Vol. 23, No. 4
from the World Health Organization
Vinyl Chloride, Environmental Health Criteria No. 215
1999, xxi + 356 pages (English, with summaries in French and Spanish),
ISBN 92-4-157215-9, CHF 72.-/USD 64.80; In developing countries: CHF
50.40, Order No. 1160215.
This book evaluates the risks to human health and the environment posed
by exposure to vinyl chloride, a colorless, flammable gas manufactured
almost exclusively for use in the production of polyvinyl chloride (PVC).
PVC is used to produce plastic materials having wide applications in
the building sector, packaging, electrical appliances, medical care,
agriculture, the automotive industry, and toys.
Conclusive evidence that vinyl chloride causes cancer in humans led
to the lowering, in the early 1970s, of occupational exposure limits
in several countries. At the same time, many countries imposed restrictions
on the levels of residual vinyl chloride permitted in PVC, thus reducing
the risk that residues in packaging materials might contaminate food
items, pharmaceutical products, and cosmetics. A chapter on sources
of human and environmental exposure covers production levels and processes,
noting the recent geographical expansion of production plants to Southeast
Asia, Eastern Europe, the Indian subcontinent, and oil-producing countries.
Production technologies that lead to lower residual levels of PVC are
also briefly described. A review of data on the environmental fate of
vinyl chloride notes that environmental releases are almost entirely
in the vapor phase. Vinyl chloride is rapidly volatilized and removed
from surface water and soil, but is not easily biodegraded. Evidence
suggests some bioaccumulation within the food chain, but no biomagnification.
Concerning human exposure, the report concludes that atmospheric concentrations
in ambient air are low, resulting in very little exposure of the general
population. Much higher concentrations have been recorded near industry
and waste disposal sites, and following accidental spills, including
spills of chlorinated solvents in dry cleaning shops. Findings confirm
a reduced risk of exposure for the general population via residues in
packaging materials. The report identifies inhalation as the main route
for occupational exposure, which occurs primarily in plants producing
vinyl chloride and PVC. A chapter on kinetics and metabolism in laboratory
animals and humans concludes that vinyl chloride is rapidly absorbed
and widely distributed following exposure via the inhalation and oral
routes. Following inhalation, the main metabolic route involves oxidation
to form chloroethylene oxide, which is rapidly transformed to chloroacetaldehyde.
Effects on laboratory mammals and in vitro test systems have been extensively
studied. The compound shows low acute toxicity when administered by
inhalation. Long-term feeding studies in several species show significantly
increased incidences of liver angiosarcoma, hepatocellular carcinoma,
and tumors at several other organ sites.
An assessment of effects on humans draws on clinical findings following
accidental exposures, supported by a large number of well-designed epidemiological
studies of occupationally exposed workers. Apart from defining the symptoms
of "vinyl chloride illness", these studies provide strong and consistent
evidence that vinyl chloride causes the rare tumor, angiosarcoma of
the liver. Brain tumors and hepatocellular carcinoma may also be associated
with exposure, though the evidence is less conclusive.
On the basis of this analysis, the report calls for measures to minimize
emissions at production sites and sanitary landfills, and to ensure
low residual levels in PVC. Moreover, as vinyl chloride is a known carcinogen,
the report stresses the need to keep occupational exposures as low as
possible and to educate workers about the risks involved and the need
for safe working procedures.