He is facing federal charges over allegations that he sold a type of toxic bleach as a "miracle potion" meant to cure COVID-19.
In a series of tweets Tuesday night, the office of Colombia's attorney general announced that officers in Santa Marta had arrested Grenon and his son, Joseph Timothy Graham.
The arrest was in response to charges filed in the US for "marketing in that country a supposed 'miracle potion' to treat Covid-19" and other diseases, the announcement said.
Business Insider has extensively reported how the substance — called Miracle Mineral Solution, or MMS — has been promoted as a cure for a range of illnesses.
Since the coronavirus pandemic began, advocates have also claimed it is effective against COVID-19.
According to the attorney general's office, Mark and Joseph Grenon "served as spiritual guides of an international religious congregation to sell their followers the 'miracle solution."
It said that prosecutors believe the substance had a role in "the death of 7 American citizens."
Colombian authorities also accused Grenon of selling the substance locally, and arranging shipments from the Caribbean port of Santa Marta to parts of Europe and Africa.
A Food and Drugs Administration spokesman said the agency does not comment on ongoing investigations.
Grenon, along with Joseph Grenon and two of his other sons, was charged by prosecutors in Florida in July with conspiracy to defraud the United States, conspiracy to violate the Federal Food, Drug and Cosmetic Act, and criminal contempt.
They are accused by US prosecutors of promoting and selling MMS as a miracle cure for illnesses including cancer, Alzheimer's, autism, multiple sclerosis, HIV/AIDS — and COVID-19.
The substance is really chlorine dioxide, a form of toxic bleach created by mixing sodium chlorite with a common acid or by drinking it neat.
The Food and Drugs Administration has issued a series of warnings against consuming MMS, saying it causes severe vomiting, diarrhea, and life-threatening low blood pressure, and in large doses can be fatal.
Grenon styled himself as the "archbishop" of the Florida-based Genesis II church, the central claim of which was was that the chlorine dioxide is a cure with miraculous healing powers.
According to court documents filed in Florida, Grenon admitted to investigators in the US in an interview that the church "has nothing to do with religion," and that it exists to "legalize the use of MMS" and avoid "going [ ] to jail."
The documents say that as the coronavirus began to spread earlier this year, Grenon's earnings from selling MMS increased from about $30,000 a month to around $120,000 as he began to promote it as a cure for the disease.
In recent years advocates of MMS have established a significant presence in Latin America.
To the horror of medical experts, Bolivia's Senate recently passed a bill legalizing MMS as a COVID-19 treatment after a misinformation campaign about its miraculous powers swept the country.
Business Insider has exposed Grenon's promotion of MMS on social media. In response to the investigation YouTube in 2019 removed a channel in which Grenon promoted MMS, and updated its policies to explicitly ban promoting it.
In Uganda, individuals connected to the Genesis II church were arrested last year for giving the substance to people in remote rural communities as a malaria treatment, including infants and young children. The arrests followed investigations by Business Insider and The Guardian.
So often people are working hard at the wrong thing. Working on the right thing is probably more important than working hard.