Five of the country’s worst mercury-emitting power plants are located in Texas, according to a new report from an environmental watchdog.

The Environmental Integrity Project determined that four Luminant plants in East Texas—Martin Lake, Big Brown, Monticello, and Sandow—rank in the top five mercury emitters in the country. Harrison County’s H.W. Pirkey Power Plant, owned by  American Electric Power, rounds out the top ten. Other states with top emitters include Alabama, Missouri, Michigan, North Dakota, and Oklahoma.

“Nationwide, equipment has been installed over the years to reduce emissions of sulfur dioxide and particulate matter. That has helped cut down on the release of mercury, toxic metals and acid gases from power plants over the last ten years,” Ilan Levin, an attorney for the Environmental Integrity Project, wrote in a statement. “However, that progress is uneven, and the dirtiest plants continue to churn out thousands of pounds of toxins that can be hazardous to human health even in small concentrations. For example, emissions of mercury from coal-fired power plants have actually increased in the last decade in the state of Texas.”

Why is this a problem? Well, mercury is a potent neurotoxin that is particularly harmful to children and developing fetuses. And “[e]missions from local power plants deposit mercury and other toxic metals in nearby rivers and streams, where these pollutants concentrate in aquatic organisms at levels that can make fish unsafe to eat,” Levin said in a statement. This process is called bioaccumulation, and the Mobile Press-Register‘s Ben Raines explained the dangers of it on his paper’s website:

Mercury levels have increased all over the globe during the last 100 years. Mercury enters the environment after being burned, particularly at coal burning power plants, but also in forest fires. Minute particles fall from the sky and wash into rivers and lakes, where a chemical conversion takes place.

Bacteria change elemental mercury into a form known as methylmercury, which can build up in aquatic creatures and work its way up the food chain, collecting first in small creatures, such as minnows and frogs. Ultimately, larger fish and predators including fish eating birds and humans build up the highest levels.

The nonprofit used data from the Environmental Protection Agency to compile the report. Plants self report emissions information to the agency’s Toxic Release Inventory.

D Magazine‘s Bradford Pearson reached out to Luminant spokeswoman Ashley Barrie for a comment:

Luminant stands by its strong track record of exemplary compliance in meeting or outperforming all state and federal environmental laws, rules and regulations. Our voluntary installation of activated carbon injection systems on all of our coal-fueled power plant units demonstrates our commitment to protect air quality and the environment well in advance of state or federal mandates. This equipment has resulted in the reduction of fleet-wide mercury emissions by more than 20 percent since 2005, despite the addition of 2,200 MW of coal-fueled units. In addition, we’ve continued to make investments including $300 million in emission control equipment across our fleet – $80 million at Martin Lake Power Plant – which will further reduce mercury and SO2.

America’s top ten power plants for mercury pollution:

1. Luminant Generation, Martin Lake Steam Electric Station & Lignite Mine in Rusk County, Texas (1,501 lbs. of mercury emissions)

2. Southern Co., Gaston Steam Plant in Shelby, Alabama (1,244 lbs. of mercury emissions)

3. Luminant Generation, Big Brown Steam Electric Station & Lignite Mine in Freestone County, Texas (1,240 lbs. of mercury emissions)

4. Luminant Generation, Monticello Steam Electric Station & Lignite Mine in Titus County, Texas (911 lbs. of mercury emissions)

5. Luminant Generation, Sandow Steam Electric Station in Milam County, Texas (841 lbs. of mercury emissions)

6. Great River Energy, Coal Creek Station in Mclean County, North Dakota (812 lbs. of mercury emissions)

7. Ameren Corp., Ameren Missouri Labadie Energy Center in Franklin, Missouri (795 lbs. of mercury emissions)

8. Grand River Dam Authority, Grand River Coal Fired Complex in Mayes County, Oklahoma (722 lbs. of mercury emissions)

9. DTE Energy Co., Detroit Edison Monroe Power Plant in Monroe County, Michigan (708 lbs. of mercury emissions)

10. American Electric Power, H.W. Pirkey Power Plant in Harrison County, Texas (683 lbs. of mercury emissions)