The ability of household pitcher-style water purifiers to remove microcystins depends on filtration rate and activated carbon source

Toxic cyanobacterial blooms are a global threat to human health due to contamination of drinking water. To ensure public safety, water treatment plants must have the capability to remove cyanotoxins from water. Recently, however, there have been several instances when microcystins, a common group of cyanotoxins, have been detected in tap water. This research investigated if commercially available pitcher-style water purifiers were able to remove microcystins from water. Microcystins were extracted from two naturally occurring blooms in Lake Erie, diluted to initial concentrations ranging from 1 to 5 μg/L, and then subjected to three purifier types. Results showed that the purifier with the fastest percolation rate (126 seconds/L) and a filter cartridge comprised solely of coconut-based activated carbon removed 50% or less of the microcystins, while the purifier with the slowest percolation rate (374 seconds/L) and a blend of activated carbon decreased microcystins to below detectable levels (<0.10 μg/L) in all experiments. Thus, pitcher-style purifiers with slow percolation rates and composed of a blend of active carbon can provide an additional layer of protection against microcystins; however, it is recommended that consumers switch water sources when cyanotoxins are confirmed to be in tap water. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/ws.2018.081 om https://iwaponline.com/ws/article-pdf/19/1/336/507251/ws019010336.pdf 020 Justin D. Chaffin (corresponding author) Erica L. Fox Callie A. Nauman Kristen N. Slodysko F.T. Stone Laboratory, The Ohio State University, 878 Bayview Ave., Put-in-Bay, OH 43456, USA E-mail: chaffin.46@osu.edu Callie A. Nauman Aquatic Ecology Laboratory, The Ohio State University, Columbus, OH 43210, USA Kristen N. Slodysko Department of Environmental Science, State University of New York College of Environmental Science and Forestry, Syracuse, NY 13210, USA

Unfortunately, cyanobacterial blooms are predicted to become more severe and wide-spread with climate change if land-use practices are not altered to minimize nutrient (phosphorus and nitrogen) input to surface waters (Paerl et al. ). Recent improvements in land use and sewage treatment are ongoing to prevent blooms, but in the meantime, the ability to remove microcystins from surface water to ensure public safety is crucial.
The majority of research conducted regarding removing microcystins from drinking water has occurred at the water treatment plant scale. Conventional methods include activated carbon (Ho et al. ), UV light and hydrogen peroxide oxidation (He et al. ), and ozone (Hitzfeld et al. ). If microcystins break through water plant treatment, the distribution system will send the cyanotoxins to consumers; however, the fate of microcystins in the distribution system is not understood. Point-of-use treatment options are the last layer of defense against microcystins for consumers concerned about cyanotoxins in tap water (Roegner et al. ). For example, Pawlowicz et al. () showed that carbon-based under-the-sink filters connected to a faucet would remove more than 99.7% of microcystins spiked into deionized water. However, they also showed that pleated paper and string wound filters allowed more than 90% of microcystins to pass through (Pawlowicz et al. ). Thus, the effectiveness of the filters depends on composition and design. The ability of point-of-use filters, such as pitcher-style water purifiers, to remove microcystins from water has not been tested; however, they may provide consumers concerned about microcystins an additional layer of protection.
The objective of this project was to determine if household pitcher-style water purifiers are effective at removing microcystins from water. Microcystins extracted from two natural Lake Erie cyanobacterial blooms (Microcystis and Planktothrix blooms) were subjected to the pitcher purifier treatment.
Initial concentrations of total microcystins in these experiments were between 0.8 and 5.0 μg/L, which spans the range of likely microcystins concentrations in Toledo's tap water during the 2014 crisis (Qian et al. ). This method replicates a more realistic scenario than spiking pure microcystins in deionized water because water treatment plants draw in lake water that contains natural organic matter (NOM) in addition to potentially toxic cyanobacteria. Furthermore, it is likely that if microcystins break through the treatment process, NOM will as well. This is supported by taste and odor issues in drinking water, which are associated with the metabolite products of algal blooms (Watson et al. 

Water purifiers
Three different purifier brands were tested in this research, and the components of each brand's filter cartridge were unique (Table 1). Thus, tests were conducted on the components of the filter cartridge and not necessarily the brands as each brand may manufacture different 'grades' of filter cartridge. All three purifier brands were certified by NSF International/American National Standards Institute standards #42 and #53 for health and aesthetic effects; however, microcystins were not included in the certification. These purifiers are commercially available and can be purchased at a local supermarket. All pitchers used in the study held between 2.4 L and 2.6 L of water. Three separate pitcher-style water purifiers of each type were used as replicates (nine total pitchers), and water poured into pint glasses served as a non-purified control.
New filter cartridges were installed according to manufacturer instructions. To determine if the filter cartridges could produce a false positive for microcystins, 1 L of deionized (DI) water was poured through each purifier, which was sampled for microcystins after percolating into the reservoir. All samples in this test were below the detection limit. Additionally, pH and chloride concentrations were measured and verified to be within the range specified by the microcystins enzyme-linked immunosorbent assay (ELISA) kit (pH between 5 and 11, Cl < 0.10 mg/L), so as not to interfere with the assay. The water samples were subjected to three freeze/thaw cycles to lyse cells and extract microcystins, and the concentration was measured using ELISA (see below). After total microcystins concentrations were measured, the water was held at À20 C until experimentation. On the day of an experiment, water was thawed (four total freeze/thaw cycles), filtered through glass fiber filters (0.45 μm) to remove cellular debris, and diluted in a 20 L carboy with DI water to lower the total microcystins concentration to a range of 1 to 5 μg/L. Samples for initial measurements of total microcystins and DON concentrations were collected from a 1 L subsample.

Experimental methods
In the experiment testing filter compositions, 1 L of water containing microcystins was poured into each purifier.
Samples were collected from the purifier's reservoir beneath the filter cartridge immediately after all of the 1 L percolated through the filter cartridge. Each purifier was subsampled three times for microcystins by pipetting 10 mL of water from the pitcher purifier into three separate amber glass vials (results from these subsamples were averaged to determine total microcystins concentration for that purifier). A 150 mL sample was poured from the pitcher into a 250 mL polycarbonate bottle for DON analysis. Then, the purifiers were resampled 4 hours after initial percolation to determine if the filter cartridges leaked microcystins back into the water. Finally, the water was discarded from the pitcher, and 1 L of DI water was poured into the purifier and sampled to determine if microcystins became unbound from the filter cartridge. These experiments were conducted with new filter cartridges and with water from the Lake Erie Microcystis and Planktothrix blooms. An additional experiment was conducted to test expired filter cartridges following the above method and utilized the Microcystismicrocystins water. Local tap water was poured through filters until the cartridge was considered to be expired according to manufacturer guidelines, and all manufacturers indicated that the capacity was approximately 150 L per cartridge. This cartridge capacity indicates that a family of four that consumes 2.5 L/person/day would need to replace the cartridge every 15 days.
Because percolation rates differed remarkably among the three types of purifiers (see results, Table 1), which introduced a contact time bias into the study, another experiment was designed to determine if increased filter contact time would increase microcystins and DON removal. In separate experiments using new filter cartridges, 1 L of Microcystis-microcystins water was poured into each purifier and sampled for microcystins as above. The filtered

Percolation rates
Filter contact times were remarkably different among the three types of purifiers as 1 L of tap water needed 125.9 ± 2.41 seconds, 230.9 ± 7.30 seconds, and 374.0 ± 2.41 seconds to pass through the filters (Table 1). These contact times were converted to percolation rates to give 0.48 ± 0.009 L/min, 0.26 ± 0.009 L/min, and 0.16 ± 0.001 L/min. For the remainder of this report, each filter type is identified by the contact time of 1 L (126-purifier, 231-purifier, 374-purifier). However, it is important to note that contact time was not the only variable that affected microcystins removal because the purifiers had different components (see discussion). Initial total microcystins concentration in the Microcystis-extracted water was 3.3 μg/L (Figure 1(a)). Total microcystins concentration significantly decreased (P < 0.001) following percolation through each purifier, but was detected in the filtered water from two of the three purifiers ( Figure 1(a)). The 126-purifier decreased total microcystins to 1.88 ± 0.21 μg/L and the 231-purifier decreased microcystins to 0.50 ± 0.05 μg/L. Microcystins were decreased to non-detectable levels by the 374-purifier. Total microcystins concentration in the filtered water did not change 4 hours after percolation, and microcystins were not detected in DI water that was filtered through the purifiers. Planktothrix-extracted microcystins had an initial concentration of 2.90 μg/L (Figure 1(b)). The 126-purifier decreased total microcystins to 0.28 ± 0.03 μg/L, while the 231-and 374purifiers decreased microcystins to below detectable levels.

Microcystins removal
Again, the total microcystins concentrations did not change after 4 hours and were not detectable following a DI water flush. The expired filter cartridge experiment with Microcystis-extracted microcystins had an initial concentration of 1.94 μg/L (Figure 1(c)). Following percolation, water from the 126-purifier was significantly similar to the non-filtered control (P > 0.05). The 231-purifier decreased total microcystins to 0.25 ± 0.03 μg/L and the 374-purifier decreased microcystins to non-detectable levels.
Again, the total microcystins concentrations did not change after 4 hours and were not detectable following a DI water flush.
Water percolated through the 126-purifier nearly three times as fast as the 374-purifier. Water from the 126-purifier was filtered three times in total (refiltered two times after initial contact) to increase contact time to a similar contact time as the 374-purifier. The filter with the intermediate contact time In the high microcystins experiment, the 231-purifier decreased total microcystins to 1.00 ± 0.03 μg/L after one percolation then to 0.29 ± 0.02 μg/L after two percolations, while the 126-purifier decreased total microcystins to 2.64 ± 0.01 μg/L, 1.60 ± 0.05 μg/L, and 1.01 ± 0.02 μg/L, respectively, after each percolation step (Figure 2(b)).

DISCUSSION
It has been forecast that toxic cyanobacterial blooms will increase in magnitude under current climate change scenarios (Paerl et al. ). Therefore, it is paramount that all possible actions (land use and water treatment actions) are taken to remove cyanobacterial toxins from water to provide  The global public health organization NSF International recently issued a new protocol (#477) that will allow manufacturers of point-of-use water purifiers to make claims that their product can decrease microcystins to concentrations less than 0.3 μg/L (NSF International ). Results from this study indicate only the 374-purifier would achieve that certification. However, the lower the initial total microcystins concentration, the higher the chance that any purifier can decrease total microcystins to 0.3 μg/L. For example, the 126-purifier achieved 0.3 μg/L when the initial total microcystins concentration was 0.89 μg/L (Figure 2(a)), but the 126-purifier did not achieve 0.3 μg/L when initial total microcystins concentration was 1.9 μg/L or greater (Figures 1(a)-1(c) and 2(b)).

CONCLUSIONS
In conclusion, the amount of microcystins removed by point-of-use pitcher-style purifiers differed by type of filter cartridge. The purifier that was most effective at removing microcystins had the slowest percolation time and a cartridge consisting of a blend of activated carbon, whereas the purifier with the quickest rate of percolation and coconut-based activated carbon removed the least amount of microcystins. Because cyanobacterial blooms will likely persist in the near future, pitcher-style water purifiers may provide consumers with an additional layer of protection against microcystins. Nonetheless, it is still recommended that consumers switch water sources during times when microcystins are known to be present in tap water.