichloroethylene for cold cleaning. Margins of exposure were estimated for exposure durations of 120 days/yr and 200 days/yr using the atmpspheric monitoring data obtained in the NICNAS cold cleaning project. Dermal exposure was assumed to occur for 5% of the shift. Estimated MOE for combined exposures (inhalation and dermal) for the various activities for 200 days/yr were 105 for dip cleaning, 91 - 34 for combined dip cleaning and rag wiping and 52 - 5 for rag wiping alone and for 120 days/year were 174 for dip cleaning, 152 - 56 for combined dip cleaning and rag wiping and 87 - 8 for rag wiping alone. Other monitoring data available for assessment was available from Dow Chemical Company Product Stewardship Program, which focussed on the exposure profiles encountered during use of trichloroethylene in vapour degreasing and cold cleaning operations. For the average concentration obtained in this program (68.4 ppm), the estimated combined MOE (inhalational+dermal) was 4.4. Some of the MOE calculated for rag wiping and dip cleaning combined with rag wiping (ie MOE < 50) indicate that there is a concern in these situations. Dermal exposure may occur as cold cleaning involves immersion of metal parts in tubs or tanks accompanied by scrubbing or brushing of the immersed parts leading to agitation of trichloroethylene liquid with loss of vapour to the atmosphere and splashes and spills of the chemical. Dermal exposure may be higher where cold cleaning involves immersion of the hands into the tub or tank during scrubbing. High dermal and inhalation exposure is associated with manual wipe cleaning, where trichloroethylene is applied on a rag and used to clean surfaces. In many workplaces no engineering controls are in place during cold cleaning and, in one of the places interviewed, the gloves used during manual wipe did not offer any protection against trichloroethylene.
Acute adverse effects such as headache, dizziness and irritability have been reported by some workers using a degreasing product indicating exposure to high concentrations of trichloroethylene. The product was sprayed onto a cloth and used for wipe cleaning metal rods during the entire shift. Products used in spray form present a greater risk of exposure as the small aerosol particles are likely to be readily absorbed through the lungs and skin. Some data was obtained on use of adhesives containing trichloroethylene. An atmospheric concentration of 1.15 ppm was detected in an adhesive spraying area with good natural ventilation. Concentrations of up to 21.4 ppm over a sampling time of 5-6 h were recorded in a US automotive factory using trichloroethylene containing adhesives. As part of the project commissioned by NICNAS, WorkCover monitored atmospheric levels of trichloroethylene and urinary levels of trichloroacetic acid in workers using trichloroethylene products. Concentration of trichloroethylene in the products varied from spray painting (35% and 25%) to rag wiping for surface cleaning (20%) to brushing on the product (90%). Atmospheric levels monitored varied from 0.7 ppm to 4.8 ppm (spray painting); 3.8 ppm to 4.1 ppm (rag wiping); 2.5 ppm (brush application). Assuming incidental dermal exposure, the estimated margins of safety varied from 69 to 395 (spray painting) to 85 to 90 (rag wiping) to 117 (brush application). The MOE were estimated for an 8 h exposure and would be higher at places using the products for shorter periods. 13.3.9Areas of concernThe risk assessment has indicated that there may be health concerns for workers exposed to trichloroethylene in some workplaces. The limited short term exposure data available indicate that there may be a risk of acute CNS effects during certain stages of vapour degreasing when high exposure to trichloroethylene vapours may occur. Acute effects are also likely during use of trichloroethylene in cold cleaning for 8 h shifts in places with poor ventilation and during use of trichloroethylene products, especially in the form of aerosols. Although it is not possible to determine how representative monitoring data was in the NICNAS project for cold cleaning and trichloroethylene products, there is cause for concern as anecdotal evidence of dizziness, headache and irritability during these uses have been obtained during the assessment. Estimates of MOE for repeated exposure indicated that there is little risk of adverse health effects during formulation, however there was concern for workers repeatedly exposed to trichloroethylene during vapour degreasing and cold cleaning, particularly from inhalation exposure. Dermal exposure was minor during vapour degreasing, however, as the risk of skin contact during cold cleaning is greater, the contribution by dermal exposure towards the risk of adverse health effects during cold cleaning may be significant. In addition, while estimating human exposure in this assessment an average male weight of 70 kg was used. This may not be applicable to the majority of the population in sections of the metal industry and the textile and footwear industry which have a high proportion of female employees who are likely to be 70 kg. The MOE would therefore be lower for these persons. 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:
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