Prediction of [3-14C]phenyldodecane biodegradation in cable insulating oil-spiked soil using selected extraction techniques

This study investigated the use of an aqueous hydroxypropyl-β-cyclodextrin (HPCD) shake extraction in predicting microbial mineralisation and total loss of [3-14C]phenyldodecane associated activity in soils spiked with cable insulating oil; phenyldodecane represents a major constituent of cable insulating oil. Direct comparisons were made between freshly spiked and aged soils, and following composting. Soil was spiked with [3-14C]phenyldodecane (10 mg kg−1) and stored in microcosms and aged for 1, 23, 44, 65, 90 and 153 d. At each sample time point, a variety of analyses were performed to assess the relationship between chemical and biological techniques in determining mineralisation and loss of 14C-activity in soils under composting and non-composting conditions. Methods included determination of total 14C-activity remaining, dichloromethane (DCM) and HPCD extractions. Mineralisation assays were also carried out to quantify the fraction of 14C-phenyldodecane associated activity available for degradation in the soil at each time point. DCM and HPCD extractability were compared to contaminant mineralisation and to total loss of 14C-phenyldodecane associated activity from the microcosms, after 153 d incubation. Poor relationships were found between (i) the amount of 14C-activity mineralised and the fraction removed from the soils using DCM extraction and (ii) DCM extraction and total loss of [14C]phenyldodecane associated activity from the soil systems. Good relationships were observed between (i) the amount of 14C-activity mineralised and the fraction removed from the soils using the HPCD extraction and (ii) HPCD extraction and total loss of [14C]phenyldodecane associated activity from the soil systems. The results of this study indicate that an aqueous HPCD extraction may be a useful tool in assessing the microbial availability of phenyldodecane in freshly and aged spiked soils. An aqueous-based cyclodextrin extraction can determine the amount of 3-phenyldodecane that is available for microbial degradation in soil.