Back

Some interesting things to know about used cooking oil.

The next time you go out for a meal, or buy fried chicken, chips or fish, you might want to consider the following facts about the cooking oil being used to prepare your food:

Abused cooking oil is cooking oil that has been repeatedly re-heated and re-used. The oil is thick, dark coloured and smells or tastes unpleasant. This is why the food at some outlets all tastes the same.

Abused cooking oil is oil that has been repeatedly used more than 4 times in food preparation.

What happens to cooking oil when it is being used to prepare meals?
Vegetable oils are reactive substances that can undergo chemical changes during storage, heating or exposure to light. These chemical changes can create "breakdown products" in the oil, which are potentially harmful substances.

The common obvious changes to the cooking oil are a darkening of colour, a thickening, a rancid odour, and sometimes a rancid taste.

Oxidation is a major reason for the chemical breakdown of oil, but there are several other causes of degradation with potentially toxic effects. It is important to note that not all oil breakdown products are potentially harmful. Some products are harmless and are normal products of digestion.

What harm can abused oil cause?

• Diarrhea
• Heart and liver disorders
• Destroy the vitamins A and E in the food, which could lead to nutritional deficiencies.

A major area of concern is the level at which the harmful “breakdown products” in the oil start becoming hazardous to your health. Scientists have not yet been able to say that a certain level or amount of “breakdown products” is hazardous to one’s health. All they do know is that the “breakdown products” are not good for your health.

There have been unconfirmed studies linking the abused oil to cancer and HIV/AIDS. The nutritional deficiencies in the foods prepared using abused oil and the free radical in the abused oil, do not complement the general health of a person suffering from HIV/AIDS or cancer.

Abused oil is more easily absorbed by foods, as compared to foods prepared using fresh oil.

Used motor oil

Used motor oil contains wear metals such as iron, tin, copper and lead from leaded petrol used by motorists. Zinc arises from the additive packages in lube oils.

Many organic molecules arise from the breakdown of additives and base oils. The most harmful is the polycyclic aromatic hydrocarbon (PAH) such as benz(a)pyrene and chrysene. Petrol engines generate the most PAH molecules

per 1000km, with diesel engines below that and 2 stroke engines generating the least amount of PAH.

Used oil can damage the environment in several different ways:

• Spilled oil tends to accumulate in the environment, causing soil and water pollution. Oil decomposes very slowly. It reduces the oxygen supply to the micro-organisms that break the oil down into non-hazardous compounds.
   
• Toxic gases and harmful metallic dust particles are produced by the ordinary combustion of used oil. The high concentration of metal ions, lead, zinc, chromium and copper in used oil can be toxic to ecological systems and to human health if they are emitted from the exhaust stack of uncontrolled burners and furnaces.
   
• Some of the additives used in lubricants can contaminate the environment. E.g. zinc dialkyl dithiophosphates, molybdenum disulphide, and other organometallic compounds.
   
• Certain compounds in used oil - eg polyaromatic hydrocarbons (PAH) - can be very dangerous to one's health. Some are carcinogenic and mutagenic. The PAH content of engine oil increases with operating time, because the PAH formed during combustion in petrol engines accumulates in the oil.
   
• Lubricating oil is transformed by the high temperatures and stress of an engine's operation. This results in oxidation, nitration, cracking of polymers and decomposition of organometallic compounds
   
• Other contaminants also accumulate in oil during use - fuel, antifreeze/coolant, water, wear metals, metal oxides and combustion products.