paper I wrote helped ban mercury as a satellite propellant due to environmental toxicity concern

In 2019, co-authors and I published a paper analyzing how mercury (Hg), if used as a propellant for massive satellite constellations, would re-enter the atmosphere and contribute massively to environmental contamination of oceans and fisheries.

Mercury was being seriously considered as a thruster propellant because it is inexpensive, can be stored in lightweight low pressure tanks, and affords excellent ionization and thrust characteristics.

This Silicon Valley Space Startup Could Lace the Atmosphere with Mercury - Bloomberg Nov 2018

At the time there were about 3,500 total satellites in Earth orbit. Now, 7 years later, there are upwards of 16,000 [1]. Most of these (~10,000) are part of the Starlink constellation [2]. It's estimated that each of the initial generation (2020) of these each carried about 30kg of krypton propellant [3]. The V2 generation satellite is more than twice as heavy and uses a less efficient argon propellant [4] [5], so probably carries upwards of 60kg of propellant. 2026 FCC filings indicate V3 generation satellite mass at upwards of 2,000kg [6], which means a propellant mass of upwards of 200kg. SpaceX plans to launch 100k of these [7]. That's 2x10^7 kg (2x10^4 (20,000) tonnes or Mg (megagrams)) of propellant.

If mercury propellant were to be used by these constellations, then the resultant emissions re-entering the atmosphere and contaminating ecosystems would amount to ten times the current total global annual emissions of mercury.

Fortunately, environmental lawyer Kevin Bell and colleagues in environmental and health organizations took up our work as evidence on the national and international level. In particular, the Zero Mercury Working Group, a coalition of more than 100 public interest NGOs, brought the issue to the 2022 COP4 of the UNEP (United Nations Environmental Program) Minamata Convention, an international treaty designed to protect health and environment from anthropogenic emissions of mercury, first established in 2013. Representatives from Canada and Switzerland proposed an amendment banning the use of mercury as propellant for satellites and spacecraft, and it was adopted.

Canada Switzerland Amendment Proposal at COP4.

ZMWG Blog – April 2022 summarizing COP4.

UN Bans Mercury Satellite Propellants Under New Minamata Treaty Provisions - a press release from ZMWG and PEER, Kevin's former organization.

Compilation of Evidence for banning Hg propellant at COP4

A few more interesting documents and articles: 

Public Letter from NGOs to Apollo Fusion 2018 urging the company to stop using mercury.

Mercury Thrusters: A Worldwide Disaster Averted Just In Time - Hackaday

Environmental concerns ground mercury-based satellite thrusters - Chemistry World

U.N. Kills Any Plans to Use Mercury as a Rocket Propellant - IEEE

As far as I'm aware, mercury propellant has only flown to space once in this century, on a 2020 test flight of Apollo Fusion's Hall thruster on an Astro Digital launch. But even this may have actually used a different, more typical propellant.

In some of the documents and articles, there's confusion about why the mercury returns to Earth once it's in space. The nuance is interesting. The reason is not that it mercury ions are particularly heavy, but because they are either travelling slower than escape velocity (only because they are usually fired out the back of the satellite to accelerate it), or because they become trapped in Earth's magnetic field and bounce around from pole to pole before hitting another particle and slowing down enough to de-orbit.

It's an incredible story of the power of a team to effect change on an international level of law.

And it's a future I'm glad to have helped avert.