Annals of Occupational Hygiene Advance Access originally published online on January 13, 2005
Annals of Occupational Hygiene 2005 49(3):233-240; doi:10.1093/annhyg/meh083
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© 2005 British Occupational Hygiene Society Published by Oxford University Press;
Original Article |
Evolution of Occupational Exposure to Environmental Levels of Aromatic Hydrocarbons in Service Stations
Instituto de Seguridad y Salud Laboral, c/Lorca 70, 30120 El Palmar, Murcia, Spain
* Author to whom correspondence should be addressed. E-mail: JuanF.Periago{at}carm.es
ABSTRACT
During refuelling, people may easily be exposed to extremely high levels of gasoline vapour for a short time, although such exposure takes on more importance in the case of service station attendants. The volume of gasoline sold in refuelling operations and the ambient temperature can significantly increase the environmental level of benzene, toluene and xylene (BTX) vapours and, subsequently, the occupational risk of service station attendants. This is especially true in the case of benzene, the most important component of gasoline vapours from a toxicological point of view. The European Directive 98/70/EC, limiting the benzene composition of gasoline, and 94/63/EC, concerning the use of vapour recovery systems in the delivery of gasoline to services stations, were applied in Spain from January 2000 and 2002, respectively. In addition, a new limit value for occupational exposure of 3.25 mg/m3 was fixed for benzene in Directive 97/42/EC, applied from June 2003. However, recent years have seen the growing use of diesel as well as of unleaded and reformulated gasoline. In this study, we analyse the differences found between air concentration levels of BTXs in 2000 and 2003, analysing samples taken from the personal breathing-zone of occupationally exposed workers in service stations. The results are compared with those obtained in a similar study carried out in 1995 (before the new regulations came into force). The study was carried out in two phases. The first phase was carried out in 2000, after application of the new legal regulation limiting the benzene concentration in gasoline. In this case, an occupationally exposed population of 28 service station attendants was sampled in July, with a mean ambient temperature of 30–31°C. In the second phase, 19 exposed subjects were sampled in July 2003, one of the warmest months in recent years with mean temperatures of 35–36°C during the time of exposure monitoring. The results were then compared with those obtained in 1995, for similar summer weather conditions (environmental temperature between 28 and 30°C). A significant relationship between the volume of gasoline sold and the ambient concentration of aromatic hydrocarbons was found for each worker sampled in all three of the years. Furthermore, a significant decrease in the environmental levels of BTXs was observed after January 2000, especially in the case of benzene, with mean time-weighted average concentrations for 8 h of 736 µg/m3 (range 272–1603) in 1995, 241 µg/m3 (range 115–453) in 2000 and 163 µg/m3 (range 36–564) in 2003, despite the high temperatures reached in the last mentioned year.
Keywords: benzene • environmental levels • gasoline • occupational exposure assessment • volatile organic compounds
INTRODUCTION
Gasoline is a complex mixture of low molecular-mass compounds, mainly paraffinic, naphtenic, olefinic and aromatic, with a carbon number typically within the range 3–11. Its composition varies depending on the crude origin and the refining process. The occupational exposure of service station attendants and other workers to gasoline vapours during the loading and unloading tasks and during the transport of fuels may be substantial because of the high levels of gasoline vapours emitted. Among other chemical hazards, the group of aromatic components of gasoline constituted by benzene, toluene and xylenes (BTXs) are considered to be the most hazardous components, especially benzene because of its known carcinogenic properties, according to several organizations, such as the International Agency of Research on Cancer IARC (1982)
, American Conference of Governmental Industrial Hygienists ACGIH (2003), Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area DFG (2002) and EPA (2002). This fact has also been emphasized by many other authors (Carere et al., 1995; Tondel et al., 1995; Hayes et al., 2001). European Directives 90/394/ECC (1990) and 97/42/EC (1997) consider that benzene is a carcinogen present in many work situations and that a large number of workers may be exposed to a potential health risk. While current scientific knowledge is not such that a given level can be established below which risks to health cease to exist, a reduction in exposure to benzene will nonetheless reduce these risks. For this reason, the directive established a new limit value for the occupational exposure to benzene.
This type of exposure has been evaluated by many authors (Carere et al., 1995; Moen et al., 1995; Javelaud et al., 1998; Liljelind et al., 2000; Peretz et al., 2000) and, more recently, studies focused on the risk for self-service operations have been carried out (Vainiotalo et al., 1999; Egeghy et al., 2000). Monitoring methods based on dynamic or diffusive procedures for personal exposure to gasoline vapours have been developed.
In a previous study carried out in 1995, the environmental levels of BTX were measured in the breathing zone of service station attendants. This evaluation was made during two different periods of time with quite different temperatures (March and July), analysing the influence of temperature and volume of gasoline sold during the exposure time. The results obtained showed that both variables could significantly increase the environmental levels of gasoline vapours and, subsequently, the risk of occupationally exposed workers (Periago et al., 1997). Since then, technical specifications for gasolines have been changed and technical solutions have also been designed to reduce the occupational risk.
Since January 2000, the technical specifications for gasolines specified in the European Directive 98/70/EC (1998) have been applied throughout the European Union. This new regulation reduces the content of benzene, which must be <1% v/v instead of the previous 5%, and also regulates the technical specifications of ‘unleaded’ gasoline. Since this would have influenced the conditions of occupational exposure, we thought it would be interesting to study how the time-weighted concentration levels of aromatic hydrocarbons from gasoline vapours have changed. In addition, the establishment by European Directive 97/42/EC of a new limit value for the occupational exposure to benzene of 3.25 mg/m3, which has been effective since June 2003, means that this is an opportune time to compare the occupational levels of this compound with the current limit value.
In this study, we evaluated the occupational exposure of service station attendants to aromatic vapours (BTX) in two phases. The first phase was carried out in 2000, after the legal modification that had limited the maximum content of benzene in gasoline and promoted a greater use of unleaded gasoline, and the second phase in 2003, after new legal regulation concerning the storage and distribution of gasolines. From this date onwards, all new road tankers need to be capable of accepting vapours emitted during the transfer of fuel to storage tanks at service stations and Stage I vapour recovery systems must be in use. The samples were always collected in July, one of the warmest months of the year, with high environmental temperatures. During July 2003, the environmental temperatures were even higher than usual.
The goal of this study was to evaluate the occupational exposure of service station attendants to BTX compounds in 2000 and 2003 and, taking as a starting point the results obtained in July 1995, to analyse the evolution of environmental levels of aromatic hydrocarbon vapours, relating the findings with technical and legal modifications carried out in the same period.
METHODS
Study description
The study was carried out in two phases, in 2000 and 2003. In the first year, 28 occupationally exposed workers were monitored in July, while in the second year, 19 exposed workers were monitored in the same region and same summer weather conditions (July).
All the experimental studies were carried out in service stations within a reduced geographical area of south-east Spain and near a meteorological station. In all phases of the study, the samples of air obtained from the personal breathing-zone of service station attendants were collected on the same day of the week. For each exposed subject, the volume of gasoline dispensed during a particular sampling time was registered. Mean environmental temperatures during the sampling time were taken from the automatic register of the nearby meteorological station.
Exposure measurements
The concentration of BTX in ambient air was monitored continuously for each worker with a 3M-3500 personal diffusive sampler badge attached to the clothing within the breathing zone throughout the whole working shift. These samplers, which are designed to measure average concentrations over a measured time interval, require no sampling pump because the contaminants enter by diffusion and are adsorbed on activated charcoal inside the badge. The amount of contaminant adsorbed is determined from the exposure time and contaminant concentration present in the sampled environment. The experimental conditions of sampling are shown in Table 1.
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The diffusive samplers were desorbed with 1.5 ml of carbon disulphide for 30 min. Volumes of 3–5 µl were injected into a gas chromatograph, equipped with a split–splitless injector and a flame ionization detector. The compounds were separated in a cross-linked methyl silicone capillary column 50 m long x 0.2 mm internal diameter, with a phase thickness of 0.5 µm. We used helium at 180 kPa as the carrier gas with a split-ratio of 1:20. Injector and detector temperature was 200°C, and the oven temperature was programmed from 40 to 130°C. The weight of every organic contaminant, as determined by gas-chromatographic analysis, was converted to the time-weighted average concentration in air. The specific sampling rates (SR) used to calculate the time-weighted average concentration of each compound were 35.5 ml/min for benzene, 31.4 ml/min for toluene and 27.3 ml/min for xylene (3M, 2000
).
RESULTS
Between 1995 and 2003, there was a significant change in the type of engine bought by the average motorist. A progressive increase in the number of diesel motors sold was matched by a decrease in the proportion of gasoline engines. The type of fuel sold during each phase of the study is shown in Fig. 1. Furthermore, this period also saw a gradual change from leaded to unleaded gasoline. The percentage of unleaded gasoline sold in the refuelling stations involved in the 1995 study was 23%, whereas in 2000 it was 53%, which rose to 81% in 2003.
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Table 2 shows the occupational exposures of service station workers, expressed as time-weighted average concentrations for 8 h, corresponding to 2000 and 2003, together with the previously reported results corresponding to 1995 (Periago et al., 1997
). During refuelling operations, a volume of air saturated with gasoline vapour is evacuated from the fuel tank of the car, the volume of contaminated air being exactly equal to the volume of gasoline pumped. For this reason, the volume of gasoline sold during a shift will have a decisive influence on the contamination of the air near the respiratory zone of each exposed worker.
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A significant relationship between the levels of aromatic compounds in the air and the volume of gasoline dispensed was found in all cases. Table 3 summarizes the parameters of the regression lines obtained for each compound and period sampled. A similar statistical association was obtained by Lagorio et al. (1994)
between levels of benzene in air and the volume of gasoline sold.
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Since the levels of aromatic compounds in air and the daily volume of gasoline sold are closely related, the aromatic hydrocarbon concentrations in air were standardized, dividing the time-weighted average concentration of each compound by the volume of gasoline sold during the shift, in order to analyse the differences between exposure levels in the three phases of our study. Figure 2 shows the mean of the standardized values of BTX plotted for each period sampled.
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The ANOVA test was used to test the statistical significance of the difference between the means of each pair of the three sample populations corresponding to the three different years studied. The results, summarized in Table 4, show that there was a statistically significant difference between the three means at the 95% confidence level.
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The obtained time-weighted average benzene concentration for each occupationally exposed worker in the second phase of the study (2003) as well as the different limit values for benzene is depicted in Fig. 3.
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DISCUSSION
Current occupational exposure limit values corresponding to BTX set by several institutions are shown in Table 5. The mean value of time-weighted average concentrations of toluene in 1995 was 1167 µg/m3 (range 597–2324) falling to 580 µg/m3 (range 194–1141) and 752 µg/m3 (range 172–2142) in 2000 and 2003, respectively. The exposure levels of toluene for the exposed population studied was always very much lower than the above mentioned limit values. This was also the case for xylene, the mean value of the time-weighted average concentrations decreased from 530 µg/m3 (range 26–5119) in 1995 to 215 µg/m3 (range 91–411) in the first phase of this study, and in the second phase to 315 µg/m3 (range 125–871). Levels of exposure to xylene for the exposed population were also much lower than the limit value. In other words, the occupational exposure risk in service stations by inhalation of toluene and xylene is practically negligible.
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A drastic reduction in the TLV-TWA for benzene from 180 000 to 300 µg/m3 was proposed by ACGIH in 1993–94. However, this proposed value was modified to 960 µg/m3 in the 1996–97 edition of threshold limit values (TLVs). If we compare our results for 1995 with this proposed limit, 20% of those sampled in this period were exposed to time-weighted average concentrations of benzene above this level (Periago et al., 1997
). Finally, from 1998 the limit value adopted by ACGIH was 1600 µg/m3 and only one of the subjects sampled in 1995 was exposed to a concentration slightly above this limit. The maximum values of time-weighted average concentrations obtained in 2000 and 2003 were below this limit. The current OSHA permissible exposure limit (PEL) is 3250 µg/m3, and consequently none of the subjects sampled in the two parts of our study were exposed to concentration levels above this limit. However, if we compare the values obtained in our study with currently recommended exposure limit (REL) proposed by NIOSH, 325 µg/m3, only the mean value of time-weighted average concentration corresponding to 1995 was above this limit value. Nevertheless, the mean values corresponding to 2000 and 2003 were below this limit value. Furthermore, only one of the sampled subjects in the 2003 survey, when temperatures were very high, was exposed to concentration levels above this limit (Fig. 3). The limit value for occupational exposure to benzene adopted in the European Directive 97/42/EC (1997) was 3250 µg/m3, although provisionally, up to June 2003, a limit value of 9750 µg/m3 could be used. None of the subjects sampled were exposed to concentration levels above these two limit values.
The arithmetic mean of time-weighted concentrations of benzene in 1995 was lower than the 1730 µg/m3 reported by Lagorio et al. (1994), who sampled 27 service station attendants, and higher than the 350 µg/m3 obtained in the study carried out in March and April, by Purdham et al. (1994). In 2000, the mean obtained in our study was very close to the reported exposure mean value of 256 µg/m3 obtained among service station attendants in Italy, with its similar climatic conditions to Spain (Brugnone et al., 1997). Nevertheless, the results obtained in our study were higher than the reported mean values of time-weighted concentration of benzene in air breathed by service station attendants of 320 µg/m3 (Carere et al., 1998) and 359 µg/m3 (Meneses et al., 1999). The lowest levels of benzene in air were found in 2003, after legal regulation of the maximum level of benzene permitted in gasoline (1% v/v) and after installation of vapour recovery systems in all the service stations sampled to reduce the emission of benzene vapour during delivery operations from road tankers. The arithmetic mean of benzene time-weighted concentrations for 8 h exposures obtained in our study was 163 µg/m3, which was comparable to the mean values for 8 h exposures in similar jobs, such as drivers of road tankers engaged in out loading operations, carried out in similar conditions, with reduced benzene levels in gasoline and the presence of vapour recovery systems. Thus, our results are similar to the arithmetical mean values of 190 µg/m3 recorded in 11 exposed workers (Talamanca and Salera, 2001) and 150 µg/m3 recorded in 13 exposed workers (Hakkola et al., 2001).
The gradual decrease in the concentration levels of benzene in each of the phases of our study must be emphasized, as can be seen from Fig. 2, which represents the mean values of benzene concentration in air obtained from personal breathing-zone samples of gasoline station attendants in 1995, 2000 and 2003. In order to confirm that the decrease was not due to reduction in the ratio of gasoline/diesel dispensed (Fig. 1), the values were standardized by dividing the environmental concentration in air by the volume of gasoline sold during the shift for each subject sampled. The ANOVA test (see Table 4) showed significant differences between the means of the sample populations corresponding to the three years compared. The levels of benzene in air were also seen to have decreased in other jobs also exposed to gasoline vapours. For example, in the case of car mechanics, values ranging from 6800–1600 µg/m3 (Nordlinder and Ramnäs 1987), 2600 µg/m3 (Popp et al., 1994) and 480 µg/m3 (Javelaud et al., 1998) to a mean value of only 118 µg/m3 (Egeghy et al., 2002) have been reported.
In our country, the observed differences in benzene exposure could be explained by the new specifications concerning the composition of gasolines proposed by Directive 98/70/EC (1998), which established the maximum content of benzene in gasolines as 1% (v/v), and which came into effect in Spain in June 2000. This decrease in the concentration of benzene in gasoline would have resulted in a considerable decrease in levels of benzene vapour in the air breathed by the exposed workers. In addition to this, a new legal regulation came into force in 2002, as a consequence of Directive 94/63/EC (1994), which regulated the emission of volatile organic compounds resulting from the storage of petrol and its distribution from terminals to service stations. From this date (but with a gradual application), the vapours displaced during the transfer of petrol into storage tanks at service stations must be returned by a vapour-tight connection line to the mobile container. This requirement has led to the development of vapour recovery systems (called Stage I), for the storage and distribution of gasoline. All road tankers are now designed to retain and return vapours from storage tanks at service stations during unloading and delivery operations.
Both legal requirements, whose initial objectives were environmental in nature, have contributed to improving the work conditions of service station personnel. Thus, the concentration levels of benzene in air obtained from personal breathing-zone samples of service station attendants in 2003 were the lowest values obtained in the study, in spite of the very high mean temperatures of about 36°C, during exposure time.
An increased risk of cancer is the most hazardous toxicological effect of benzene. The increased incidence of leukaemia (cancer of the tissues that form white blood cells) has been observed in people occupationally exposed to benzene. Using mathematical models based on human and animal studies to estimate the probability of a person developing cancer as a result of breathing air containing a specified concentration of a chemical, it has been estimated that if an individual were to continuously breathe air containing benzene at an average of 13–45 µg/m3 the result would be no greater than a one in 10 000 increased chance of developing cancer (EPA, 2002).
The European Scientific Expert Group for occupational exposure limits estimates that an occupational exposure limit value of 1600 µg/m3 would reduce the range of best estimated lifetime risks down to 0.25–3.3 additional leukaemia cases per 1000 exposed workers (EUR 15091 EN, 1994). The first amendment of Directive 90/394/EC (1990) on exposure to carcinogens at work establishes an occupational exposure limit value for benzene of 3250 µg/m3 over a time-weighted average of 8 h a day. Pressure from certain sectors of industry led to the inclusion of a transition period for selected activities, in which a maximum limit value of 9750 µg/m3 could be allowed. However, some critical comments should also be made, the first concerning the fact that even a limit value of 3250 µg/m3 is equivalent to a mortality risk between 0.5 and 6.6 per 1000 workers during an average working life of 40 years, a possibility that is still quite significant.
The difficulty of establishing the limits that are desirable from a toxicological point of view and of making these limits compatible with the ability of industry to achieve particular levels of control in the workplace, have conditioned the adoption of occupational exposure limits, which are focused on reaching a compromise solution in an attempt to harmonize economic, technological and toxicological aspects. Anyway, these limit values should be revised periodically to adapt them to the technological innovations resulting from technical and scientific research, and in some cases, it may be necessary to adopt working limits, which incorporate safety factors to allow for uncertainties in the underlying risk to health and because of the need to reduce air concentrations to the lowest levels that are feasible (Rappaport, 1991).
The results obtained in our study have demonstrated that the exposure levels of service station attendants to benzene have diminished. According to the mean values obtained in the last phase of the study, which was carried out in unfavourable environmental conditions, in practically all cases exposure levels were below even the most rigorously demanding limit mentioned above (325 µg/m3, REL NIOSH).
CONCLUSIONS
European legal regulations limiting the maximum content of benzene in gasoline and the compulsory adoption of technical procedures that limit the emission of gasoline vapours during storage and transportation operations have led to a notable decrease in the benzene levels recorded in the breathing air of service stations workers, one of the activities with the highest exposure rates to this type of product. This is confirmed by the results obtained in our study, especially those referring to the last phase, when sampling was carried out in some of the most unfavourable climatic conditions of the EU. The fact that in this study the values of benzene in air were much lower than the established limit values strongly suggests that current EU limit values lag behind existing technical possibilities. Because of this, the current limit values for the occupational exposure to benzene in the European Union could perhaps be revised downwards to guarantee greater safety for workers, and to reach values that are nearer the recommendations of scientific committees.
At the same time, the EU should continue implementing technical and legal measures that contribute to reducing both occupational and non-occupational exposure to benzene, since self-service car-refuelling is rapidly becoming the norm. Although, in this case, the short exposure times reduce the intake dose to very low levels, the problem should continue to receive attention, because benzene is a confirmed human carcinogen. The implementation of technical regulations, such as Stage II vapour recover systems, which are designed to reduce the vapour emissions during the refuelling of small vehicles, should be made as soon as possible.
Received April 7, 2004; in final form September 2, 2004
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