One billionth of a gram.
- ‘In oral fluid, drugs of abuse can be detected for 5-48 hours at a low nanogram per milliliter level.’
- ‘The North Pacific contains about 1 nanogram of PCBs per litre.’
- ‘Dioxins in old incineration plants were emitted at a rate of between 200 and 300 nanograms per cubic metre.’
- ‘He tested positive for the banned substance methamphetamine when a nanogram of the chemical was detected in his urine sample.’
We take a look at several popular, though confusing, punctuation marks.