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Environmental and Health Assesment of Alternatives to Phthalates and to
flexible PVC
6.1 Polyurethane
6.1.1 Use, emission and exposure
6.1.2 Health assessment
6.1.3 Environmental assessment
6.2 Polyethylene (PE)
6.2.1 Use, emission and exposure
6.2.2 Health assessment
6.2.3 Environmental assessment
Polymers may be divided into two categories defined by their chemical
structure (OECD 1998):
Thermoplastic polymers are melted or softened in order to be formed
under pressure into the required shape, which is established on cooling
the product. The process is reversible and the plastics materials can be
reshaped and reused. Polyethylene (PE) is a thermoplastic polymer.
Thermosetting resins are converted into finished products with the
application of heat and pressure. Chemical cross-linking takes place and
the process is not reversible. The materials cannot readily be recovered
and reused. Polyurethane (PU) is a thermosetting polymer.
Such properties may have implications in a recycling process e.g.
allowing only downcycling. However, the problems associated with these
aspects, and the risks associated with production processes for the
polymers, the energy consumption or the use of specific (perhaps
undesired) chemicals in the production process are not part of the
evaluation.
The evaluation of materials is directed toward a comparison with the
properties found for the chemicals proposed as substitutes for phthalates
in PVC. Being polymers PU and PE and cannot be assessed by the ordinary
tools for health and environmental assessment of chemicals. A different
approach is used, where migration of mono- or oligomers is considered and
their potential for effects are evaluated. The polymer itself is
considered in a general assessment. Polymers most often contain various
additives, such as pigments, extenders, slip agents, antioxidants etc.
Both PU and PE are already used extensively in the society and the use
considered here is therefore an addition to the existing exposure to the
polymers. The choice of exposure scenarios is directed toward maximum
human contact at the consumer level. There will be given no assessment of
the combined load of PU respectively PE to humans or to the environment
from the total use of the polymers.
PU is assessed through the monomer methylene diphenylene diisocyanate
(MDI). In the applications where PU may be a substitute for flexible PVC
(e.g. water proof clothing), PU will most likely be based on MDI. This PU
is a thermoset plastic formed in a step growth process.
Physical-chemical properties
MDI in commercial form typically exists as a mixture of the 4,4’-MDI
(monomer) and various oligomers of MDI. The commercial mix has CAS no.
9016-87-9 and the 4,4’-monomer has no. 101-68-8. The content of
monomeric MDI generally is between 45% and 65 % on a w/w basis. The
monomer is rarely separated from the mixture, which typically contains 50%
monomer and 50% trimers and higher oligomers (US EPA 1998). This
composition, which is very similar to that used in the workplace, renders
the material semisolid and suitable for aerosol generation. Monomeric MDI
is formed as a by-product of PMDI synthesis and is rarely separated from
the mixture except in special-use applications. The exact composition of
monomeric MDI in a mixture likely varies with the manufacturer. Any change
in the monomeric composition is expected to be compensated by an increase
or decrease in oligomer content.
Monomeric MDI is a solid at room temperature whereas the PMDI mixture
is a viscous liquid at room temperature and the vapour pressure is
extremely low, about 2 x 10-6 kPa at 20 °
C of both mixture and MDI (US EPA 1998). Vapour pressure of MDI according
to Swedish Chemicals Inspectorate (1994) is 0.003 kPa at room temperature.
Theoretically, isocyanates hydrolyse readily to amine and carbonate
moieties. This hydrolysation may, however, also lead to methylene
dianiline according to Gilbert (1988), but no data is presented. Monomeric
MDI solidifies to a hard crust upon contact with soil or water, if spilled
in the pure form. The polymeric mixture has a density larger than water’s
and will sink without being finely dispersed (Gilbert 1988).
The fate of MDI under test conditions in Salmonella test has been
studied. A rapid disappearance was observed in test media, 28% and 0.3%
remaining in solution after 45 seconds depending on the co-solvent. A
slight increase in the concentration of the aniline degradation product
diaminodiphenyl methane occurred (up to ~3%). In distilled water 95%
remained (Seel et al 1999).
Migration
No data on migration of monomer MDI from PU has been identified.
Isocyanates belong to a chemical family of high reactivity with biological
functional groups, such as hydroxyl, amine, and sulfhydryl groups (US EPA
1998).
After loss of MDI from products to air, soil or water exposure of
humans or the general flora and fauna in the environment is not expected.
The reactivity of the monomer will presumably lead to binding of MDI to
abiotic dissolved or particulate organic material before interaction with
biota. The complexes are typically not bioavailable and no exposure takes
place. After spraying with commercial mix and consequent loss to the
atmosphere in a working environment no unreacted MDI was found on filters,
only urethane and MDI-urethane (US EPA 1998).
Use pattern for compound
The main use of PU as substitute for PVC-products is anticipated in
the waterproof clothes, shoes, boots and waders (see section 4.3.2).
Exposure in the work place
The vapour pressure of MDI at room temperature is less than 10-5
mmHg. Due to the low vapour pressure at room temperature, only negligible
amounts of MDI vapours are expected to be released into the environment
during normal application, e.g. by roller coating, brushing or curtain
coating of products containing MDI and when using such products in the
form of fillers or joint sealants. Experience gained in monitoring the air
during application of MDI-based coatings shows that the concentrations,
which from under these conditions are below the occupational exposure
limit (0.05 mg/m3) provided that there is a minimum of air
circulation.
Monitoring of MDI concentrations must however be accorded particular
attention. Especially when spraying MDI-based formulations or when working
at high temperatures, e.g. exposure to sunlight or coating of heated
surfaces. Under such conditions, concentrations of MDI aerosols for
exceeding the occupational exposure limit can be formed, either by
mechanical means or by recondensation of MDI vapours which are
supersaturated at room temperature. At high application temperatures, the
vapour pressure and the saturation concentration of MDI increase
considerable (Bayer, 1996). Based on information in OECD (1998) for the
UK, PU is processed in closed systems.
Consumer exposure
It is not possible to conduct an EASE-calculation on a polymer such
as PU. The exposure of consumers may be associated with the release of MDI
and oligomers from the polymer. However, no data on migration has been
identified.
Environmental exposure of humans
It is not possible to conduct an EUSES-calculation on a polymer such
as PU. The exposure of humans from environmental sources may be associated
with the release of MDI and oligomers from the polymer. However, no data
on migration has been identified.
Observations in humans
Exposure to isocyanates is a leading cause of occupational asthma
worldwide. High exposure concentrations, such as might occur during a
spill, are a likely risk factor in human sensitisation.
In a cross-sectional study, MDI-induced sensitisation was evaluated in
243 PMDI/MDI foam workers in a 3-year-old facility in which air levels
were monitored continuously be area monitors for 24 h per day, during
which time the air levels never exceeded 5 ppm. The average duration of
employment was 18.2 months. Three cases of occupational asthma were
identified, one of which was attributable to a spill.
The available human data concerning occupational exposure to PMDI/MDI,
coupled with lack of knowledge about mechanism of action and the possible
role of genetic predisposition are insufficient to identify exposure
conditions and scenarios responsible for the isocyanate-induced
sensitisation.
In a retrospective cohort, mortality and cancer incident study
involving 4,154 workers employed at any of nine Swedish polyurethane
manufacturing plants, the association between excess cancer deaths or
excess deaths from destructive lung diseases was investigated. Workers
were exposed to both TDI and MDI. Exposure levels to MDI were normally
below the detection limit of the analytical method (<0.01 mg/cm3)
and nearly all were below 0.1 mg/m3. At the 10% level of
significance, no statistically significant association was formed between
all-cause cancer and diisocyanate exposure using any of five exposure
measures, or for non-Hodkin's lymphoma and rectal cancer (five cases).
Acute toxicity
The LC50 in rats has been estimated at 178 mg/m3
in rats. An LD50 in rats of 9,200 mg/kg is reported
corresponding to low acute toxicity by ingestion.
Subacute and chronic toxicity
In a subchronic toxicity study (range finding) rats were exposed to
PMDI aerosol in concentrations of 4, 8 or 12 mg/m3 for 6h/day,
5 d/week for 13 weeks. Severe aspiratory distress, degenerative lesions in
the olfactory epithelium of the nasal cavity and mortality was observed at
the highest close level. Histo-pathological lesions of the lungs were also
observed in the 8 mg/m3 dose group suggesting impaired lung
clearance. This study demonstrated adverse effects in the lungs and nasal
cavity at levels of 4 mg/m3 and above. However, because of lack
of data on aerosol sizes, a quantitative LOAEL could not be derived.
Long term effects
According to IARC, MDI is classified as Group 3: The agent is not
classifiable as to its carcinogenicity to humans.
The results of a two-year inhalation study in rats using aerosols of
PMDI revealed a carcinogenic potential. These observations have however
been discussed as a result of the irritant effect of the high
concentrations of aerosols to which the rats were exposed.
In the cancer bioassay, rats were whole-body exposed to aerosols of
PMDI for 6h/d, 5d/w for 24 months in concentrations of 0, 0.2, 1.0 and 6.0
mg/m3. A NOAEL of 0.2 mg/m3 and a LOAEL of 1.0 mg/m3
for respiratory tract effects in both the pulmonary and extrathoracic
regions were identified. Although there were no compound-related nasal
tumours solitary pulmonary adenomas, described as rare in Wistar rats,
were observed. Only one pulmonary adenocarcinoma was observed in one male
exposed to 6 mg/m3. Although the study provides evidence of a tumourigenic
response to treatment, the significance of only one pulmonary
adenocarcinoma is insufficient to distinguish PMDI as an animal
carcinogen.
Prenatal toxicity was evaluated in a study with pregnant Wistar rats
exposed to respirable PMDI in concentrations of 1, 4, and 12 mg/m3
for 6h/d from day 6 to day 15. Statistically, significant effects were
observed at the high dose level, effects, which may be a result of
maternal toxicity. The study identified a maternal NOAEL at 4 mg/m3
and a developmental LOAEL of 12 mg/m3. The study suggests that
the potential of PMDI to cause prenatal toxicity and teratogenic effects
in this strain is low.
In another developmental study where Wistar rats were whole-body
exposed to aerosols of MDI in concentrations of 1, 3 and 9 mg/m3 for 6h/d
from day 6 to 15, the NOAEL for developmental effects was identified at 3
mg/m3.
MDI yielded mixed results in genotoxicity tests. Technical grade MDI
was positive in the salmonella reverse-mutation plate-incorporation assay
in strains TA 98, TA100 in the presence of metabolic actuation and
negative in TA1537 at concentrations of up to 100 m
g/plate. Conflicting findings are however observed with strains TA98 of
TA100. This may partly be attributed to the instability of MDI in DMSO.
Genotoxic metabolic reaction products of MDI have been identified. Free
MDA (methylene dianiline) and AMD (N-acetylmethylene dianiline) have been
detected in e.g. urine. The level of AMD was about three times higher than
that of MDA. MDA is a known animal carcinogen.
Irritability
MDI causes irritation of skin and development of rashes by contact.
Exposure to vapours and aerosols irritates eyes, nose, throat and lungs
causing coughing, wheering, chest tightness and/or shortness of breath.
Sensitisation
MDI may produce skin sensitisation and allergic symptoms like
redness, swelling and inflammation.
An impairment of pulmonary function and induction of sensitisation of
the respiratory tract are generally observed when a MDI concentration of
0.2 mg/m3 (vapours, aerosols) is exceeded. These effects are
believed to be no more frequent in exposed persons than in non-exposed
control persons, if a maximum air concentration of 0.1 mg/m3 is
maintained.
Allergic sensitisation usually develops after months of exposure.
Asthma characterised by bronchial hyperreactivity, cough, wheeze,
tightness in the chest and dysnea, was observed in 12 of 78 foundry
workers exposed to MAI concentrations greater than 0.02 ppm (0.2 mg/m3).
Inhalation provocation tests in 6 out of 9 of the asthmatics resulted in
specific asthmatic reaction to MDI.
NOAEL/LOAEL
Lowest reported LOAEL in the available literature was 1.0 mg/m3
for respiratory tract effects in a chronic study. A NOAEL of 0.2 mg/m3
in the same study was identified.
Summary of known toxicity
Exposure to MDI has been shown to cause irritation and occupational
asthma in humans. Skin sensitisation has been observed as well. Impairment
of pulmonary function is also observed.
Sensitisation from low-level exposure is not described.
MDI is classified in Group 3 by IARC: The agent is not classifiable as
to it’s carcinogenicity to humans. Positive tumourgenic response to
treatment has however been shown in a two-year rat study. Findings were
not significant.
Conflicting results in Ames mutagenicity tests have been reported.
Exposure of pregnant rodents to MDI has not been shown to cause
prenatal effects.
Aquatic and terrestrial ecotoxicity
Data quoted from other studies in Gilbert (1988) reportedly show that
MDI is virtually non-toxic to crustaceans and fish as tested with a series
of standard OECD tests. A result from a 24 hours test on reproduction in
crustaceans is reported as no effect at the highest concentration (10
mg/l). The original data are not available. In an experiment with a
simulated spill of MDI in marine water the concentration after one day had
fallen to 5% of the initial value (Brockhagen, Grieveson 1984), however,
zooplankton organisms were reduced in numbers. The same authors report a
study showing that mortality in 0.001% MDI over 35 days was 7 of 8
animals.
In comparison acute toxicity of toluen-2,4-diisocyanate to freshwater
fish ranged from 165-195 mg/l on exposures from 24 to 96 hours (Curtis et
al. 1979). No significant mortality was observed in exposure of saltwater
fish up to 500 mg/l.
Biodegradation
Aerobic biodegradation is reported as ‘None’ in the OECD test for
inherent biodegradability (Gilbert 1988). No data was reported for
anaerobic biodegradation.
Table 6.1 Ecotoxicity and fate data on MDI
|
MDI |
Aquatic(mg/l) |
|
|
Microorganisms |
Terrestrial |
Bioaccumulation |
Biodegradation
(%) |
| |
Algae |
Crustaceans |
Fish |
EC50 24h |
|
|
Aerobic |
Anaerobic |
| |
|
|
LC0 |
|
|
BCF |
28 days |
|
|
Acute |
N.D. |
> 1,000 |
> 1,000 |
> 50 |
N.D. |
N.D. |
None (Inherent test) |
N.D. |
|
Chronic |
N.D. |
>10
(LC0 – 24h) |
N.D. |
N.D. |
N.D. |
- |
- |
- |
N.D.: No data available.
Bioaccumulation
Bioaccumulation data have not been identified for MDI or for the PU.
The reactivity (and polarity) of MDI makes the use of equilibrium
distribution models unsuitable for prediction of bioaccumulation. For the
PU polymer as such the average molecular weight is above the value of
600-1000 considered a maximum for uptake in living organisms.
Risk assessment
The risks of significant release of MDI from PU polymer leading to
acute effects in the environment seem highly unlikely. Although the data
on chronic effects is incomplete, the risks to the environment based on
these limited data set seem limited.
PE is a thermoplastic produced from ethylene as an addition or chain
growth polymer. It is commercially available in two main forms: high and low
density polyethylene (H and LDPE). The former is an almost linear polymer
both rigid and hard.
LDPE is branched leading to a more spacious compound and lower density
polymer. LDPE substitutes flexible PVC as such, and not only the phthalate
plasticiser of the PVC. The assessment evaluates the LDPE material and
although PE may be added various substances, e.g. antioxidants (Wessling et
al 1998,), the additives are not included in the assessment.
Polyethylene and LDPE has the same CAS no. 9002-88-4.
Physical-chemical properties
The polymer has a melting point of 130-145 C and a density of 0.92. No
information on vapour pressure or LogPow are available. The
average molecular weight ranges from 100.000 to 500.000 depending on the
application.
Migration
There is no data available on migration of base monomers or oligomers.
The monomer ethylene is a highly volatile chemical and if present in the
crude formulation it will evaporate quickly from the polyethylene matrix.
Typically, the production process (a chain growth reaction) is also ended
with capping of the ends of the chains. There is very limited reaction with
the polymer, which is also treated with additives such as antioxidants to
avoid the introduction of reactive groups in the polymer skeleton leading to
a less stabile material. Thus, no migration is anticipated.
Use pattern for compound
LDPE has to some extent already substituted PVC used in flexible toys.
It is expected that a major part of PVC application can be substituted with
LDPE products. In the substitution matrix all flexible PVC in toys is
converted to LDPE.
Exposure in the work place
PE is produced from ethylene and for (Linear) LDPE also variable
amounts of higher alkenes depending on the branching. LDPE is produced in
closed systems, but processed in both opened (88%) and closed systems (12%),
based on data for the UK (OECD 1998).
Typically, PE granules are heated to 160-260 C before processing into
shape. If excessive heat is applied thermooxidation may take place above 360
C and aldehydes of short chain alkanes can be formed. These may irritate the
respiratory tract.
Consumer exposure
It is not possible to conduct an EASE-calculation on a polymer such as
LDPE. It is anticipated that mouthing of LDPE toys by children will be a
primary exposure route. A considerable recovery of the volatile alkenes
takes place in production (Danish EPA 1995) and it is not expected that
consumer products will contain monomers.
Environmental exposure of humans
No environmental exposure to LDPE or it’s monomer is anticipated from
the polymer due to the apparent lack of migration potential. Ethylene occurs
naturally, and is also used in small amounts to ripen fruit and vegetables.
No toxicity data on LDPE are available.
Observations in humans
The massive production of ethylene and polyethylene and the general use
of the polymer over the past several decades indicate that exposure of
workers and the general population is common. In addition, medical use
(e.g., for intrauterine contraceptive devices) has been extensive.
Acute toxicity
No data on LDPE has been identified.
Subacute toxicity
Relevant data were not found.
Chronic toxicity
There is no information on LDPE, except for carcinogenicity of implants,
which the IARC classification is ’Organic polymeric materials as a group
are not classifiable as to their carcinogenicity to humans (Group 3)’.
The base chemical ethylene is ’not classifiable as to its carcinogenicity
to humans (Group 3)’ (IARC 1998).
Long term effects
Relevant data were not found.
Irritability
Relevant data were not found.
Sensitisation
Relevant data were not found.
NOAEL/LOAEL
Relevant data were not found.
Summary of known toxicity
Incomplete information is available for an assessment. As a reflection of
the general recognition of low toxicity no limit value exist for working
environment for the base chemical ethylene although considerable amounts is
used (Danish EPA 1995).
Aquatic and terrestrial ecotoxicity
No toxicity data for aquatic or terrestrial organisms have been
identified. The lack of biological availability due to the high molecular
weight of LDPE indicates that the unbroken polymer itself will not have
direct toxic effects in the environment.
Aerobic and anaerobic biodegradation
There is no data identified for biodegradation. However, LDPE is often
referred to as a non-degradable polymer, and the primary environmental
concern (visible pollution) is associated with lack of degradability.
Bioaccumulation
Bioaccumulation data have not been identified for LDPE. The large
molecular weight (100,000-500,000) of the polymer is above the value of
600-1000 considered a maximum for uptake in living organisms.
Risk assessment
The lack of information precludes an assessment of the risk to the
environment based on test data or calculation of predicted environmental
concentrations. The characteristics of LDPE are those of an inert substance
in the environment, which will not enter the biosphere until the polymeric
structure begin to break. Thus, as LDPE do not release large quantities of
mono- or oligomers, the possible effects would be associated with unknown
long-term exposure or accumulation. Possible effects associated with the
existence of fibres and polymers under slow degradation in the environment
have not received the same intense investigation as the effects associated
with the chemical substances.
PE is generally considered one of the least problematic plastics, and no
indications of toxicity associated with the polymer have been identified
from authorities, industry or NGOs. Environmental or health problems are
only described in relation to synthesis of the polymer (energy consumption,
base chemicals etc.), which is beyond the scope this evaluation.
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