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In a closed bottle biodegradability test (considered the most relevant test for poorly-soluble compounds), conducted according to a modified OECD Guideline 301D/EU Method C.4 -E, the ready biodegradability of Cereclor 50LV (a C10-13 chlorinated paraffin; 50% chlorination) was assessed by measuring oxygen consumption during incubation with either secondary activated sewage sludge or river water for up to 56 days. The test material was introduced in to the incubation medium at a nominal concentration of 2 mg/L either as a thin film on the bottle surface deposited from a volatile solvent (dichloromethane), as a solution in silicone oil or as an emulsion in a polyalkoxylate surfactant (agnique). The biodegradation of the test material by activated sludge at 28 days was 36, 7 and 72% after introduction by volatile solvent, silicone oil and as an emulsion, respectively. The corresponding values for incubation in river water were 18, 10 and 42%, respectively. The biodegradation of test material introduced as an emulsion increased to 75% by day 42 with activated sludge and 63 and 64% by days 42 and 56 respectively in river water. The biodegradation of solvent-introduced material by 56 days was 47 and 37% in activated sludge and river water respectively , the corresponding values following introduction in silicone oil were 25 and 38% respectively. The test material did not inhibit endogenous respiration by either inoculum. The biodegradation of the C10 -13 chlorinated paraffin (50% chlorinated) reached the pass level (>60% within a 10-day window in no more than 28 days), indicating ready biodegradability when incubated as an emulsion with activated sludge (van Ginkel and Louwerse, 2010).

In a GLP study conducted according to OECD Guideline 301C, Chlorowax 500C (a C10-12 chlorinated paraffin; 58% chlorination) at concentrations of 20 and 100 mg/L was mixed with 30 mg/L of an activated sludge inoculum and oxygen uptake was measured daily for up to 28 days to assess biodegradation. No oxygen uptake was found in the presence of either concentration of Chlorowax 500C over the 28 day period. Analysis for residual chlorinated paraffin in the test vessels revealed that 98-100% of the test substance nominally added was recovered, thus confirming that no biodegradation had taken place after 28 days. Chlorowax 500C was therefore not readily biodegradable under the conditions of this study, however, it should be noted that the concentrations tested are well above the apparent solubility of the test material (Street et al. 1983).

The biodegradation of three C10-13 chlorinated paraffins (of 49, 60 and 70% chlorination) was studied over a 25-day period, using the extended Biological Oxygen Demand (BOD) test, at substrate concentrations of 2, 10 and 20 mg/L. The tests were carried out using non-acclimated micro-organisms isolated from the effluent of a laboratory activated sludge unit treating dosmestic waste and with organisms isolated from soil taken from near a chlorinated paraffin production plant and acclimated to the chlorinated paraffins by incubation for 8 weeks. Appreciable BOD was only seen with the 49% chlorinated paraffin, the overall extent of biodegradation after 25 days being 25% with the non-acclimated organisms and 87% with the acclimated organisms. No significant oxygen demand was detected with the higher chlorinated paraffins (Madeley and Birtley, 1980).

In a GLP study, the inherent biodegradability of a C10-12 chlorinated paraffin (58% chlorinated) has been determined under aerobic conditions using activated sludge from a commercial sewage works. The test material was introduced into the digestion system as an aqueous emulsion at concentrations of 68.7 and 137.4 mg/L (equivalent to 25 and 50 mg C/L respectively) and degradation followed by determining CO2 evolution over 32 days. The effect of the chlorinated paraffin on the degradation of a control substance (aniline) was also assessed. The extent of degadation of the test material was 16 and 7.4% at 68.7 and 137.4 mg/L, respectively. Since the removal of carbon from the test system did not exceed 20% after 28 days during incubation with the C10-12 chlorinated paraffin, the test material can not be considered to be inherently biodegradable in this test. The lack of inhibitory effect on the degradation of the control substance, aniline, indicates that the chlorinated paraffin does not inhibit normal microbial degradation (Mather et al. 1983).

In a GLP study conducted according to OECD Guideline 308, the rate of mineralisation under aerobic conditions of a C10 and a C13 chlorinated paraffin (65% chlorination) was low, with an average half-life of the two substances of around 1630 days in freshwater sediment and around 450 days in marine sediment. Little or no mineralisation was evident under anaerobic conditions in both freshwater and marine sediment over the timeframe of this study (Thompson and Noble (2007).

In a GLP study to OECD Guideline 303A, the fate of radiolabelled Chlorowax 500C (C10 -12 chlorinated paraffin; 58% chlorinated) in model aerobic sewage treatment test units was assessed. After 33 days of equilibration, the test material was introduced to the test units at an influent concentration of 10 mg/L for a period of 18 days. It was found the test material had no effect on DOC (dissolved organic carbon) removal in the test units indicating that at the concentration used, Chlrowax 500C was not toxic to the organisms present. The mean concentration of the test material in the system effluent was 0.7 mg/L for weeks 6-8. With a feed concentration of 10 mg/L, this equilibrium concentration of test material in the effluent indicates 93% removal. The authors attributed this removal primarily to adsorption of the test material to the activated sludge phase (rather than biodegradation) and also suggested most of the test material detected in the effluent was adsorbed to suspended solids (Street and Madeley, 1983).

The half-lives of two 14C-labelled C12 chlorinated paraffins were estimated to be about 13 and 30 days for a 59 and 69% chlorinated paraffins, respectively, in an aerobic sediment system (freshwater) containing oligochaetes (Lumbriculus variegatus). The extent of degradation was determined at day 0 and day 14 of the experiments based on the difference between toluene-extractable 14C measurements (taken to represent unchanged chlorinated paraffin) and total 14C measurements.The r2 value for the degradation rates were greater than 0.93 for both the chlorinated paraffins. [The results of this test should be treated with caution as the identity of the 14C present in the samples was not determined, and it was only assumed that the non-extractable 14C represented metabolites. It should also be noted that as the analysis was based on the amount of 14C present in the sediment, these data show that little mineralization of the C12 chlorinated paraffins was occurring] (Fisk et al. 1998).

Co-metabolic degradation studies were carried out with Toyoparax 265 (a C12 chlorinated paraffin; 63% chlorination) at a concentration of chloride equivalent to 180 mg/1.2 L solution, using a mixed bacterial inoculum (strains HK-3, HK-6, HK-8 and HK-10) at 30oC for 48 hours. The bacteria were isolated from soil using an enrichment culture containing n-hexadecane as sole carbon source. Significant degradation was detected, with approximately 21% of the chloride being released after 36 hours, at which time bacterial growth and release of chloride ceased (Omori et al. 1987). These results show that dechlorination of SCCPs may occur in a cometabolic process.

Allpress and Gowland (1999) identified a bacterium (Rhodococcus sp.) that was able to grow using various chlorinated paraffins as the sole source of carbon and energy. The bacterium was isolated from stream water from an industrial area of the United Kingdom using a minimal salts medium containing 1% by volume of a C14-17, 45% wt. Cl chlorinated paraffin product. The ability of this bacterium to utilise short-chain chlorinated paraffins was investigated by inoculating minimal salts medium containing either a C10-13, 49% wt. Cl product and a C10-13, 63% wt. Cl product) at a concentration of 1% by volume and determining the chloride release compared with controls over 71 days incubation at 20oC. The test media also contained anti-bumping granules to aid dispersion of the test substance within the media. Only the C10-13, 49% wt. Cl product was utilised by the bacterium with 49% of the chlorine present in the chlorinated paraffins being released as chloride after 71 days. The C10-13, 63% wt. Cl product showed little or no increase in chloride ion levels above the control values during the experiment. Several other chlorinated paraffins were tested using this system and it was concluded that the Rhodococcus sp. identified in the study was able to utilise chlorinated paraffins as sole source of carbon and energy, but little or no utilisation occurred with chlorinated paraffins with high degrees of chlorination (at or above around 59-60% wt. Cl) (Allpress and Gowland, 1999).

References (for which no ESR has been created - move to reference list in CSR)

Allpress J D and Gowland P C (1999). Biodegradation of chlorinated paraffins and longchain alkanes by Rhodococcus sp. International Biodeter. Biodeg., 43, 173-179.