Puerto Rican Gov. Ricardo Rossello signed a law yesterday (July 4) to ban coal ash from the U.S. territory’s landfills. He does plan, however, to export the toxic byproduct of coal combustion after converting it to construction material.

This move comes after much pressure from environmentalists in the territory’s southern region who have been protesting coal ash since 2014. The new law leaves them unsatisfied, as they would prefer that the governor ban the use of the substance outright.

Coal ash is produced in coal-fired power plants. The byproduct contains dangerous contaminants like mercury, cadmium and arsenic, per the EPA. If not disposed of properly, coal ash can leach into waterways, drinking water and the air. Then, ultimately, it can harm human bodies.

Tensions in Puerto Rico grew toward the end of 2016 when activists staged large-scale protests in Peñuelas, Puerto Rico, where Applied Energy Systems (AES), the energy company transporting the coal ash, would dump the substance. In November 2016, Latino USA reported, protests led to more than 60 arrests. One protest is ongoing, reports The Associated Press, and it is keeping trucks carrying coal ash from reaching a landfill in Peñuelas.

The territory had used coal ash in the past to build roads, parking lots and malls in the form of Agremax, a filler that AES developed, according to The Conversation. By 2014, AES stopped manufacturing Agremax after environmental groups raised concerns over toxic dust resulting from the ash’s transport.

Many opponents of the coal industry remain skeptical of the governor’s law, as it will grow the commercial use of coal ash. Rossello announced he will also create a $10 million company to convert the ash into construction material.

“This law is one step forward and two steps back,” said biologist Miguel Canals to the AP.