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Diss Factsheets

Environmental fate & pathways

Biodegradation in soil

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Link to relevant study record(s)

Description of key information

Key value for chemical safety assessment

Half-life in soil:
500 d

Additional information

Degradation of 14C-DSDMAC in sandy loam and loam mixed with digested sewage sludge was measured with a batch incubated flask method (Fieler, G. M. (1975a). The fate of DHTDMAC in sewage treatment processes, internal report of Procter & Gamble,

Brussels, cited in ECETOC 1993.). The 14CO2-production was approximately 48% after 55 weeks in both soils, when 50 mg DSDMAC per kg dry soil were applied. Addition of 30 mg/L LAS reduced the result to 38%. Degradation of 0.5 mg DSDMAC/kg dry soil was measured in a loam amended with or without digested sewage sludge and two other soils. The 14CO2-production after 62 weeks was as follows: ca. 27% in sandy loam and loam with sludge; ca. 18% in loam without sludge and silt loam. At concentrations of 5 and 50 mg/kg DSDMAC degradation increased in all soils with highest results of 50 and 63% in sludge amended soils. Degradation of DSDMAC in soils over a long period of 116 days was reported also from other tests (Weston (1987). 14CO2 production test on S1093.01R, S1094.01R, S1095.01R, S1096.01R and S1097.01R in sludge amended soil, project no 87-054 for Procter and Gamble, unpublished, cited in ECETOC 1993.). 0.1 mg DSDMAC/kg dry soil were degraded to 18-27% based on 14CO2-production and at 1.0 mg/kg degradation was 34-38%. A comparable degradation test with DHTDMAC lasted 120 days (Weston (1989). 14CO2 production test on S1189.01R, S1190.01R, S1191.01R, S1192.01R and S1193.01R in sludge

amended soil, project no 88-015 for Procter and Gamble, unpublished, cited in ECETOC 1993.). In sandy loam with sludge 0.1 mg DHTDMAC/kg dry soil showed 36 and 52% 14CO2-production. Corresponding values of 38 and 41% were derived with 1.0 mg/kg under the same conditions. Procter & Gamble (1992, unpublished study, cited in ECETOC 1993.) performed various studies on the biological degradation of DSDMAC in soils using several types of dispersion of the substance. Aqueous dispersion resulted in about 35% 14CO2-production after a mean test period of 118 days. The mean degradation of a solution with a solvent was below 15% after a mean test period of 184 days. In these cases the majority of the test results was obtained between 130 and 169 days test duration where the 14CO2-production was less than 10%. Results with lecithin emulsions were in between. In a 72-day study no degradation of 14C-DHTDMAC could be observed under anaerobic conditions (Fieler, G. M. (1975b). DTDMAC soil degradation studies, internal report of Procter & Gamble, Brussels, cited in ECETOC 1993.). About 90-95% of the test substance (20, 200 and 1500 mg/l) were adsorbed to particles. Solids concentration in the digester was 30 g/L. No other study could find any evidence that DHTDMAC undergoes anaerobic degradation. Biodegradation studies performed in soil indicated that 18-60% mineralisation was observed within 120-430 days. As a first approach, a half-life of 500 days is used for the terrestrial exposure assessment (kbiosoil = 1.4 . 10-3 d-1).