Now, le pingouin. How much lead is used in Australia's avgas every year ?
Your question got me curious.
Without spending a lot of time double-checking numbers the internet told me that 100LL contains 2 grams of TEL per US gallon. And the the US Avgas consumption (yes I know you asked about Australia) is 186,000,000 US gallons/year so that gives 372 tonne of TEL. According to my poorly remembered chemistry, Lead is 78% of the mass of TEL, so that would be 290 tonne of lead. Not as much as volcanoes, but not vanishingly insignificant either.
As far as Australia itself, one source I saw put AU avgas sales at about 80Ml/yr or about 21,000,000 US gal, which is about 11 percent of the US consumption, so that suggests roughly 31 tonne of lead for Australia.