Drinking Water Disparities in Tennessee: The Origins and Effects of Toxic Heavy Metals

Several toxic metals, commonly present in drinking water, are believed to play important roles in the development of cancerous tumors. Although the US Safe Drinking Water Act requires drinking water to meet health standards set by the Environmental Protection Agency, violations occur regularly. In this study, we have investigated the role of the two predominant toxic heavy metals identified in the drinking water sources in Tennessee: copper and lead. We have analyzed the levels of copper and lead, as well as the total water hardness among different counties of Tennessee, with different socioeconomic backgrounds. We determined that the effects of lead and copper in drinking water were random, although counties with typically lower average household incomes typically had higher levels of the metals. The contaminant levels were found to remain below the threshold established by the Environmental Protection Agency and the State of Tennessee. Water from the Cumberland River was harder than water obtained from other rivers in Tennessee. Furthermore, the total hardness of water did not correlate with the average household income of the various counties.


Introduction
Water sustains life and is essential for a healthy ecosystem, agriculture, as well as for industrial and economic growth. Clean water is essential to the health and well-being of the general populace, worldwide. The World Health Organization (WHO) estimates that approximately eight hundred million people still do not have access to basic drinking, clean, or advanced water sources (World Health Tennessee, like other places, uses the same water purification techniques to ensure that the public drinking water is free of contaminants. The water treatment process typically includes some form of pre-chlorination or aeration to limit the growth of microorganisms and algae. Following the pre-chlorination process, coagulation is performed to remove any reactive chemicals that might be present in the water source. In addition to coagulation, slow-sand filtration may also be utilized to remove reactive chemicals from the water source. Copper can be removed from drinking water using various analytical techniques such as reverse osmosis, ultrafiltration, and adsorption. Reverse osmosis is used to purify water from macromolecules and non-dissolved water contaminants. It employs a permeable membrane, allowing only non-charged particles to pass through; hence removing any ions or big particles, and even bacteria, from consumable water (Warsinger et al., 2016). During reverse osmosis, an artificial pressure is applied to prevent the natural flow of solute from an area of high concentration to one of low concentration. The membranes used for reverse osmosis do not possess any pores, but rather function solely based on chemical charge (Baker, 2004;Baker & Wijmans 1995). The disadvantage of using these non-porous membranes is that they waste too much water that cannot be recovered (Freeman, 1995;Zhu et al., 2013). Another technique, known as ultrafiltration, is also used to purify consumable water and remove copper. Ultrafiltration uses a membrane system to separate or extract contaminants based on molecular weight, rather than size. This system can effectively remove macromolecules the size of 103 to 106 Daltons, and can achieve 90% -100% pathogen removal as required by water quality regulatory standards (Crystal Quest Water Filters, 2019). Ultrafiltration is efficient in removing water contaminants, and is desirable, as it does not require the use of chemicals. The only disadvantage to using ultrafiltration is that the membranes used are very fragile and susceptible to damage, leading to high cost of replacing the filters (Edwards et al., 2001). A third filtration process is known as adsorption, during which a solid surface is utilized to store or carry liquid molecules. It serves as a cheaper and more efficient alternative to traditional filtration systems (Aydin et al., 2008).

Lead
Lead is mainly used in construction of buildings and batteries. Lead poisoning can damage the nervous system and cause brain disorders (Canfield et al., 2003).
Children, in particular, absorb more lead than adults due to their growing bodies. Infants and children under the age of six are most susceptible to the toxic effects of lead, which can enter our drinking water from household plumbing or The most widely used technique to remove lead from water is through sand filtration. In this technique, solids can be separated from fluids by using surface filters and depth filters. Surface filters capture the solids on a permeable surface while depth filters intercept the solids within a porous body of material. The latter is more widely used to separate small amounts of lead from water. Coagulation and ion exchange are two other techniques for the removal of lead from water. During coagulation, aluminum sulfate (alum) is added to water to clump the lead particles together, enabling them to settle out of the water or be removed by filtration. In ion-exchange, resins, which contain small beads, are used to purify water and get rid of lead ions, by replacing them with non-toxic ions such as sodium and potassium. The best way to remove lead from water is through reverse osmosis, during which water is pushed through a series of filters and the membrane system filters out lead and other contaminants, allowing only water to pass through (ESP Water Products, 2019).
Older homes tend to have lead in the service pipes, which carry city water to communities living on the same street. As changing pipes can be costly, communities with lower household incomes are unable to invest in newer pipes. Hence, older neighborhoods with lower household income are likely to have a higher lead content in their tap water.

Total Hardness of Water
The State of Tennessee has hard water, which is defined as water that has a high content of minerals or solid chemical compounds. Some of these minerals, such as calcium and magnesium, seep into water systems as water passes through limestone. Although drinking moderately hard water can be beneficial to human health, high concentrations of minerals in water can have adverse health and economical effects. According to EPA standards, 0 -60 mg/L of calcium and magnesium in water is considered soft water, 61 -120 mg/L is considered moderately hard water, 121 -180 mg/L is hard water, and anything above 180 mg/L is considered very hard water (USGS Science for a Changing World, 2019). One of the indicators of water's hardness is its inability to produce soap lather (Royal

Data Collection
Secondary data was collected to obtain the 2017 yearly water safety report for each county in Tennessee. Additional information was obtained from each county's water service office, that was not provided on the yearly water safety report. Data including average annual household income was obtained from the United States Census Bureau, which was compiled and published in 2010. This data is about 9 years old, because census is carried out once every ten years, and the next census data will be published in 2020.

Statistical Analysis
After the compiling the information, the water quality data was prepared for descriptive statistical analysis. Histograms were used to illustrate the levels of copper and lead levels in different counties in Tennessee. Furthermore, the disparities among the average household income in different counties and their water quality are shown using multi-variable charts.

Results and Discussion
The annual copper and lead levels detected in the drinking water of different counties in Tennessee are listed in Table 2. The copper level in Anderson county has been measured at 0.1 parts per million (ppm), which is well below the limit set at 1.3 ppm by the EPA. Similarly, the copper levels of the other counties are also below the EPA limits. According to the Annual Water Safety Report, detected copper levels are due to the leaking of wood preservatives, eroding of natural  Commission, 2018). The reported levels of lead in various counties are higher than the copper levels, but are still within the federal and state-legislated amounts of 15 parts per billion (ppb). Lead typically occurs due to erosion of old plumbing systems and natural deposits. The water turbidity data for each county was collected and found to be well below 1%, as mandated by local and federal legislations. Turbidity is typically resolved via the use of coagulants or through sedimentation.
As listed in Table 2  Data related to total water hardness was collected for each county and compared to the corresponding average household income and population, as listed in Table 3. The hardness of water refers to the amount of dissolved minerals, typically calcium and magnesium. It was determined that water from the Cumberland River is much harder than water obtained from other river sources. Journal of Geoscience and Environment Protection Cumberland River serves as the primary water source for the Tennessee's capital Nashville and its surrounding areas. According to Table 3, water hardness is the greatest for Williamson county, at 139 mg/L. The average household income of Figure 1. Differences in copper and lead levels among different counties in Tennessee. Williamson county is the highest ($87,832) while that of Carter county is the lowest ($31,173). Figure 2 shows a graphical comparison of the average household income to the total water hardness. The total hardness of water does not seem to correlate with the average household incomes of the counties.
The average household incomes were also compared to the copper and lead levels to determine whether more affluent counties had access to cleaner water when compared to less affluent counties. As shown in Figure 3, the counties with higher average household incomes seem to typically have lower levels of detectable copper compared to counties with lower average household incomes.
A similar correlation exists between average household income and lead levels.

Conclusion
Analysis of drinking water for trace metal contamination is an important step in ensuring both human and environmental health. Several counties in the State of Tennessee were examined in order to determine the levels of copper and lead in drinking water, water hardness as well as their correlation to the socioeconomic background of the residents. It was determined that, although several counties with typically lower average household incomes had higher copper and lead levels in their drinking water, these effects were random, and the contaminants remained below the EPA and state-regulated guidelines. Water obtained from the Cumberland River was found to be much harder than water obtained from other river sources. However, the total hardness of water had no correlation with the average household income of the counties in Tennessee.