Abstract
We investigated the potential toxicities associated with the sub-acute ingestion of transformer mineral oil (TMO) at a heated low dose (HLD-50 mg/kg), heated high dose (HHD-500 mg/kg) and unheated high dose (UHD-500 mg/kg) in Wistar rats. There were increases in red blood cells and haemoglobin levels in HHD females and UHD males respectively versus control. The serum total proteins, albumin, and creatinine of the HHD females showed a significant increase versus control. The HHD males and UHD groups showed significant increase in liver malondialdehyde versus control. The livers of HHD groups had bile duct proliferation while those of HLD females and UHD groups showed focal areas of periportal chronic inflammation. HHD groups had kidneys with mild chronic inflammation and the HHD and UHD groups showed small intestines with chronic inflammation. In conclusion, sub-acute oral administration of TMO induced various degrees of dermal, haematological, hepatic, renal and small-intestinal toxicities in rats.
Highlights
Transformer mineral oil (TMO) is a clear liquid with an odour of petroleum
The mild histopathological findings from this oral sub-acute toxicity study suggest that oral sub-chronic or chronic exposures or exposures to higher doses of TMO to rats could potentially result in effects of toxicological relevance
Some of the hematological and biochemical effects reported are of questionable toxicological significance or might even be adaptive responses as there was absence of clear dose-response compounded with the limitation of low number of animals in each experimental group
Summary
Transformer mineral oil (TMO) is a clear liquid with an odour of petroleum. It is used as insulating oil in transformers because it is stable at high temperatures (Modenes et al, 2018). Crude oil or petroleum has always been the primary source of TMO. In the past few decades, siloxane-based synthetic fluids and C7-, C8-based fatty acid ester products, have been used as sources of TMO in various parts of the world (Kaplan et al, 2010). Petroleum-based transformer fluids are normally divided into paraffinic and naphthenic-rich oils (Kaplan et al, 2010; Wang et al, 2018). TMO has a complex structure of hydrocarbon molecules and contains the following main components: paraffin (10–15 %), naphthyl or cycloparaffins (60–70 %), aromatics (15–20%), asphalt resinous substance (2.1 %), sulphur compounds (
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