Some cursory investigations have revealed that there are lots of lead-painted surfaces [1]. Even children's play equipment [2]. And kitchen utensils [3]. And all the other usual sources, too.

[1, 2] = https://www.researchgate.net/publication/365897933_Potential...

[3] = https://www.bbs.bt/national-blood-lead-level-survey-reveals-...

The typical sources are:

- Lead paint

- Water supply

- Lead in cookware

- Lead in spices, especially tumeric, where leaded dye is used to make it more yellow

- Industrial airborne emissions

Leaded gasoline used to be on that list but not anymore. Not sure about the specifics in Bhutan.

If you'd like to help prevent lead exposure in countries like Bhutan, the two charities I know about are Pure Earth and LEEP. Not sure if they have Bhutan programs.

This is very common in the developing world, due to lax regulations on lead in products.

Poverty. Regulation and testing are not just a matter of will, they cost money. We like to pretend like all the wealth in richer economies goes to TVs and cars and fashion but health, education, safety, etc are all luxury goods.