Transcript Computational Toxicology in EPA’s Office of Research and

Introduction to
Brominated Flame
Retardants
Linda S. Birnbaum
Director, Experimental Toxicology Division
NHEERL
Research Triangle Park, NC
Region 2 Science Day/Non-Regulated Pollutants Workshop
NYC – October 25, 2005
Flame Retardants
• Fires kill >3000, injure >20,000,
and cause damages exceeding
$11 billion annually in US alone
• >175 different types of FRs
 Halogenated (~46%)
 Phosphorus-containing (24%)
 Melamines (4%)
 Inorganics (27%)
Brominated Flame
Retardants
• BFRs are the largest market group due to low
cost and high efficiency
• BFRs account for 38% global demand for
bromine
• >75 BFRs recognized commercially
 Br-BPs, BDEs, CDs, phenols, phthalates,++
• Global, transboundary problem
 Persistence
 Potential for bioaccumulation
• Limited Data Base
Global Market Demand for
Major BFRs in 2001
(metric tons) [BSEF]
America Europe
Asia
RestoW Total
TBBPA
18,000
11,600
89,400
600
119,700
HBCD
2,800
9,500
3,900
500
16,700
DBDE
24,500
7,600
23,000
1,050
56,100
OBDE
1,500
610
1,500
180
3,790
PBDE
7,100
150
150
100
7,500
TBBPA
(Tetrabromobisphenol A)
• Reactive & additive
 Primary use - Electronics
•
•
•
•
•
Acute tox data – oral LD50: 5-10 g/kg
Low chronic toxicity
Not teratogenic or mutagenic
Limited data in biota
Dimethyl-TBBPA
 Metabolite eliminated in bile
 Little retained in tissues
Health Effects of TBBPA
• Immunotoxic
 Inhibits T cell activation : blocks CD25
(<3µM)
• Hepatotoxic
 Toxic to primary hepatocytes: destroys
mitochondria; membrane dysfunction
(inhibits CYP2C9)
• Neurotoxic
 Inhibits dopamine uptake
 Generates free radicals
Health Effects of TBBPA (cont.)
Endocrine Disruption
• AhR Effects
 Not relevant for commercial product
(Contaminants? Combustion products?)
• Thyroid
 TBBPA>T4 in relation to binding to
transthyretin
 Blocks T3 binding to TR
 Perturbations observed in vivo
• Estrogenic
 Inhibits sulfotransferase (decreases
estrogen clearance)
 Mostly in vitro data
Hexabromocylododecane
(HBCD)
• Additive
 Used in Electronics; Textile Backings
• Ecotox –
 Algae, daphnia, NOEC = 3 ug/L
 Fish, LC 50>water solubility; PNEC=.03ug/L
• General Toxicity
 High absorption; mild irritant and skin
sensitizer; liver effects after repeated
exposures (rat LOAEL ~13 mg/kg/day)
• Need more info: repeated dose studies,
repro tox
HBCD (cont.)
• Neurotoxicity
 Developmental neurotoxicant
 Blocks dopamine uptake
• Concern for occupational settings
• Found in human breast milk
• Persistent, bioaccumulative, toxic, long
range transport
• Isomeric composition in environmental
samples differs from commercial mixture
Polybrominated Diphenyl
Ethers (PBDEs)
• Major Additive BFRs(~67 metric
tons/yr)
• DBDE – largest volume (75% in EU)
 97% DBDE; 3% NBDE
 Polymers, electronic equipment, textile
O
backing
• OBDE
 6%HxBDE; 42%HpBDE;36% OBDE;
Br
13%NBDE;2%DBDE–multiple congeners
• unclear if any PeBDE)
 Polymers, esp. office equipment
• PeBDE
 Flexible polyurethane foam (up to 30%)
• Cushions; mattresses; carpet padding
 Mainly PeBDE+TeBDE, some HxBDE
Br
Properties
• Solids with low solubility (< 1ug/kg), high log
Kow (>5)
• Lower congeners - more bioaccumulative,
persistent
• Strong adsorption to soil/sediment/sludge
• No significant biodegradation in air/water
• Bioaccumulation - BCF > 5000
• Long-range transport - Evidence of remote
contamination (e.g., Arctic)
• Persistence- t 1/2 Atmospheric >2 days;Water
>2 mos; Soil, sediment >6 mos
Sources of
Environmental Release
• Polymer Processing
• Formulating/applying to textiles
• Volatilization and leaching during
use
• Particulate losses over
use/disposal
 Incineration
 Recycling
Pathways of Exposure?
• Indoor air >> outdoor air
 May account for ~4%, on average, of daily
intake by inhalation (could be much higher for
some)
 BDE209 as well as 47, 99, 100, 153, 154
• House dust
 Recent studies in Cape Cod, Northwest,
Texas, Europe
 Wide range
• Recent study: N = 10. Range: 705-69,000 ppb; Mean:
12,100 ppb; Median: 2,500 ppb
 Levels in US, UK>>Europe, Japan
 Patterns resemble commercial products
(Penta, Deca)
Breast Milk vs. Dust
Log of PBDEs in Breast
Milk (penta congeners only)
(BDE 47+99+100+153+154)
2.5
2
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
Log of PBDEs in Dust (ug/g)
r=0.76 (p=0.006);not confounded by diet; (T.Webster)
5
Daily US Adult PBDE Dietary Intake
(A. Schecter)
20-39 Males
PBDE intake pg/kg bw per day
800
20-39 Females
723
700
600
500
451
400
300
200
88
100
82
101
77
0
Meat
Fish
Dairy
US Human Breast Milk PBDE levels,
2005, N=62.
(A. Schecter)
450
350
300
250
200
150
100
50
70
67
64
61
58
55
52
49
46
43
40
37
34
31
28
25
22
19
16
13
10
7
4
0
1
PBDEs ng/g or ppb, lipid
400
Median Levels of PBDE 47, 99, 153 in
Human Milk from Different Countries.
PBDE levels (ng/g. ppb. lipid)
BDE 47
BDE 99
BDE 153
30
25
25
20
17
15
13
10.1
10
5
4.5
5.1
2.1
3
1.3
1.4
0.5 0.3
0.8 0.2 0.5
1.7
0.2 0.5
1 0.4 0.3
0.2 0.06 0.09
0
USA
USA, TX, Canada Canada Germany Sw eden Finland
EWG
2004
2002
1992
2000
2000
1994-98
2003
(n = 59) (n = 92) (n = 72) (n = 7)
(n = 40) (n = 11)
(n = 20)
Hanoi,
Vietnam
2004
(n = 2)
PBDEs in Human
Samples
• Pattern of congeners is different from commercial
mixtures (and food)
 47>99 (others: 100,153,183, 209,…)
 In some people (and biota)
• 153>47
• Large inter-individual differences
 People as high as ∑PBDEs ~10 ppm lipid!!!!
• Increasing time trends – levels doubling every 2-5
years
• PBDEs and PCBs levels are not correlated
 different sources and/or time sequence
• North American levels ~ 10X Europe/Japan
• WHY?
SPBDE in Huma n s, Se als a nd F ish fro m th e
SF Ba y Area
3 00 0
ng/g lipid
2 50 0
2 00 0
1 50 0
1 00 0
50 0
0
Hu man s
F ish
Sea ls
(Petreas et al., 2002)
Ecotoxicity
 PeBDE>>OBDE>DBDE
 PeBDE - Highly toxic to invertebrates
• Larval development, LOECs in low μg/l range
 DE71 – developmentally toxic to fish (1ng/l)
• Tail asymmetry; delayed hatching; behavioral changes;
learning deficits
 ∑PBDEs associated with die-off of Baltic porpoise
• Lymphoid depletion
 BDE99 - depletion of Vitamin E in duck eggs
 BDE 47, 99, 100 - decreases in T4/retinoids,
increases in oxidative stress in Kestrals
Ecotoxicity (cont.)
• DBDE/OBDE
 May be low risk to surface water
organism and top predators
 Concern for waste water, sediment,
and soil organisms
 Concerns for lower brominated
congeners in OBDE, potential for
debromination, and generation of
PBDDs/PBDFs
Mammalian Toxicity in
Adult Rodents
• Hepatotoxic
• Enzyme induction
 UDP-glucuronyl transferase
• Weak inducer
 Cytochrome P450
• Induction of CYP2B,3A
• Purified BDEs are NOT CYP1A inducers
• DBDE – hepatocarcinogen (high dose)
Endocrine Disrupting Effects
• AhR Effects
 Contamination of commercial PBDEs
 Combustion can produce PBDDs/PBDFs
• Thyroid Homeostasis
 Decrease in T4
 OH-PBDE metabolites bind to transthyretin
in vitro
 Parent PBDEs - Effects on T4 seen in vivo
• Induction of UDP-glucuronyl transferase
 Not a low dose effect
Endocrine Disrupting
Effects (cont.)
• Progestins
 In vitro – Anti-progesterone
• Estrogens
 In vivo
• BDE99 – decreased E2
 In vitro
• OH-PBDEs may be anti-estrogenic
• Sulfotransferase inhibition could be
estrogenic
Endocrine Disrupting
Effects (cont.)
• Androgens
 In vivo
• DE71 – decreased weight of seminal
vesicles and ventral prostate,
decreased LH
• BDE99 – decreased Testosterone
 In vitro
• DE71, BDE100, BDE47 –
antiandrogenic (non-competitive
inhibition)
Developmental
Reproductive Effects
• DE71– pubertal exposures
 Delay in puberty
 Effects on male organs
 Anti-androgenic in vitro – esp BDEs100, 47
• BDE-99/47– in utero exposures
 Delay in puberty
 Ovarian toxicity
 Male organ effects and decreased sperm
Developmental
Neurotoxicity
• DE-71 – Rats
 Deficits in sensory and cognitive function
 Altered sex-dependent behaviors
 Effects on thyroid, cholinergic, and dopaminergic
systems
• BDE-99 (47,153,206,208,209) - Mice and
rats
 Infantile exposure (“Rapid Brain Growth”) -
Permanent effects on learning
 Perinatal exposure – Delay in sensory-motor
development
• BDE-99+PCB-52 – Mice
 Effects may be more than additive
Developmental Neurotoxicity
of PBDEs
• Mechanisms?
 Depression in serum T4
 Anti-cholinergic
 Anti-dopamingergic
• PBDEs alter cell signaling in vitro
 DE71, BDEs 47, 99, 153
 Altered PKC and calcium homeostasis
(associated with learning and memory)
 Alter phorbol ester binding
BDE 47 Toxicokinetics?
• BDE47 - Major PBDE in most people
and wildlife
• Well Absorbed
(Oral~Inhalation>Dermal)
• Distribution dictated by lipophilicityFat
• Limited Metabolism -Hydroxylation,
Debromination
• Excretion – mice and rats differ
• Long Half-life-Potential for
Bioaccumulation
% BDE 47 Dose in Urine
Cumulative Urinary Excretion:
Effect of Dose
60
50
0.1 mg/kg
1.0 mg/kg
10 mg/kg
100 mg/kg
40
30
20
10
0
0
1
2
3
Day
4
5
6
Percent BDE 47 Remaining in
Body Over Time
% Dose Remaining
100
*
75
*
Pup ^
Adult
*
50
*
25
0
0.0
2.5
5.0
7.5
Day
10.0
12.5
24 hr Urine Concentrations
2000
22
29
40
70
ng/g
^
1000
*
*
0
22
29
40
Day
70
Comparative Urinary
Excretion of PBDEs
Cumulative Excretion via Urine
50
40%
40
% Dose
BDE 47
BDE 99
BDE 100
BDE 153
30
20
16%
10
0
6%
2%
0
1
2
3
Day
4
5
6
PBDE Brain Concentrations
ng/g (wet weight)
125
a bc
100
75
a bd
50
25
cd
cd
0
47
99
100
153
PK of BDE 47,99, 100, and
153
• Well absorbed
• Higher urinary elimination in mice than
rats
• Urine elimination decreases as
#Bromine atoms increase
• BDE99 is most metabolized
• What does this all mean for people?
New Information on Deca
• Deca is major PBDE in outdoor air (Butt et al., 2004)
• Deca can break down in the environment
 Photolytic Debromination (Soderstrom et al, 2003)
• Matrices affect time course but not outcome
• BDE 154 and 183 found in all matrices; BE47 only in
silica gel
• Deca can break down in fish
 Detection of BDE-181 and 190 in carp (congeners not in
commercial products) (Rice et al, 2002)
 7 penta to octa metabolites found (Stapleton et al, 2003)
• Deca can be absorbed (>10%) and break down in
rodents
 Debrominated, Hydroxylated, Methoxylated
 Reactive Intermediates - Covalent binding
• Deca MAY BE developmentally neurotoxic
DBDE in Human
Samples
• Rarely Measured – but its there!
• Serum
 Levels as high as 200ppb lipid in
occupational exposed workers
• Breast Milk
 Mean~0.9 ppb lipid
• Analytical Issues
 High background levels in dust lead to
laboratory contamination
Potential Health Risk of
PBDEs
• Top 5% of current human exposure in US >400 ng/g lipid
 If humans are 25% lipid, then their “dose” is ~0.1
mg/kg body weight
• Significant dose causing DNT
 Mice < 0.8 mg BDE99/kg
 Rats <0.7 mg BDE47/kg
• Preliminary Developmental Repro ~.06mg/kg
• Rodent body burdens associated with DNT
are only ~10X higher that total PBDE body
burdens in people in North America
• Margin of exposure for PBDEs appears low
• Additional concern: are PBDEs interacting
with other PBTs?
Conclusions
• Growing international concern
 P, B, and T
• Presence in biota
• Presence in human tissues
 North American levels much higher than
Europe or Japan
 Relative Biotic levels are very different
from commercial mixtures
• Increasing potential for health effects
With Special Thanks
•
NHEERL

•
EPA HQ

•
Tom Webster
Cal EPA

•
Arnie Schecter
BU

•
Heldur Hakk, Janice Huwe
UT

•
Tom Burka, Mike Sanders, Ed Lebetkin, John Prichard
USDA

•
Dan Axelrad, Tala Henry, Hend Galal-Gorchev
NIEHS

•
Daniele Staskal, Janet Diliberto, Mike Devito, Vicki Richardson,
Kevin Crofton, Tammy Stoker, Prasada Kodavanti
Tom McDonald
Duke

Heather Stapleton
And all of my colleagues worldwide!