Polycyclic Aromatic Hydrocarbons in Work Atmospheres

Occurrence and Determination

Alf Bjorseth

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351092210
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

This book deals with the sources, distribution, analytical methods, and monitoring of Polycyclic aromatic hydrocarbons (PAH) in the occupational environment. It is hoped that this book will make a contribution to understanding the formation and determination of PAH in work atmosphere and that it will make a particular contribution to occupational health projects. Much of the information given in this book has been generating in studies carried out in cooperation with the Norwegian aluminium industry.

Chapter 1

PAH AS OCCUPATIONAL CARCINOGENS

I. HISTORICAL REVIEW

The history of the detection, synthesis, and biological study of polycyclic aromatic hydrocarbons (PAH) is closely related to the establishment of the carcinogenicity of coal tar. Already in 1775, the British surgeon Sir Percivall Pott published studies which indicated increased incidences of scrotal cancer among chimney sweeps in England, resulting from prolonged contact of the skin with coal soot.¹ These chimney sweeps were, as children, forced to climb the narrow English chimneys and remove soot from the inside of the chimney flue. Dr. Pott assumed that the cause of the cancer development was soot and tar. It is, in retrospect, interesting to note that Dr. Pott did not regard scrotal cancer as a serious problem, since it could be removed without the least inconvenience. This part of Dr. Pott’s observations is probably not valid today.

About 100 years later, high incidences of skin cancer were reported among workers in the paraffin refining,² shale oil,³ and coal tar industries.⁴ However, early attempts to produce cancer in experimental animals with the raw materials of these industries were unsuccessful. It was not until 1915 that the Japanese pathologist Yamagiwa and his colleagues at the Imperial University of Tokyo⁵ succeeded in inducing tumors with coal tar. Professor Yamagiwa and his assistant Ichikawa showed⁵ that if they repeatedly painted the inside of the ears of rabbits (two to three times a week), malignant tumors developed at the site of the skin painting after 3 months, and these later proved to be cancer tumors which grew over the whole ear. This was the first time that cancer tumors were produced experimentally by means of chemicals. It is interesting to note that Yamagiwa and Ichikawa made a very good choice by painting the ears of rabbits, since these show very high sensitivity toward experimental carcinogens. If they had painted the skin of dogs or guinea pigs instead of rabbits, they probably would not have found any tumor development. Soon thereafter, Tsutsui⁶ obtained malignant skin tumors in mice also by painting them with coal tar. This was the first experiment with a design that later should prove to be one of the most-used animal models for studies of carcinogenic compounds: skin painting on mice. Following Tsutsui’s observation, other scientists showed that soot could be extracted and that these extracts also produced skin cancer on mice. Therefore, by 1925 it was well established that coal, tar, and soot contained material that was carcinogenic both to animals and to man.

In the 19th century, a discovery was also made which was of basic importance to the chemical understanding of PAH. The recognition in 1865 that carbon atoms could be linked in closed rings was one of the great conceptual advances of chemistry. The discovery was made by August Kekulé.⁷ It is said that he solved the riddle of the structure of the benzene molecule after having a dream in which dancing snakes bit their own tails. From the understanding of the structure of the benzene molecule it was only a short step to the recognition that the naphthalene molecule has two fused benzene rings. The structure of the multiple-ring, or polycyclic compounds will be discussed below.

Soon after Kekulé’s discovery, the classical paper of Berthelot was published⁸ in which he showed that the heating of acetylene formed a tar which contained benzene and other aromatic hydrocarbons. A likely source of the PAH was therefore recognized.

After the animal studies had demonstrated the presence of carcinogenic compounds in coal tar, studies were undertaken to attempt to characterize the carcinogens in this material. All that was known then was that the carcinogenic compounds were concentrated in the high-boiling fractions of the tar. Kennaway and his group at the (then) Research Institute of the Cancer Hospital in London (subsequently the Chester Beatty Research Institute and now the Institute of Cancer Research) started in 1922 a series of chemical and physical studies of coal tar. After years of studies of various synthetic tars and synthesized PAH, they found that the fluorescence spectrum of benz(a)anthracene was very similar to those of the carcinogenic tars, although shifted to longer wavelengths.^9,10 This suggested that the carcinogens in coal tar contained a benz(a)anthracene nucleus with some additional substituents. They then synthesized dibenz(a,h)anthracene and its 3-methyl-derivative. The fluorescence spectra of the two hydrocarbons showed the same characteristic bands as benz(a)anthracene and the tars, now at intermediate wavelengths. When these compounds were tested by skin painting of mice, they were found to produce tumors.¹⁰ This was the first recognition of the carcinogenic activity of a chemical of defined structure.

Shortly thereafter, Hieger and co-workers¹¹ initiated a large-scale isolation of the carcinogen(s) in coal tar. Starting with two tons of pitch, they performed a series of fractional distillations, differential extractions, and crystallizations. The various fractions were characterized by their fluorescence spectra and their carcinogenic activity by skin painting on mice. In the course of about 2 years they had isolated about 7 g of a yellow crystalline material which had the correct fluorescence spectrum and exhibited high carcinogenic activity. This material was found to consist of two isomeric compounds, benzo(a)pyrene (BaP) and benzo(e)pyrene (BeP). Both the synthetic and the isolated samples of BaP were highly carcinogenic.¹¹

By 1930, the English research group had managed to isolate dibenz(a,h)anthracene and BaP, both of which proved to be strongly carcinogenic in skin-painting experiments, and BeP which did not show carcinogenic properties. In the years to follow, the English researchers isolated 60 new compounds and performed in one period 146 different skin-painting experiments simultaneously. During these years, a large number of PAH compounds were isolated and synthesized, and were tested for carcinogenic effects by skin painting.

These studies were the first of a large number of studies of the carcinogenic properties of PAH. By 1976, more than 30 parent PAH compounds and several hundred alkyl derivates of PAH were reported to have some carcinogenic effects.^12,13 This makes PAH and their derivatives the largest single class of chemical carcinogens known today. Recently, the International Agency for Research on Cancer (IARC) made a critical evaluation of all available data on the carcinogenic effect of 32 PAH.¹⁴ It was concluded that 11 PAH were found to be proven carcinogens in experimental animals, 6 were found likely to be carcinogens, 12 had inconclusive evidence, and 3 were proven noncarcinogens. The results from the IARC evaluation are summarized in Table 1.

II. EPIDEMIOLOGICAL EVIDENCES FOR CANCER RISK FROM PAH

To t...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Chapter 1 PAH as Occupational Carcinogens
• Chapter 2 Mode of PAH Formation
• Chapter 3 Physical and Chemical Properties of PAH
• Chapter 4 Sources and Exposure
• Chapter 5 Sampling of PAH in Work Atmospheres
• Chapter 6 Analytical Methods for Airborne PAH
• Chapter 7 Biological Monitoring of PAH Exposure
• Chapter 8 PAH in Different Workplace Atmospheres
• Chapter 9 PAH Profiles and Proxy Methods
• Chapter 10 Methods of Analysis
• Index