Chemistry International
Vol. 22, No. 2
March 2000
New
Books and Publications
New
Publication from the World Health Organization
Polybrominated Dibenzo-p-dioxins and Dibenzofurans,
Environmental Health Criteria No. 205
1998, xxi + 303 pages (English with summaries in French and Spanish),
ISBN 92-4-157205-1, CHF 66.-/USD 59.40; In developing countries: CHF
46.20, Order No. 1160205.
This book evaluates the risks to human health and the environment posed
by exposure to polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated
dibenzofurans (PBDFs). Of no commercial use, these compounds are generated
as unwanted by-products of various industrial and combustion processes
and have been detected as contaminants in a number of brominated organic
chemicals, many of which are used as flame retardants.
Thermolysis of brominated flame retardants is an important source of
emissions, as is the incineration of products containing these flame
retardants, most notably scrap computers and business machines. PBDDs
and PBDFs have also been detected in emissions of motors using both
leaded petrol and unleaded petrol, with and without catalytic converters,
and in emissions of diesel engines.
In view of the complexity of these compounds, the problems with analytical
procedures, and substantial gaps in the experimental database, the report
makes a special effort to determine the extent to which the environmental
behavior and toxic effects of PBDDs and PBDFs resemble those of their
better characterized chlorinated analogs, polychlorinated dibenzo-p-dioxins
(PCDDs) and polychlorinated dibenzofurans (PCDFs). An effort is also
made to determine the extent to which PBDDs and PBDFs contribute to
the overall hazard posed by environmental ìdioxins'.
The opening sections consider currently available analytical methods
for detection and analysis, and discuss the principal sources of human
and environmental exposure. Although data are limited, the available
evidence confirms formation of PBDDs and PBDFs during fire accidents,
especially when electrical appliances are involved, during the use of
flame retardants and fire extinguishers, during waste disposal and treatment,
and during combustion processes in engines. Current environmental levels
are judged to be much lower than those for the ubiquitous PCDDs and
PCDFs. Evidence suggests that occupational exposure may occur in a variety
of workplaces. Workers at greatest risk are those employed in the plastic
and recycling industry, where brominated flame retardants or products
containing them are used; fire fighters; and cleanup personnel associated
with fires. Some monitoring results are also available for exposures
in workplaces equipped with a number of electrical appliances continually
in use, such as displays and computer monitors.
A section on environmental behavior cites evidence that these compounds
are similar to their chlorinated analogs, with preferential distribution
to carbon- or fat-rich compartments and long persistence. Data on kinetics
and metabolism are assessed in the next section, which concludes that
these compounds are distributed throughout the body, with major deposits
found in liver and adipose tissue, followed by skin and muscle.
Data from experimental studies of toxicity support the conclusion that
the thymus, lymphatic tissue, and liver are the principal targets of
toxic action. Thymus atrophy and other signs of immunotoxicity were
the effects most consistently seen in laboratory animals. Data on human
exposures and health effects were judged inadequate to support an assessment
of hazards for the general population or a recommended safe level of
exposure.
In view of the growing worldwide production and use of brominated flame
retardants as additives to a series of polymers, the report concludes
that the amount of bromine-containing waste will be increasing in the
future, and that electronic scrap from casings and printed circuit boards
of computers, flame-retarded with brominated compounds, will reach the
waste streams as a potentially major source of release to the environment.
As the potential for toxic action of these compounds is judged similar
to that of their chlorinated analogs, the report recommends that every
effort should be made to prevent environmental pollution with PBDDs
and PBDFs. To avoid release in the environment, the report further concludes
that brominated flame retardants should be phased out and that all products
flame-retarded with bromine compounds should be labeled and disposed
of only in properly constituted waste incinerators designed to minimize
emissions.