杏吧原创

A NOTORIOUS toxicity test that involves killing half the animals in the
experiment is finally to be phased out around the world. Animal welfare
campaigners are delighted by the landmark decision.

鈥淚t鈥檚 absolutely fantastic,鈥� says Les Ward, director of the Edinburgh-based
Advocates for Animals. 鈥淲e鈥檙e talking about saving many, many thousands of
animals from further suffering.鈥�

The OECD, the Paris-based club of the world鈥檚 richest 29 nations, announced
its decision to abolish the LD50 test last week. Most European countries have
long argued that the LD50 test is a cruel and unnecessary way of assessing how
toxic a chemical is. LD50 stands for 鈥渓ethal dose to 50 per cent鈥�: in each test,
20 rats receive escalating doses of a chemical until half die.

The US and Japan were the strongest opponents of the ban but they have at
last accepted the alternatives. So companies applying to have chemicals approved
in the US and Japan need no longer do the LD50. 鈥淐ompanies now know that
everywhere in the world, regulatory authorities will accept results of
alternative tests,鈥� says Bob Combes, the scientific director of Britain鈥檚 Fund
for the Replacement of Ani-mals in Medical Experiments (FRAME).

Apart from its sheer cruelty, the LD50 is of questionable scientific value,
Combes says. 鈥淵ou had to dose the animals so high that death was unlikely to be
a direct effect of the chemical itself,鈥� he says. 鈥淎nd if you repeat a test in
the same lab with the same doses, you can get different results.鈥�

Applicants must now pick one of three alternative tests, says Herman Koeter,
who runs the OECD鈥檚 test guidelines programme. The first alternative, developed
in Britain, requires only four animals. They seldom die. Instead, toxicologists
note signs that hint at the lethal dose. 鈥淭he important point is that you don鈥檛
dose the animals to ridiculous levels,鈥� says Koeter.

In the second, German test, a single animal receives escalating doses, often
but not always until it dies. Again, there鈥檚 a cut-off point where no more
chemical is given even if the animal remains alive. The final dose, whether
lethal or not, is confirmed in two other animals.

The third, American alternative is dubbed the 鈥渦p and down method鈥�.
Experimenters raise or lower the initial dose, depending on what happens in the
first animal. Although half die, only around nine animals are used.

Regulatory authorities now have a year to get rid of the LD50 test. 鈥淲e鈥檙e
very pleased to see the back of it,鈥� says Combes.