Instead of commonly used highly toxic substances, Townsend discovered that it can be done with nontoxic salts.

而且特温斯德发现可以使用无毒的盐来替代通常使用的剧毒性物质。

Polonium is a highly toxic substance and just one microgram -- about the size of a speck of dust -- is enough to kill a person.

钋是一种剧毒物质，仅仅一微克，也就一点灰尘大小的钋便可致人死亡。