Water is essential for human life. A person can live only three days without water. Since water is the primary resource, water quality is vital. Technological progress brought significant advances to humanity. However, water pollution became the by-product of it. People use natural water resources for their purposes, as well as plants and different production operations. As a result, natural water resources are polluted by various chemicals that differ in toxicity, chemistry, and origin. Therefore, it is vital to understand the risks to human health.
In this paper, we will consider three inorganic and three organic substances and the health risks they bring. For every pollutant, we will define the effective water treatment methods.
In low concentrations, some of them are present in the environment, for example, fluoride or nitrate ions. Though, they are toxic in high concentrations. Others, such as mercury, phenol, polychlorinated biphenyls (PCB), dibenzodioxins (PCDD), etc., are the result of anthropogenic activity.
Mercury is found in drinking water in the form of inorganic (Hg+ or Hg22+) and organic compounds (methyl mercury, found in rare cases).
Maximum contaminant level (MCL) established by Environmental Protection Agency (EPA) is 2 ppb (0.002 mg/l). Mercury affects the nervous system, bringing up nervousness, irritability, difficulties with memory, and changes in hearing or vision. It also causes kidney damage. Young children are more sensitive to inorganic mercury than adults. Typically, mercury does not occur in drinking/tap water in the U.S. in concentrations that can seriously affect health. For example, mercury concentrations in the ground and drinking water in Washington State measured by EPA are 0.
3 ng/l. Since a concentration of mercury is very low, it can be removed from water by highly selective methods described below.
Nitrates are the salts of nitric acid and are present in water as NO3- (nitrate ion) or NO3N (nitrate-nitrogen). Nitrate is one of the nutrients required for plants’ high yields. Nitrate ions are highly mobile and can easily migrate to groundwater. EPA states the MCL of nitrate in water as 10mg/l. Its higher concentration in water cause methemoglobinemia or blue baby syndrome. The acid in a baby’s stomach is not as strong as in adults’; so, the nitrate ion is converted to nitrite (NO2-) that turning hemoglobin into methemoglobin. Blood hemoglobin transports oxygen, while methemoglobin is not able to transport it effectively. Severe case methemoglobinemia can cause damage to the brain or death. Pregnant women and people with reduced stomach acidity are exposed to the risk of methemoglobinemia too. The symptoms of nitrate poisoning are difficulties in breathing, dizziness, headache, and weakness. Although nitrates are rare in urban water supply systems, rural water supply contain water-bearing formations, which are, sometimes, polluted.
Fluoride (F-) is an anion of hydrofluoric acid. Intentional water fluoridation has been widely used for over 60 years to reduce tooth decay. However, the excess concentrations of fluoride bring potential risks to human health. Chronic exposure to high concentrations of fluoride in water may cause pain and tenderness of the bones and mottled teeth in children. Le%u0301vy presents the research results that deny the bone fractures and skeletal fluorosis caused by fluoride in water. Numerous researches presented in the work state that there are no reproductive or developmental health effects of water fluoridation. Thus, EPA determines the MCL for fluoride as 4 mg/l. EPA’s position on water fluoridation is neutral; so, it neither stimulates the process nor states its harmfulness.
Since mercury, nitrate, and fluoride are present in drinking water in ion form, the methods for their removal are alike. Distillation is a water treatment process that requires water boiling with subsequent collection and condensation of vapor. The salts (fluoride and nitrate) remain in the precipitate. This method is not suitable for mercury removal, since mercury vapors even at room temperatures. Reverse osmosis can remove these three inorganic pollutants. During the process, water is filtered through the selective membrane while pressure is applied. Large molecules, such as Hg2+, F-, NO3.