DERMAL EXPOSURE TO POLYCYCLIC AROMATIC HYDROCARBONS AMONG FINNISH COKE OVEN WORKERS

L. Pyy, M. Mäkelä, Oulu Regional Institute of Occupational Health

Aapistie 1, FIN-90220 Oulu, Finland

The exposure of workers to polycyclic aromatic hydrocarbons (PAH) was studied at a Finnish coking plant during the seven years period in 1988-94 since the beginning of production. Hygienic measurements including dust and vapour sampling were performed. Measurements suggested that the progress of working conditions has been very favourable because the mean exposure level of shift workers to benzo(a)pyrene (BaP) has decreased from 2.5 µg/m³ to 0.3 µg/m³. The mean concentration of 1-pyrenol in urine has been 0.2 µmol/mol creatinine in the last years of stydy. It is very close to the refererence limit recommended in Finland for non exposed. The maximum concentration reaches the biomonitoring action level (2.3 µmol/mol creatinine) recommended for pyrenol⁽¹⁾.

The results have been previously published on biomonitoring and occupational hygiene^(2,3,4). In last decade several studies have indicated that among coke oven workers, the skin is the main route of uptake of PAHs^(5-10).

On the basis of that situation a new more comprehensive study has been started with a view to plan measures for control the skin exposure. The purpose of the study was to measure the dermal pyrene uptake of the workers. The intention was also by means of field measurements to further develope evaluation methods for dermal PAH exposure.

In the occupations where dermal exposure will prove remarkable the aim was to improve personal hygiene and working methods as well as to intensify the use of proper personal protective means and overalls.

After the study phases in 1988 - 94 the follow up of exposure has been continued as a routine occupational hygiene services and biomonitoring.

In connection of occupational hygienic measurements in1998 also dermal exposure was tentatively estimated among three workers.

In 1999 33 cokeoven workers participated in the dermal exposure study. The main part of them has also participated in earlier study phases and their exposure levels have been annually followed up at regular intervals if the BaP concentration exeeds the level of 1 µg/m³. With these criteria the regular follow up refer to the occupations of gas workers, larry car operators, relief workers, maintenance workers and all workers in day shift.

Skin contamination samples were taken as two hours intervals. Samples were collected with washing method and with exposure pads.

The washing method was the reference method for which the subjects washed their hands with 3 ml of sunflower oil and hands were wiped with a disposable tissues. The tissues were extracted with pentane/DMSO⁽¹¹⁾ and analyzed for PAH compounds (EPA 610) with a same method used for air samples⁽¹²⁾. That PAH profile includes etc. naphthalene, pyrene and bentso(a)pyrene.

The skin contamination of the workers was measured with activated exposure pads, which were fastened in tentative first three tests with adhesive tape on wrist and in actual study in last september on back of hand. Commercial filter disks were used as adsorbing material. The area of filter was 12 cm². The aim was to collect four successive samples from every worker (altogether 132 pads). In practise it was possible to get from some workers only two or three samples because their working hours were short and thus the total number was 111 pads. The pads were analyzed for PAHs and the intention is to compare results with washing method. This comparison is not ready yet and it is possible to compare only the tentative results of the year 1998.

PAH compounds were collected during 8 working hours on filters as personal and stationary sampling. Personal samples were collected in the breathing zone of all the study subjects and stationary samples in the control cabin of larry car and at four working areas on the top of the battery.

Urine samples were collected as morning specimens (0600) and after the working shift (1400). Besides spot samples workers were requested to collect also 24 hours samples (in the evening and next morning). Urine samples were stored at - 20 ^oC and analyzed for 1-pyrenol⁽¹³⁾. In that paper only the results of post-shift samples will be discussed.

The first tentative measurements of skin contamination in May 1998 indicated following figures. Pyrene contamination in wipe samples was 7 – 48 ng/cm² and on pads 1 – 31 ng/cm². The pyrene concentration in the breathing zone was 4 – 8 µg/m³ and the average urinary 1-pyrenol concentration 41 nmol/l wich approximate 4.7 µmol/mol creatinine. According to the model of Leung and Paustenbach⁽¹⁴⁾ it may be estimated that under these air concentrations the respiratory pyrene dose is less than a third of total pyrene and the dermal pyrene uptake is 66 – 86 % of the total absorbed amount of pyrene. These results are consistent with earlier published results⁽⁵⁾.

Tentative results demonstrate that exposure pads slightly underestimates skin exposure as ompared with oil washing results (skin wipes) but still indicate the level of exposure very well. It is interesting to compare the collection efficiency of a pad and washing method. As an example the picture represents the results of one of the three tested workers. The PAH concentrations on pad are compared to those measured by oil wash method. For particle bound PAHs the collection efficiency of exposure pad is good partly because of its dimensions, about 1,3% of the area of hands. Since fluoranthene and pyrene the difference is small and the peak heights are nearly comparable with each other.

The table describes the statistics of pad samples in the actual study in last September. The concentration/area are calculated generally as a sum of four two hours samples. Air concentrations are full shift figures and pyrenol results post-shift figures.

It seems also that a significant correlation between pyrene on exposure pads, in personal air samples and in post-shift urinary pyrenol was found.

Finnish coking plant workers have been exposed to benzo(a)pyrene concentrations on average 0.3 – 4 µg/m³. During 1994 BaP concentration was on the level of 0.3 µg/m³ and exposure levels in the first years of production were lower than in many older coking plants. For example the exposure level of Swedish coking plant workers (16 personal samples) to BaP was on average 4 µg/m³ (median, variation 0.9 - 37 µg/m³) before the renewal of the coking plant⁽¹⁵⁾ and after repair work the median of the BaP concentration has been 0.7 µg/m³.

In May 1998 it was found that the PAH concentration in the air was surprisingly increased. In Tables I and II this data are presented for benzo(a)pyrene (BaP). The average BaP concentrations in the personal samples of the shift workers in 1998 and 1999 were 1.4 and 1.0 µg/m3 respectively. During the years 1998-99 all measured BaP concentrations, with the exception of one in both year, were below the Finnish TLV of 10 µg/m³. In 1998 the maximum concentration of 12.1 µg/m³ appeared in one of the maintenance workers who changed a gasket of a steam tube and wore respirator during measurement (Table I). In 1999 the exception arose as the result of one deck worker who had a high spot exposure during one day and wore also respirator. However even with the gas workers the average exposure level was less than 1 µg/m³.

Average pyrene concentrations were 4.4 and 1.3 µg/m³ in 1998 and 1999 respectively.

This situation is not caused by the selection of workers to most exposed because also stationary measurements which were performed at the permanent sites indicated the same tendency. In the stationary samples the concentration 78.7 µg/m³ measured on top of the battery were the highest (Table II) and may represent the worst, extreme condition.

The 1-pyrenol results of all urine samples are presented in Table III. (The considerable differences between the arithmetic and geometric averages (medians) show that the 1-pyrenol concentrations are rather distributed logarithmically normally than normally.) Before the commencement of the coking plant the arithmetic average of concentrations was 3.7 nmol/l and the average values increased slightly during the first two years of operations (8.3 during 1988 and 6.2 in 1989). The average concentration has remained on the same level of 2 - 4 nmol/l from 1990. In the series of 1993 and 1994 the pyrenol concentration rose slightly during the work shift, but the change in pyrenol concentrations did not correlate with the pyrene concentration of the air.

The average concentrations of urinary 1-pyrenol of 2 - 8 nmol/l (0.1 - 0.6 µmol/mol creatinine) are low if these are compared to the recommended biological exposure limit (BEL) of 20 nmol/l (2.3 µmol/mol creatinine) for coking plant workers⁽¹⁵⁾. The median pyrenol concentrations of Swedish coking plant workers before renewal have been 40 nmol/l (variation 3 - 260) (4.67 µmol/mol creatinine, variation 0.33 - 30)⁽¹⁵⁾. After the renewal the median has been 11 nmol/l (variation 3 - 49) (1.27 µmol/mol creatinine variation 0.33 - 5.67). The 1-pyrenol median of 24 non-exposed persons in the same study has been 0.5 nmol/l (0.06 µmol/mol creatinine).

In years 1998 and 1999 also the mean urinary 1-pyrenol concentrations 17.6 and 9.4 nmol/l were increased clearly if compared with the level in 1994. The maximum concentrations of 60 - 70 nmol/l appeared in the samples of maintenance workers.

Partially tentative results of our skin absorption study indicate that the skin contamination caused by PAHs is significant also among Finnish coke oven workers. It is to be expected that processing of reseach results will give more information about the significance of the dermal uptake. The study report for sponsor will be completed at the end of this year.

The sampling efficiency of tested exposure pads seems to be higher than that of commonly used polypropylene pads and seems to approach the efficiency of skin.

Significant correlation between pyrene on pads, air pyrene and urinary pyrenol seems to appear. The importance of biomonitoring by means of urinary pyrenol will emphasize also in our conclusions. It is evident that the research of dermal exposure of PAHs is further needed.

It is also evident that prevention measures should be focused on the reduction of dermal contamination and that personal factors such as personal hygiene, individual working methods and use of protective clothing influence the skin contamination of PAHs.

The authors wish to express their gratitude to the Finnish Work Environment Fund for economic support.

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Table I. Concentrations of Benzo[ a] pyrene at a Finnish Coking Plant (µg/m³); Personal Dust Samples.

Table II. Concentrations of Benzo[ a] pyrene at a Finnish Coking Plant (µg/m³); Stationary Samples.

Table III. Urinary 1-Pyrenol Results (nmol/l) Among Coke Workers During All Study Phases.

Notes: Pre, pre-shift sampling; Post, post-shift sampling.