The dispersant Corexit 9500 being used on the oil spilling from the Rena stranded on the Astrolabe Reef first came to public attention during the Deepwater Horizon well head blowout in 2010.

Corexit 9500 was widely used in the Gulf of Mexico, and shared the blame with its predecessor Corexit 9527A for the severe health effects reported by people who came in contact with it. Corexit has a reputation for rupturing red blood cells, causing internal bleeding and liver and kidney damage.

Corexit 9500 is the dispersant being aerially dropped into the oil slick around the grounded Rena.

According to Maritime NZ, the Corexit being used on the Rena spillage 'has been widely tested and has very low toxicity”.

It is 10-20 per cent less toxic than dishwashing liquid and the ingredients that make up the dispersant are in most shampoos.

MNZ is blaming any toxicity on the oil, not the dispersant, but a fact sheet for medical practitioners tells a completely different story. http://www.sciencecorps.org/crudeoilhazards.htm

The Manufacturer's Safety Data Sheet for one of the Corexit ingredients, Norpar 13 includes these recommended safety precautions.

Use supplied-air respiratory protection in confined or enclosed spaces, if needed.

Use chemical-resistant gloves, if needed, to avoid prolonged or repeated skin contact.

Use splash goggles or face shield when eye contact may occur.

Use chemical-resistant apron or other impervious clothing, if needed, to avoid contaminating regular clothing, which could result in prolonged or repeated skin contact.

Minimize breathing vapour or mist. Avoid prolonged or repeated contact with skin. Remove contaminated clothing; launder or dry-clean before re-use. Remove contaminated shoes and thoroughly clean and dry before re-use.

Cleanse skin thoroughly after contact, before breaks and meals, and at the end of work period.

Product is readily removed from skin by waterless hand cleaners followed by washing thoroughly with soap and water.

Norpar 13 is also highly flammable, but it has a low order of acute oral and dermal toxicity, but minute amounts aspirated into the lungs during ingestion or vomiting may cause mild to severe pulmonary injury and possibly death.

Corexit contains arsenic, chromium and copper. Copper and Chromium are essential trace elements.

Arsenic is present at a concentration of 0.16 parts per million. If direct dermal contact, inhalation, or ingestion (as with ocean spray) occurs, this metal could cause health effects, depending on the dose, specific exposure conditions and individual susceptibilities. Arsenic attacks many of the same organs as chemicals in crude oil and dispersants. With sufficient exposure, it can damage the liver, kidneys, nervous system, reproductive system, respiratory system, skin, reproductive/urogenital system, and immune system. It can cause mutations and endocrine disruption, cancer, and can harm the developing foetus.

Combined effects of multiple chemicals on the same organ system can be far more serious if they are sufficient to overwhelm the body's ability to detoxify or otherwise defend against toxic effects.

When Norpar 13 is used in a dispersant, it is diluted by other ingredients. The toxicity of the product depends on the combination of its ingredients and so may be more or less toxic than this ingredient.

There is confusion about the relative toxicity of the oil on the ocean beach. Yesterday's press conference the MNZ line remains, don't touch, don't try to clean it up, people handling it need protective clothing.

However, medical officer of health Dr Jim Miller's advice is more relaxed.

While reiterating the request for the public to stay away from the oil he says the affects can be irritating to the skin, or people could have an allergic reaction.

Wash it off with soap and water.

Environmental advisor Leigh Stevens says Corexit is probably the most well tested dispersant in use in the world and says its toxicity is less than that of dish washing detergent.

Oil is toxic at 11ppm while Corexit 9500 is toxic at only 2.61ppm, according to one website. Corexit 9500 is four times as toxic as the oil itself.