Vol. 23, No. 6
Publications from the World Health Organization
Flame Retardants: Tris(2-butoxyethyl) Phosphate, Tris(2-ethylhexyl)
Phosphate, and Tetrakis(hydroxymethyl) Phosphonium Salts, Environmental
Health Criteria No. 218, 2000, xix + 130 pages (English, with summaries
in French and Spanish), ISBN 92-4-157218-3, CHF 30.-/ USD 27.00; In
developing countries: CHF 21.-, Order No. 1160218.
This book evaluates the risks to human health and the environment posed
by exposure to selected flame retardants, including chemicals widely
used to treat textiles. Although data were inadequate to support a full
scientific evaluation, the report reaches several preliminary conclusions
concerning the likelihood of risks to human health.
Compounds are covered in separate monographs. Tris(2-butoxyethyl) phosphate
(TBEP) is covered in the first. TBEP is used in floor polishes and as
a plasticizer in rubber and plastics. Studies of concentrations in various
environmental samples show that TBEP is readily biodegradable. Most
potential exposure of the general population arises from the use of
TBEP in packaging materials for food and from the possible contamination
of drinking-water from synthetic rubbers used in plumbing washers. The
report concludes that exposure from both sources is very low. The risk
to workers, exposed by the dermal route during manufacturing, was likewise
judged to be very low. Studies in experimental animals indicate that
the liver is the target organ for TBEP toxicity. Data on other toxic
effects were judged to be weak or inconsistent.
Tris(2-ethylhexyl) phosphate (TEHP) is covered in the second monograph.
TEHP is used as a flame retardant, a plasticizer for polyvinyl chloride
and cellulose acetate, and a solvent. While the compound has not been
detected in outdoor air, some studies have found concentrations in indoor
air. The limited data on environmental fate indicate that the compound
is rapidly biodegraded in natural waters. In experimental animals, the
compound demonstrates low acute toxicity. Studies conducted in rats
revealed no toxic effects. Although some long-term studies suggest carcinogenic
potential, the report concludes that TEHP does not represent a significant
carcinogenic risk to humans. In studies conducted in human volunteers,
no skin irritation was reported. The report concludes that the risk
to both the general population and occupationally exposed workers is
The final and most extensive monograph evaluates tetrakis(hydroxymethyl)
phosphonium (THP) salts.
These compounds are the major class of chemicals used as flame retardants
for cotton, cellulose, and cellulose-blend fabrics. Data were considered
inadequate to support an evaluation of effects on the environment. Studies
conducted in animals show moderate acute toxicity and low dermal toxicity.
The liver is the main target organ for toxic effects in experimental
animals. The report found no convincing evidence that fabrics treated
with THP salts are mutagenic or carcinogenic. Concerning possible migration
from textiles, the report cites evidence that the flame retardant polymer
is not released during cleaning processes that would normally be employed
All three monographs conclude with a list of further studies needed
to support a full scientific evaluation.