Chemistry International
Vol. 21, No. 4
July 1999
New
Books and Publications
New
Publications from the World Health Organization
Selected Nonheterocyclic Polycyclic Aromatic Hydrocarbons, Environmental
Health Criteria, No. 202
This book evaluates the risks to human health and the environment posed
by exposure to 33 nonheterocyclic polycyclic aromatic hydrocarbons (PAH),
of which benzo[a]pyreneis the most extensively investigated. Compounds
from this large class were selected for evaluation on basis of abundant data
documenting toxic effectsincluding carcinogenicity. More than 2 000 references
to recent literature are included.
The book opens with a discussion of physical and chemical properties of PAH
relevant to their toxicological ecotoxicological evaluation. Chapter 2, on
sources of human and environmental exposure, notes that PAH are ubiquitous
in the environment, with the largest emissions resulting from incomplete combustion
of organic materials during industrial processes and other human activities.
The most important sources are identified as coal coking; production of aluminum,
iron, and steel; heating in power plants and residences; cooking; motor vehicle
traffic; environmental tobacco smoke; and the incineration of refuse. Data
on the environmental behavior of PAH are discussed in Chapter 3, which cites
evidence that PAH accumulate in organisms in water and sediment and in their
food, and that sediment and soil are the principal environmental sinks. Because
most organisms have a high biotransformation potential for PAH, the report
concludes that biomagnification is unlikely to occur.
A chapter on environmental levels and human exposure summarizes results from
numerous studies aimed at detecting concentrations in the general environment,
in indoor air, and in various occupational settings. For the general population,
the main sources of exposure are identified as polluted ambient air, smoke
from open fireplaces and cooking, environmental tobacco smoke, contaminated
food and drinking water, and the use of PAH-contaminated products. Evidence
shows that PAH are formed during food processing, roasting, frying, and baking.
In occupational settings, exposure occurs via the lung and skin, with the
highest exposures occurring during the processing and use of coal and mineral
oil products, such as in coal coking, petroleum refining, road paving, asphalt
refining, and impregnation of wood with creosotes. High concentrations have
also been detected in the air of aluminum production plants using coal/pitch
electrodes, and steel and iron foundries.
A review of data on kinetics and metabolism cites evidence that PAH are absorbed
through the pulmonary tract, the gastrointestinal tract, and the skin, and
are widely distributed throughout the organism following administration by
any route. Although these lipophilic compounds have been detected in almost
all internal organs, levels are highest in organs rich in lipids. Knowledge
about the complex metabolism of PAH, which sheds light on mechanisms of carcinogenic
action, is also considered in detail.
The most extensive chapters assess the large number of studies of toxic effects
in laboratory mammals, in vitro test systems, and humans, giving particular
attention to evidence of carcinogenicity. Findings from animal studies and
in vitro tests confirm the carcinogenicity of 17 compounds. Many others
are known to be mutagenic. While data indicate a relationship between the
site of tumor development and the route of administration, PAH can induce
tumors at other sites as well, because tissues such as the skin can metabolize
PAH to their ultimate metabolites, and metabolites formed in the liver can
reach various sites via the bloodstream. Current theoretical explanations
for the carcinogenic action of PAH are considered in detail. The report also
cites animal studies demonstrating the immunotoxic potential of a number of
PAH.
In view of the paucity of data on human exposure to single, pure PAH, the
chapter on health effects in humans draws on findings from epidemiological
studies of occupational and environmental exposures to mixtures of PAH. These
studies confirm the association between exposure to PAH and an increased risk
of cancer in humans. Increased lung tumor rates linked to exposure were found
in coke-oven workers, asphalt workers, and workers in Soderberg potrooms of
aluminum reduction plants. The highest risk was found for coke-oven workers.
In aluminum plants, adverse effects included increased risk of urinary bladder
cancer, asthma-like symptoms, lung function abnormalities, and chronic bronchitis.
Adverse effects on the immune system were also documented in several studies
of exposed workers. The report further concludes that PAH are almost certainly
one of the carcinogenic agents responsible for lung cancers in cigarette smokers.
Selected Nonheterocyclic Polycyclic Aromatic Hydrocarbons, Environmental
Health Criteria, No. 202 1998, xxii + 883 pages (English with summaries in
French and Spanish), ISBN 92 4 157202 7, CHF 174.-/USD 156.60; In developing
countries: CHF 121.80, Order no. 1160202.