It works at a very low concentration-10 parts per billion-so you can't smell the compound.

这种物质在极低浓度下(10ppb)就可以发挥作用，因此，你是闻不到这种物质的。

youdao

To prove that MTBE concentrations below the EPA's threshold still made water taste terrible, Summy unearthed documents like a 1983 Shell letter detailing that water was no longer drinkable where MTBE'S concentration was 7 to 15 parts per billion.

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