Impact of electrical cable insulating oil on the mineralisation of [l-C-14]glucose in soil

Subsurface high voltage electric cables are commonly insulated using dodecy lbenzene in combination with mineral oil. This work assessed the impact of increasing concentrations of cable insulating oil (0-10% dry weight) on soi l microbial respiration as determined by mineralisation of [1-C-14]glucose (11 mu g C g(-1) soil). Acute impact was assessed from 0 days to 21 days, a nd chronic impact was assessed after 300 days. This study found that cable insulating oil increased respiratory activity of soil microflora. The exten t of impact was found to depend on both oil concentration and the length of oil-soil contact time. Following acute exposure (21-days oil-soil contact time), it was found that oil concentrations up to 1% promoted a significant (P < 0.05) increase in the extent of [1-C-14]glucose mineralisation to (CO 2)-C-14 relative to the control. In contrast, higher concentrations of cabl e insulating oil (5% and 10%) promoted no significant (P > 0.05) increase i n the extent of [1-C-14]glucose mineralisation to (CO2)-C-14 relative to th e control. Following chronic exposure (300-days oil-soil contact time), the extent of mineralisation was greater at all oil concentrations applied rel ative to the control. For oil concentrations up to and including 1%, there was a decrease in the extent of elevation in mineralisation relative to the values after 21-days exposure. At higher oil concentrations, namely 5% and 10%, the extent of elevation in mineralisation was comparable with that af ter 21-days oil-soil contact time. We suggest that the increase in minerali sation of glucose indicates that cable insulating oil is a readily availabl e carbon source to the carbon-limited soil microflora. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. A ll rights reserved.