Washington — Since President Trump took office in January, his Environmental Protection Agency has been both slashing and reconsidering dozens of rules designed to fight pollution. The White House is also firing many of the EPA staffers who enforce the rules that remain. 

This week, CBS News visited a Houston neighborhood that's near an NRG Energy coal-fired power plant, the largest in Texas. 

When CBS News visited the same neighborhood in December, Mr. Trump had just been elected to a second term, promising the energy industry that he would roll back environmental regulations that protect air quality. 

"I think of pollution as a silent and invisible killer," Dr. Winston Liaw, chair of the Health Systems and Population Health Sciences Department at the University of Houston, told CBS News.

Liaw treats patients who run a higher risk of lung disease, asthma and heart attacks due to emissions from oil refineries, chemical plants and coal plants in the Houston area. 

He explained how the air in Houston can impact human health.

"There are these tiny particles, and they're so small that they bypass a lot of our defenses," Liaw said. "And then they start injuring all sorts of tissue in our body."

A from Rice University found that pollution from the NRG plant contributes to 177 premature deaths per year. 

In April, the Trump administration   — including the NRG plant in the Rice study — a two-year exemption from complying with federal regulations intended to lower mercury emissions, a powerful  that can affect the brain.

CBS News analyzed the Trump administration's exemptions and found that nearly 65% of these plants are located within 3 miles of low-income, minority communities.  

"Bottom line is, who's more at risk are poor people," said Ben Jealous, executive director of the Sierra Club, an environmental advocacy group that has led an effort to try and close almost two-thirds of the nation's coal plants.

"When you start increasing production of coal-fired power plants, you're going to kill more people, and you're going to cause more heart attacks, and you're going to cause more asthma attacks," Jealous said.

In a statement provided to CBS News, NRG Energy said its "coal units operate in compliance with the current Mercury Air Toxics Standards (MATS) and will operate in compliance with any future MATS requirements."

In a separate statement, the Trump administration said Biden-era coal plant regulations "stacked burdensome regulations on top of the longstanding Mercury and Air Toxics Standards, raising the risk of coal-fired plants shutting down – which would eliminate thousands of jobs, strain our electrical grid, and undermine our national security by leaving America vulnerable to electricity shortages." 

Jealous argues that coal is not a more reliable energy source than renewable energies.

"The argument that coal gives you more reliable energy isn't valid," Jealous said. "Solar, wind and batteries gives you the most reliable, the most resilient grid."

More importantly, he said, for the people of Houston and across the country, renewable energy means less pollution.