As the summer months grow warmer throughout the U.S., the presence of algae in some surface water supplies has increased. Although not all algae produce toxins that affect public health, a spike in recent years of harmful algal blooms (HABs) is triggering some concern among the public as well as the water industry. One such occurrence took place last August. A major algal bloom in Lake Erie caused the city of Toledo, Ohio, to issue a “do not drink” order for more than 400,000 residents.
The 2009 National Lakes Assessment from the U.S. Environmental Protection Agency (EPA) estimated that 20 percent of the nation’s lakes are highly impacted by algae, and one-third contains some level of HABs.
To address the rise in HABs, on May 6, 2015, EPA issued health advisory values that states and utilities can use to address elevated levels of algal toxins in drinking water. In the issued health advisory, EPA determined toxin levels in tap water that are safe for human consumption and offered recommendations for how utilities can monitor and treat drinking water for algal toxins and notify the public if/when the water exceeds these levels.
The growing awareness of algal toxins has triggered some debate within the water industry as to the actual threat of HABs to consumers. The industry must be mindful of the latest research, regulations and available water treatment for HABs to properly educate end users on the potential health concerns of algal toxins.
Algae in review
“Algae are found naturally in lakes, streams, ponds and other surface waters,” explains Keith Thompson, president of the Gas Chlorine Education Committee. “When conditions are favorable, they multiply rapidly and cause an ‘[algal] bloom’ characterized by a pea-soup green color or blue-green scum.”
Additionally, adds Thompson, the intensity of sunlight, water temperature, nutrient availability (especially nitrogen and phosphorous), pH, and water movement can affect the formation of algal blooms.
Cyanobacteria, certain varieties of fresh water algae often referred to as blue-green algae, have increased in severity and toxin production in Lake Erie according to EPA and were responsible for last year’s Toledo incident.
“Cyanobacteria … proliferate in stagnant or slow-moving bodies of water with high levels of nutrients — nitrogen and phosphorous — often due to agricultural runoff or wastewater,” says Orren D. Schneider, Ph.D., P.E., manager of water technology for American Water. “Many algae are not harmful and serve as the base of a food web for higher organisms, such as fish. However, when the ecosystem becomes unbalanced, cyanobacteria can proliferate (bloom).”
These fresh water algae can produce cyanotoxins, which, notes Thompson, are considered one of the more harmful types of algal toxins.
“Cyanotoxins can cause health problems primarily affecting the nervous system, liver or skin,” states Thompson. “If present in recreational water or drinking water at high enough levels, a wide range of symptoms may occur — including fever, headaches, muscle and joint pain, blisters, stomach cramps, diarrhea, vomiting, mouth ulcers and allergic reactions. [These] effects can occur immediately or several days after exposure.”
Schneider reports that some of the most common classes of algal toxins are microcystins, anatoxins and cylindrospermopsins, adding that microcystins, which have a World Health Organization (WHO) guideline of 1 mg/l for drinking water, and cylindrospermopsins primarily affect the liver, and anatoxins affect nerve synapses. However, continues Schneider, appropriate guidelines, limits and standards for these toxins are still in development.
When cyanobacteria are present in a water source, explains Schneider, removing them from the water before toxins are released is preferred. This can be accomplished through processes such as dissolved air flotation. He adds, “If the toxins are dissolved in the water, other processes can be used to remove them.” However, Schneider believes the best approach is to prevent the growth of algae that can produce the toxins through watershed management.
Many solutions are available to treat algal toxins. Disinfectants and oxidants such as chlorine, chloramine, ozone, ultraviolet (UV) and chlorine dioxide are frequently used or can be added in a treatment facility. Most algal cells can be removed by chlorine disinfection, in addition to coagulation, sedimentation and flocculation, but toxin removal can be a little more difficult. Schneider asserts that granular activated carbon (GAC), ozone, advanced oxidation processes, nanofiltration and reverse osmosis (RO) can remove algal toxins to varying degrees.
“Technologies already exist that can remove/destroy these toxins. All it takes is space or energy,” notes Schneider. “It is a matter of identifying the risks for particular utilities and implementing those that are the most cost-effective. In the future, I believe we will be seeing solutions that are prophylactic and prevent the cyanobacteria in the first place rather than being reactive and having to remove toxins from the water. These will include better watershed controls, nutrient uptake measures and ultrasonic devices.”
In light of the treatment solutions currently available and despite the rise in the concern over HABs, Thompson believes the public should rest assured that the health risks associated with algal toxins in drinking water are slight. “Perhaps an advisory would be better aimed at other more probable means for people to be exposed, such as swimming, rather than the public drinking water systems,” suggests Thompson, adding that when educating consumers about potential health concerns regarding algal toxins, “good science and information is always helpful. Scare tactics never benefit anyone.”
Editor’s note: Visit WaterTechOnline.com later this month for an update on EPA’s guidelines on allowable algal toxin levels. In a previous Professor POU/POE, Technical Editor Dr. Joseph Cotruvo discusses algal toxins. You can find this article here. Search “algal toxins” on our website for further information on HABs.