New suits for old bottles

At the beginning of this month, Britain was gripped by fear that substances called phthalates could be contaminating infant formula feeds. The scare was prompted by concerns that these were "gender-bending" chemicals. An earlier phthalate scare of the 1970s accused them of causing cancer. However, phthalates cause neither cancer nor infertility in humans.

Phthalates are man-made and widespread; even in remote regions of the planet analysts have recorded 0.05 parts per million (ppm) in rainwater. Each of us gets a daily dose, and the MAFF surveys Phthalates in Paper & Board Packaging (1995) and Total Diet Survey (1996) found them in almost all food analysed. Levels in milk and milk products were around 1 ppm, but the suspected source of contamination, PVC tubing used in milking parlours, accounts for only a tenth of this.

Phthalates were first made in the 1850s and called naphthalates, from naphtha the ancient Greek name for natural petroleum, but this was soon shortened to phthalate. There are two types, which differ slightly from each other in their chemical structure.

Phthalate polyester was discovered by the chemists Rex Whinfield and James Tennant in Manchester in 1941, when they heated together methyl terephthalate and ethylene glycol. They called their new polymer fibre Terylene and found it ideal for blending with other fibres to make crease- resistant suits, or, as Crimplene,uncrushable blouses and dresses. Today we are more likely to encounter polyester as PET (polyethylene terephthalate), which is what most fizzy drinks bottles are made of. These are generally regarded as environmentally friendly because they save energy and can be recycled.

A PET bottle needs a quarter less energy to make than a glass bottle and a delivery truck can carry 60 per cent more drink and 80 per cent less packaging when loaded with PET-bottled drinks. In Germany and Austria PET bottles are returned for refilling, while in the US more than 30 per cent are recycled into other products such as carpets, anoraks, duvets and paint brushes. In 1995 in the UK 1,000 tons of PET bottles were collected to become fibre insulation and yarn.

The phthalate in polyester is permanently fixed as an integral part of the polymer. The other type has a different use - as a molecular lubricant. It is blended into plastics to make them pliable. PVC is a rigid solid used for window frames and drainpipes, but when phthalate is added it becomes flexible because this allows the polymer chains to move over one another. So we get PVC as garden hoses, wallpapers, shower curtains, clothes, blood bags and water beds. Electric cable and vinyl flooring account for most phthalate.

Polyester phthalate does not escape to the environment. Plasticiser phthalates do, and are among the most investigated of all chemicals. The leading plasticiser is DEHP, short for di(ethylhexyl) phthalate, which, according to Dr David Cadogan of the EC Council for Plasticisers and Intermediates, poses little risk: "As far as humans are concerned it causes neither cancer nor reproductive effects. Nor do phthalates accumulate in the environment; they are biodegradable, and levels are falling. Leakage from plastics in old landfill sites is tiny."

In 1990 the EU Commission said DEHP should not be classified as a carcinogen, because no carcinogenic or oestrogenic activity was found with fish, hamsters, guinea-pigs, dogs or monkeys. Rats did show increased risks of liver tumours and decreased testes, but they are known to be particularly prone to these conditions.

Humans are not at risk. The Danish Institute of Toxicology concluded that an intake of 500mg a day was without effect. Our average daily intake is around 0.35mg. For babies, the tolerable daily intake is 0.05 milligrams per kilogram body weight, but MAFF admits some feeds have 0.13 mg per kg. However, it points out that the 0.05 guideline has a large inbuilt safety factor and in any case is based on the tests on rats. The danger to human babies is negligible.

Dr John Emsley is science writer in residence at Imperial College, London.