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Environmental fate & pathways

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Biotic degradation in water and sludge

1. Lee et al. (2001) described a sludge die-away test using test concentrations of 5 and 50μg/l 14C-AHTN. Several polar metabolites were detected after 3 days, and after 20 days the test item was largely biotransformed. Half-life of the parent AHTN was 12-24 h. This half-life refers to disappearance of the parent compound.

 

2. A similar die-away test was conducted in river water (Schaefer and Koper 2007). AHTN was tested at a concentration of 5μg/l and sludge inoculum 10 mg/l TSS. AHTN steadily disappeared with an overall half-life of 200 hours, by a combination of processes, including also volatilisation. By correction for volatilisation and combining with the data of the abiotic control, it was shown that the loss of parent material due solely to biodegradation (therefore primary biodegradation) was 42% after 28 days. The extracts from the sludge study were combined and analyzed for Kow by HPLC with on-line radioactivity detection. In this study, log Kow of AHTN was 5.88. Biotransformation products eluted in two major groups. The log Kow value of the first group is 0.34 - 0.73 and of the second 3.92. Thus it is concluded that the metabolites are much more polar than the parent material.

 

3. Lee et al. (2001) carried out also a CAS-test with 10μg/l 14C-labelled AHTN in realistic STP operational conditions (addition of waste water, sludge retention time 10 d, hydraulic retention time 6 h). A complete mass balance could be derived and it showed that the total removal of the parent AHTN was 87.5% of which a half (42.5%) was caused by biotransformation and a half by sorption (44.3%). Volatilisation played a minor role (3.3%) (Lee et al. 2001, Federle et al. 2002).

 

4. In another study, concentrations of AHTN in activated sludge samples were followed for 2 days. The samples were not additionally spiked and the initial dissolved and total concentrations were 1.15 and 5.25 μg/l, respectively. Loss due to volatilisation was also determined. The ‘true biodegradation rate constant’ based on the dissolved concentration was 0.023 ± 0.010 per hour. The rate constant based on total concentrations was 0.0075 per hour (Artola 2002).

 

No data are available on degradation in sediment.

 

Biodegradation in soil 

1. From soils collected in the Netherlands, several pure cultures of the ubiquitous fungi Aureobasidium pullulans and Phanerochaete chrysosporium were isolated which were capable of degrading AHTN and AHTN-alcohol (PFW 1996 and 1997). Approximately 28% of the 64 soil samples degraded AHTN. 80% of AHTN disappeared in 3 weeks in A. pullulans cultures, and AHTN disappeared within 3 days from cultures with the white rot fungus P. chrysosporium.

 

2. AHTN and HHCB concentrations in 13 field locations in Baden-Württemberg, Germany, were measured in 2002 and compared to estimated concentrations after last sludge application. Different but recorded quantities of sludge had been applied in different periods to each field and the time from the last sludge application varied from field to field. Reference fields were also included (LfU-BW 2003). Using the data in the report, the remaining AHTN+HHCB concentration after the last application was calculated to be 0.2 % after 13 years, 0.5 % after 7 years, < 0.4 % after 4 years, 1.9 % after 3 years and < 0.3 % after 3 years, 1,8 after 2 years and 1.3 % after 1 year. The estimated disappearance reflects the influence of all losses. On the basis of physical-chemical properties of AHTN and HHCB, loss via leaching can be considered as very low, whereas volatilization might have caused a part of disappearance.

 

3. In a 1-year mesocosm scale a 1-year die-away study of fragrance materials in four different soils, soil samples were amended with sludge and contained initially AHTN between 0.1 and 0.27 mg kg-1dwt. A set of soils was amended with sludge and in addition spiked with AHTN resulting initial concentration of 6 and 13 mg kg-1dwt. The test trays were placed outdoors. In the spiked soils, concentrations rapidly decreased during the first month and then decreased steadily. During the next three months period the soil was frozen and the concentrations of all test materials remained stable. After one year, the concentrations of AHTN in unspiked soils ranged from 42 to 61% of the initial concentration. In spiked soils the concentrations were slightly more variable. Leachate was collected during the first 3 to 5 months; it was concluded that the influence of leaching was negligible on the disappearance. The share of volatilization and degradation of the disappearance were not determined (DiFrancesco et al. 2004).

 

Other information

The available temporal series of monitoring data indicate that AHTN is not persistent in sediment. The decrease of concentrations in sewage sludge, water and suspended mater, which reflect the reduction of the input of AHTN to sewers over the years, are followed by a similar decrease of concentrations in sediment. This phenomenon is illustrated by Figure 1 and Table 2 in the PBT Working Group Report. Figure 1 illustrates the immediate decrease of AHTB in the environment in Hessen (by a factor of circa 5) after a decrease in the use of AHTN starting in the 1990's. Table 2 is reproduced below, and completed for 2011 monitoring data and data on the use volume in the EU. Other available sediment monitoring data show a similar trend (European Commission, 2008).

 

Figure 1. Trend in the concentrations of AHTN in Hessen. Note the logarithmic scale (Data from HLUG 2001) (see attached picture)

 

Table 2. Decrease of the AHTN concentrations in samples from STPs along Teltow Canal and sediment, Berlin (compiled from: Heberer 2002, Fromme et al. 2000, Fromme et al. 2001a, Blok et al. 2005; Balk et al. 2012[1]).

 

 

 

1996/97

2000

2004

2011

Reduction factor

EU use volume, ton/yr

 

585

358

247

(2008-2011) circa 300

2

Effluent,

µg/L

median

90-perc

max

2.2

3.4

4.4

 

0.23

 

0.29

 

 

10

Sludge,

mg/kg dw

median

90-perc

max

 

3.6

 

5.1

2.9

 

3.8

1.6

 

1.8

2

Sediment,

mg/kg dw

median

90-perc

max

0.9

2.2

2.6

 

0.22

 

0.46

<0.1

 

0.2

10

 

The decrease in the concentrations seems to be disproportionally high (a factor 2 to 10) as compared to the decrease in use volume (a factor of 2). Explanations might be that in the past samples were over-representing contaminated sites and relevant improvement of the performance of STPs.

 

Summary and discussion of persistence

 

Degradation simulation tests are not available for marine water or sediment. Evidence of relatively fast primary degradation is provided from the available experiments with sludge, river water and soil. However, the studies reviewed detected low mineralization rates of AHTN. Instead, polar metabolites were formed readily and polarity increased over time.

The half-life for primary degradation of AHTN in activated sludge was less than 1 day (Lee et al. 2001, Federle et al. 2002, Artola 2002). The overall half-life of AHTN in a river water die-away test (Schaefer et al. 2007) was shown to be 200 hours and the biological degradation after 28 days was 42%. With 10 mg suspended solids from activated sludge, the conditions in the river die-away test simulate the situation after release of test substance in effluent into river with respect to the concentration and origin of suspended solids in the receiving river. The sediment downstream of a STP is formed by settlement of suspended solids that will originate at least partly from the solids discharged with the effluent (30 mg/L). Therefore the conditions are environmentally relevant but do not correspond exactly with standard biodegradation simulation tests in surface water, where an amendment with sediment from the same site is allowed, but not with suspended solids derived directly from an STP.

 

Lee et al. (2001) observed that during the degradation process over time three different metabolites were formed with an increasing polarity with log Kow going down from 3.9 to circa 0.5. This observation was confirmed in later studies by Schaefer and Koper (2007).

 

The available monitoring data from sludge, surface water, suspended matter and sediment provide evidence that AHTN degrades in the aquatic compartment. Measured concentrations in these compartments have been decreasing over time and follow hence the diminishing use volume. It must be noted, however, that no monitoring data on metabolites have been reviewed.

 

The available mesocosm scale soil dissipation study of DiFrancesco et al. (2004) resulted in a very slow disappearance of AHTN as 42 to 61 % of the initial concentration was left in soil after one year (including 3 months of frost). Opposite results have been gained in the large German study (LfU-BW, 2003) measuring disappearance of AHTN and HHCB over several years in 13 field locations, where the substances had been applied with STP sludge to soil. On the basis of this study, the test item is not expected to have long residence time in soils. The study does not distinguish between different dissipation routes and volatilisation may have caused part of the disappearance. However, the test item is fast degraded in air by indirect photochemical reaction with OH –molecules and hence the part volatilised is not distributed further.

Conclusion on P-criterion

On the basis of these data, the TC NES Subgroup on Identification of PBT and vPvB substances concluded that the test item does not meet the P-criterion:

 

·        Evidence of inherent biodegradability from tests with activated sludge is available. Rapid primary biodegradation was observed and polar metabolites were readily formed. In an activated sludge die-away test a primary degradation half-life of 12-24 h was found and in a CAS test 42.5 % of parent compound was degraded to its metabolites. In a river water die-away test 42% was degraded after 28 days. Mineralization was negligible, but the formation of metabolites was observed with an increasing polarity resulting in metabolites showing log Kow from 3.9 to circa 0.5.

·        Since 1995 the use volume in the EU was reduced by a factor of 2. Monitoring data show a decreasing trend of concentrations in sludge, water, suspended matter, biota and sediment which is evidence that the test item degrades in the aquatic environment.

·        A study investigating the residence of the test item in 13 soils with different histories of sludge application showed that the substance had disappeared almost completely regardless of the time elapsed since the last sludge application. Volatilisation may have contributed to the disappearance but this distribution route is not considered relevant, because the test item is rapidly degraded in the atmosphere.

[1]Confidential report to IFF and PFW, Fragrance ingredients in STPs and sediment in Berlin. Available on request