Toxic Tap: The Compound Behind the Deadly Tap Water in California’s San Joaquin Valley

Apr 13, 2021

by Pia Ramos 

California’s San Joaquin Valley is one of the world’s most productive agricultural regions, providing crops that feed large sectors of the United States. The San Joaquin Valley is also home to some of the most contaminated drinking water in the country, housing about half of all the failing water systems in California [12]. Safe drinking water is considered a human right in California since 2012 and yet, in the San Joaquin Valley, nearly 1 million residents are affected by unsafe drinking water [11]. In some counties, contaminated groundwater is the source of drinking water for 99 percent of the population [12]. Most of those affected reside in small, rural communities which are predominantly Latino and disproportionately poor, thus posing a great public health and social justice emergency [9]. The contaminants range from heavy metals, to nitrates, to organic chemicals derived from historic pesticide use. One of the most ubiquitous contaminants found in this area is 1,2,3-Trichloropropane (TCP), a legacy contaminant of soil fumigants which has epidemiological links to geographic pockets of disproportionately large cancer rates [11]. 

So what is TCP?

TCP is an organic molecule classified specifically as a chlorinated hydrocarbon (CHC). CHCs are man-made compounds with structures consisting of a carbon backbone bound to hydrogen and chlorine atoms [10]. They are a family of molecules consisting of dozens of compounds with extensive uses in industry and agriculture, we usually hear about them when they are used in pesticides such as DDT [10].

TCP is presently used as a paint thinner and varnish remover and is also an intermediate product in the manufacture of separation membranes and plastics [7]. Despite these current applications, the most important source of TCP in groundwater contamination in California comes from its widespread presence in soil fumigants such as Telone (1,3-Dichloropropene) and D-D (Dichloropropane-dichloroprpene mixture) [14]. Although such fumigants are usually no longer extensively used in agriculture in the United States, TCP’s chemical characteristics have allowed it to become an important groundwater pollutant [10]. Its properties have caused it to become concentrated in aquifers following its continuous migration down-gradient from previously concentrated surface sources.

Due to its chemical structure, TCP has high chemical stability, is highly soluble in water, and does not sorb to surfaces very effectively.  The combination of all these properties allows TCP to easily migrate down soil and into groundwater, where it is highly mobile and therefore easily transported along the aquifer [7]. In addition, because it is denser than water, TCP in its liquid state easily sinks down into the depths of the aquifer where it exists as a class of contaminants known as Dense Non-Aqueous Phase Liquid (DNAPL) [7]. This makes it very difficult to remove.

But how is this related to the San Joaquin Valley or even to Southern California?

The relevance of this problem is particularly pertinent in areas of high agricultural production which historically made widespread use of pesticides and fumigants such as D-D [3]. In the San Joaquin Valley the majority of residents rely on groundwater for some or all of their drinking water supply and in 2016, 63 percent of California public water systems that detected TCP were located there [11]. According to the EPA, exposure to TCP can occur through vapor inhalation, dermal exposure, or ingestion, and studies have shown that long-term exposure to the compound may cause liver and kidney damage as well as increased incidences of tumors in various organs [1,7]. It is therefore unsurprising that cancer rates in the San Joaquin Valley are among the highest in the state, especially considering that TCP represents but one of a myriad of pollutants in this area where opening the tap is reportedly risky for a number of different reasons.

TCP first became an issue of concern in California in the 1980s after it was found to have migrated into water supplies all over Southern California from a Superfund site in the San Fernando Valley [7,12]. Environmental agencies such as the EPA often enact regulations that dictate the maximum levels of specific contaminants that can be present in the water supply in order for utilities to be allowed to legally distribute water. In the United States this corresponds to the metric of Maximum Contaminant Level (MCL) [14], which is defined as the legal limit on the amount of a substance that is allowed to be present in public water systems. These ranges are based on factual evidence of the relative public health risk associated with the continuous exposure to each compound. However, despite it being a known carcinogen, and despite having been used extensively since the 1950s, TCP’s MCL was only established in California in late 2017 [15]. California is only one of two states with an MCL for TCP, despite its known presence in the drinking water of 21 other states [15].

The establishment of an MCL for TCP in California was the result of a widespread grassroots movement that pushed litigators to instate this regulation. However, establishing the regulatory limit is only the beginning of the battle because of the extremely high costs associated with cleaning up the problem. This is further complicated by that fact that the most affected entities of the state are also some of the smallest, most rural, and poorest. The MCL was set at 5 parts per trillion, a threshold that ensures a theoretical risk of cancer of less than 1 in 143,000 for those exposed to TCP in drinking water over their entire lifetime [7].  To put this in context one part per trillion is equal to one gallon per one trillion gallons, corresponding to a number that is approximately 1,000 times smaller than a drop of water in an Olympic-sized swimming pool. This means that the concentrations that must be attained before safely distributing water are extremely low, an expensive challenge considering the difficult-to-remove nature of TCP. So where does that leave us?

 According to state data from 2018, 220 water systems contained at least one well with detectable concentrations of TCP above 5 parts per trillion [8]. Two thirds of these were in the San Joaquin Valley, and among those the highest concentration detected was 10,000 parts per trillion (2,000 times higher than the established MCL) [8]. This means that is has become necessary for water utilities to install expensive treatment systems in order to get their water up to standards. It has been estimated that the required infrastructure will cost water utilities between $22,668 and $473,740 per year [8]. For many of the affected small rural communities in the San Joaquin Valley, this has proven to be almost impossible. So how will the problem get fixed?

Many hope to attain the required funds through lawsuits aimed at the companies that produced the soil fumigants such as Dow Chemicals and Shell Oil [2]. The hope is that the new MCL will make the impact of the harmful presence of this chemical evident in litigation, leading to large monetary compensations that would help update the treatment systems. What exactly will the treatment solutions look like?

 There are several options for removing TCP from water. Depending on the level of contamination, some water systems may simply blend contaminated water with clean water from another source, essentially diluting the total concentration present. In other cases, water utilities may use technologies such as granular activated carbon (GAC) filtration to remove the pollutant.

Removing TCP using GAC follows the principle of adsorption. Adsorption occurs when material is accumulated at the interface between a liquid and a solid and is therefore a common technique for removing dissolved compounds from water. Contrary to absorption, which can be visualized as transporting a substance from an outside space to an inside space, adsorption can be envisioned as a dissolved species “sticking” onto a solid and is thus a process involving surface interactions [13].

GAC is a common adsorbent because it has a unique physical structure, containing different sized pores along its inner and outer surfaces. This translates into a very large internal surface area, which means that there are a lot of sites to which contaminants can “stick”.  Adsorption by GAC is the concept employed by several household filtration mechanisms, including Brita filters. Removing TCP from drinking water can therefore be visualized as simply passing the water through a giant Brita filter [13]. GAC adsorption is one of the cheapest environmental remediation solutions that exist, however TCP’s unique physicochemical traits make removal by GAC somewhat challenging. This means that the filtration system installed to remove it would have to be very large, creating a significant financial burden. So where does this leave us?

Solving the issue of TCP in drinking water in the San Joaquin Valley holds a great moral imperative considering its role in social and racial inequality in public access to services and basic human rights. The establishment of a MCL for this pollutant in California was a great first step in a battle to resolve the issue, however continued public pressure is required in order to ensure that affected communities get the funds they need to meet the standards, without increasing the financial burden of the already burdened populations. Solving the issue of TCP in the San Joaquin Valley will be an important step towards ensuring that the communities who play such a pivotal role in sustaining the rest of the population have access to the services that they deserve.

To check the drinking water quality in your area, visit: https://www.ewg.org/tapwater/

Bibliography:

  1. Addendum to the Toxicological Profile for 1,2,3-Trichloropropane (Tech.). (2011). Atlanta, GA: Agency for Toxic Substances and Disease Registry. Division of Toxicology and Environmental Medicine.
  2. Amarelo, M. (2017). Report: Shell and Dow Hid Cancer-Causing ‘Garbage’ in Pesticide, Contaminating Drinking Water for Millions in California. Retrieved December 7, 2018, from https://www.ewg.org/release/report-shell-and-dow-hid-cancer-causing-garbage-pesticide-contaminating-drinking-water
  3. California State Water Quality Control Board. (2016.). 1,2,3-Trichloropropane (1,2,3 – TCP). Retrieved December 9, 2018, from https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/123TCP.html
  4. Groundwater Information Sheet: 1,2,3-Trichloropropane (TCP) (Issue brief). (2017). California: State Water Resources Control Board Division of Water Quality GAMA Program.
  5. Oki, D. S., & Giambelluca, T. W. (1987). DBCP, EDB, and TCP Contamination of Ground Water in Hawaii. Ground Water, 25(6), 693-702.
  6. Tardiff, R. G., & Carson, M. L. (2010). Derivation of a reference dose and drinking water equivalent level for 1,2,3-trichloropropane. Food and Chemical Toxicity, 48, 1488-1510.
  7. Technical Fact Sheet – 1,2,3-Trichloropropane (TCP) (Issue brief). (2014). Retrieved https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_tcp_january2014_final.pdf
  8. Klein, K. (2018). To Pay For 1,2,3-TCP Cleanup, A Viable Strategy: Sue. Retrieved from https://www.kvpr.org/post/pay-123-tcp-cleanup-viable-strategy-sue
  9. Meadows, R. (2017). How Water Contamination Is Putting California’s San Joaquin Valley at Risk. Retrieved from https://psmag.com/environment/how-water-contamination-is-putting-this-california-town-at-risk
  10. TCP in California’s Drinking Water. (2017). Retrieved from https://www.cleanwateraction.org/features/tcp-californias-drinking-water
  11. Meadows, R. (2017). How Water Contamination Is Putting California’s San Joaquin Valley at Risk. Retrieved from https://psmag.com/environment/how-water-contamination-is-putting-this-california-town-at-risk
  12. Meadows, R. (2017). Living in California’s San Joaquin Valley May Harm Your Health. Retrieved from https://www.newsdeeply.com/water/articles/2017/07/05/living-in-californias-san-joaquin-valley-may-harm-your-health
  13. EPA. (n.d.). Drinking Water Treatability Database. Retrieved from https://iaspub.epa.gov/tdb/pages/treatment/treatmentOverview.do?treatmentProcessId=2074826383
  14. State Water Board. (2016). 1,2,3-Trichloropropane (1,2,3-TCP) Maximum Contaminant Level (MCL) Development Process. Retrieved from https://www.waterboards.ca.gov/drinking_water
  15. Walker, B. (2017). Cancer-Causing Pesticide ‘Garbage’ Taints Tap Water for Millions in California. Retrieved from https://www.ewg.org/research/cancer-causing-pesticide-garbage-taints-tap-water-millions-california

 

Pia is part of the 2019-2020 INFEWS program cohort and a PhD candidate in the Department of Civil and Environmental Engineering at UCLA. Her research focuses on optimization of surface interactions of materials and microbes in the context of water treatment and remediation of groundwater contaminated with recalcitrant pollutants by combining biotic and abiotic techniques.

This is a pop science article and is part of the INFEWS Social Media Series.