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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
other: corresponding information taken from the EU Risk Assessment Report on coal-tar pitch, high-temp. (R323) (summary report)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
data taken from the comprehensive EU Risk Assessment Report of coal-tar pitch, high temperature
Principles of method if other than guideline:
RAR covers and reports data from relevant reviews and experimental studies
Specific details on test material used for the study:
The report covers individual studies and reviews that also include studies. In the studies, data on the biodegradation of various individual PAH that are onstituents of CTPht alone or in mixtures are reported.
Oxygen conditions:
other: various
Inoculum or test system:
other: various
Key result
Compartment:
sediment
DT50:
> 1 250 d
Type:
other: (Q)SAR estimate based on model calculations (Mackay 1992)
Temp.:
25 °C
Remarks on result:
other: substance pitch, coal tar, high-temp.; with regard to its constituents and chemcal structure
Key result
Compartment:
sediment
DT50:
ca. 700 d
Type:
other: (Q)SAR estimate based on model calculations (Mackay 1992)
Temp.:
25 °C
Remarks on result:
other: substance phenanthrene; estimate based on model calculations: half-life class 7 (mean ca. 708 days, range 420 - 1250 days)
Key result
Compartment:
sediment
DT50:
> 1 250 d
Type:
other: (Q)SAR estimate based on model calculations (Mackay 1992)
Temp.:
25 °C
Remarks on result:
other: substances fluoranthene, pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene; half-life class 8 (half-lives > 1250 days)
Transformation products:
not specified
Details on transformation products:
Excerpt from the EU RAR of Coal-Tar Pitch, High temperature:
The biochemical pathway for the aerobic biodegradation of PAHs has extensively been investigated. It is understood that the initial step in the aerobic catabolism of a PAH molecule by bacteria occurs via oxidation of the PAH to a dihydrodiol by a multicomponent enzyme system. These dihydroxylated intermediates may then be processed through either an ortho cleavage type of pathway, in which ring fission occurs between the two hydroxylated carbon atoms, or a meta cleavage type of pathway, which involves cleavage of the bond adjacent to the hydroxyl groups, leading to central intermediates such as protocatechates and catechols. These compounds are further converted to tricarboxylic acid cycle intermediates (Van der Meer et al., 1992).
For the lower molecular weight PAHs, the most common route involves the fission into a C3 compound and a hydroxyl aromatic acid compound. The aromatic ring can thereafter either undergo direct fission or can be subjected to decarboxylation, leading to the formation of a dihydroxylated compound. This compound can be dissimilated as described above. When degraded via these pathways, the low molecular weight PAHs can be completely mineralized to CO2 and H2O (Volkering and Breure, 2003).

References:
Van der Meer JR, De Vos WM, Harayama S, Zehnder AJB (1992) Molecular mechanisms of genetic adaptation to xenobiotic compounds. Microbiol. Rev, 56, 677-694
Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

Aquatic degradation (incl. sediment)

[...]

Biodegradation

The results from standard test for biodegradation in water show that PAH with up to four aromatic rings are biodegradable under aerobic conditions but that the biodegradation rate of PAH with more aromatic rings is very low (EHC 1998). Although some evidence for anaerobic transformation of PAHs has been obtained (Coates et al., 1997; Thierrin et al., 1993), PAHs are usually considered to be persistent under anaerobic conditions (Neff, 1979; Volkering and Breure, 2003). Because marine sediments are often anaerobic, degradation of PAHs in this compartment is expected to be very slow.

[…]

Although the biodegradation pathway of the different PAHs is very similar, their biodegradation rates differ considerably. In general the biodegradation rate decreases with increasing number of aromatic rings. For example, for degradation by bacteria from estuary, half lives for anthracene and BaP of more than 145 and 1750 days, respectively, were found (Gerlach, 1981). For anthracene in pond water, however, a half-life of over 2 days was found (Leslie et al., 1987). In static experiments complete decomposition for naphthalene and phenanthrene, partial decomposition for anthracene and chrysene, and no decomposition for fluoranthene was found (Richards & Shieh, 1986). According to Volkering and Breure (2003), two factors are considered responsible for the difference in degradation rate. First, the bacterial uptake rates of the compounds with higher molecular weight have been shown to be lower than the uptake rates of the low molecular weight PAHs. The second and most important factor is the bioavailability of PAHs, due to sorption on suspended organic matter and sediment. Since the Kow and the Koc are strongly correlated, high molecular weight PAHs will degrade slower than low molecular weight PAHs. This is illustrated by Durant et al. (1995) who found that the half-life of PAHs in estuarine sediment was reversely related to the Kow. Biodegradation rates also are extremely dependent on the (a)biotic conditions both in the lab and in the field. Important influencing factors are

(1) the substrate concentration; with low PAH concentrations leading to longer half-lives,

(2) temperature, which reversely relates to the half-live, and

(3) the presence or absence of a lag-phase (De Maagd, 1996).

In addition, the desorption rate of PAH appears to decrease with increase of the residence time of PAHs due to slow sorption into micropores and organic matter, and polymerisation or covalent binding to the organic fraction. The consequence of this aging process is a decreased biodegradability and a decreased toxicity (Volkering and Breure, 2003).

Obviously, due to the large variations, it is difficult to predict half-lives of PAHs. For the risk assessment, it is decided to use the suggested mean half-lives by Mackay et al. (1992),

[…]

Summary of environmental degradation

On the basis of model calculations, Mackay et al. (1992) ranked the 16 EPA PAH according to their persistence in water, soil and sediment in different classes (Table 3.24) which correspond to a specific half-live in these compartments (Table 3.25). For the risk assessment these values are used.

End of excerpt

 

Table 3.24: Suggested half-life classes of polynuclear aromatic hydrocarbons (PAHs) in various environment compartments at 25°C (according to EU 2008, p 67)

 

 

Water

Soil

Sediment

Compound

Class

Class

Class

Naphthalene

3

5

6

Acenaphthene*

3

5

6

Acenaphthylene*

3

5

6

Fluorene

4

6

7

Phenanthrene

4

6

7

Anthracene

4

6

7

Fluoranthene

4

7

8

Pyrene

5

7

8

Chrysene

5

7

8

Benz[a]anthracene

5

7

8

Benzo[b]fluoranthene*

5

7

8

Benzo[k]fluoranthene

5

7

8

Benzo[a]pyrene

5

7

8

Benzo[ghi]perylene*

5

7

8

Dibenz[ah]anthracene

5

7

8

Indeno[1,2,3-cd]pyrene

5

7

8

* classified based on information from literature by the rapporteur (The Netherlands for EU)

 

Table 3.25: Suggested half-life classes of PAH in various environmental compartments

 

Class

Mean half-life (hours)

Range (hours)

1

17 (~1 day)

10 - 30

2

55 (~2 days)

30 - 100

3

170 (~7 days)

100 - 300

4

550 (~23 days)

300 - 1,000 (12.5 - 42 days)

5

1,700 (~71 days)

1,000 - 3,000 (42 - 125 days)

6

5,500 (~229 days)

3,000 - 10,000 (125 - 420 days)

7

17,000 (~708 days)

10,000 - 30,000 (420 - 1.250 days)

8

55,000 (~6 years)

> 30,000

 

References:

Coates JD, Woodward J, Allen J, Philp P, Lovley DR (1997) Anaerobic degradation of polycyclic aromatic hydrocarbons and alkanes in petroleum-contaminated marine harbour sediment. Appl. Environ. Micr., 63, 3589-3593

De Maagd PGJ (1996) Polycyclic aromatic hydrocarbons: fate and effects in the aquatic environment. Academic Thesis, Rijksuniversiteit Utrecht, The Netherlands

Durant ND, Wilson LP, and Bouwer EJ (1995) Microcosm studies of subsurface PAH-degrading bacteria from a former manufactured gas plant. J Contam. Hydrol., 17, 213-223

EHC (1998) Environmental Health Criteria 202: Selected Non-heterocyclic Policyclic Aromatic Hydrocarbons; United Nations Environmental Programme; International Labour Organisation, World Health Organisation, Geneva, 1998

Gerlach SA (1981) Marine pollution. Diagnosis and Therapy. Springer Verlag

Leslie TJ, Dickson KL, Jordan JA, and Hopkins DW (1987) Effects of suspended solids on the water column biotransformation of anthracene. Arch. Environ. Contam. Toxicol., 16, 637-642

Mackay D, Shiu WY, and Ma KC (1992). Illustrated Handbook of Physical–Chemical Properties and Environmental Fate of Organic Chemicals. Lewis Publishers, Boca Raton, FL.

Neff JM (1979) Polycyclic aromatic hydrocarbons in the aquatic environment. Sources, fate and biological effects. Applied Science Publishers, London

Richards D.J. and Shieh W.K. (1986). Biological fate of organic priority pollutants in the aquatic environment. Water Res., 20 (9), 1077-1190

Thierrin J, Davis GB, Barber C, Patterson BM, Pribac F, Power TR, and Lambert M (1993) Natural degradation rates of BTEX compounds and naphthalene in a sulphate reducing groundwater environment. Hydrol. Sc. J., 38, 309-322

Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

Validity criteria fulfilled:
not applicable
Conclusions:
Pitch, coal tar, high-temp. (CTPht) includes PAH as constituents ranging from phenanthrene to benzo[ghi]perylen. For the assessment of biodegradability, PAH with four and more ring systems are relevant. Concentrations in CTPht range from ca. 0.3 % (phenanthrene) to ca 1.1 % (max. 1.5 %) (benzo[a]pyrene). As most relevant to characterise biodegradation properties of CTPht, phenanthrene (0.3 %), fluoranthene (0.84 %), pyrene (0.73 %), (chrysene (0.84 %), benz[a]anthracene (0.67 %), benzo[b or k] fluoranthene (1.13 / 0.59 %), and benzo[a]pyrene (1.1 %) are selected.
Based on estimated ((Q)SAR) half-lives of CTPht constituents (Mackay 1992, see above), biodegradation of pitch, coal tar, high-temp. in sediment is estimated to be very slow with a half-life clearly above the P / vP criteria of REACH regulation, Annex XIII (estimated half-life > 1250 d).
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
other: corresponding information taken from the ECHA SVHC support document of coal tar pitch, high temperature
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
data taken from the ECHA SVHC support document of coal tar pitch, high temperature
Principles of method if other than guideline:
The SVHC support document reviews and reports data relevant for the assessment of biodegradation of pitch, coal tar, high-temp.
Specific details on test material used for the study:
In the SVHC support document, 12 PAHs are selected as indicator constituents of CTPht relevant for PBT/vPvB assessment. These are included in the assessment of biodegradation.

1. Anthracene
2. Phenanthrene
3. Fluoranthene
4. Pyrene
5. Benz[a]anthracene
6. Chrysene
7. Benzo[a]pyrene
8. Benzo[b]fluoranthene
9. Benzo[k]fluoranthene
10. Benzo[ghi]perylene
11. Dibenzo[ah]anthracene
12. Indeno[1,2,3-cd]pyrene
Oxygen conditions:
other: various
Inoculum or test system:
other: various
Remarks on result:
other: results are taken from an assessment report that does report only general findings but no individual experimental data for the specific endpoint.
Transformation products:
not specified

Excerpt from SVHC support document

Biodegradation

[…]

Biodegradation in sediments

In general, PAHs are considered to be persistent under anaerobic conditions (Neff (1979); Volkering and Breure (2003) cited in The Netherlands, 2008). Aquatic sediments are often anaerobic with the exception of a few millimetre thick surface layer at the sediment-water interface, which may be dominated by aerobic conditions. The degradation of PAHs in aquatic sediments is therefore expected to be very slow.

[...]

 

Summary and discussion on degradation

[…] The degradation kinetics of PAHs in the different environmental compartments are influenced by a number of factors, and to a great extent determined by their very low water solubility and tendency to adsorb to particles and organic matter in the environment. Their low bioavailability (especially of PAHs with more than two aromatic rings) is one of the limiting factors for their biodegradation.

[…]

In the assessment for persistence of the PAHs representing CTPHT, half-lives obtained under realistic conditions, i.e. field conditions, are given priority [...]. The study by Wild et al. (1991) reports half-lives in soil for 10 of the 12 PAHs addressed in the present assessment [anthracene, phenanthrene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene and benzo(ghi)perylene] above the P and vP criteria set in REACH, Annex XIII (180 days) […]. Experimental data on half-lives for dibenzo(a,h)anthracene and indeno(1,2,3-cd)pyrene are lacking in this study.

Mackay et al. (1992) estimated half-lives in the different environmental compartments based on model calculations and literature search. On the basis of the results of this study, dibenzo(a,h)anthracene and indeno(1,2,3-cd)pyrene are expected to be as well persistent in soil and sediment: the estimated half-lives for the two PAHs were in soil in the range of 420 to 1250 days, and in sediments longer than 1250 days.

End of excerpt

 

References:

The Netherlands (2008) Annex XV Transitional Dossier. Coal Tar Pitch High Temperature (November 2008). Rapporteur: The Netherlands. Documentation of the work done under the Existing SubstanceRegulation (EEC) No 793/93 and submitted to the European Chemicals Agency according to Article136(3) of Regulation (EC) No 1907/2006. Published by the European Chemicals Agency at:

https://echa.europa.eu/documents/10162/13630/trd_netherlands_pitch_en.pdf/a8891f7e-59c8-4d67-97f7-93bb9a9e2676

Mackay D, Shiu WY, Ma KC (1992) Illustrated Handbook of Physical-Chemical Properties and Environmental Fate of Organic Chemicals. Lewis Publishers, Boca Raton, FL

Neff JM (1979) Polycyclic aromatic hydrocarbons in the aquatic environment. Sources, fate and biological effects. Applied Science Publishers, London.

Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

Wild SR, Berrow ML, Jones KC (1991) The persistence of polynuclear aromatic hydrocarbons (PAHs) in sewage sludge amended agricultural soils. Environ. Pollut., 72, 141-157

 

Overall, biodegradation in sediment is generally considered to be slower than biodegradation in soil (see IUCLID section 5.2.3). Half-lives of most CTPht constituents in soil are assessed to exceed the vP criterion of REACH Regulation, Annex XIII. Thus, biodegradation in sediments of pitch, coal tar, high-temp. as such is assessed as well to be slow exceeding the vP criterion of REACH Regulation, Annex XIII.

Validity criteria fulfilled:
not applicable
Conclusions:
Based on biodegradation data of its PAH constituents, biodegration in sediments of pitch, coal tar, high-temp. is determined to be slow exceeding the vP criterion of REACH regulation, Annex XIII.
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
other: related information taken from the ECHA SVHC support document of fluoranthene, a major constituent of pitch, coal tar, high-temp.
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
information taken from the ECHA SVHC support document for fluoranthene, a major constituent of pitch, coal tar, high-temp.
Principles of method if other than guideline:
The SVHC support document reviews and reports data relevant for the assessment of biodegradation of fluoranthene, a major constituent of pitch, coal tar, high-temp.
Specific details on test material used for the study:
Substance is specified by EC and CAS number. Data reported relate to this substance.
Oxygen conditions:
other: various
Inoculum or test system:
other: various
Compartment:
sediment
Remarks on result:
other: results are taken from an assessment report that does report only general findings but no individual experimental data for the specific endpoint.
Transformation products:
not specified

Excerpt from SVHC support document

 

Biodegradation

 

Estimated data

As indicated in the Annex XV transitional dossier for CTPHT (The Netherlands, 2008), Mackay et al. (1992) ranked 16 PAH according to their persistence in water, soil and sediment in different classes which correspond to a specific half-live in these compartments. The calculated half-lives of fluoranthene in water are in the range of 300-1000 h and for sediment longer than 1250 days.

 

Biodegradation in water and sediment

The biodegradation in water was already assessed in the Support Document for identification of CTPHT as SVHC (ECHA, 2009):

Standard tests for biodegradation in water have demonstrated that PAHs with up to four aromatic rings are biodegradable under aerobic conditions, but that biodegradation rates of PAHs with more aromatic rings are very low (The Netherlands, 2008). In general, the biodegradation rates decrease with increasing number of aromatic rings. This correlation has been attributed to factors like the bacterial uptake rate and the bioavailability. The bacterial uptake rate has been shown to be lower for the higher molecular weight PAHs as compared to the PAHs of lower molecular weight. This may be due to the size of high molecular weight members, which limits their ability to cross cellular membranes. In addition, bioavailability is lower for higher molecular PAHs due to adsorption to organic matter in water and sediment. It has further been shown that half-lives of PAHs in estuarine sediment are proportionally related to the octanol-water partition coefficient (Kow) (Durant et al., (1995) cited in The Netherlands, 2008).

In general, PAHs are considered to be persistent under anaerobic conditions (Neff (1979); Volkering and Breure (2003) cited in The Netherlands, 2008). Aquatic sediments are often anaerobic with the exception of a few millimetre thick surface layer at the sediment-water interface, which may be dominated by aerobic conditions. The degradation of PAHs in aquatic sediments is therefore expected to be very slow.

Mackayet al. (1992) predicted that fluoranthene persists in sediment with half-lives higher than 1250 days. For water degradation, Mackayet al. (1992) predicted elimination half-lives between 300 and 1000 hours. Fluoranthene consists of 4 aromatic rings, so standard tests for biodegradation in water may reveal that fluoranthene is biodegradable under aerobic conditions (European Commission, 2008).

Smith et al. (2012) studied biodegradation kinetics of phenanthrene and fluoranthene by the bacterium Sphingomonas paucimobilis EPA505 using a dynamic passive dosing technique. Similar mineralization fluxes were observed for both substances, which increased by two orders of magnitude with increasing dissolved concentrations.

[…]

At present fluoranthene has not been tested in a sediment simulation study (OECD 308). However, during the public consultation a summary of such a study was provided in which the degradation of phenanthrene was studied (Meisterjahn et al. 2018). When converted to 12°C, the half-lives observed were higher than the vP criterion. Considering that the biodegradation rates decrease with increasing number of aromatic rings and the half-lives of PAHs in estuarine sediment are proportionally related to the octanol-water partition coefficient (Kow) (Durant et al. (1995) cited in the Annex XV transitional dossier for CTPHT (The Netherlands, 2008)), it can be assumed that fluoranthene also meets the P and vP criterion in sediment.

 

[…]

 

Summary and discussion on biodegradation

For water degradation, Mackayet al.(1992) predicted half-lives between 300-1000h.

It is assumed that fluoranthene meets the P and vP criterion in sediment, as in the available simulation study with phenanthrene the half-life meets the P and vP criterion. Considering that the biodegradation rates decrease with increasing number of aromatic rings and the half-lives of PAHs in sediment are proportionally related to the octanol-water partition coefficient (Kow), the half life of fluoranthene should meet the P and vP criteria in sediment as well.

The half-life predicted by Mackayet al.(1992) supports the persistency of fluoranthene in sediments (half-life > 1250 days).

[…]

Fluoranthene biodegrades very slowly in soil and field conditions, with different parameters impacting the biodegradation process. Data indicate that a low biodegradation of fluoranthene is observed in sediments, based on which fluoranthene meets the vP criteria for sediment.

Therefore, it is concluded that based on the available data, fluoranthene biodegrades very slowly in soil and sediment.

End of excerpt

 

References:

ECHA (2009) Support Document for identification of Coal Tar Pitch, High Temperature as a SVHC because of its PBT and CMR properties

http://echa.europa.eu/documents/10162/73d246d4-8c2a-4150-b656-c15948bf0e77

European Commission (2008) European Union Risk Assessment Report, Coal Tar Pitch High Temperature, CAS No: 65996-93-2, EINECS No: 266-028-2

https://echa.europa.eu/documents/10162/433ccfe1-f9a5-4420-9dae-bb316f898fe1

The Netherlands (2008) Annex XV Transitional Dossier for substance Coal Tar Pitch High Temperature, CAS Number 65996-93-2

https://echa.europa.eu/documents/10162/13630/trd_netherlands_pitch_en.pdf/a8891f7e-59c8-4d67-97f7-93bb9a9e2676

Durant ND, Wilson LP, Bouwer EJ (1995) Microcosm studies of subsurface PAH-degrading bacteria from a former manufactured gas plant. J Contam Hydrol 17, 213-223.

Mackay D, Shiu WY, Ma KC (1992) Illustrated Handbook of Physical-Chemical Properties and Environmental Fate of Organic Chemicals. Lewis Publishers, Boca Raton, FL

Meisterjahn et al. (2018) (Report in preparation) Degradation of 14C labelled hydrocarbons in Water-Sediment using standard and optimized OECD test guidelines - 308. Germany: Fraunhofer IME-AE

Neff JM (1979) Polycyclic aromatic hydrocarbons in the aquatic environment. Sources, fate and biological effects. Applied Science Publishers, London.

Smith KEC, Rein A, Trapp S, Mayer P, Karlson UG (2012) Dynamic passive dosing for studying the biotransformation of hydrophobic organic chemicals: Microbial degradation as an example. Environmental Science and Technology 46, 4852-4860

Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

 

Overall, it can be concluded that microorganisms are present in the environment that can degrade fluoranthene under aerobic conditions. But based on the structure of fluoranthene (four-ring PAH) and its log Kow value, degradation rates will already be slow in water and even slower in sediment. In soil, maximum dissipation half-lives of 184 and 377 days at a temperature of 20 °C or slightly higher have been determined (Wild and Jones 1993 and Park et al. 1990, respectively). It can be assumed that biodegradation in sediment will be slower than biodegradation in soil. In addition, the biodegradation of fluoranthene in sediment is assessed to be slower than the biodegradation of phenanthrene based on the structure and log Kow of both substances. Consequently, the half-life of fluoranthene in sediment is estimated to be longer than the half-life of phenanthrene obtained in a simulation study (216 to 319 days at 12 °C). The vP criterion of REACH, Annex XIII will be exceeded for fluoranthene.

Validity criteria fulfilled:
not applicable
Conclusions:
By comparison with the biodegradation potential of other PAH and with biodegradation in other environmental compartments, biodegradation of fluoranthene in sediments is assessed to be very slow. Based on model calculations, the half-life of fluoranthene in sediment was estimated to be > 1250 days (Mackay 1992).
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
other: related information taken from the ECHA SVHC support document of chrysene, a major constituent of pitch, coal tar, high-temp.
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
information taken from the ECHA SVHC support document for chrysene, a major constituent of pitch, coal tar, high-temp.
Principles of method if other than guideline:
The SVHC support document reviews and reports data relevant for the assessment of biodegradation of chrysene, a major constituent of pitch, coal tar, high-temp.
Specific details on test material used for the study:
Substance is specified by EC and CAS number. Data reported relate to this substance.
Oxygen conditions:
other: various
Inoculum or test system:
other: various
Compartment:
sediment
Remarks on result:
other: results are taken from an assessment report that does report only general findings but no individual experimental data for the specific endpoint.
Transformation products:
not specified

Excerpt from SVHC support document

 

Biodegradation

Biodegradation in water and sediments

The biodegradation in water was already assessed in the Support Document for identification of CTPHT as SVHC (ECHA, 2009) and will not be assessed again within this dossier.

Tests for biodegradation in water have demonstrated that PAHs with up to four aromatic rings are biodegradable under aerobic conditions, but that biodegradation rates of PAHs with more aromatic rings are very low (The Netherlands, 2008).

As assessed in the Support Document for identification of CTPHT as SVHC (ECHA, 2009):

 

In general, the biodegradation rates decrease with increasing number of aromatic rings. This correlation has been attributed to factors like the bacterial uptake rate and the bioavailability. The bacterial uptake rate has been shown to be lower for the higher molecular weight PAHs as compared to the PAHs of lower molecular weight. This may be due to the size of high molecular weight members, which limits their ability to cross cellular membranes. In addition, bioavailability is lower for higher molecular PAHs due to adsorption to organic matter in water and sediment. It has further been shown that half-lives of PAHs in estuarine sediment are proportionally related to the octanol-water partition coefficient (Kow) (Durant et al, (1995) cited in The Netherlands, 2008).

[…]

In general, PAHs are considered to be persistent under anaerobic conditions (Neff (1979); Volkering and Breure (2003) cited in The Netherlands, 2008). Aquatic sediments are often anaerobic with the exception of a few millimetre thick surface layer at the sediment-water interface, which may be dominated by aerobic conditions. The degradation of PAHs in aquatic sediments is therefore expected to be very slow.

 

Estimated data

As assessed in the Support Document for identification of CTPHT as SVHC (ECHA, 2009)Mackay et al. (1992) estimated half-lives in the different environmental compartments based on model calculations and literature research.The calculated half-lives of CHR in water are in the range of 42 to 125 days and for sediment longer than 1250 days (The Netherlands, 2008).

 

[…]

 

Summary and discussion on biodegradation

The half-life predicted by Mackay et al. (1992) indicates that CHR persists in sediment with half-lives higher than 1250 days. For water degradation, Mackayet al.(1992) predicted long elimination half-lives between 42 and 125 days. However, considering the chemical structure of CHR that consists of four aromatic rings, standard tests for biodegradation in water may reveal that CHR is biodegradable under aerobic conditions (EC, 2008). Biodegradation studies in laboratory soil microcosms show dissipation half-lives up to 313 days (Wild and Jones, 1993). Biodegradation studies on soil done by Wildet al.(1991) revealed a half-life of CHR of more than 8.1 years under field conditions.

Hence, CHR biodegrades very slowly in sediments and soil.

This conclusion was already drawn in the Support Document for identification of CTPHT as SVHC (ECHA, 2009).

End of excerpt

 

References:

ECHA (2009) Support Document for identification of Coal Tar Pitch, High Temperature as a SVHC because of its PBT and CMR properties

http://echa.europa.eu/documents/10162/73d246d4-8c2a-4150-b656-c15948bf0e77

EC (European Commission) (2008) European Union Risk Assessment Report, Coal Tar Pitch High Temperature, CAS No: 65996-93-2, EINECS No: 266-028-2

https://echa.europa.eu/documents/10162/433ccfe1-f9a5-4420-9dae-bb316f898fe1

The Netherlands (2008) Annex XV Transitional Dossier for substance Coal Tar Pitch, High Temperature, CAS Number: 95996-93-2

https://echa.europa.eu/documents/10162/13630/trd_netherlands_pitch_en.pdf/a8891f7e-59c8-4d67-97f7-93bb9a9e2676

Durant ND, Wilson LP, Bouwer EJ (1995) Microcosm studies of subsurface PAH-degrading bacteria from a former manufactured gas plant. J Contam. Hydrol., 17, 213-223

Mackay D, Shiu WY, Ma KC (1992) Illustrated Handbook of Physical-Chemical Properties and Environmental Fate of Organic Chemicals. Lewis Publishers, Boca Raton, FL

Neff JM (1979) Polycyclic aromatic hydrocarbons in the aquatic environment. Sources, fate and biological effects. Applied Science Publishers, London.

Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

Wild S.R., Jones K.C. (1993) Biological and abiotic losses of polynuclear aromatic hydrocarbons (PAH) from soils freshly amended with sewage sludge. Environmental Toxicology and Chemistry, 12, 5-12

Wild SR, Berrow ML, Jones KC (1991) The persistence of polynuclear aromatic hydrocarbons (PAHs) in sewage sludge amended agricultural soils. Environmental Pollution, 72, 141-157

Validity criteria fulfilled:
not applicable
Conclusions:
By comparison with the biodegradation potential of other PAH and with biodegradation in other environmental compartments, biodegradation of chrysene in sediments is assessed to be very slow. Based on model calculations, the half-life of chrysene in sediment was estimated to be > 1250 days (Mackay 1992).
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
other: related information taken from the ECHA SVHC support document of benzo[k]fluoranthene, a major constituent of pitch, coal tar, high-temp.
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
information taken from the ECHA SVHC support document for benzo[k]fluoranthene, a major constituent of pitch, coal tar, high-temp.
Principles of method if other than guideline:
The SVHC support document reviews and reports data relevant for the assessment of biodegradation of benzo[k]fluoranthene, a major constituent of pitch, coal tar, high-temp.
Specific details on test material used for the study:
Substance is specified by EC and CAS number. Data reported relate to this substance.
Oxygen conditions:
other: various
Inoculum or test system:
other: various
Compartment:
sediment
Remarks on result:
other: results are taken from an assessment report that does report only general findings but no individual experimental data for the specific substance and endpoint.
Transformation products:
not specified

Excerpt from the SVHC support document

 

Biodegradation

 

Estimated data

As indicated in the Annex XV transitional dossier for CTPHT (The Netherlands, 2008),Mackay et al. (1992) ranked 16 PAHs according to their persistence in water, soil and sediment in different classes which correspond to a specific half-live in these compartments.The calculated half-lives of benzo[k]fluoranthene in water are in the range of 42 to 125 days and for sediment longer than 1250 days.

 

Biodegradation in water and sediment

Benzo[k]fluoranthene was shown to biodegrade under aerobic conditions in water than PAHs containing up to four aromatic rings. Furthermore, degradation in aquatic anaerobic sediments is expected to be very slow, as assessed before in the Support Document for identification of CTPHT as SVHC (ECHA, 2009):

Standard tests for biodegradation in water have demonstrated that PAHs with up to four aromatic rings are biodegradable under aerobic conditions, but that biodegradation rates of PAHs with more aromatic rings are very low (The Netherlands, 2008). In general, the biodegradation rates decrease with increasing number of aromatic rings. This correlation has been attributed to factors like the bacterial uptake rate and the bioavailability. The bacterial uptake rate has been shown to be lower for the higher molecular weight PAHs as compared to the PAHs of lower molecular weight. This may be due to the size of high molecular weight members, which limits their ability to cross cellular membranes. In addition, bioavailability is lower for higher molecular PAHs due to adsorption to organic matter in water and sediment. It has further been shown that half-lives of PAHs in estuarine sediment are proportionally related to the octanol-water partition coefficient (Kow) (Durant et al., (1995) cited in The Netherlands, 2008).

In general, PAHs are considered to be persistent under anaerobic conditions (Neff (1979); Volkering and Breure (2003) cited in The Netherlands, 2008). Aquatic sediments are often anaerobic with the exception of a few millimetre thick surface layer at the sediment-waterinterface, which may be dominated by aerobic conditions. The degradation of PAHs in aquatic sediments is therefore expected to be very slow.

[…]

At present benzo[k]fluoranthene has not been tested in a sediment simulation study (OECD 308). However, during the public consultation a summary of such a study was provided in which the degradation of phenanthrene was studied (Meisterjahn et al. 2018). When converted to 12°C, the half-lives observed were higher than the vP criterion. Considering that the biodegradation rates decrease with increasing number of aromatic rings and the half-lives of PAHs in estuarine sediment are proportionally related to the octanol-water partition coefficient (Kow) (Durant et al. (1995) cited in The Netherlands, 2008), it can be assumed that benzo[k]fluoranthene will also meet the P and vP criterion in sediment.

 

[…]

 

Summary and discussion on biodegradation

For water degradation, Mackayet al.(1992) predicted long elimination half-lives between 42 and 125 days. It is assumed that benzo[k]fluoranthene meets the P and vP criterion in sediment, as in the available simulation study with phenanthrene the half-life meets the P and vP criterion. Considering that the biodegradation rates decrease with increasing number of aromatic rings and the half-lives of PAHs in sediment are proportionally related to the octanol-water partition coefficient (Kow), the half-life of benzo[k]fluoranthene should meet the P and vP criteria in sediment as well.

The half-life predicted by Mackayet al. (1992) supports the persistency of benzo[k]fluoranthene in sediments (half-life> 1250 days).

[…]

[…]. Data indicate that a low biodegradation of benzo[k]fluoranthene is observed in sediments, based on which benzo[k]fluoranthene meets the vP criteria for sediment.

Therefore, it is concluded that based on the available data, benzo[k]fluoranthene biodegrades very slowly in soil and sediment.

End of excerpt

 

References

ECHA (2009) Support Document for identification of Coal Tar Pitch, High Temperature as a SVHC because of its PBT and CMR properties

http://echa.europa.eu/documents/10162/73d246d4-8c2a-4150-b656-c15948bf0e77

The Netherlands (2008) Annex XV Transitional Dossier for substance Coal Tar Pitch High Temperature, CAS Number: 65996-93-2

https://echa.europa.eu/documents/10162/13630/trd_netherlands_pitch_en.pdf/a8891f7e-59c8-4d67-97f7-93bb9a9e2676

Durant ND, Wilson LP, Bouwer EJ (1995) Microcosm studies of subsurface PAH-degrading bacteria from a former manufactured gas plant. J Contam Hydrol, 17, 213-223.

Mackay D, Shiu WY, Ma KC (1992) Illustrated handbook of physical-chemical properties and environmental fate of organic chemicals. Lewis Publishers, Boca Raton, FL, USA

Meisterjahn et al. (2018) (Report in preparation) Degradation of 14C labelled hydrocarbons in Water-Sediment using standard and optimized OECD test guidelines - 308. Germany: Fraunhofer IME-AE.

Neff JM (1979) Polycyclic aromatic hydrocarbons in the aquatic environment. Sources, fate and biological effects. Applied Science Publishers, London.

Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

Validity criteria fulfilled:
not applicable
Conclusions:
By comparison with the biodegradation potential of other PAH and with biodegradation in other environmental compartments, biodegradation of benzo[k]fluoranthene in sediments is assessed to be very slow. Based on model calculations, the half-life of benzo[k]fluoranthene in sediment was estimated to be > 1250 days (Mackay 1992).
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
other: related information taken from the ECHA SVHC support document of benzo[def]chrysene (benzo[a]pyrene), a major constituent of pitch, coal tar, high-temp.
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
information taken from the ECHA SVHC support document for benzo[def]chrysene (benzo[a]pyrene), a major constituent of pitch, coal tar, high-temp.
Principles of method if other than guideline:
The SVHC support document reviews and reports data relevant for the assessment of biodegradation of benzo[def]chrysene (benzo[a]pyrene), a major constituent of pitch, coal tar, high-temp.
Specific details on test material used for the study:
Substance is specified by EC and CAS number. Data reported relate to this substance.
Oxygen conditions:
other: various
Inoculum or test system:
other: various
Compartment:
sediment
Remarks on result:
other: results are taken from an assessment report that does report only general findings but no individual experimental data for the specific substance and endpoint.
Transformation products:
not specified

Excerpt from SVHC support document

 

Biodegradation in water

 

Estimated data

As already assessed in the Support Document for identification of CTPHT as SVHC (ECHA, 2009),Mackay et al. (1992) estimated half-lives in the different environmental compartments based on model calculations and literature research. The calculated half-lives of B[a]P in water and sediments are in the range of 42 to 125 days and > 1250 days respectively.

 

Simulation tests (water and sediments)

In the Support Document for identification of CTPHT as SVHC (ECHA, 2009) the following is stated:

 

“Standard tests for biodegradation in water have demonstrated that PAHs with up to four aromatic rings are biodegradable under aerobic conditions, but that biodegradation rates of PAHs with more aromatic rings are very low (The Netherlands, 2008). In general, the biodegradation rates decrease with increasing number of aromatic rings. This correlation has been attributed to factors like the bacterial uptake rate and the bioavailability. The bacterial uptake rate has been shown to be lower for the higher molecular weight PAHs as compared to the PAHs of lower molecular weight. This may be due to the size of high molecular weight members, which limits their ability to cross cellular membranes. In addition, bioavailability is lower for higher molecular PAHs due to adsorption to organic matter in water and sediment. It has further been shown that half-lives of PAHs in estuarine sediment are proportionally related to the octanol-water partition coefficient (Kow) (Durant et al,(1995) cited in The Netherlands, 2008).

[…]

In general, PAHs are considered to be persistent under anaerobic conditions (Neff (1979); Volkering and Breure (2003) cited in The Netherlands, 2008). Aquatic sediments are often anaerobic with the exception of a few millimetre thick surface layer at the sediment-water interface, which may be dominated by aerobic conditions. The degradation of PAHs in aquatic sediments is therefore expected to be very slow.”

 

Due to the chemical nature and low water solubility of B[a]P, it is concluded that the substance which consists of five aromatic rings is resistant to biodegradation in water and sediment.

 

Summary and discussion on biodegradation

[…]

The model calculations by Mackay et al. (1992) indicate that B[a]P persists in sediment and soil with half-lives of > 1250 and 420 to 1250 days, respectively. Biodegradation studies in soils show dissipation half-lives between 120 and 270 days (Wild and Jones, 1993). Additionally, a dissipation half-life of more than 8.2 years was measured in a field study (Wild et al., 1991).

Hence, B[a]P biodegrades very slowly in water, sediment, and soil.

This conclusion was already drawn in the Support Document for identification of CTPHT as

SVHC (ECHA, 2009).

 

[…]

 

Summary and discussion of degradation

B[a]P has a low water solubility and shows a high tendency to adsorb to particles and organic matter in the environment. The resulting low bioavailability is one of the limiting factors of its biodegradation.

For assessing the persistence of B[a]P, half-lives obtained under realistic conditions, such as field conditions, are given priority.Selected key studies report dissipation half-lives in soil in the range from 120 to 270 days (Wild and Jones, 1993). Additionally, a dissipation half-life of more than 8.2 years was measured in a field study (Wild et al., 1991).

Mackay et al. (1992) estimated half-lives in the different environmental compartments based on model calculations and literature research. The estimated half-lives of B[a]P in sediments and soil range from 420 to 1250 days.

Hence, it is concluded that B[a]P is a persistent substance.

This conclusion was already drawn in the Support Document for identification of CTPHT as SVHC (ECHA, 2009). The reviewed additional information supports this conclusion on the degradation properties of B[a]P.

End of excerpt

 

References:

ECHA (2009) Support Document for identification of Coal Tar Pitch, High Temperature as a SVHC because of its PBT and CMR properties

http://echa.europa.eu/documents/10162/73d246d4-8c2a-4150-b656-c15948bf0e77

The Netherlands (2008) Annex XV Transitional Dossier. Coal Tar Pitch High Temperature (November 2008). Rapporteur: The Netherlands. Documentation of the work done under the Existing Substance Regulation (EEC) No 793/93 and submitted to the European Chemicals Agency according to Article 136(3) of Regulation (EC) No 1907/2006. Published by the European Chemicals Agency at:

https://echa.europa.eu/documents/10162/13630/trd_netherlands_pitch_en.pdf/a8891f7e-59c8-4d67-97f7-93bb9a9e2676

Durant ND, Wilson LP, Bouwer EJ (1995) Microcosm studies of subsurface PAH-degrading bacteria from a former manufactured gas plant. J Contam Hydrol, 17, 213-223.

Mackay D, Shiu WY, Ma KC (1992) Illustrated Handbook of Physical-Chemical Properties and Environmental Fate of Organic Chemicals. Lewis Publishers, Boca Raton, FL, USA

Neff JM (1979) Polycyclic aromatic hydrocarbons in the aquatic environment. Sources, fate and biological effects. Applied Science Publishers, London.

Volkering F, Breure AM (2003) Biodegradation and general aspects of bioavailability. In Douben (ed.) PAHs: An Ecotoxicological Perspective., Wiley, 81-98

Wild SR, Berrow ML, Jones KC (1991) The persistence of polynuclear aromatic hydrocarbons (PAHs) in sewage sludge amended agricultural soils. Environ. Pollut., 72, 141-157

Wild S.R., Jones K.C. (1993) Biological and abiotic losses of polynuclear aromatic hydrocarbons (PAH) from soils freshly amended with sewage sludge. Environmental Toxicology and Chemistry, 12, 5-12

Validity criteria fulfilled:
not applicable
Conclusions:
By comparison with the biodegradation potential of other PAH and with biodegradation in other environmental compartments, biodegradation of benzo[def]chrysene (benzo[a]pyrene) in sediments is assessed to be very slow. Based on model calculations, the half-life of benzo[def]chrysene (benzo[a]pyrene) in sediment was estimated to be > 1250 days (Mackay 1992).

Description of key information

Pitch coal tar, high-temp (CTPht) [CAS no. 95996-93-2] is a UVCB substance consisting of a complex combination of polycyclic aromatic hydrocarbons. Simulation tests on the biodegradation of the substance in sediment have not been identiefied. But there are reports available that assess the biodegradation of CTPht and of its major PAH constituents. Information extracted from these reports into study records of this endpoint is used to characterise the biodegradation in sediment of the substance.

Biodegradation properties of CTPht are characterised by the properties of its PAH constituents. For several of these constituents, information on their biodegradation properties is available. Available data have been summarised in SVHC support documents of these substances prepared by ECHA (Member State Committee). This information in combination will be used to specify the biodegradation of CTPht in sediment.

Key value for chemical safety assessment

Half-life in freshwater sediment:
1 250
at the temperature of:
25 °C

Additional information

CTPht is a UVCB substance and comprises mainly polyaromatic compounds with four and more aromatic rings. Major constituents especially selected regarding biodegradation are fluoranthene, chrysene, benzo[k]fluoranthene, and benzo[def]chrysene (benzo[a]pyrene).

Data on the biodegradation of CTPht in sediment is not available. Due to its complex composition, it is technically not practical in many cases to determine its biodegradation properties applying standard test procedures. But the biodegradation properties of CTPht can be described using data arising from important constituents of CTPht. In combination, these data are assessed to characterise the biodegradation properties of CTPht satisfactorily.

Four main constituent of the substance are considered to be relevant for the characterisation of the biodegradation of CTPht in sediment (see above). These are selected regarding their concentrations in CTPht (see IUCLID Sect. 1.4 - Analytical composition: GC chromatogram) and regarding their biodegradation characteristics. The constituents are of increasing size and log Kow and have a low water solubility (below 1 mg/L, see EU RAR of COAL-TAR PITCH; HIGH TEMPERATURE; Table 1.6, p 18), properties that greatly affect biodegradation performance of PAH.

Information available on the biodegradation of CTPht itself and of its four PAH constituents was already assessed in the context of REACH Regulation (1907/2006) by different authorities or regulatory bodies. Data are collected in the Risk Assessment Report for pitch coal tar, high-temp. and in the SVHC support documents of CTPht and the selected constituents prepared by ECHA (Member State Committee). This information is summarised in the six study records of this endpoint.

 - EU 2008; RAR Coal-Tar Pitch High Temperature; excerpt biodegradation

 - ECHA 2009; SVHC support document - coal tar pitch, high temperature

 - ECHA 2018; SVHC support document - fluoranthene

 - ECHA 2017; SVHC support document - chrysene

 - ECHA 2018; SVHC support document - benzo[k]fluoranthene

 - ECHA 2016; SVHC support document - benzo[def]chrysene/benzo[a]pyrene

The information in these study records is frequently of general nature. Data are not systematically separated covering the different environmental compartments. Therefore, the information is extracted and presented in the study records as present in the respective SVHC support documents.

 

Concurrent information on biodegradation in sediment

Information on the biodegradation of PAH constituents of CTPht in sediment are scarce. In the study records of this endpoint (excerpts of assessment reports), information on degradation and especially on biodegradation in sediment is more of a general nature. It is reported that PAH up to four aromatic rings can be biodegraded (in water), but that the biodegradation of PAH with more aromatic rings is very low. Biodegradation of PAH in sediment will be much lower than in water and also lower than biodegradation in soil.

Biodegradation rates differ considerably. They decrease with increasing number of aromatic rings. Two factors are considered responsible for the difference in degradation rate. First, the bacterial uptake rates of the compounds with higher molecular weight have been shown to be lower than the uptake rates of the low molecular weight PAH. The second and most important factor is the bioavailability of PAHs, due to sorption on suspended organic matter and sediment. Since the Kow and the Koc are strongly correlated, high molecular weight PAH will degrade slower than low molecular weight PAH. Additional important influencing factors are

a) the substrate concentration; with low PAH concentrations leading to longer half-lives,

b) temperature, which reversely relates to the half-live, and

c) the presence or absence of a lag-phase.

Microorganisms in water, sediment, and oil can adapt to PAH. After pre-exposure to PAH or crude oil, increased degradation rates could be observed.

In general, PAH are considered to be persistent under anaerobic conditions (Neff 1979; Volkering and Breure 2003). Aquatic sediments are often anaerobic with the exception of a few millimetre thick surface layer at the sediment-water interface, which may be dominated by aerobic conditions. The degradation of PAH in aquatic sediments is therefore expected to be very slow.

At present, no sediment simulation studies according to OECD TG 308 have been performed with major constituents of CTPht. However, recently a sediment simulation study has been identified using besides others phenanthrene as test substance (Meisterjahn et al. 2018). After recalculation of experimental results obtained at 20 °C to a temperature of 12 °C, half-lives ranged from 216 to 319 days. Major constituents of CTPht are of larger molecular size (larger number of aromatic rings) and have a higher log Kow. Taking into account that biodegradation rates decrease with increasing number of aromatic rings and that the half-lives of PAH in sediment are proportionally related to the octanol-water partition coefficient (Kow), the half-lives of major constituents of CTPht in sediment can be expected to be clearly increased compared to phenanthrene. As the properties of its PAH constituents, sum up to the properties of CTPht, it can be concluded that the half-life of CTPht in sediment is highly increased compared to phenanthrene. The vP criterion of REACH Regulation, Annex XIII for sediment is greatly exceeded.

Measured half-lives do not exist for the biodegradation of PAH in sediment. As substitute, Mackay estimated half-lives of PAH in water, sediment, and soil based on model calculations (Mackay 1992). For all relevant constituents of PAH, a half-live in sediment above 1250 days was estimated. This value is taken to characterise the biodegradation of CTPht in sediment, and it is used as key value for the chemical safety assessment.

In addition to the low intrinsic biodegradation of PAH/CTPht in sediment, biodegradation half-lives of CTPht constituents in sediment will be further reduced by the low water solubility of PAH that are released from the solid matrix of CTPht. This effect was demonstrated in a column elution study investigating the water solubility of individual PAH (16 EPA PAH and two methylnaphthalenes) when CTPht was used as test material. In five experiments, the accumulated concentration of the 18 PAH analysed ranged between 0.82 and 1.9 µg/L. The maximum concentration of a single PAH (fluoranthene) was 0.445 µg/L (see IUCLID Sect. 4.8, study record Noack/NOACK 2009).

For references see the study records of this endpoint and the references listed in the study records.