"It's inexcusable that governments around the world still allow mercury-based compounds in healthcare -- and safe alternatives exist," said US Health Secretary Robert F. Kennedy Jr.

In a video message to the conference in Geneva, Kennedy asked why mercury was deemed "dangerous in batteries, in over-the-counter medications and make-up", but acceptable in dental fillings.

The World Health Organization considers mercury one of the top 10 chemicals of major public health concern, calling it "toxic to human health".

Some countries have already banned its use in dental amalgam, a common filling material for treating tooth decay used for more than 175 years.

The Minamata Convention on Mercury is an international treaty to protect human health and the environment from the adverse effects of mercury and mercury compounds.

More than 150 countries are party to the convention, which was adopted in 2013 and came into force in 2017.

It stipulates that signatories must take measures to phase out the use of mercury-based dental amalgams.

However, a bloc of African countries want to go further, with a ban on their production, import and export, starting in 2030.

They have submitted a draft amendment to the convention, to be examined at this week's conference on the treaty.

Opening the debate, Burkina Faso's representative said that in less-wealthy countries, "there is insufficient -- or even a complete lack of -- infrastructure" for dealing with mercury waste.

A few countries opposed the African proposal, including Britain, Iran and India.

Britain's representative said 2030 was "too soon", and despite "strong environmental reasons for reducing our global reliance on dental amalgam", the cost and longevity of alternatives should be a factor in any decision to phase out mercury use.

- Mercury in cosmetics -

The conference will also examine how better to combat skin-lightening cosmetics containing mercury.

"The convention already bans the use of mercury in cosmetics," the convention's executive secretary Monika Stankiewicz told reporters.

"However, we know that the sales of skin-lightening products with mercury and other hazardous substances have exploded globally, especially on online markets."

When added to cosmetics, mercury lightens the skin by suppressing melanin production. However, the process is not permanent and is dangerous to health, Stankiewicz warned.

According to a study published Monday by the Zero Mercury Working Group -- a coalition of more than 110 non-governmental organisations in 55 countries -- approximately 66 million pots of mercury-based skin-lightening cream are produced each year.

Thailand, China, and Pakistan account for more than half of global production, it said.

This week, countries will also discuss the use of mercury in small-scale gold mining, and the feasibility of mercury-free catalysts for the production of vinyl chloride monomer (VCM) -- a key component of PVC plastic.