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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Biodegradation in water (screening):

Key study:

In an OECD TG 301B study, conducted to GLP, methylene bis(dibutyldithiocarbamate) attained 21% degradation after 28 days and therefore cannot be considered to be readily biodegradable (Safepharm Laboratories Limited, 2004).

Biodegradation in water and sediment:

Key studies:

Surface Water Mineralisation

In an OECD 309 study, the biodegradation and fate of the test material was investigated at two concentrations in aerobic surface water under laboratory conditions according to OECD Testing Guideline No. 309. Surface water was treated with radiolabeled test material at nominal application rates of 10 ug/L and 100 ug/L. Treated surface water samples were attached to air flow lines with traps to collect carbon dioxide and incubated with continuous stirring to maintain aerobic conditions at 12 +/- 2 deg C in darkness for periods of up to 62 days. 

Total recoveries of radioactivity (mass balances) for samples treated at 10 ug/L and 100 ug/L were between 80.4 and 100.4% applied radioactivity. Samples with low total recoveries of radioactivity (<90%) tended to be those that were sampled in the latter stages of the study (≥29 days) at both concentration levels. Carbon dioxide accounted for a maximum of 39.5% applied radioactivity.

Separate sterile samples were treated to provide abiotic controls. Total recoveries of radioactivity (mass balances) for these sterile samples treated at 10 ug/L and 100 ug/L were between 86.4% and 97.5% applied radioactivity. Carbon dioxide accounted for a maximum of 2.8% applied radioactivity.

The mean amount of parent material in the test system treated at 10 ug/L (nominal) declined from 90.1% of applied radioactivity at the time of application to 1.6% after 62 days of incubation. The mean amount of parent material in the test system treated at 100 ug/L declined from 96.2% of applied radioactivity at the time of application to 5.2% after 43 days of incubation. Parent material was detected at a higher level in one replicate in the test system treated at 100 ug/L after 62 days incubation; however, this result could be considered anomalous.

The estimated DT50 values for the decline of parent material in aerobic surface water were 10.3 days and 16.0 days at 10 ug/L and 100 ug/L concentrations, respectively. The estimated DT90 values for the decline of parent material in aerobic surface water were 34.2 days and 53.2 days at 10 ug/L and 100 ug/L concentrations, respectively.

Analysis of the surface water by HPLC resolved up to 22 components in addition to parent material, including 4 major degradates; several other minor degradates were distributed throughout the chromatograms but did not contain any discrete, resolved radioactive components.  Analysis of the surface water samples showed that the applied parent material degraded to Unknown 1, Unknown 3, Unknown 4 and an unknown polar material, accounting for maximums of 21.1, 30.5, 7.7 and 25.4% applied radioactivity, respectively. Degradate identification is underway. Other (unidentified) degradation products were present individually at ≤5.8% applied radioactivity.

Aquatic Sediment Transformation

In an OECD 308 study, the fate of the test material was studied in two natural aquatic sediment systems under laboratory conditions according to OECD Guideline 308. The sediment from Emperor Lake was a sandy clay loam with an acidic pH and low organic carbon content, while that from Calwich Abbey Lake was a neutral silt loam with a higher organic carbon content. Samples of each aquatic sediment system were allowed to acclimatize separately under aerobic or anaerobic conditions before being treated with radiolabelled test material at a rate of 0.1 mg/L based on the amount of water in the test vessel including that present within the sediment. The samples were incubated under aerobic or anaerobic conditions at about 12 deg C in darkness for periods of up to 100 days.

 

Mean total recoveries of radioactivity (mass balances) for both aquatic sediments incubated under aerobic or anaerobic conditions were between 92.7% and 101.5% applied radioactivity. 

 

In Calwich Abbey Lake aquatic sediment incubated under aerobic conditions, the radioactivity in the water layer declined from a mean of 95.7% applied radioactivity at time zero to 3.7% after 100 days of incubation. In the sediment, the total radioactivity increased to a mean of 91.7% applied radioactivity after 30 days and remained at a similar level up to 100 days. The proportion of remaining non-extractable radioactivity in the sedimentaccounted for a mean of ≤7.3% applied radioactivitythroughout. Volatile radioactivity accounted for a maximum mean of 3.5% applied radioactivity after 100 days.

 

In Emperor Lake aquatic sediment incubated under aerobic conditions, the radioactivity in the water layer declined from a mean of 92.0% applied radioactivity at time zero to 4.0% after 100 days of incubation. In the sediment, the total radioactivity increased to a mean of 89.3% applied radioactivity after 58 days and remained at a similar level up to 100 days. The proportion of remaining non-extractable radioactivity in the sediment accounted for a mean of ≤8.5% applied radioactivity throughout. Volatile radioactivity accounted for a maximum mean of 4.1% applied radioactivity after 100 days.

 

In Calwich Abbey Lake aquatic sediment incubated under anaerobic conditions, the radioactivity in the water layer declined from a mean of 90.3% applied radioactivity at time zero to 24.8% after 100 days of incubation. In the sediment, the total radioactivity increased to a mean of 70.6% applied radioactivity after 100 days. The proportion of remaining non-extractable radioactivity in the sediment accounted for a mean of ≤5.6% applied radioactivity throughout. Volatile radioactivity accounted for a maximum mean of 1.2% applied radioactivity after 100 days.

 

In Emperor Lake aquatic sediment incubated under anaerobic conditions, the radioactivity in the water layer declined from a mean of 86.0% applied radioactivity at time zero to 21.6% after 57 days and remained at a similar level up to 100 days of incubation. In the sediment, the total radioactivity increased to a mean of 73.8% applied radioactivity after 57 days and remained at a similar level up to 100 days. The proportion of remaining non-extractable radioactivity in the sediment accounted for a mean of ≤7.4% applied radioactivity throughout. Volatile radioactivity accounted for a maximum mean of 1.9% applied radioactivity after 100 days.

 

DT50 and DT90 values were estimated using single first order kinetics modelling based on the observed degradation of the parent test material from the water, the sediment and from the total aquatic sediment system at approximately 12 deg C. In the two aerobic systems, DT50 values were determined to be 5.03 - 6.67 days (water), 226 - 406 days (sediment), and 215 - 240 days (whole system), and DT90 values ranged from 16.7 - 22.2 days (water), 749 - 1350 days (sediment), and 713 - 799 days (whole system). In the two anaerobic systems, DT50 values were determined to be 39 - 46.4 days (water), 1390 days (sediment), and 958 - 1660 days (whole system), and DT90 values ranged from 130 - 154 days (water), 4610 days (sediment), and 3180 - 5500 days (whole system). The DT values for sediment were estimated only for Emperor Lake only, as there was no decline in parent material in Calwich Abbey Lake sediments.

The test material was degraded to one major degradate, Unknown 1 (up to a mean of 6.8% in the total system) and 15 low level unidentified degradates (mean recovery did not exceed 2.9% applied radioactivity for any one minor degradate on any sampling occasion), was incorporated into bound (non-extractable) radioactivity, or was mineralized to carbon dioxide.

Biodegradation in soil:

In an OECD 307 study, the overall recoveries of radioactivity ranged from 96.1 to 104.1% of applied radioactivity in the four soils incubated under aerobic conditions for 120 days, and 96.9 to 99.6% AR in the soil (#3, Kennett) incubated under anaerobic conditions for 119 days.

Extractable radioactivity declined during the aerobic incubation for all four soils treated with the radiolabeled test material, with mean values ranging from 95.2% applied radioactivity at time zero to 72.1% after 120 days.  Extractable radioactivity also showed a small decline during the incubation of the anaerobic Kennett soil (#3) treated with the radiolabeled test material, ranging from 98.5% AR to 89.5% AR over the acclimation period, declining to 85.3% AR 119 days under anaerobic conditions.  

One major degradate, preliminarily designated as Unknown 1 (RT 27.2 min), was detected in the four aerobic soils and one anaerobic soil (maximum mean value of 19.0% AR was observed in the aerobic Kennett #3 on Day 62).  Analysis by LC-MS/MS suggests that this is an oxidative metabolite of the test material i.e., S-(((dibutylcarbamothioyl)thio)methyl) dibutylcarbamothioate.  An authentic reference would be required to definitively confirm this proposed identification. The remaining extractable radioactivity was attributed to up to five low level degradation products (aerobic soils) or four low level degradation products (anaerobic soil) and other components that did not constitute any discrete regions of radioactivity in the chromatograms.  

Based on first order kinetic models (single or multi-compartment), DT50 values in the aerobic soils were determined to be 285 days (Brierlow, #1), 119 days (Calke, #2), 286 days (Kennett, #3) and 200 days (South Witham, #4) for the parent material and 285 days for the major degradate (RT 27.2 min). Based on the single first order kinetic model, the DT50 value for the parent material in the anaerobic soil (Kennett, #3) was determined to be 516 days.