Cyanobacteria are one of nature’s great opportunists. Every summer, these primitive organisms erupt in vast blooms in ponds and lakes, soaking up the sun’s energy. Feeding on nitrogen and phosphorus, these bacteria colonies multiply and eventually die, releasing toxic waste products called cyanotoxins that accumulate during their growth.
These events are known as harmful algal blooms, because the pose a threat to public health. Cyanotoxins are unstable and change rapidly, making detection difficult. Some harm the nervous system. Others, known as hepatotoxins, can severely damage the liver and kidney. HABs can occur in marine or freshwater environments, closing fisheries, beaches and even entire lakes.
Evidence is mounting that HABs are increasing in both frequency and intensity. Drought conditions brought on by climate change can depress lake levels, concentrating nutrient-rich agricultural runoff in areas of low turbidity. Torrential rainfall can also trigger a sudden influx of agricultural nutrients, as occurred in Florida’s Lake Okeechobee this year, where a HAB flowed seaward, forcing beaches to close. Blooms containing the most common type of harmful cyanotoxin—microcystin—struck the Mormon Reservoir in Idaho, several lakes in Montgomery County in Maryland and Bonney Lake in Washington. In the latter case, a dozen swimmers became ill after swimming in the HAB.
Freshwater blooms can poison drinking water supplies as well. Ideal HAB conditions in Western Lake Erie cause blooms annually, but microcystin concentrations were particularly severe in the summer of 2014. A treatment plant that supplies drinking water to more than 500,000 residents in and around Toledo reported a microcystin level of 3.191 parts per billion (ppb) in fully treated tap water. This concentration, which is three times the World Health Organization limit of 1 ppb, forced the city to issue an unexpected “do not use the water” warning.
Tested by a Growing Problem
In 2015, the U.S. Environmental Protection Agency issued health advisories for microcystin and another cyanotoxin, cylindrospermopsin, to help guide municipalities’ cyanotoxin test and response procedures. Though several U.S. states, and Canada, have recommended limits, these advisories included the first nationwide acceptable levels for microcystin: 0.3 ppb for children under age six and 1.6 ppb for adolescents and adults.
In addition to these limits, the Centers for Disease Control in June 2016 launched the first national reporting system for HABs and associated illnesses. Growing federal awareness doesn’t mean municipalities are always well equipped to respond to toxic HABs. In Toledo, officials now conduct seasonal microcystin testing daily, instead of weekly. This move improves response time because cyanotoxin reduction requires different treatment methods and equipment.
However, these adjustments cost money. In many states without a significant history of HABs, testing frequency and lack of appropriate equipment may put the public drink water supply at risk. Detection and treatment is tricky. Blooms are unpredictable, and cyanobacteria release toxins as waste products, or when their cells walls rupture. Toledo’s crisis highlighted these shortcomings and shed light on the fact that residents had no option for reducing microcystin in their home water supply.
Municipalities are responsible for notifying residents of a dangerous bloom, but having the additional protection of a carbon filter for the home can be helpful in certain situations. Microcystin levels may rise before officials can adjust their treatment methods, or it may be present below action levels at a treatment plant.
A coalition of organizations are responsible for developing new HABs response practices, including Toledo city officials, the U.S. and Ohio Environmental Protection Agency, and Health Canada. They asked NSF International, a not-for-profit public health organization, to help develop a protocol for home filtration to reduce microcystin below HA levels.
An Added Layer of Protection
A protocol would allow filter manufacturers to verify their product’s ability to reduce microcystin at or below EPA-recommended levels. But microcystin is a challenging contaminant. Laboratory-ready methods to synthesize microcystin do not exist, and until recently no supplies of any quantity were available for sale. The limited amounts that were initially available cost more than $100,000 for about 40 mg, enough to test just a single filter.
In order to build a “challenge water,” which simulates the water conditions with the actual contaminant that might be encountered by a point-of-use (POU) filter installed at the tap in a kitchen sink, more microcystin was needed. After a false start using unpurified water, a new commercial source brought down testing costs significantly. This was important because if filter manufacturers found testing too expensive, they might not be able to bring filters to market. Complicating matters further, microcystin is a controlled substance toxic enough to be considered a biological weapon by the U.S. Department of Defense.10 The testing team needed a permit to obtain it.
With the help of the EPA and Health Canada, scientists identified the appropriate challenge level of microcystin in the test water. This topped out at 4 ppb, which is higher than any level seen in treated water in Toledo. Then the team established an analytical method using high-performance liquid chromatography to test both influent and treated water. In developing the protocol, scientists had to account for the more than 80 different congeners, or variants, of microcystin. Microcystin-LR is the most toxic congener, but in order to be protective of public health, other similar but less toxic congeners were included in the development of challenge water and testing methods.
The new protocol—NSF P477: Drinking Water Treatment Units – Microcystin—verifies several aspects of a filter, including whether the treatment system is structurally sound, the contaminant reduction claim on the label is true and that the system does not add any harmful contaminants. A filter certified to this protocol is capable of reducing microcystin throughout its lifetime.
Water filters are considered supplemental treatment, and are not intended to treat private, untreated water supplies. However, events in Toledo and elsewhere have affected a great many people, illustrating the potential harm of HABs. Filters certified to the new protocol provide a useful additional layer of protection for those who receive their drinking water from municipalities that source from surface water.