Chlorine: Killing Pathogens, Not Aquatic Life

That “pool” smell that may trigger fond memories for some while nauseating others isn’t from chlorine. It’s from chloramines, chemicals formed from chlorine reacting with other elements, such as ammonia—a component of sweat and urine. Bad news for avid pool-goers. This brief chemistry lesson came courtesy of Art Spivack, University of Rhode Island oceanography professor, during the 2017 Ronald C. Baird Sea Grant Science Symposium, where participants came together to discuss ecological changes in Narragansett Bay and next steps forward to improve management.

Spivack, who specializes in biochemistry, was responding to perceptions that chlorine used by wastewater treatment facilities to kill pathogens from human and industrial sewage is being dumped into the bay along with the treated wastewater (effluent) and harming aquatic life—and leaving its tell-tale odor as evidence of its presence.

The 1901 Field’s Point Wastewater Treatment Facility Chemical Building is one of the oldest buildings at Providence’s main sewage treatment facility. Dechlorination helps neutralize the chlorine used to kill pathogens in wastewater.

Since chlorine—a very reactive, naturally occurring chemical—is a powerful tool for killing pathogens, it is the most common form of treatment at wastewater facilities. Bleach was first introduced as a disinfectant in Rhode Island wastewater treatment in 1912, said Tom Uva, director of environmental science and compliance at the Narragansett Bay Commission, who discussed the history of human impacts to Narragansett Bay in his presentation at the symposium.

“There’s a decline in fatal diseases once we started disinfecting water and wastewater,” he said. “As a result, the upper bay can support beaches, and shellfishing has opened up.”

All but three of the state’s 19 wastewater treatment facilities, as well as those in Massachusetts that discharge into connecting watersheds, use chlorine in dealing with the 100 million gallons of human and industrial sewage they receive daily. The other three facilities—located in East Greenwich, Narragansett Bay Commission’s Bucklin Point, and West Warwick— switched to ultraviolet light to disinfect wastewater.

This method obviates the potential toxic impacts of chlorine, but comes with added costs, which is why most facilities have continued using chlorine, said Angelo Liberti, chief of surface water protection at the Rhode Island Department of Environmental Management (DEM), who discussed the state’s efforts to reduce pollution in the bay from wastewater discharge.

For example, in 2014, the city of Newport decided to upgrade existing chlorination/dechlorination systems after determining that construction and annual operation and maintenance costs for ultraviolet treatment would be between 24 and 35 percent greater. Sulfites are added to wastewater to prevent chlorine-related toxins from entering the bay.

Twenty pounds of chlorine dumped into Narragansett Bay from wastewater discharge is equivalent to seven drops of chlorine in an Olympic-size pool.

These sulfites, the same chemicals that preserve freshness in baked goods, react with the chlorine that’s left over after treatment to form sulfate and chloride—both of which are natural components of seawater, Spivack said. “The relative amount of sulfate and chloride we’re adding is at a level that’s immeasurable compared to the background,” he explained, “The chemicals that we’re adding already exist [in Narragansett Bay] and add a tiny amount compared to the natural abundance.”

The amount of sulfate naturally in seawater is 1,000 times higher than it is in dechlorinated water, according to DEM. Mitigation efforts have reduced the amount of chlorine entering the bay since the late 1990s by about 98 percent, Spivack said.

“In 2016, only 20 pounds of chlorine from all the wastewater treatment facilities combined was discharged into the bay,” said Angelo Liberti, chief of surface water protection at DEM, who discussed the state’s efforts to reduce pollution in the bay resulting from wastewater treatment facilities in his presentation at the symposium. Twenty pounds, he added, is the equivalent of adding 80 gallons of household bleach to the total volume of the bay. “That’s the same as seven drops of chlorine in an Olympic-size pool,” he noted. “The permit we set for the Fields Point treatment plant is 800,000 times less strong than household bleach. That’s how protective we’re being to aquatic life.”

The amount of chlorine that aquatic life can tolerate, Liberti said, is actually much higher. To ensure that the effluent discharged into the bay will indeed not have any deleterious effects on aquatic life or, by extension, seafood consumers, the state conducts “bioassay,” or toxicity, tests of effluent. These tests are based on Environmental Protection Agency (EPA) methods to determine the effects on an organism’s ability to survive, grow, and reproduce.

Rhode Island has been conducting these tests since 1990 at the EPA’s Environmental Research Lab in Narragansett to determine acute or chronic effects of pollutants on aquatic life using the most sensitive species found in Narragansett Bay. “Organisms are immersed in the effluent to see whether it causes toxicity. So, if there are particular pollutants that we’re not monitoring for, this is a catch-all test to see if there are any lethal or reproductive effects,” Liberti said. “It can account for chemicals interacting with one another that are more toxic than they would be individually or things we’re not monitoring.”

The species used in these tests are native to Rhode Island marine and estuarine waters (including mysid shrimp, Atlantic purple sea urchins, silversides, copepods, and Eastern oysters). They can be easily cultured in the lab, are sensitive to a variety of pollutants, and are generally available throughout the year from commercial sources. “The reason we don’t collect [species] from the wild is because you don’t want some that might have a separate problem or unrelated stress,” said Liberti, addressing concerns raised about the EPA lab tests.

He explained that species taken from the wild may have other ailments, so it would be hard to isolate and determine the full effect of effluent toxicity if there was any. “Species are carefully raised in the lab where there’s quality control so it’s a fair test.” “The toxicity tests, the bioassays … done … in the past after chlorination were highly toxic, which is what you’d expect,” he said. “You want your chlorine to kill bacteria and viruses, but it also kills phytoplankton and zooplankton. But after dechlorination, there’s virtually no toxicity detected in the effluent.”

– Meredith Haas | Ronald C. Baird Sea Grant 2017 proceedings

More information about the Baird Symposium, including links to videos of the morning and afternoon sessions and the PowerPoint presentations, is available online. Results will be used to inform the upcoming Rhode Island Sea Grant research request for proposals and the Rhode Island Coastal Resources Management Council’s Narragansett Bay Special Area Management Plan.

The symposium was sponsored by GSO, Rhode Island Sea Grant, the URI Coastal Resources Center, and the van Beuren Charitable Foundation. 

 

+ Read full proceedings

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