On a visit to Acerra, south of Rome, the first US pope urged the world to "reject temptations of power and enrichment linked to practices that pollute the land, water, air, and social coexistence".
Leo said he wanted to come to the area near Naples known as the "Land of Fires", where the European Court of Human Rights ruled in 2025 that authorities had failed to protect residents from waste dumping since at least 1988, to "gather the tears" of families who had lost loves ones to related illnesses.
Arriving by popemobile in an outside square on a sunny spring day, Leo was greeted by people waving small yellow-and-white Vatican flags and wearing yellow hats, some holding up poster boards with pictures of family members who had died.
Leo, who in recent months has been speaking more forcefully and will issue his first major document on Monday, said "unscrupulous people and organisations have been allowed to act with impunity for too long".
During his four-hour visit to Acerra on Saturday, he also referred to "the dizzying profits of a few, blind to the needs of people, their work and their future".
He also met victims.
For years, collection, treatment and disposal of garbage in southern Italy was largely in the hands of a small group of private owners, with contracts sometimes tied to the Camorra, a Mafia group based around Naples.
In January 2025 the European court found that Italian authorities had repeatedly failed to act to stop illegal dumping in a region also known as the "Triangle of Death", due to abnormally high rates of cancer for residents.
The court gave the Italian government two years to establish a comprehensive database of toxic waste sites and communicate the risks to the public.
Prime Minister Giorgia Meloni in February 2025 appointed an Italian general to head a task force aimed at helping victims and pursuing environmental clean-up.
Leo will issue his first encyclical, a major text, to the world's 1.4 billion Catholics, on Monday.
It is expected to address the rise of AI and how the technology is being used in warfare and challenging workers' rights.
