Brominated flame retardants and endocrine disruption
J. G. Vos, G. Becher, M. van den Berg, J. de Boer, and P. E. G. Leonards
National Institute for Public Health and the Environment,
3720 BA Bilthoven,
The Netherlands; Norwegian Institute of Public Health, Oslo, Norway;
Institute for Risk Assessment Sciences, Utrecht University, The Netherlands;
Netherlands Institute for Fisheries Research, IJmuiden, The Netherlands
Abstract: From an environmental point of view, an increasing
important group of organohalogen compounds are the brominated flame
retardants (BFRs), which are widely used in polymers and textiles and
applied in construction materials, furniture, and electronic equipment.
BFRs with the highest production volume are the polybrominated diphenyl
ethers (PBDEs), tetrabromobisphenol A (TBBP-A), and hexabromocyclododecane
(HBCD). Because of their persistence and low biodegradation profile,
several of the PBDE congeners accumulate in biota and are widely found
in the aquatic food chain. Their levels in the environment and in humans
have increased during the last decades, in contrast to compounds such
as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane
(DDT), for example. Humans may be exposed to PBDEs mainly through consumption
of fatty food of animal origin (e.g., fish), but exposure through skin
contact with textiles protected with flame retardants or through inhalation
of BFRs volatilized from electronic and electric equipment may also
occur. The levels of PBDEs in Swedish human milk showed a doubling in
concentration every five years over the period 1972 to 1997 (2,2',4,4'-tetraBDE
being the predominant congener). The levels of penta- and hexa-BDEs
increased at the same rate in ringed seals collected in the Canadian
Arctic from 1981 to 2000. PBDEs exhibit a great variety of biological
effects, depending on the bromine substitution pattern. PBDEs are potential
endocrine disrupters, based on shared toxicity with the structurally
related PCBs, polychlorinated dibenzofurans (PCDFs), and polychlorinated
dibenzo-p-dioxins (PCDDs) (partial aryl hydrocarbon- [Ah-] receptor
agonist and antagonist activity in vitro, thyroid toxicity, and immune
effects), including developmental toxicity. The potency of TBBP-A to
interact with thyroid hormone homeostasis is indicated from in vitro
studies in which the compound competes with thyroxin (T4) for binding
to transthyretin (TTR). So far, the toxicological profile of many BFRs
is too incomplete and insufficient to perform an adequate risk assessment,
and further information is required regarding the potential for endocrine
disruption of these compounds that are of increasing environmental concern.
*Report from a SCOPE/IUPAC project: Implication of
Endocrine Active Substances for Human and Wildlife (J. Miyamoto and
J.Burger, editors). Other reports are published in this issue,
pp. 1617-2615.