DBP: Contamination in Water and Proposed Regulations
By: Helen Davoodi, Camilla Westberg and Antonio F. Machado
Department of Environmental and Occupational Health
California State University, Northridge
Abstract
DBP is a chemical used in consumer products. Due to its high
production volume and leachability, it is found at low levels in
air, water and soil throughout the world. Exposure occurs
through ingestion, inhalation and dermal contact. It acts as an
endocrine disruptor in animals and humans, and can be
especially dangerous to aquatic organisms. Currently in the
U.S., DBP is only regulated in some children’s products.
Introduction
Di-n-butyl phthalate (DBP):
•Man-made chemical used as plasticizer to add flexibility,
durability, and transparency.1,3
•Used in solvents, varnishes, time-released pharmaceuticals,
food packaging and personal care products.
•DBP is not covalently bound to the product in which it is used
and is therefore easily released into the environment.2
•Endocrine-disrupting chemical due to its anti-estrogenic and
anti-androgenic activities. 4
•Can make up to 40% of the plastic volume5
•Reference dose: 0.1 mg/kg bw/day
•Carcinogenicity: Class D – not classifiable6
Chemical Properties
•Oily liquid that is colorless to faint yellow.
•Formula: C16H22O4
•Molecular weight: 278.4 g/mol
•Melting point: -35oC
•Boiling point: 340oC
•Metabolite: Mono-N-butyl phthalate (MBP)
Occurrence in Environmental Matrices
Ecotoxicology
•DBP is one of the most common phthalates detected in
environmental samples.13
•Air is the primary element to which DBP is emitted.13
•DBP is prevalent in aquatic environments due to its ubiquitous use.15
•DBP enters water from industrial facilities, wastewater treatment
plants, consumer products, and incorrect disposal.15
•The majority of DBP dissolves rapidly in water, the remainder binds
to suspended materials.11
•U.S. data for DBP in waters is limited and/or >20 years old.
•There is less bioconcentration of DBP/MBP in aquatic organisms
with more sophisticated metabolic systems:
algae > crustaceans > insects > fish.11
•Exposure to aquatic organisms occurs via gill respiration, dermal
contact and by eating contaminated food.
•Is as an anti-estrogen in female fish, affecting the ovaries and
leading to reduced fecundity. 15
Location
Surface water
(µg/L)
Sediments
(mg/kg)
Sewage sludge
(µg/L)
Germany14
0.12-8.8
0.06-2.08
0.2-10.4
Humans
•Majority of humans are exposed to DBP.
•Exposure occurs primarily through ingestion, but also inhalation
and to a limited extent dermal contact. 18
•Example of DBP concentrations in drinking water:19
Country
Tap Water
(µg/L)
Bottled Water
(µg/L)
China
0.6
54.6
Portugal
0.52
0.35
Tchek Republic
0.05
0.2
Remediation of Water
1. Ultra-Violet (UV) Irradiation at 254 nm
•Reduces DBP concentrations in water and wastewaters.
•pH levels 5-9 have the longest lag time, but highest efficiency.
•Can be used in acidic, neutral and basic environments.
•End products include phthalic acid, ketones, and alcohol. 16
2. Bacterial Degradation
•Microorganisms are capable of using DBP as their food source.
•Sphingobium sp. can break down DBP in water containing <4%
NaCl, making it a good candidate for remediating salty wastewater.10
3. Ozonation
•Ozone (O3) degrades DBP directly or indirectly by interaction with
the O3 molecule or the hydroxyl radicals as O3 breaks down.
•O3 can degrade <90% of DBP. Increased efficiency at higher
temperatures and low dose of humic substances. 17
•Example of DBP/MBP levels in new mothers in Sweden (values
are similar to studies conducted in Germany and the U.S.):20
Body Fluid
DBP conc.
MBP conc.
(average)
(average)
2.8 ng/mL
1.2 ng/mL
Urine
n/a
46 ng/mL
Blood
1.2 ng/mL
1.8 ng/mL
Breast milk
•There is a negative correlation between MBP in urine and
testosterone levels in human males. DBP may target the pituitary
gland and disrupt the negative feedback mechanism for
testosterone production. 18
Health Effects and Proposed Mechanisms
The following effects are from experimental levels of DBP exposures in laboratory settings. Exact mechanisms are unknown. Suggested mechanisms are indicated by arrows.
1. Prenatal exposure in male rats:
2. Exposure in pubertal male rats:
•Infertility as adults
•Fewer offspring later in life
•Decreased seminal vesicles
•Reduced steroidogenesis
•Reduced anogenital distance2
•Chryptorchidism
•Hypospadia5
•Damaged /reduced number of Sertoli
cells and loss of spermatogenesis 5, 7
•reduced weight of testes and epididymis
•histological changes in the testes
•increased expression of heterogeneous nuclear
ribonucleoprotein A2/B1
•increased expression of vimentin proteins
•reduced superoxide dismutase
•increased malondialdehyde
•altered luteinizing hormone levels (LH)
•reduced sperm quality
•Reduced sperm count
•Impacted motility and
viability
•Deformed sperms 2
Increased follicle-stimulating
hormone (FSH) 7
Regulators
•Formation of vacuoles
•Leydig cell (LC) hyperplasia
•Increased reactive oxygen species7
Seminiferous tubular
degeneration2,5
Reduced estrogen and
androgen receptor 2
Less
inhibin
Figure 1: Overview of seminiferous tubule in mammals.
LC: Estradiol  testosterone
•Reduced testosterone
•Increased estradiol7
Lipid peroxidation of epididymal tubules
Impaired sperm motility8
The combined effect of reduced testosterone, fewer Sertoli cells, damaged LCs, increased FSH and LH,
reduced estrogen and androgen receptor may lead to fewer spermatogenic cells and reduced
spermatogenesis.7
3. Exposure in female mice:
Regulations
Impacts ovarian antral follicles:
•Increased apoptosis, possibly due to reduced B-cell leukemia/lymphoma 2 levels.
•Reduced 17β-estradiol accumulation.
•Alters cell cycle
regulators.9
•Banned in children’s toys and certain childcare articles in the U.S., E.U., and Canada.21, 22, 23
• Banned in cosmetics and restricted in food packaging in the E.U. 22
•Currently not regulated in drinking water in the U.S.
•Included in CERCLA’s Priority List of Hazardous Substances. 24
•Reduced Cyc D9
•Halted progression/
accumulation of
follicles in G1 phase.
•Reduced Cyc E
•Increased p219
•Reduced Cyc A
and B9
•Suppressed/delayed
growth in follicles9
•Reduction of follicles
in S phase9
Fate and Transport
•DBP can be removed by hydrolysis, photolysis and biodegradation.10
DBP 11
•Gram positive/ negative bacteria and actinomycetes can use DBP as
MBP + Alcohol
a carbon and energy source.
•Degradation rate is slowed at low temperatures & nutrient poor
Phthalic Acid (PA)
environments.
+ Alcohol
•Fresh water or marine water does not impact degradation
Aerobic
Anaerobic
rate (<30 days).
•Hydrolysis half-life is 22 years. 11
Dihydrophthalate
PA-CoA
•In humans:12
Protochatecuate
Glucoronide
Intestine:
Body:
Benzoyl-CoA
DBP hydrolyzed MBP oxidized
conjugates
Urine:
excreted
Acetate + CO2 +
pyruvate/succinate
DBP’s effects on humans at environmentally relevant levels are still not clear. Further studies are
necessary to decipher how it affects humans and through what mechanisms. The main exposure route
is through ingestion, but drinking water is not the main contributor. Instead of regulating DBP in
water, current regulations for DBP in childcare products should be expanded to include consumer
products, primarily those that are marketed to teenagers and women of childbearing age. Regulating
DBP in consumer products will lead to lowered production of DBP and will potentially reduce human
exposure and the likelihood of environmental releases. As a result, such regulations would offer
protection for both humans and aquatic organisms. In theory, limiting the widespread use of DBP
would reduce clean up costs in the future. Ongoing water monitoring is required to evaluate if
proposed regulations are effective.
References
Figure 2: Overview of cell cycle.
Multi-step process
Conclusion
Multi-step process
Acetate +
CO2 + H2
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