meaning of a word
Of the six pollutants monitored by WHO-carbon dioxide, nitrogen dioxide, ozone, sulphur dioxide, lead and particulate matter—it is this last category that is attracting the most attention from health researchers.

What does "lead" mean here?(I assume its a noun here but I can't find any sensible explaination in the dictionary.)

Question

meaning of a word
Of the six pollutants monitored by WHO-carbon dioxide, nitrogen dioxide, ozone, sulphur dioxide, lead and particulate matter—it is this last category that is attracting the most attention from health researchers.

What does "lead" mean here?(I assume its a noun here but I can't find any sensible explaination in the dictionary.)

Answer

It's the heaviest non radioactive element, symbol Pb:

https://en.wikipedia.org/wiki/Lead_(element)