Impact of electrical cable insulating oil on the mineralisation of [1-¹⁴C]glucose in soil

Abstract

Subsurface high voltage electric cables are commonly insulated using dodecylbenzene in combination with mineral oil. This work assessed the impact of increasing concentrations of cable insulating oil (0-10% dry weight) on soil microbial respiration as determined by mineralisation of [1-(14)C]glucose (11 microg C g(-1) soil). Acute impact was assessed from 0 days to 21 days, and chronic impact was assessed after 300 days. This study found that cable insulating oil increased respiratory activity of soil microflora. The extent 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-(14)C]glucose mineralisation to (14)CO(2) relative to the control. In contrast, higher concentrations of cable insulating oil (5% and 10%) promoted no significant (P0.05) increase in the extent of [1-(14)C]glucose mineralisation to (14)CO(2) relative to the control. Following chronic exposure (300-days oil-soil contact time), the extent of mineralisation was greater at all oil concentrations applied relative 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 after 21-days oil-soil contact time. We suggest that the increase in mineralisation of glucose indicates that cable insulating oil is a readily available carbon source to the carbon-limited soil microflora.

The development of phenanthrene catabolism in soil amended with transformer oil

“…For each of the assessment criteria set, transformer oil was not observed to inhibit the evolution of phenanthrene catabolism, indeed the presence of oil putatively enhanced mineralisation. Application of oil to soil has been shown to result in an increase in microbial biomass since it can act as an available substrate for some groups of organisms [24], an especially important criterion in a carbon‐limited environment, such as soil [25]. Furthermore, total bacterial cell numbers and the proportion of oil‐decomposing bacteria have been shown to increase as a result of oil application [26,27].…”

A simple 14C-respirometric method for assessing microbial catabolic potential and contaminant bioavailability

“…Although not described here, another use for this respirometric system is the assessment of contaminant impact on microbial function in environmental samples. We have previously investigated contaminant impact using the mineralisation of 14 C-labelled glucose as a measure of microbial activity in soils amended with cable-insulating oil [17] and PAHs [18] in relation to microbial biomass. However, although carbon turnover tests may indicate the overall e¡ects of contaminants on the respiration of unstimulated and stimulated micro£ora, these tests give no indication of the impact on particular taxonomically different groups or species.…”

The impact of carbon nanomaterials on the development of phenanthrene catabolism in soil

“…Therefore it can be argued that the uctuations within microbial communities may be due to the changes in the respiratory activity of the soil microora. 28 However, the lower extent of 14 Cphenanthrene mineralisation in the 1% amendment of CNMs and at the later stages of aging was not due to the lack of active phenanthrene-utilising microorganisms, but due to sorption effects of the CNMs. 4,12,29 It was observed that the low concentrations of C 60 had reduced CFUs, which is in agreement with the results obtained by Johansen, et al; 12 however, it is not understood how this had no effect on the extent of 14 C-phenanthrene mineralisation.…”