h.5Occupational exposure to manganese from MMT use

h.5Occupational exposure to manganese from MMT use

In addition to exposure to MMT, petrol station and maintenance workers may experience occupational inhalation exposure to Mn particulates in exhaust emissions. The exposure of petrol station attendants is likely to be highly variable depending on the required duties – purely retail versus petrol pumping, the level of customer traffic, the separation of retail from service areas and the vehicle fleet i.e. cars using LRP versus unleaded fuel.

Automechanics may be particularly exposed to Mn particulates when servicing operating automotive engines in poorly ventilated workshops.

Attendants, security and other personnel who work in enclosed car parks such as underground parking stations also have a potential for inhalation exposure to particulates containing Mn during routine duties. Exposure to MMT for these workers is unlikely given the enclosed nature of automotive petrol systems, low vapour pressure of MMT and expected very low levels of MMT emissions in exhaust. Like service station workers, exposure during the working day is likely to be highly variable and dependent on the level of and proximity to customer traffic and the effectiveness of ventilation of the enclosed parking station.

Professional drivers such as taxi and truck operators and road maintenance workers may also be exposed to Mn from inhalation of particulates from automotive exhaust. Again, exposure is likely to be highly variable and dependent on traffic, particulate filtering within automotive airconditioning systems and, in the case of road workers, whether work is on new, uncommissioned or light duty roads or on heavily trafficked arterial roads repaired whilst in service.

h.5.1Exposure data and estimates

Manufacturing 16-1600 (arithmetic mean 200) μg/m³ (n = 12)

Laboratory Analysis < 40 - < 200 μg/m³ (n = 3)

Shipping < 100 μg/m³ (n = 2)

Anecdotal exposure data for refinery handling have also been supplied by Ethyl Corporation. These are based on data provided by Ethyl Corporation customers:

Refinery Handling < 10 μg/m³ (TWA8)

References, location and details of the extent and type of sampling for these refinery handling data are not available.

No information is available regarding Australian refinery exposures or occupational exposure during formulation of aftermarket fuel additives. No MMT manufacture occurs presently in Australia and so these manufacturing, laboratory analysis and shipping data are not directly comparable to those of local occupational environments. However, it is likely that local exposures to MMT would be much lower than those associated with overseas manufacturing because Australian occupational use scenarios involve handling MMT in diluted forms on a much more intermittent basis. Similarly, exposures associated with local refinery handling are expected to be less than those overseas due to the more limited use of MMT.

No quantitative data are available regarding personal exposures to or environmental levels of MMT in workplaces in Australia. However, some limited overseas non-manufacturing data are available. Zayed et al. (1999a) measured airborne MMT (measured as Mn) and total and respirable (< 5 μm) Mn levels in selected occupational microenvironments in Montreal. Stationary sampling was conducted over 36 hours and six samples were collected at each site (outlined in Environmental Concentrations Section 8.3.2). The highest levels of both MMT and total Mn were found at petrol stations (MMT, total and respirable Mn were 12, 141 and 35 ng/m³ respectively) whilst the highest levels of respirable Mn were found in the vicinity of an expressway (MMT, total and respirable Mn were 6, 127 and 53 ng/m³ respectively). Lower levels of MMT, total and respirable Mn were found in the underground car park (0.4, 78 and 30 ng/m³ respectively).

It should be emphasised that these are environmental monitoring data and their relevance to personal occupational exposures is unclear.

In a limited personal occupational exposure study, Zayed et al. (1994) monitored the exposure of garage mechanics and taxi drivers to airborne Mn (> 0.8 μm) using personal breathing zone air samplers. Ten garage mechanics from the same garage and ten taxi drivers were assessed for 5 consecutive working days and for 2 days off work. For both worker groups, exposure levels were significantly higher at work compared to off-work (Table 8).

Table 8. Personal total manganese exposure of Montreal taxi drivers and garage mechanics (Zayed et al., 1994)

	Off-Work		At Work
	Mean Exposure (ng/m3)	Number of Samples	Mean Exposure (ng/m3)	Number of Samples
Taxi drivers (total)	7	19	24	48
Garage Mechanics (total)	11	8	250	49
Open Workshops	-		152	nr
Closed Workshops	-		314	nr

Garage mechanics showed very high levels of exposure compared to taxi drivers (mean Mn exposures of 250 ng/m³ versus 24 ng/m³ respectively). Moreover, garage exposures varied significantly depending upon whether garage doors were open or closed. Highest levels were measured in closed garages (mean Mn exposure of 314 ng/m³), supporting the notion that automobiles, whether as a result of the inhalation of exhaust or generation of airborne particulates from servicing Mn-contaminated components, are the source of Mn.

A further similar study of personal occupational exposures to Mn from automotive use of MMT was conducted by Sierra et al. (1995) where personal exposures of 35 garage mechanics to airborne Mn (> 0.8 μm) were compared to those of 30 nonautomotive workers. In this study, garage doors were reported “mostly” closed and exhaust gases were not always vented to the outside. The average Mn exposure for garage mechanics at work was even higher than the previous study with Mn exposures at 448 ng/m³ versus 250 ng/m³ respectively (Table 9).

Table 9. Personal total manganese exposure of Montreal garage mechanics and non-automotive workers (Sierra et al., 1995)

	Off-Work		At Work
	Mean Exposure (ng/m3)	Number of Samples	Mean Exposure (ng/m3)	Number of Samples
Non-automotive workers	8	60	44	143
Garage Mechanics	12	59	448	160

Occupational exposures to total (> 0.8μm) and respirable (< 5 μm) Mn particulates in Canada were also studied by Zayed et al. (1996) for 9 taxi drivers and 20 office workers in Toronto. For office workers, the average total and respirable Mn levels measured over 7 days, 24 hours per day were 12 ng/m³ and 10 ng/m³ respectively. Levels were significantly higher for taxi drivers at 28 ng/m³ and 15 ng/m³ respectively. The average fraction of respirable to total Mn was 76-90%.

Personal exposures to airborne Mn were studied in London taxi drivers and office workers in 1995 and 1996 by Pfeifer, Harrison and Lynam (1999) prior to and following the introduction of MMT as a diesel fuel additive. Personal exposures to Mn in total suspended particulates did not increase as a result of MMT introduction. For PM_2.5 Mn particulates, there were no significant differences between exposures of taxi drivers and non-underground railway commuting office workers. Interestingly, underground railway commuting office workers showed significantly higher Mn exposures.

The extrapolation of these data to Australian occupational settings should be conducted with extreme caution. As indicated in Section 8.3, background atmospheric levels of Mn are an order of magnitude lower in Australia compared to Canada and this is attributable at least in part to the more widespread, multifunctional use of MMT in Canada. Also, no data are available to compare overseas and local work practices and these may be subject significantly to local conditions. For example, autorepair, which is identified in the above studies as a critical occupation with respect to exposure to atmospheric Mn, is likely to occur more frequently within closed workshops with greater contact with cars using MMT-supplemented fuels in Canada compared to Australia. Finally, these Canadian studies are only of small duration (1-2 weeks) with small sample sizes and the representativeness of the sampled populations cannot be assessed.

Notwithstanding study uncertainties, these overseas microenvironmental and personal exposure data suggest that automotive maintenance workshops are potential sites of high airborne particulate Mn levels and that garage mechanics may experience relatively high exposures to Mn from MMT use. However, given the potential differences in occupational conditions and extent of use of MMT, it is likely that local occupational exposures to Mn would be significantly less than those of Canada.