The AES power plant in Puerto Rico generates 300,000 tons of coal ash, the toxic byproduct of coal burned to generate electricity, each year. The residents of the island, understandably, don't want to be near the toxic elements, so they passed a law "to prohibit the deposit and disposal of coal ashes or coal combustion residues in Puerto Rico."

In addition, the law prevents the ash from being stored on the island for more than 180 days.

So where does the coal ash go? A lot of it — tens of thousands of tons — makes its way to the mainland U.S.

CBS News tracked one cargo ship, the Mississippi Enterprise, as it was hauling coal ash into Jacksonville, Florida. From there, the ash is taken to Chesser Island landfill in Folkston, Georgia, as reported by local Puerto Rican journalist Abner Dennis and Omar Alfonso.

Lawyer and activist Ruth Santiago, who has been battling AES to provide better safeguards in disposing the coal ash, warned communities in Florida and elsewhere where the ash was being disposed: "They should not allow the import of the toxic coal ash to their communities."

Santiago claimed that people in the community of Miramar in Guayama, Puerto Rico, have been adversely affected by exposure to the ash, as well as those in other communities surrounding the plant.

"People don't want this coal ash waste to go anywhere else. It's toxic. We know it's gonna do harm wherever it goes other than a Subtitle-C landfill," Santiago said, referring to landfills specifically designated to house hazardous solid waste. Her concern is shared by Puerto Rican residents who worry about the transportation of the coal ash.

Exposure to the ash is concerning for Dr. Osvaldo Rosario, professor of environmental chemistry at the University of Puerto Rico.

"When you look at what it's made of, what are the key elements, chemical substances that make up the ash — you find horrendous things such as arsenic, selenium, chromium-6, vanadium. Many of these are toxic and carcinogenic materials," he said.

The metals in coal ash are particularly harmful due to the nature of burning coal. "These metals don't burn off. They don't evaporate," Rosario explained. "But through the burning process, you have concentrated them — making it a more dangerous material to dispose of."

Rosario said exposure can lead to respiratory problems, higher levels of cancer and skin rashes.

Multiple studies have shown the risks.

On December 22, 2008, a dike ruptured at the Tennessee Valley Authority power plant and spilled more than a billion gallons of coal ash. Elmer Lowe was hired as a clean-up worker and is part of an ongoing lawsuit against the company that hired him.

Lowe said he had been "in perfect health" when he was tasked with cleaning up the spill without the necessary protective gear.

"It looked like it was white, and it was clay, and it was nasty mud," Lowe's wife, Donna, said. "But it wasn't mud, it was the coal ash on him." Lowe had gone from an active, healthy man to weighing just 112 pounds and prescribed several medications.

The Obama administration responded to the spill in 2015, establishing new federal regulations for coal ash storage, which included monitoring nearby groundwater as well as the disposal.

However, under President Donald Trump's EPA head, former coal industry lobbyist Andrew Wheeler, regulations are being weakened. Wheeler declined CBS News' request for an interview.

Gina McCarthy, who led the agency when the regulations were implemented, said that the thousands of tons of coal ash coming into the mainland U.S. from Puerto Rico concern her, as does the current administration's weakening of regulations.

"We were dealing with contamination that had direct impact on human beings," she stressed. "Rulemaking is supposed to protect people. What I would call a rollback and a weakening of protections is focused more on making the industrial pollutant not have to pay to clean up their pollution, and much less about protecting the disadvantaged communities that government is supposed to protect."

AES responded to CBS News with a statement highlighting the EPA's coal ash classification.

"Today our power plants provide nearly one-fourth of Puerto Rico's electric energy, which is vital for the well-being of the island's people and economy. Without this electricity, the people of Puerto Rico would suffer a greater number of blackouts which impact hospitals, schools, and homes," the statement said.

"We comply with all local and federal regulations, and furthermore, the EPA classifies coal ash as a non-hazardous material. In fact, it is a major component in most cement and concrete produced in the United States. We continue to work with Puerto Rico in its transition to greener energy while maintaining the system's safety and reliability."

An EPA spokesperson defended the agency against accusations of cutting regulations, stating in a statement that "a majority of 2015 rules remain in place and are being implemented on schedule." The statement highlighted a list of proposals the EPA has made, including improving accessibility of publicly available information and addressing infrastructure needs of hazardous waste management facilities, among other monitoring requirements.

Full statement from the EPA Spokesperson:

A majority of 2015 Rules remain in place and are being implemented on schedule. EPA's CCR proposals makes changes to implement the Water Infrastructure Improvements to the Nation (WIIN) Act, respond to petitions, address litigation, and ensure smoother implementation by applying lessons learned. EPA's proposals include: