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EC number: 266-028-2
CAS number: 65996-93-2
The residue from the distillation of high temperature coal tar. A black solid with an approximate softening point from 30°C to 180°C (86°F to 356°F). Composed primarily of a complex mixture of three or more membered condensed ring aromatic hydrocarbons.
Abiotic removal was measured in separate tests prior to the
determination of biodegradation.
Abiotic removal [%]
Kilman sandy loam
McLaurin sandy loam
Statistical analysis indicated that abiotic degradation was
significant only for 2- and 3-ring compounds (labelled by an asterisk).
The losses were statistically insignificant for those PAH that
contained greater than 3 rings (no label).
Half-lives of biodegradation[days (95% CI)]
The estimated amount biologically degraded was
= mass added - (volatilised mass + abiotic loss of mass + mass of
The measured biological degradation rates of PAHs were not
statistically different between the two soils studied. The kinetic
calculations resulting in first order rate constants and half-lives gave
r² values ranging from 0.71 - 0.95 and 0.57 - 0.93 for the Kidman and
McLaurin soils, respectively.
loss of PAH from soils were determined using the sterilised soil samples
(treated by irradiation and sodium azide) assuming a linear rate of
loss. Results are presented in the following table
Estimated abiotic losses (percentage of losses and loss rates in µg/kg
dw/day) from irradiated/sodium azide-treated soils over the whole
experimental period (Table 3 of publication)
AS1 = rural agricultural soil, no previous sludge application
AS2 = rural agricultural soil
FS = rural coniferous forest soil
RS = roadside soil
Significantly different from zero Loss (0.05)
structure strongly influences abiotic losses. The lower-molecular weight
PAH with fewer than four rings all appear to be susceptible to
non-biological degradation mechanisms. Losses of these compounds were
collectively significantly different from zero loss (p = 0.05).
(including losses by non-biological processes) for sludge-amended and
for spiked soils
PAH due to combined biological and non-biological mechanisms were
estimated from sludge-amended soil samples. Significant losses of the
higher-molecular-weight PAH occurred, probably due to biological
processes. However, it is possible that some PAH are strongly associated
with the soil humus and become much less readily extracted.
modelled by linear or first-order regression methods. Half-lives were
derived from the regression equations given as the best fit.
Half-lives (days) derived for soils used in the microcosm study
(percentage of losses are shown in parentheses) (combined Table 4 and 5
Sum of PAH
AS1 = rural
agricultural soil, no previous sludge application
AS2 = rural
FS = rural
coniferous forest soil
expected increase in half-life with increasing molecular weight was
observed in all the soils. Abiotic loss processes are clearly very
important for some of the low-molecular-weight PAH, possibly more
important than biodegradation.
the sludge-amended AS2 and the RS soils, sum of PAH concentrations
started to fall immediately after sludge application. Reduction in sum
of PAH concentrations were not detected in the AS1 and FS soil until 40
to 80 days after application, suggesting that PAH degradation began much
more rapidly in the soils with previous exposure to PAH, whereas the
other soils required a period of acclimation.
loss of spiked PAH from the AS1 soil were more rapid than the loss of
sludge-applied PAH (Table 2). Losses by abiotic processes are higher for
spiked PAH than for sludge-applied PAH (Table 1). Overall, the half-life
data derived for the spiked PAH are significantly lower than those for
all the sludge-applied compounds. PAH spiked to soil are more
susceptible to biological and abiotic loss mechanisms and do not mimic
the behaviour of sludge-applied PAH compounds. Application of sewage
sludge increases the soil adsorption potential, thus higher losses of
spiked PAH may be observed in the lower organic matter content of the
Biodegradation of PAH in soil has been investigated in two studies
similar to OECD TG 309. In both studies, dissipation half-lives showed a
substantial variance. Eight of the substances examined are constituents
of Pitch, coal tar, high-temp. In one study, biodegradation was tested
in two different soils, while in the second study four soils were used.
Half-lives ranged in the first study from 16 days to 377 days and in the
second study from 48 to 535 days. A 90th percentile value is selected as
key value for the chemical safety assessment (see below).
CTPht is a solid UVCB substance consisting of an inert matrix, in
which individual PAH are enclosed. PAH comprise mainly four- and
five-ring polycyclic aromatic compounds. Major constituents that are
also part of the 16 EPA PAH are phenanthrene, fluoranthene, pyrene,
benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[a]pyrene,
Indeno[1,2,3-cd]pyrene and benzo[ghi]perylene with concentrations
between approx. 0.3 and 1.1 %. Biodegradation studies in soil
(simulation tests) for anthracene oil itself are not available.
Due to the complex composition of CTPht, a distinct half-life in
soil for the substance as a whole cannot experimentally be determined.
Main components (all PAH) will have their individual half-lives and in
combination can be used to specify a soil biodegradation half-life of
Experimental results for individual PAH (Park et al. 1990, Wild
and Jones 1993) show a high variability of half-lives especially when
determined in different soils. There is a tendency that soil
biodegradation half-lives of PAH increase with growing molecular size
and ring-number. But the high variability indicates that there are other
important factors that affect soil biodegradation. 14 PAH were used in
these studies, eight of them constituents of CTPht that is, one PAH with
three annulated aromatic rings (phenanthrene), four PAH comprising
four-ring aromatic systems (fluoranthene, benz[a]anthracene, pyrene, and
chrysene), and three five- and six-ring PAH (benzo[b]fluoranthene,
benzo[a]pyrene, and either indeno(1,2,3-cd)pyrene or benzo[ghi]perylene).
In the study of Wild and Jones, PAH were not directly added to
soil as in the study of PARK et al., but applied as components in STP
sludge. Biodegradation of test materials was investigated in two
different soils (Park et al.; test duration in soil #1 196 days and in
soil #2 105 days) or in four different soils (Wild and Jones; test
duration uniformly 205 days). The four soils used in the study of Wild
and Jones were very different resulting in quite different
biodegradation half-lives. Besides other differences, original PAH
content in two agricultural soils were quite similar, while PAH
concentrations in the two other soils before treatment were distinctly
higher. For the following evaluation, only the two agricultural soils
with low original PAH burdens are considered.
For components of CTPht, half-lives between 16 days (phenanthrene)
and 387 days (chrysene) were determined in the study of Park et al.,
while in the study of Wild and Jones half-lives ranged from 106 days
(benz[a]anthracene / pyrene) to 460 days (benzo[ghi]perylene).
Phenanthrene was best biodegraded in the two different soils of
Park et al. with half-lives of 16 and 35 days. Most persistent was
chrysene with half-lives of 371 and 387 days. In the study of Wild and
Jones, chrysene/benz[a]anthracene (substances not separated during
analysis) was biodegraded best (half-lives of 135 and 113 days in soils
AS1 and AS2, respectively), while benzo[ghi]perylene was the most
persistent PAH (half-lives of 460 and 365 days in soils AS1 and AS2,
respectively. The higher half-lives observed in the study of Park et al.
in soil #2 bear some uncertainties, as the duration of the tests (105
days) was considerably shorter than the half-lives determined.
The study results clearly indicate that soil biodegradation
half-lives of substantial components of CTPht have values far above 120
and 180 days, the P / vP criteria of REACH Regulation, Annex XIII. In
order to specify a value for the total of CTPht, the data are combined
that have been obtained in the two studies and in four different soils
(two soils considered relevant in each study). The approximate 90
percentile of this data set calculated using the QUANTIL.INKL function
in MS Excel 2013 is used as key value in the chemical safety assessment
(half-life of 370 days). This approach takes into account the broad
range of different PAH constituents of CTPht and the high variability of
half-lives determined for these substances.
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