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EC number: 204-411-8
CAS number: 120-61-6
The atmospheric oxidation half-life of
dimethyl terephthalate was estimated using the AOPWIN v1.91QSAR model
available from the US EPA. The estimated atmospheric oxidation DT50 of
dimethyl terephthalate ranged from 18.64 days (default settings) to
27.96 days, estimated by applying the recommended northern hemisphere
settings that are considered relevant in a European context.
Since dimethyl terephthalate is readily
biodegradable, a formal study of the hydrolysis behaviour of DMT at
three pH values is not required and has not been performed.
Nevertheless, some insight is provided indirectly from other sources.
Hydrolysis of dimethyl terephthalate is exploited as one of the
commercial production methods of terephthalic acid, but this process
requires high temperatures
(260 to 280 degrees C) and pressures (4500 to 5500 kPa) and on this
basis DMT may be considered unlikely to hydrolyse rapidly under normal
environmental conditions.Further insight is provided by a study of the
toxicity of DMT to unicellular aquatic algae (Salinas, 2010b). The
concentration of dimethyl terephthalate, initially dosed to non-sterile
aqueous algal growth test medium at 29.4 mg/L (measured), was reduced by
10% over the course of 72-h incubation at pH 8.1 and 23 degrees C.
Although this small reduction may have been the result of
biodegradation, photolysis, hydrolysis or any combination of these
processes, these data (DT50 > 3 days) provide clear evidence that DMT is
not prone to rapid hydrolysis in the aquatic environment.
Similarly, no studies are required or have
been performed to investigate the phototransformation of dimethyl
terephthalate in water, however the results of the same algal study, in
which DMT remained stable following continuous bright illumination for
72 hours, suggest that dimethyl terephthalate is not prone to rapid
In summary dimethyl terephthalate is
generally resistant to physico-chemical degradation processes under the
range of conditions likely to be encountered in the aquatc and
terrestrial environment. Other data (see Point 5.2.1) show that dimethyl
terephthalate is readily biodegradable, with >60% mineralisation
(oxidation to CO2) occuring within 14 days. Biodegradation may therefore
be considered a more significant dissipation mechanism than
physico-chemical processes tor DMT in the environment.
Two screening tests of the ultimate "ready"
biodegradability of dimethyl terephthalate are available.
In the first (Anonymous, 1993a) dimethyl
terephthalate was tested for ready biodegradability according to the
BODIS procedure, at a concentration of approximately 11 mg/L. Periodic
measurements of biochemical oxygen demand (BOD) were compared to a
theoretical oxygen uptake calculated assuming the complete
mineralisation of DMT to its terminal oxidation products, and showed
that 83.8% degradation occurred within 14 days. The 60% pass level was
exceeded within the 10 -day window.
In the second study (CITI, 1980), dimethyl
terephthalate (100 mg/L) was tested for biodegradability by the
Chemicals Inspection and Testing Institute of Japan to fulfil the
requirements of the Japanese Chemical Substances Control Law. A
composite inoculum (applied at 30 mg suspended solids/L) originating
from ten specified locations around Japan, not deliberately adapted to
the test substance, fed with peptone and glucose prior to use and
renewed at regular intervals (see OECD Guideline 301C 1984 and 1992 for
details) was employed as standard practice at CITI for these
investigations. An automated respirometer was used to make continuous
measurements of biochemical oxygen demand (BOD) and recorded BOD was
compared to a theoretical oxygen uptake. Measured BOD expressed as %ThOD
reached 84% within 14 days in this study. Confirmatory indications are
provided by specific analyses for the test substance using an HPLC
method - this compound-specific technique showed 100% loss of the parent
test substance (primary degradation) and is consistent with the figure
of 84% for ultimate biodegradation that was recorded in this study.
Both studies demonstrate that dimethyl
terephthalate is readily biodegradable and this result signifies that
dimethyl terephthalate will degrade rapidly and completely, without the
formation of stable metabolites, under aerobic conditions in a variety
environmental compartments (aquatic and terrestrial), and that extensive
biodegradation may be anticipated in aerobic biological wastewater
treatment processes. This (in addition to exposure considerations)
obviates the need for studies of the degradation of dimethyl
terephthalate in water/sediment systems or in soil.
Based on its physico-chemical properties,
dimethyl terephthalate is expected to partition mainly toward the
aqueous compartment during wastewater treatment and to be channelled
predominantly toward aerobic biological (e.g. activated sludge)
treatment. Nevertheless, a significant (albeit minor) proportion may
become associated with sludge solids during primary settlement or with
waste activated sludge and be directed toward thermophilic anaerobic
digestion, which typically precedes the disposal of wastewater treatment
sludges to land or alternatively by land-filling or incineration.
No guideline studies of the degradation of
dimethyl terephthalate under anaerobic conditions have been located,
however data are available for its close structural analog dimethyl
phthalate (see Point 5.6). Dimethyl phthalate was biodegraded by >90% in
8 days in a series of tests designed to simulate conditions in anaerobic
sludge digesters at STPs (Ziogouet al., 1989). Since dimethyl
phthalate and dimethyl terephthalate are isomers, dimethyl terephthalate
may be expected to undergo a similarly high degree of anaerobic
biodegradation during methanogenic sludge digestion. Dimethyl
terephthalate is also likley to be degraded anaerobically in
water-logged soils or sediments. These findings relate to specific
analytical measurements of concentrations of the parent molecule (the
same method was applied to five other, related phthalate compounds in a
series of similar investigations); they therefore indicate primary
biodegradation (a structural transformation of the phthalate moiety) but
not necessarily ultimate degradation - complete mineralisation to the
terminal products CO2 and CH4.
Evidence confirming the ultimate anaerobic
biodegradation potential of phthalic acid (and hence DMP and DMT
following primary cleavage) is provided by Battersby and Wilson (1989)
who demonstrated that phthalic acid was completely mineralised
(converted to CH4 and CO2) within 4 weeks in a screening test designed
to assess the potential of organic compounds to undergo biodegradation
under methanogenic conditions in digesting sludge. Since the screening
method employed conservative conditions (a high test substance
concentration and no other substrate feed, combined with a very low
inoculum density) it may be assumed that phthalic acid will undergo
complete degradation during the full-scale digestion process. This study
provides evidence that the anaerobic biodegradation of dimethyl
phthalate demonstrated by Ziogouet al. - and implied by read
across for dimethyl terephthalate - will proceed to completion (i.e. to
CO2 and CH4).
Consequently any dimethyl phthalate that
partitions to wastewater treatment sludge solids (either primary sludge
and/or surplus activated sludge) may be expected to be completely
degraded before the digested product becomes available for application
to soil. Since dimethyl phthalate and dimethyl terephthalate are
isomers, dimethyl terephthalate may be expected to undergo a similarly
high degree of anaerobic biodegradation during methanogenic sludge
Confirmation is provided by tests performed
by Kleerebezem et al. (1999) to assess the amenability of DMT-laden
process waste waters to anaerobic treatment. Half-lives for DMT dosed at
ca. 290 mg/L to test systems inoculated from anaerobic treatment plants
operated under three different regimes ranged from 39 to 58 days. These
test results show that DMT is biodegradable under anaerobic,
methanogenic conditions and it may be inferred that dimethyl
terephthalate is also likely to be degraded in other anaerobic
environments, such as water-logged soils or sediments.
Dimethyl terephthalate is not persistent
The threshold that triggers the need to
investigate a potential bioconcentration/bioaccumulation tendency
experimentally is a log10 Kow value greater than or equal to 3.0. A
study of the octanol/water partition coefficient performed according to
the shake-flask procedure of OECD Guideline 107 provides a measured
value for log Kow of 2.21 for dimethyl terephthalate (DMT). The US EPA's
KOWWIN model predicts a log Kow of 1.66 for DMT and the database on
which the model is constructed contains a published (public domain)
value of 2.25 (Hansch, C.et al., 1995). All three of these log10
Kow values lie below the trigger of 3.0 and dimethyl terephthalate is
therefore not expected to exhibit significant bioconcentration or
bioaccumulation tendencies. Studies of bioconcentration/bioaccumulation
are not triggered for DMT.
It may be concluded that dimethyl
terephthalate is not bioaccumulative (not B).
Transport and distribution
(Q)SAR-modelled Koc values for dimethyl
terephthalate (obtained with the KOCWIN v2.00 model of the US EPA) range
from 30.96 to 109.3 L/kg. Based on these values, dimethyl terephthalate
is classed as moderately mobile to mobile and is expected to have a low
tendency to adsorb to soils and sediments.
The low Koc values modelled for dimethyl
terephthalate also imply a low tendency to associate with sludge solids
during the primary settlement and secondary biological stages of waste
water treatment. The majority of the DMT load contained in a treatment
plant influent load may therefore be expected partition to the aqueous
phase and to be routed toward aerobic biological treatment.
Henry's Law constant was calculated using
experimental values for vapour pressure and water solubility. The value
determined is 0.870696 Pa m3/mole at 20°C (equivalent to Log H value of
The resulting value indicates that dimethyl
terephthalate is unlikely to partition from aqueous systems to the
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