Mineral oils are complex mixtures of hydrocarbons (saturated and unsaturated) deriving from petroleum. Different products such as combustible oils, fuel oils, bases for lubricating oils, motor oils, hydraulic oils and purified mineral oils (food grade), are obtained from fractional distillation and further processing of petroleum. Toxicity of mineral oils depends on the molecular weight of the hydrocarbons and the refining degree. Raw mineral oils contain high amounts of aromatics and are classified as carcinogens to humans, meanwhile refined paraffins are responsible for adverse effects when administered to rats (F-344) at levels ranging from 0.01 to 20 mg/kg b.w. (Depending on the oil type and its viscosity). High contamination levels have been also found in human milk and adipose tissues.
There are many possible sources of contamination for vegetable oils and we can not exclude a contribution by the environment. Among other possible sources we can remember: the lubricating oils used in the extraction plant, storage and transport in jute bags, transport in ship previously used to transport mineral oils, handling and storage of the raw matter (it is the case of pomace) under inappropriate conditions.
Coupled LC-GC represents an optimal choice for determining the contamination: it allows to analyse a high number of samples per day, minimising sample preparation which is reduced to a simple sample dilution before injection. Except for extra virgin olive oils, which rarely result contaminated with levels above the detection limit, the different types of vegetable oils have a contamination level generally above 10 mg/kg. Among the different vegetable oils, pomace olive oils result to be the most contaminated (with amounts always higher than 100 mg/kg)
