By Rick Andrew

One of the main focuses of the NSF Joint Committee on Drinking Water Treatment Units is the expansion of the available contam­inant-reduction claims for various technologies. As more and more contaminants are detected in source water and drinking water, it is highly beneficial to have American National Standards establishing criteria and test methods to demonstrate conformance of readily available drinking water treatment systems to treat these contaminants.

We have seen several recent developments for developing criteria for typical POU and POE systems to demonstrate reduction of PFOA and PFOS, nitrosamines and microplastics. Now, another test method for contaminant reduction is being added to NSF/ ANSI 53. This newest contaminant reduction test method and criteria are for 1,2,3-trichloropropane (TCP) reduction.

TCP does not occur naturally – it is exclusively a man-made chemical. Technically categorized as a chlorinated hydrocarbon, TCP has been used in multiple industrial and agricultural appli­cations. These include use as a paint or varnish remover, a cleaning and degreasing agent and a solvent. It is a crosslinking agent for polysulfide polymers and sealants. TCP is also used as an inter­mediate chemical in producing other chemical end products.

Agriculturally, chloropropane-containing soil fumigation chemicals were used as pesticides throughout the United States. Dating back to the 1940s, soil fumigation chemicals that included TCP as a minor component were marketed for the cultivation of various crops, including citrus fruits, pineapples, soy beans, cotton, tomatoes and potatoes. Newer formulations were developed in the 1950s that also contained TCP as a minor component. These formulations were used until the 1990s, when the soil fumigation chemicals were either taken off the market or reformulated to no longer contain TCP.

Environmental contamination
This widespread use of soil fumigation chemicals, along with the various industrial uses, has resulted in environmental contami­nation by TCP. Interestingly, TCP does not contaminate soil. Rather, it migrates through the soil into groundwater aquifers, where it ultimately moves to the bottom of the aquifer due to its density being higher than the density of water. TCP is therefore considered to be a dense non-aqueous phase liquid (DNAPL) because of its density and lack of solubility in water. This DNAPL characteristic makes it more difficult to remove from groundwater in remediation activities. TCP is also chemically stable and has very slow, natural decomposition rate, causing it to be environmentally persistent.

Impact on human health
Given this history, it is not surprising that TCP has been detected in groundwater and drinking water from wells in agricultural areas. This is concerning because TCP classified as likely to cause cancer by US EPA and it is recognized by the State of California as a human carcinogen. With this recognition as a human carcinogen, California began to regulate TCP in drinking water by establishing a maximum contaminant level (MCL) on July 18, 2017, of 0.005 μg/L, or 5 parts per trillion (ppt).

Interest in POU/POE treatment of TCP in drinking water
Due to the widespread agricultural use of TCP and the very low MCL adopted by the State of California, there are a significant number of private well owners and residents using small drinking water systems who are either known to be impacted by TCP contamination, or are concerned about it. In fact, California is implementing a statewide initiative to utilize POU and POE technologies for compliance with drinking requirements, in par­ticular dedicating significant resources in time and financial support for small communities who need assistance. In this ini­tiative, TCP is one of the primary contaminants that needs to be addressed based on the prevalence of violations by small sys­tems.

Activity of the NSF Joint Committee on Drinking Water Treatment Units
At the May, 2020 meeting of the Joint Committee, information was shared regarding California’s initiative to use POU and POE systems for compliance with Safe Drinking Water Act requirements for small systems. The Committee discussed that while TCP is one of the top contaminants that would be valuable for use of POU and POE for small system compliance violations for the state, there were no criteria or test methods to establish reduction of TCP in the NSF Drinking Water Treatment Unit standards. Accordingly, the Joint Committee formed a task group to develop criteria for the addition of a TCP reduction claim under NSF/ANSI 53.

The task group reviewed available occurrence data from California and US EPA’s Third Unregulated Contaminant Monitoring Rule (UCMR3). This review of occurrence data suggested an influent challenge level of 0.30 μg/L (300 ppt), based on the 95th percent­ile of occurrence. The 95th percentile of occurrence is the typical value selected by the Joint Committee for health contaminant challenge concentration. The task group further recommended a maximum allowable treated water concentration of 0.005 μg/L (5 ppt), based on California’s state MCL.

Further, the task group supervised laboratory work that validated the performance of third-party certified POU systems, selected because the systems had certified VOC reduction and PFOA/PFOS reduction claims under NSF/ANSI 53. This laboratory work was successfully completed late in 2020. Upon completion of this work, the task group brought their recommendations to the Joint Committee, who in turn approved the recommendations of the task group through a formal ballot process to establish the criteria and test method for TCP reduction under NSF/ANSI 53.

Test method
The test method for TCP reduction under NSF/ANSI 53 is the method used for reduction of all organic contaminants. The test water used is the General Test Water (see Figure 1). The influent challenge level and maximum effluent concentration, as described above, are summarized in Figure 2, which includes information regarding variation allowed for each influent sample point and for the average influent throughout the test, as well as indicating what US EPA analytical methods are used.A public water supply shall be used with the following specific characteristics maintained throughout the test. Methanol shall be used as the solvent when needed to introduce a contaminant to the test water.The test is conducted using a 20 minute cycle, which is normally 50-percent flowing and 50 percent with flow turned off. This cycle can be altered to 10-percent flowing and 90-percent with flow turned off at the discretion of the manufacturer. Two POU or POE test systems are tested in parallel, with samples of the influent and effluent collected at start-up, 50, 100, 150, 180 and 200 percent of the manufacturer’s rated treatment capacity. For systems with a performance indication device (filter change indicator), samples are collected at start-up, 25, 50, 75, 100 and 120 percent of the manufacturer’s rated treatment capacity. All samples must meet the requirements for a passing result.

Continuing to meet needs
Treating drinking water contaminated with TCP by POU and POE technologies in small communities in California was a need identified by the NSF Joint Committee on Drinking Water Treat­ment Units. The Joint Committee responded by developing new criteria and test requirements to evaluate these POU and POE systems to effectively treat drinking water with TCP contamina­tion. As with other emerging contaminants, the Joint Commit­tee will continue their work to advance the NSF Drinking Water Treatment Unit Standards to enhance their relevance as valu­able tools to help improve the quality of drinking water.

References

  1. US EPA. Technical Fact Sheet – 1,2,3-Trichloropropane (TCP). https://www.epa.gov/sites/default/files/2017-10/documents/ffrro­factsheet_contaminants_tcp_9-15-17_508.pdf
  2. California State Water Resources Control Board. Groundwater Information Sheet 1,2,3-Trichloropropane (TCP). https://www.wa­terboards.ca.gov/gama/docs/coc_tcp123.pdf

Andrew_Rick_mugAbout the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: Andrew@nsf.org

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