Factories around the world are pumping out toxic brine at a rate much higher than previously estimated and dumping it back into the ocean, according to a report published on Monday.

This super-salty brine is toxic to marine life, and as many nations become more dependent on desalination to supply drinkable water to their citizens, the report argues that this form of water purification could be a serious environmental hazard.

According to the report, which is part of the United Nations University Institute for Water, Environment and Health’s project on Unconventional Water Resources, the amount of toxic brine produced at desalination plants—which convert salt water into drinkable fresh water—is 50 percent higher than previously estimated. Roughly 16,000 desalination plants around the world produced about 141.5 million cubic meters of brine each day, the report says.

To put that in perspective, that’s equal to about two-thirds of the average daily water flow over Niagara falls and results in enough brine each year to submerge the state of Florida under a foot of the toxic waste.

Most of the world’s desalination plants are concentrated in the Middle East and northern Africa, where water resources are increasingly scarce. According to the report, 42 percent of toxic brine produced by desalination can be traced to just two countries: Saudi Arabia and the United Arab Emirates. In recent years, these countries have invested heavily in desalination technology as a way to cope with water shortages brought on by drought and unsustainable agricultural practices.

Desalination is usually achieved either by boiling salt water and collecting the steam, so that the salt is left behind, or reverse osmosis, which uses pressure to force saltwater through a semipermeable membrane that filters out salt and other particles.

After clean water is extracted from salt water, desalination plants are left with a large reservoir of brine, which is about twice as salty as normal sea water. Indeed, according to the new report, desalination process produce about 1.5 liters of brine for every 1 liter of fresh water produced.

Desalination plants often dispose of this toxic brine by pumping it back into the same marine environment the water was drawn from, which poses a serious threat to aquatic life. The reason for this is that the salty brine sinks to the ocean floor, where plants and other aquatic life struggle to adapt to the rapid increase in the salinity of their environment. Moreover, the saturated salt water in these areas decreases the amount of oxygen available to plants and animals on the ocean floor, which slowly suffocates them.

Aside from producing incredible amounts of brine, all forms of desalination are incredibly energy intensive. Although Saudi Arabia is increasingly turning to solar energy to power its desalination plants, the country still uses an estimated 300,000 barrels of oil a day to keep its coastal facilities running—more oil than most of the world’s countries consume in a day.

Global distribution of desalination facilities. Image: Science of the Total Environment

According to the report, 66 percent of the world already deals with water scarcity for at least one month out of the year. By 2025, it is expected that 60 percent of the world will live in a state of permanent water scarcity. Although desalination is a leading option for meeting the world’s water needs in the future, this solution hinges on the adoption of sustainable energy sources to power desalination plants and water conservation policies that cover how fresh water is used and how brine from desalination plants is disposed of.

Fortunately, the researchers behind the paper say there may be several ways to make use of the brine, instead of dumping it back into the ocean. For example, the researchers suggest that the brine could be used to irrigate plants that are tolerant of salt water, or generate electricity, or it could be mined for a variety of minerals and metals such as magnesium, gypsum, calcium, lithium, potassium and even uranium.

In many of these cases, however, the researchers note that better technology is needed to make these elements’ extraction from brine economically feasible.

"There is an urgent need to make desalination technologies more affordable,” Vladimir Smakhtin, a co-author of the report, said in a statement. “At the same time, though, we have to address potentially severe downsides of desalination--the harm of brine and chemical pollution to the marine environment and human health.”