1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylindeno[5,6-c]pyran

Biodegradation in soil

Description of key information

Soil compartment

Note: The degradation in soil is fully presented in a report attached to the Overall Endpoint summary: Environmental fate and pathways.

In the key study (DiFrancesco et al. 2004) a conservative but realistic DT50 value for soil is 35 days for a sandy soil containing 1.55% organic carbon to which HHCB containing sludge was applied to soils. This soil is most close to the proposed soils of the OECD TG 307. It is a field study in which temperature correction is not needed as such. Other reliable studies showing somewhat similar values or slightly higher.

- The Envirogen study (1998) presents roughly the outline of the OECD TG 307. Due to the poor documentation, the DT50 value of 105 days can only be indicative and is overruled by the first study.

- The fungal study of Envirogen (1997) shows that the HHCB can be further degraded into more polar metabolites than HHCB-Lactone, this lactone being the most relevant metabolite, though an environmental relevant half-life cannot be derived. It does show that the metabolites seen are hydrophilic.

Key value for chemical safety assessment

Half-life in soil:

35 d

at the temperature of:

12 °C

Additional information

Note: A complete review of degradation in soil is presented in a file attached to the Overall Endpoint summary for biodegradation.

Degradation of HHCB in the Soil Compartment: Results of the WoE

Biodegradation and DT50 in the soil compartment is also based on a WoE using studies which together can present with sufficient accuracy the information from an OECD TG 307 study: ‘the rate of transformation of the test substance, and (ii) the nature and rates of formation and decline of transformation products to which plants and soil organisms may be exposed’.

Three key studies are selected: DiFrancesco et al. (2004) for transformation of the parent, Envirogen (1998) for indication of removal of the parent and increase of more polar degradation products and Envirogen (1997) for showing the intrinsic potential of HHCB and HHCB-Lactone of degradation by soil fungi into more hydrophilic products as measured by TLC.

In the primary study of this WoE HHCB is tested in sludge amended soils in a yearlong outdoor lysimeter study (DiFrancesco et al., 2004), which reflect the sludge application containing HHCB to soils. This study assessed HHCB dissipation in several soil types receiving sludge from two municipal wastewater treatment plants containing background levels of HHCB (i.e. unspiked) and sludge containing background levels of HHCB spiked with additional HHCB (i.e. spiked). Georgetown sludge is applied to several soils containing 86 µg HHCB/g sludge. From these soils one was selected: Sandy Georgetown soil, because it is a sandy soil and it had an OC content of 1.55%, both parameters are within the criteria of the OECD TG 307 on soils. The final HHCB concentration was 8.6 µg/kg soil. The study was performed outdoors with an average annual temperature in the testing location of 13°C but started in summer. There were no transformation products measured.

Results and discussion: The DT50 in this Sandy Georgetown soil is 35 days. Leaching as a mechanism for dissipation was ruled out as leaching was measured and did not occur. The DT50 measured is therefore representative of both biotic and abiotic degradation and volatilization. Volatilization is not considered a key removal process for HHCB, being a low volatile substance. These 35 days can be used for the risk assessment.

The second study for the WoE is a lab-based simulation study performed by Envirogen et al. (1998) analogous to the OECD 307 in design but the study is poorly documented. The soil with sludge application was used for assessment being the realistic as an exposure scenario. OC carbon content is not given. The temperature was 22°C and the test concentration was 10 mg/kg soil, while maximally 1 mg/kg soil dwt is used in the OECD TG 307. Also the study lacks robust reporting and has methodological constraints (e.g. type of soil was not mentioned, no OC content was given, too high concentrations were used and absence of measuring transformation products) prevents it from satisfying the OECD TG 307 as a stand-alone study.

Results: This study demonstrated that removal observed in field-dissipation studies is in part due to biodegradation. This study measured a DT50 value of 14-C HHCB of 105 days at 22-23°C in sludge amended soil (Estimated rate constants and half-lives were 0.0066 d-1 and 105 days for sludge amended soil HHCB RAR, 2008). Degradation was considered the mechanism for the observed disappearance. This conclusion was made possible as it was reported that there was no significant loss of HHCB from volatilization in addition to the high recovery via extraction of the soil medium (i.e. low probability for non-extractable residue formation). The degradation of HHCB resulted in several more polar metabolites as identified by TLC, but the identity or octanol water partitioning coefficients of the metabolites were not reported.

Discussion: While this study seems more in-line with standard regulatory biodegradation studies in soil (e.g. OECD 307), the lack of robust reporting and methodological constraints (e.g. type of soil was not mentioned, no OC content was given, too high concentrations were used and absence of measuring transformation products) prevents it from satisfying the OECD TG 307 as a stand-alone study.

The third type of information for the WoE is related to the ability of soil fungal strains (common in the environment) to degrade HHCB help clarify the potential for HHCB metabolites to persist in soil and further explain the removal mechanism observed in field-dissipation studies (Envirogen, 1997). From this study the increase and decrease of the parent and the degradation products are shown using radioactive HHCB and TLC retention times. From this, however, no environmentally relevant DT50 can be estimated. This study shows the intrinsic potential of fungi to degrade HHCB.

In one test system fungi were exposed to 50 mg/l HHCB and incubated at 30°C for 12 weeks. In another test a flask containing a fungal isolate was converted to a soil bio slurry system after several weeks of incubation.

Results and Discussion: Especially one soil fungus strain was important for the degradation ENV-F002 and also P. chrysopoprium (white rot fungus) was able to degrade HHCB. The ENV-F2002 showed after 1-week exposure 19% remaining HHCB and by 4 weeks only 5.5% HHCB remained. HHCB-Lactone accounted for 28% of radioactivity after 1 week and 16% after 12 weeks. The remaining radioactivity, 78%, was metabolized to more hydrophilic metabolites than HHCB-Lactone (< Retention times)

In a follow up experiment, it showed that adding soil to a 4-week fungal culture with ENV-F002, significant mineralization to CO2 (15-20%) after ca. 100 days.

These studies indicate that HHCB degrades to HHCB-Lactone and can further degrade to more polar metabolites than HHCB-Lactone in soil and some mineralization is anticipated.

Other studies report a similar DT50s finding for similar conditions (Yang et al. 2006; Yager et al. 2014; and Chen et al. 2014a) of which a summary is presented below.

Yang et al. (2006) measured the dissipation of HHCB in soils in Ontario, Canada receiving sludge amendments. Post application of sludge containing HHCB: the concentration of HHCB rapidly dissipated from soils from 3 ppb (3 µg/kg soil) to below limit of quantification at week 4. The authors note that it was still detectable at month 6. In addition, the sludge was amended just before the winter months hence the removal could be deemed conservative. Unfortunately, limit of quantification, nor detection, was reported specifically for HHCB. Therefore, reliable DT50s cannot be extrapolated from the provided information. However, based on reported range of LOQs for the substances studied (0.2-1.9 µg/kg w/w soil), conservatively assuming that the range of LOQs provided are the lowest concentrations reliably measured at the end of the first 4 weeks, HHCB could have DT50s between 7-50 days. The authors note too that the sludge was applied just before the freezing conditions of the winter months which might explain why after 6 months it was still detectable.

Applicability for the risk assessment: These values support the DT50 in soil of 35 days.

Yager et al. (2014) evaluated the field dissipation of HHCB in sludge and sludge amended soils in a 1.5 yearlong study in Colorado, USA. HHCB in sludge and soil rapidly dissipated after application. In the sludge sample that was left on a geotextile fabric to weather, HHCB dissipated to roughly 5% the initial concentration over a period of 180 days but was still present in measurable quantities. The rate of dissipation appeared to be dynamic as opposed to constant. In soil, after 180 days HHCB dissipated to the quantities that existed pre-sludge application indicating near complete removal. In soil, vertical soil column samples were measured that indicated little leaching and hence leaching as a mechanism for removal is unlikely. While authors did not report DT50s, DT50s could be estimated from the raw data. In the weathered sludge (=geotextile), considering initial concentration compared with the concentration measured at day 180, the calculated DT50 was ~50 days. If only considering the data from day 90 to day 180, the DT50 increases to ~250 days and is not) relevant for risk assessment. This would indicate dynamic change in the rate of removal. In soil, the DT50 can be calculated from initial concentration compared with the concentration at day 180. The DT50 using 529 ppb (0.5 mg/kg soil) as the initial concentration and 31 ppb (0.03 mg/kg as the concentration measured at day 180, was calculated to be 46 days. Realistic local farming practices were applied to the study area, such as low-till immediately after biosolid application.

Applicability of the study for the risk assessment: The DT50 relevant for the risk assessment is in line with the selected key information.

Beside the Envirogen (1998) study (presented above, with a DT50 of 105 days), there is one study with two scenarios of which one scenario show HHCB half-life longer than ca 100 days, which needs discussion here.

The first study with one scenario in disagreement assessed the dissipation of HHCB under field conditions in two scenarios (Chen et al., 2014).

Chen et al. (2014) measured the dissipation of HHCB in land applied biosolids in several fields across China with no prior contamination. The fields were amended with biosolids at a rate proportional to regional practices. Soils either received one single amendment over the course of three years or repeated amendments at a rate one per year for three years. In all soils, HHCB was present in measurable quantities after three years in both the single biosolids application and repeated biosolids application. In one site, a more detailed dissipation study was performed. The results indicated DT50s ranging from 83-900 days for repeated and single biosolid amendments, respectively. These results indicate that levels of HHCB can dissipate from soils in some instances at a high rate but in others at a slow rate. During this study, real field conditions were used that incorporated the winter months. The average annual temperature for the three sites investigated ranged from 12.9 to 19.1°C. The detailed dissipation study was performed on the site with the lowest average annual temperature. The authors note that while HHCB is removed, it is persistent under some circumstances as indicated by the slow dissipation rate associated with the single amendment.

In one scenario wastewater sludge containing HHCB was applied 3 years prior to an agricultural plot. Results: The HHCB concentration measured after the 3rd year was 0.3 µg/kg soil which was at the LoD and then dissipation was assessed on the 4th year, resulting in a DT50 of 900 days. In view of the concentration being at the LoD at the time of initiation and below the LoD after the second measure, this information is not considered reliable.

The second scenario in this study of this Chen et al (2014) study contradicts the finding of the first scenario. HHCB is present in fresh sludge, which is applied to a similar agricultural plot as from the first scenario, resulting in 30 µg/kg soil HHCB. In this scenario a DT50 of 83 days was found and is considered realistic.

The second study that conflicts that HHCB is degraded is a lab-based outdoor soil simulation study performed by Litz et al. (2007), with the main focus on adsorption/dissipation and not on degradation. One sandy soil reflects the OECD TG 307 criterion for OC contents: Cambisol, OC is 1.2% (>0.5 and < 2.5% OC). This soil received sludge amendments containing high HHCB concentrations and the final soil concentration was 10 mg/kg soil while maximum concentrations used should be 1 mg/kg soil (OECD TG 307). Results and discussion: The authors reported dissipation DT50 for the Cambisol soil of ca 10 months. The authors reported >50% of HHCB removed from the system but ruled out volatilization, and both abiotic and biotic degradation. As non-extractable residues were unlikely based on their recovery efficiency of HHCB from soil in preliminary studies this leaves no possible explanation for the significant loss. This may suggest an issue with their test system and/or experimental design and therefore this study is not considered reliable and not included in the overall assessment.

Conclusion for HHCB persistency in the soil compartment

• A conservative but realistic DT50 value for soil is 35 days for a sandy soil containing 1.55% organic carbon to which HHCB containing sludge was applied to soils. This soil is most close to the proposed soils of the OECD TG 307. It is a field study in which temperature correction is not needed as such. Other reliable studies showing somewhat similar values or slightly higher.


• The Envirogen study (1998) presents roughly the outline of the OECD TG 307. Due to the poor documentation, the DT50 value of 105 days can only be indicative and is overruled by the first study.

The fungal study shows that the HHCB can be further degraded into more polar metabolites than HHCB-Lactone, this lactone being the most relevant metabolite, though an environmental relevant half-life cannot be derived. It does show that the metabolites seen are hydrophilic and need to be assessed for B-assessment.

Reference list

Chen, Feng, et al. "Field dissipation and risk assessment of typical personal care products TCC, TCS, AHTN and HHCB in biosolid-amended soils." Science of the total environment470 (2014): 1078-1086.

Chen, Feng, et al. "Field dissipation of four personal care products in biosolids‐amended soils in North China." Environmental toxicology and chemistry11 (2014): 2413-2421.

DiFrancesco, A. M., P. C. Chiu, L. J. Standley, H. E. Allen, and D. T. Salvito. 2004. Dissipation of Fragrance Materials In Sludge-Amended Soils. Environmental Science and Technology, 38(1), 194-201.

Envirogen (1997). Biodegradation Studies of HHCB: Assessment of a Two Stage Fungal/Soil Treatment. Envirogen, Inc. Princeton Research Centre, report submitted to International Flavors and Fragrances, Lawrenceville, NJ.

Envirogen (1998). Fate of HHCB in Soil Microcosms. Envirogen, Inc. Princeton Research Centre, report submitted to International Flavors and Fragrances, Lawrenceville, NJ.

Litz et al. "Occurrence of Polycyclic Musks in Sewage Sludge and their Behaviour in Soils and Plants. Part 2: investigation of Polycyclic Musks in Soils and Plants (9 pp)." Journal of Soils and Sediments1 (2007): 36-44.

Yager, Tracy JB, et al. "Dissipation of contaminants of emerging concern in biosolids applied to nonirrigated farmland in Eastern Colorado." JAWRA Journal of the American Water Resources Association2 (2014): 343-357.

Yang, Jian-Jun, and Chris D. Metcalfe. "Fate of synthetic musks in a domestic wastewater treatment plant and in an agricultural field amended with biosolids." Science of the Total Environment 363.1-3 (2006): 149-165.