Retrospective Exposure Assessment for Benzene in the Australian Petroleum

IndustryGlass, D.C.; Adams, G.G.; Manuell, R.W

and Bisby, J.A. (2000) Annual of Occupational Hygiene, Vol. 44(4),

pp.301-320Presented by Charles Christen, DrPH, Med,

Dec. 2010Exposure Assessment Course (EOH 2504)

DisclaimerThe information supplied in this

power point is taken verbatim from the literature, the reason for this is to provide as accurate an account of the study as possible.

The discussion section is the presenters own words.

BACKGROUND – BENZENE1A colorless liquid with a sweet

odor.Evaporates into air very quickly

and dissolves slightly in water. Highly flammable.Also known as BenzolBenzene has been found in at

least 1,000 of the 1,684 current or former National Priority List (NPL) sites.

1ATSDR, (2007) Toxic Substances Portal - Benzene, August, http://www.atsdr.cdc.gov/PHS/PHS.asp?id=37&tid=14#bookmark01

Industrial Sources and Uses of Benzene (source: ATSDR)

Made mostly from petroleum.

Ranks in the top 20 in production volume for chemicals produced in the U.S..

Various industries use benzene to make other chemicals such as:◦ Styrene (for Styrofoam®

and other plastics)◦ Cumene (for various

resins)◦ Cyclohexane (for nylon

and synthetic fibers).

Used in the manufacturing of some types of:◦ Rubbers,◦ Lubricants◦ Dyes◦ Detergents◦ Drugs,◦ Pesticides.

Also present in:◦ Crude Oil◦ Gasoline◦ Cigarette Smoke

Natural Sources include:◦ gas emissions from

volcanoes and forest fires

Exposure to Benzene (source: ATSDR)Exposure of the general population to benzene

mainly occurs through breathing air that contains benzene.

The major sources of benzene exposure:◦ Tobacco smoke◦ Automobile service stations◦ Exhaust from motor vehicles◦ Industrial emissions.

Vapors (or gases) from products that contain benzene, such as:◦ Glues, Paints, Furniture Wax, and Detergents

Approximately 1/2 of the exposure to benzene in the United States results from tobacco smoke.

Auto exhaust and industrial emissions account for about 20% of the total national exposure to benzene.

Exposure to Benzene (con’t)Measured levels of benzene in outdoor

air have ranged from 0.02 to 34 parts of benzene per billion parts of air (ppb) ◦1 ppb is 1,000 times less than 1 ppm.

People living in cities or industrial areas are generally exposed to higher levels of benzene in air than those living in rural areas.

Individuals employed in industries that make or use benzene may be exposed to the highest levels of benzene.

Exposure to Benzene (con’t)For most people, the level of exposure to

benzene through food, beverages, or drinking water is not as high as through air.

Exposure can result from breathing in benzene while showering, bathing, or cooking with contaminated water.

Benzene may find its way into ground and surface water through leaks and spills from underground gasoline storage tanks or from landfills and hazardous waste sites

Health Effects of Benzene Exposure (source ATSDR)The major factors related to health risk

from exposure to a toxic substance include:◦Amount a person is exposed ◦Length of time of the exposure.

Brief exposure (5–10 minutes) to very high levels of benzene in air (10,000–20,000 ppm) can result in death.

Lower levels (700–3,000 ppm) can cause drowsiness, dizziness, rapid heart rate, headaches, tremors, confusion, and unconsciousness.

Health Effects of Benzene Exposure (Con’t)Breathing benzene for long periods may

lead to harmful effects in the tissues that form blood cells, especially the bone marrow.

Exposure to benzene may be harmful to the reproductive organs

The Department of Health and Human Services has determined that benzene is a known carcinogen

Both the International Agency for Cancer Research and the EPA have determined that benzene is carcinogenic to humans.

Study Background2

Study initiated from results reported from the Health Watch Epidemiological Health Surveillance program.

Health Watch is an epidemiological health surveillance program conducted by the University of Melbourne on behalf of the Australian Institute of Petroleum (AIP) since 1980.

2The following material is taken from the study found in the title for this presentation.

Study Background (con’t)Prospective cohort study of:

◦ All-cause mortality and cancer incidence◦1988 nested case-control study of lympho-

haematopoietic (LH) cancers and benzene. Participation in the cohort is voluntary and

consists of all employees◦Except head office staff and those employed at

sites with fewer than 10 employees. Approximately 95% of eligible employees in

the industry have participated in surveys.An employee is taken into the cohort after

working 5 years in the industry and remains for life.

Study Background (con’t)Early evidence from the cohort

surveys showed that there was an excess of lympho-haematopoietic (LH) cancers in workers in the Australian Petroleum Industry that was twice that expected in the Australian male population and was statistically significant.

Study Background (con’t)Numerous industry studies have

shown benzene exposure to be associated with leukemia and multiple myelomas. ◦ (N=14, between 1964-1996)

The risk of leukemia after exposure to low concentrations of benzene has been debated over the past 20 years. ◦ (N=13, between 1977-1966)

Study Background (con’t)In 1993 early reports of the

nested case-control study showed a dose-response relationship based on a qualitative exposure ranking system for benzene

By 1996 there were 65 LH cancer cases each matched to five controls on year of birth

Purpose of the Study

To use quantitative exposure assessments of exposure to benzene for each individual

subject in the nested case-control study because a more sophisticated exposure

assessment of cases and controls was needed.

MethodNine year retrospective study

◦1981-1983 & 1986-1987 & 1991-1993 & 1994N = 390 The authors stated that the methodology

developed and used closely followed other petroleum industry studies in the USA, Canada and the UK.

Five occupational hygienists from the largest petroleum companies collaborated and reviewed the exposure assessment process.

Method (con’t)Job histories complied from the subjects

(case and control) through interviews conducted in person or by phone.◦Company◦Site worked per week◦Area of work for each calendar period in years

and months◦Names and identification of cases and controls

were not included in the data.Information provided by the subjects was

cross-checked with company records and rechecked by the individual.

Method (con’t)Site Information (N=209)

◦ Each site were subjects worked or had been located was contacted and asked to provide a brief site assessment form

◦ A follow up was performed by one of the five occupational hygienists.

◦ Questionnaire to gather information on: History of the site Major changes in staffing, plant, product and technology

Job Specific Questionnaires◦ Tasks◦ Technology◦ Products for relevant job activities◦ Spills, Skin Contact, Cleaning Regimes ◦ Other sources of exposure

Exposure Assessment ModelMajor exposure modifying factors (K-

factors) were identified for each specific task

Measured benzene exposure data was available for some current tasks and most jobs but not for all sites.

Time periods were identified for all job/activity/site along with specific tasks

No measured data available the benzene exposure was estimated using an alogrithm developed from two previous studies.

Exposure Assessment Model FormulasTask estimates (TE) of exposure for

individual tasks(TEijk) = BE x Ki x….Kx

BE = Base Estimate, i = task, j = activity of job k (in ppm), K = factors adjusting BE, i = 1

Estimated average (AE) benzene concentration (in ppm) for a subject during a particular activity.(AEjk) = S of njk TEijk x (Tijk/Aik)

Tijk=average time in hours/week on task iAik = average time in hour/week on jk

Exposure Assessment Model FormulasWorkplace estimate (WE) of exposure for

the job k (in ppm) and nk is the number of activities for each job k.(WEijk) = S of nk (j=1) AEijk x (Ajk/35hour week)

Cumulative Estimate (CE) is the exposure associated with each of the job titles held by the subject as recorded in the job history

CE = S of n (k=1) WEk x (Yk) Yk = number of years spent in job kN = total number of jobs for the subject

Estimated Average of Exposure = CE/Ytotal

Base Estimates (BE) Data for BE were obtained primarily from the participating

petroleum companies in Australia. When there was no Australian measurable data it was taken

from the literature (primarily CONCAWE3) A small amount of historic monitoring data from the Risk

Management Division of the New South Wales WorkCover Authority

Refinery and Terminal background values were taken from exposure measured on employees carrying out jobs considered by the petroleum industry occupational health to have been non-exposed.

Exposure monitoring data from the New South Wales Commonwealth Scientific and Industrial Research Organization (CSIRO) and Victorian Environmental Protection Authorities (VEPA) were used for the urban and rural background values

3The oil companies European association for environment, health and safety in refining and distribution

Criteria for BE Only person exposure data was used which had not been

normalized to an 8 hour average and included the title of the work monitored, job site/location and duration of monitoring

Incomplete data used only when no other data was available Data was unacceptable if there was inadequate information

on the monitoring method. Information always accompanying data:

◦ Limit of detection (dl), the technology in use, the products being handled.

Samples of less than 180 min duration were excluded. Data collected over less than 12 min and below dl were

excluded. A value of .5 dl was used where results were below the dl Arithmetic means of the data were used for the BE Skin exposure rating was not developed because little

benzene is absorbed through the skin.

ResultsThe CE’s ranged from 0.005 to 50.9 ppm-

years (m =5.0 ppm-years, sd =7.0 ppm-years).Estimates of average benzene

concentration ranged from 0.001 to 1.7 ppm (m =0.24 ppm, sd =0.28 ppm).

The estimates of average benzene concentration was <1 ppm for 97% and < 0.5 ppm for 84% of study subjects.

Overall exposures to benzene in the Australian petroleum industry were low.

(all activities and jobs < time weighted average of 5 ppm.)

LimitationsMuch of the data was taken from the literature,

and individual exposure data, especially for long term exposure, was lacking.

The authors state that “the information most usually omitted from the data were circumstantial details around the monitoring. “

Accidental and leak exposure was not taken into account.

The values ascribed to some exposure modifiers were subjective and since BE’s and exposure modifiers form the basis of the exposure estimation algorithm the resulting estimates are uncertain.

LimitationsThe authors also state “the

exposure estimates in the Australian petroleum industry have often been made for compliance purposes or to check “worst case” scenarios rather than having been based on sampling strategies and methods designed to yield data for use in epidemiology programes.”

DiscussionA glaring issue compromising the exposure

data is that the companies provided the benzene monitoring data rather than independent occupational hygienists.

The monitoring procedures were not described in the article.

The data used from the literature is most frequently data provided by industry for industry.

Smoking and truck traffic are major sources of benzene, it was unclear how this data was taken into account in the study.

DiscussionThis is a retrospective study with

many gaps in data and estimations.

Retrospective studies typically involve recall bias, and missing data.

Retrospective studies for exposure assessment are usually not reliable and used most infrequently.