Radionuclides are intrinsically present in varying amounts in potable water. These radiological contaminants are released into the water source from rocks and bedrocks in the aquifers. The level of radionuclides is dependent upon the lithology of the underground structures (Agbalagba et al., 2012). Over time, erosion and dissolution increase the concentration of radiological elements that enter the water source (Ivanovich & Harmon, 1992). Uranium-234 (²³⁴U) and Uranium-238 (²³⁸U) are the most abundant radionuclides in the Earth’s crust and consequently in potable water. In addition, radium-226 (²²⁶Ra), radium-228 (²²⁸Ra) and radon-222 (²²²Rn) are environmental isotopes which are formed as result of radioactive decay of uranium and thorium present in rock and soil (Water Quality Association, 2020).

Radon and gross alpha radiation are released from the decay of various radioactive elements. Gross alpha can be present in drinking water because of the decay of uranium and thorium present in the Earth’s crust (Ho et al., 2020). Although these radiations may not present any health risk outside the human body, ingesting them have been shown to be harmful, especially with long-term exposure (Ho et al., 2020).

Exposure to radiation can have various health risks depending on the source of radiation, the level of exposure (i.e. total dose), and the period of exposure (i.e. exposure length) (Ononugbo et al., 2013). The Environmental Protection Agency (EPA) enacted guidelines to mitigate the health risks associated with exposure to radionuclides, and consuming water near the federal drinking water standards (Table 1) puts consumers at low exposure levels. However, exposure of people to radionuclides through drinking water, when combined with other sources of exposure, can increase the likelihood of developing renal disease and cancer, such as radiation from medical treatments, living near coal mines and even traveling by airplanes (Avwiri et al., 2012). Considering the abundance of water and its necessity for everyday survival, the protection of water quality is an essential component of affective public health policy (WHO, 2017; IAEA, 2016).

To mitigate the health risks associated with exposure to radionuclides, the United States Environmental Protection Agency has regulated radium-226 (²²⁶Ra) and radium-228 (²²⁸Ra) to remain below 5 picocuries per litre of water (pCi/L), gross alpha including radium-226 to remain below 15 pCi/L, and uranium to remain below 30 µg/L, which has been converted by the EPA to be approximately 20 pCi/L (EPA, 2001).

Many of the drinking water standards were put in place decades ago and have not been updated. The Environmental Working Group (EWG) collaborates with state and federal agencies to obtain tap water quality data and provides health

guidelines, which may not be taken into consideration at a federal level. EWG regulations consider the heightened vulnerability of chemical toxicity to children, immunocompromised individuals, and pregnant women, to bridge the gap between the outdated federal standards (EWG, 2019; Environmental Protection Division, 2020). Hence, although many drinking water facilities are within legal compliance for toxic chemicals mandated by the federal agencies, these regulations are not always safe. These toxic chemicals and new emerging chemicals leave the general population susceptible to health problems. The Environmental Protection Agency sets the legal limits for combined radium (−226 & −228) while the EWG health guidelines limit radium levels at 0.05 pCi/L (EWG, 2019). In addition to discrepancies between the health guidelines and federally mandated guidelines, social disparities are also an undeniable problem facing drinking water treatment facilities, as shown in a study correlating race/ethnicity and socioeconomic backgrounds to arsenic and nitrate levels (Balazs et al., 2011; Balazs et al., 2012). Previous studies have demonstrated water quality disparities correlating to socioeconomic background to demonstrate chemical, biological and physiccal contaminant levels (Karim et al., 2020), but this study is the first of its kind to elaborate on the correlation and association between radioactive contaminant levels in drinking water and socioeconomic background.

Radionuclides may be removed from drinking water source via reverse osmosis and ion exchange technology to increase drinking water quality (EPA, 2015). However, communities with crippling water purification infrastructure and lower income communities may be at a higher risk of being exposed to radionuclides, which is a significant environmental justice concern (Karim et al., 2020). To understand the social disparities, it is important to conduct a quantitative analysis in order to examine whether vulnerable populations, especially those with lower-average household incomes, are disproportionately impacted by radionuclides contaminants in drinking water. This research aims to analyze the possible disparities in drinking water quality in the metropolitan cities of each state in the United States and the US territories, including Puerto Rico, Guam, and the US Virgin Islands.

Secondary data related to the concentrations of radioactive contaminants was obtained from the annual water safety report for the metropolitan areas across the United States for 2019 and the details are provided in the following table (Table 2).

Additional information was collected by contacting water service offices to obtain information not readily available in the annual consumer confidence report (CCR). Data including median annual household income was obtained from the United States Census Bureau (United States Census Bureau, 2020). The water quality data was then prepared for descriptive statistical analysis. Histograms were used to illustrate the levels of total radionuclide in metropolitan

areas across the United States, Puerto Rico, US Virgin Islands and Guam for 2019. Tables were generated to record income per capita for the metropolitan city of each state and US territories (provided by the Census Bureau) and their drinking water source (provided by the state and local water services departments), and correlated to the levels of total radionuclide concentrations. The disparities among the average household income in different counties and their water quality are shown using multi-variable charts.

The correlation between the average household income radionuclide levels is examined to determine the impact of median household income on the quality of drinking water. The drinking water sources in each state are different; however, most of the water sources are either from surface water or groundwater, as shown in Table 3. Raw water chemistry and composition can be influenced by many factors including human activity and wildlife population surrounding the water source, but rock formation is particularly responsible for level of radionuclides present in drinking water due to the decay of uranium from Earth’s crust. Radium, radon, and uranium isotopes are an intrinsic part of water, but these radionuclide levels are exasperated due gas and oil extraction like hydraulic fracturing which can leak into groundwater (USGS, 2020). Hence, the concentration of radionuclide in drinking water is dependent upon the water source (Table 3) and the underlying lithology within the aquifers.

In the United States, the Environmental Protection Agency regulates the level of radioactivity in drinking water via the gross alpha test, which is conducted to measure the emitted alpha particles due to the radioactive elements’ natural decay. The details and regulatory limits are indicated in Table 1, and were put into place decades ago. Research has shown that health agencies recommend radionuclides in drinking water to be significantly lower than the federal mandates.

The radionuclide concentrations for the metropolitan or most populated city in each state in the United States, Puerto Rico, Guam, and US Virgin Islands were analyzed and correlated to the annual household income (Table 4) to determine disparities that maybe present, as shown in Figure 1.

To investigate disparities in drinking water quality, total radionuclides were examined, including combined radium (5 pCi/L), uranium (20 pCi/L) and gross alpha (15 pCi/L) for a total of 40 pCi/L. Many states failed to document uranium and gross alpha levels. However, most of the states and the US territories

reported the combined radium levels. US Virgin Islands did not report any radionuclide levels. The data obtained for Puerto Rico was from a report conducted in 2017 showing that Puerto Rico had five violations for elevated radionuclide levels (NRDC, 2017). However, considering that radionuclides do not decay from the environment as quickly, these results are still valid, indicating that Puerto Rican drinking water does not meet federal regulations. As shown in Figure 1, as the income increases, radionuclides contaminants become less

frequent in drinking water. Indiana, Idaho, Iowa, Delaware and Pennsylvania had the highest levels of radionuclides. These state’s incomes fall in the lower- and middle-class brackets. However, states with higher incomes did not have high levels of radionuclides in their drinking water.

Upon closer examination, Idaho’s combined radium, uranium and gross alpha levels were 2.3, 18, and 6.1 pCi/L respectively, for a total of 35.4 pCi/L out of 40 pCi/L as mandated by the EPA. Indiana’s combined radium, uranium and gross alpha levels were 1.73, 9.7, and 6.7 pCi/L, respectively. Iowa’s combined radium, uranium and gross alpha levels were 2.2, 1.9, and 11.1 pCi/L, respectively. Pennsylvania’s combined radium, and gross alpha levels were 3.95 and 11.6, respectively. Finally, Delaware’s uranium and gross alpha levels were 12.78 and 6.6 pCi/L, respectively. Furthermore, Guam also had moderately elevated levels of radionuclides. Data for Missouri, Hawaii and Minnesota was not readily available, as these states did not report the levels of radionuclides. The general trend within the graph in Figure 1 indicates elevated radionuclide levels among low- and middle-income brackets, but significantly lower radionuclide among higher income states.

Although there were violations in Puerto Rico, the US states remained well below the federally mandated regulations for radionuclides in drinking water. However, these regulations were set two decades ago, and according to the Environmental Working Group (EWG), are not low enough to mitigate health issues that might arise due to exposure to radionuclides. According to the EWG health guidelines, radium levels should remain 0.05 pCi/L compared to the 5 pCi/L, which is 100 times more than the health guideline recommendations. In addition, the EPA standard for uranium is at about 20 pCi/L which is 46.5 times higher than the EWG health guidelines of 0.43 pCi/L. Tennessee ranks among the lowest for combined radium at 0.26 pCi/L, which is 5.2 times the EWG health guideline limits and significantly lower than the national average of 0.47 pCi/L (EWG, 2019).

Finally, the general trend in Figure 1 shows that low- and middle-income communities had higher radionuclides in drinking water compared to high income communities. Although, there was one incident where Delaware had a slightly more elevated radioactive contaminant level within the high-income bracket group, perhaps this is due to an outlier in the compiled data. However, the general scheme and pattern indicate that there is much more frequency in the elevated radionuclide contmiant levels among low- and middle-income bracket groups. These disparities in radionuclide levels in correlation to income levels are in conjunction with water justice inequalities that have been previously investigated by scientists and environmentalists. Our findings that lower income communities face injustice obtaining and sustaining high water quality agree with previous investigations (Karim et al., 2020). In addition, federally mandated regulations should be reviewed to better mitigate health problems that could arise from drinking contaminated water.

Water resource management is a global concern and protecting the quality of drinking water is a public health duty. Due to the carcinogenic effects of radionuclides, the presence of these contaminants in drinking water at a disproportionate level in lower income communities is dire and of social and epidemiological interest. As shown in this study, in 2019, Indiana, Idaho, Iowa, Delaware and Pennsylvania with median household incomes in the low- to mid-income communities demonstrated high levels of radionuclides. In contrast, communities with high incomes had significantly lower levels of radionuclides in their drinking water. In addition, Puerto Rico, a US territory where water quality must meet US EPA standards has five violations for elevated levels of radionuclides in drinking water. In addition, Guam’s drinking water was also slightly higher than many US states. Finally, although all the US states met the EPA’s legal standards, which were put in place two decades ago and are highly outdated. According to the EWG’s health guidelines, the standards for radionuclides are significantly lower than federal mandates.

Man-made and naturally occurring factors play a significant role in the quality and composition of water. However, public water quality should not be influenced by socioeconomic factors. Based on the results from data obtained across the United States, poor water quality is much more frequent in less affluent communities, due to the presence of industrial activity, human activity, and is exasperated by an already collapsing water infrastructure.

Based on this study, it is recommended for water infrastructures to be improved by incorporating newer technology to reduce radionuclides from drinking water, as they pose health risks. In addition, federal regulations must be improved and restrictions adequately imposed for radioactive material. Finally, states that do not report on radionuclides must be held accountable for not making this information readily available and accessible to consumers. Information obtained from the present study could also be used to draft improved health guidelines, and for the purpose of resource allocation to ensure that the general population is better informed about drinking water quality within their communities.

We acknowledge the financial support from the USDA National Institute of Food and Agriculture, Grant# TENX-1608-FS. We thank US Department of Education, Title III Part B, grant number P031B090214 for partial financial support.

The authors declare no conflicts of interest regarding the publication of this paper.

Karim, K., Guha, S., & Beni, R. (2020). Radioactive Contaminants in U.S. Drinking Water and Water Quality Disparities. Journal of Geoscience and Environment Protection, 8, 238-251. https://doi.org/10.4236/gep.2020.811016