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2.3.1: Chemical Contamination of Water

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    Learning Objectives
    • Realize how combustion processes affect water sources.
    • Define the pH and composition of acid rain (three specific formulas/names).
    • Know the precursors of acid rain.
    • Recall the environmental and biological effects of acid rain.
    • Understand the differences between hard and soft water.
    • Connect inorganic water contaminants with biological and environmental issues.
    • Know the sources of inorganic and organic contaminants.
    • Differentiate between organic and inorganic substances when given a formula.

    The US Safe Drinking Water Act defines the term "contaminant" as meaning any physical, chemical, biological, or radiological substance or matter in water. Therefore, the "contaminant" definition very broadly applies as being anything other than water molecules. Drinking water may reasonably be expected to contain at least small amounts of some contaminants. Some drinking water contaminants may be harmful if consumed at certain levels in drinking water while others may be harmless. The presence of contaminants does not necessarily indicate that the water poses a health risk.

    Air Pollutants

    Water can become contaminated at any part of the water cycle. Air pollution can affect water vapor and water liquid. Combustion sources like vehicles and power plants generate compounds like \(\ce{NO_xs}\), \(\ce{SO_xs}\), \(\ce{CO}\), \(\ce{CO2}\), and other various inorganic and organic volatile organic compounds (VOC) species. Some of these compounds can become soluble in water. This could affect pH (or acidity) level of water surface water. Rain water with a pH below 5.6 is considered to be acid rain.

    pH scale.jpg
    Figure \(\PageIndex{1}\): pH scale. (Copyright; OpenStax College via Anatomy & Physiology, Connexions Web site.

    Normally, the pH of water is a neutral value (or pH= 7). When \(\ce{NO_xs}\), \(\ce{SO_xs}\), \(\ce{CO}\), \(\ce{CO2}\) enter the water cycle, then the pH level is lowered below 7.0. If these gases are absorbed in rain clouds, then acid rain results. Specific acids involved in acid rain are sulfuric (H2SO4), nitric (HNO3), and carbonic (H2CO3). This environmental problem affects living organisms and building materials. Acid solutions can corrode metals and make them soluble as well.

    Figure \(\PageIndex{2}\): pH of rainwater over the continental United States.

    In the United States, the northeast has the most problems with acid rain. Concentrated populations that use electrical energy and vehicles contribute greatly to the pH reduction of rainwater. Reducing gaseous output requires capping combustion sources (vehicles and power plants). Acidity in rain is measured by collecting samples of rain and measuring its pH. To find the distribution of rain acidity, weather conditions are monitored and rain samples are collected at sites all over the country. The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. This pattern of high acidity is caused by a large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain.

    Acid rain from sulfuric acid

    However, the majority of acid rain is accounted for by the presence of sulfuric acid (\(\ce{H2SO4}\)).

    \[ \ce{SO2(g) + O2(g) -> SO3(g)} \nonumber \]

    Sulfur dioxide reacts with water to form sulfuric acid

    \[\ce{SO3(g) + H2O -> H2SO4} \label{eq10} \]

    Although sulfuric acid may be produced naturally in small quantities from biological decay and volcanic activity, it is produced almost entirely by human activity, especially the combustion of sulfur-containing fossil fuels in power plants.

    acid rain depo.png
    Figure \(\PageIndex{3}\): Processes involved in acid deposition (note that only \(\ce{SO2}\) and \(\ce{NOx}\) play a significant role in acid rain). (public domain; EPA)
    Acid rain from nitric acid

    Some of acid rain is accounted for by nitric acid (\(\ce{HNO3}\)) that originates from natural processes, but especially from high-temperature air combustion, such as occurs in car engines and power plants, that produces large amounts of \(\ce{NO}\) gas. This gas then forms nitric acid via several steps. First nitric oxide (\(\ce{NO}\)) is formed during lightning storms by the reaction of nitrogen and oxygen

    \[ \ce{N2 (g) + O2(g) -> 2NO(g)} \label{eq1} \]

    and \(\ce{NO}\) is oxidized to nitrogen dioxide (\(\ce{NO2}\))

    \[ \ce{NO(g) + 1/2 O2(g) -> NO2 (g)} \label{eq2} \]

    \(\ce{NO2(g)}\) then reacts with water droplets to generate nitric acid (\(\ce{HNO3}\))

    \[\ce{3NO2(g) + H2O(l) -> 2HNO3(aq) + NO(g)} \nonumber \]

    Table \(\PageIndex{2}\): Source of Water contamination in the United States
    Combustion products Sources
    CO2 and CO Combustion of any material (any fuel or tree)
    NOX (NO2 and NO3) High-temperature combustion of any fuel ( gas, diesel, or coal), a product of lightning
    SOx (SO2 and SO3) Combustion of sulfur-based fuels (diesel and coal), volcanic release
    VOC (volatile organic compound) Combustion of any carbon-based fuel (gas, diesel, or coal), fumes from paints or solvents

    Inorganic Contaminants

    Solubility of these species can be determined by consulting a solubility table (e.g., Table 4.7.1). These chemicals might be naturally present in a water source. Industry and agriculture also use and dispose of these types of chemicals as well. In determining the source of any pollutant, it is helpful to know a region's geology and proximity to chemical consumers. In this section, we will focus on a few inorganic species that can affect drinking water quality.

    Hard Water

    When water is described as being hard, then this means it has a large concentration of minerals. The ions that contribute to this problem are calcium (Ca2+), magnesium (Mg2+), carbonate (CO3)2-, and iron (Fe2+/Fe3+). Hard water is not toxic, but can affect industrial processes. These ions will bond together to form insoluble salts that are called precipitates. Building up of these newly formed solids is called scale. Precipitates can collect in boilers, cooling towers, and any equipment that employs water. This buildup can affect how the equipment works by damaging it internally.

    Video: Hard Water

    Watch this video below to get an idea of what hard water is.

    1. What chemical species cause hard water?
    2. How does hard water affect industry?
    3. Hard water is known to contribute to the formation of kidney stones. How else can this type of water affect the body?

    Soft Water

    Soft water does not contain an excessive amount of alkaline minerals. Instead, potassium (K+) and sodium (Na+) ions are present. Soft water does not form scale but does produce excessive lathers with soap. Although industry and consumers prefer soft water, the sodium content can affect health if ingested at a high concentration.

    Figure \(\PageIndex{4}\): Hardness of groundwater from domestic wells, a USGS study. A study from the National Water-Quality Assessment (NAWQA) Program assessed water-quality conditions for about 2,100 domestic wells across the United States. (Public Domain; USGS).


    When pollutants enter a water system they originate from either point or non-point sources. If a single identifiable source can be located, then the pollutant originated from a point source. In contrast, non point sources indirectly contaminant water, air, or soil. Examples of non-point sources would be run-off and acid rain. Obviously, non-point pollutants are more difficult to regulate.

    In agriculture, nitrates (NO3)- are used as fertilizers. Farmers can choose to use synthetic or natural (manure) nitrates. Regulating concentrations of these species could be difficult if all sources are not investigated and monitored. An excessive amount of these substances leads to eutrophication. Many nitrate (NO3)- and phosphate (PO4)3- containing compounds are soluble in water. Once dissolved, these substances can travel to lakes and ponds. Here, these chemicals activate plants and algae to grow. Overgrowth of plant-life in water can inhibit oxygen from entering the water. As a result, aquatic animals are more likely to die in this environment. In addition, decomposition of organic material (once living) will be slow and smelly.

    Figure \(\PageIndex{5}\): Algal bloom in village river. Taken in a small village in mountains near Chengdu, Sichuan, China. (CC BY-SA 3.0; River algae Sichuan - Trophic state index - Wikipedia)

    Eutrophication can be halted in phosphate (PO4)3- contamination is controlled. This involves limiting the use of some fertilizers and removing phosphates from detergents. Reducing nitrates can be a more challenging task. All compounds containing this polyatomic ion are extremely soluble. Moreover, controlling nitrate concentration from fecal material can be difficult.

    Toxic Inorganic Species

    Some inorganic compounds are quite soluble in water. If an aquatic system is acid, then solubility of these types of species can change. Lead and mercury based compounds are not as soluble as those in group IA of the periodic table. When the pH of water becomes acid, many of these once insoluble compounds now become dissolved and visually undetectable.

    Lead (Action Level is 0.015 ppm)

    Occupational exposure to lead is one of the most prevalent overexposures. Industries with high potential exposures include construction work, most smelter operations, radiator repair shops, and firing ranges. Other sources of lead based compounds include house paint (from before 1978), toys (older than 1976 or from abroad), pipes, faucets, jewelry, wet batteries (gasoline engine based), pottery, and Kohl/Kajol eyeliners.

    lead in portland.jpg
    Figure \(\PageIndex{6}\): Lead and drinking water. (Copyright; City of Portland)

    Gasoline products may contain lead compounds to diminish knocking of a combustion engine. These additives increase the octane level of a fuel which enables the engine to burn more effectively. Unfortunately, releasing lead-based fumes can impair a person's nervous system. In addition, other disorders and diseases (kidney issues, gastrointestinal problems, growth delays, anemia, and learning difficulties) will become more prevalent in an area that has signification combustion of lead based fuels. Children will be more impacted by lead poisoning than adults. Often, the damage done to this group of people is irreversible. By the early 1970's, the Environmental Protection Agency (EPA) started focusing on phasing out leaded fuel products. By the mid 1980's, most US vehicles used only unleaded fuels. The EPA banned lead based fuel in 1996. Today, only the aviation industry and off-road vehicles are allowed to use leaded fuel in the United States.

    Figure \(\PageIndex{7}\): ead warning on a gas pump at Keeler's Korner, Lynnwood, Washington. Keeler's Korner, a former grocery store and gas station (built 1927) listed on the National Register of Historic Places, listed 1982, NRHP listing #82004287. (CC-BY-SA 3.0;

    Arsenic (0.010 ppm or 10 ppb)

    Common sources of exposure to higher-than-average levels of arsenic include near or in hazardous waste sites and areas with high levels naturally occurring in soil, rocks, and water.

    Figure \(\PageIndex{8}\):This map shows estimates of how many private domestic well users in each county may be drinking water with levels of arsenic of possible concern for human health.(µg/L, micrograms per liter) (USGS; Arsenic and Drinking Water | U.S. Geological Survey (

    Arsenic compounds can be found in lead/copper smelting processes, lumber pressurizing (copper chromated arsenate compounds are no longer used in the United States) and pesticide applications (organic arsenic compounds are used to treat cotton fields and orchards). Exposure to high levels of arsenic can cause skin lesions, neurological problems, gastrointestinal/live illnesses, various cancers, and death.

    Mercury (0.002 ppm)

    Common sources of mercury exposure include mining, production, and transportation of mercury, as well as mining and refining of gold and silver ores. High mercury exposure results in permanent nervous system and kidney damage. Once inorganic mercury enters aquatic systems, it can transform into organic mercury or organometallic mercury. An example of one of these compounds is methyl mercury (CH3Hg). This type of compound is quite toxic and has bioaccumulation effects.

    Figure \(\PageIndex{9}\): This figure shows some common sources of mercury, the conversion to toxic methylmercury and the outline of EPA consumption recommendations for certain types of fish based on mercury levels. (Copyright; Bretwood Higman, Ground Truth Trekking.via

    Cadmium (0.005 ppm)

    Cadmium is an extremely toxic metal that exists naturally in the Earth's crust as a common. Agricultural crops absorb cadmium compounds from the soil. The average person is exposed to cadmium through the consumption of plant based food, burning of cadmium based materials (air pollution), and drinking of tap water. Tobacco consumers receive additional cadmium when they smoke. Lastly, artists might use cadmium based pigments for dramatic colors in their paintings.

    berkeley pit 2.jpg
    Figure \(\PageIndex{10}\): The Berkeley Pit, an open pit copper mine in Butte, Montana. (Copyright; User:Cybergrl23 via Wikipedica Commons)

    At industrial workplaces, cadmium can be introduced to the atmosphere when any metal ore is being processed or smelted. Some forms of steel and batteries (Ni-Cd) contain cadmium mixtures. Several deaths from acute exposure have occurred among welders who have unsuspectingly welded on cadmium-containing alloys or with silver solders. This chemical substance is carcinogenic and causes a signature painful bone disease. Lastly, cadmium exposure can cause significant damage to kidneys.

    Uranium (30 ppb)

    Natural deposits of this element are found in the earth crust are sometimes associated with mountainous regions of the world. In the United States, uranium ores can be found in the western part of the country. If uranium becomes soluble, then it can leach or move to other locations contaminating water and soil nearby.

    Figure \(\PageIndex{11}\): Your Health: Uranium and Radiation on the Navajo Nation. (; Health Effects of Uranium | US EPA)

    Enriched U-235 (2-5%) is used for fuel in all US commercial nuclear power plants. Waste products of fuel use are stored for long periods of time above ground at most nuclear reactor facilities. Fuel waste can be stored in a wet or dry environment. Either method requires isolation from humans and the environment since the waste will be radioactive for a long time. Enriched U-235 (90%) was fuel for the Little Boy atomic bomb which was dropped over Hiroshima in 1945. At the time, purification of this form of uranium was difficult and costly. This resulted in the production of only one uranium type atomic weapon.

    Organic Chemical Concerns

    Dioxin (3.0 x 10-8 ppm)

    Dioxins are mainly byproducts of industrial practices. They are produced through a variety of incineration processes, including improper municipal waste incineration and burning of trash, and can be released into the air during natural processes, such as forest fires and volcanoes. Dioxins are also produced in the bleaching process used by the paper industry. These chemicals have been classified as Persistent Organic Polluters (POPS) because of their long residual life-times in the environment. These compounds are fat soluble and will accumulate in fatty tissues of living organisms which in turn affects the health of the food chain.


    Dioxin based compounds harm hormonal and reproductive systems. In addition, immunity disorders and chloroacne can result if someone has been exposed to these types of chemicals. A famous case of intentional dioxin (TCDD) poisoning involved a former Ukrainian presidential candidate named Vicktor Yushchenko. In 2004, environmental toxicologists in Austria detected extremely high concentrations of dioxins in Yushchenko's blood. Also, medical experiments noted the change in his complexion before and after the poisoning. For more information regarding this incident, please click here.

    When synthesizing Agent Orange (a herbicide used before and during the Vietnam War), chemists simultaneously and unintentionally produced dioxin. Exposure to this chemical derivative increased cancer rates to those exposed.

    (PCB) Polychlorinated Biphenyls (5.0 x 10-4 ppm)

    Once used as electrical insulators, the United States produced this family of compounds from the late 1930's through the 1970's. These compounds did not decompose, conduct electricity, and could withstand high temperature environments. For these reasons, PCBs were commonly incorporated into electrical transformers, fluorescent lights, capacitors and older household appliances (televisions and refrigerators).

    Figure \(\PageIndex{12}\): Structures of dioxin-like PCBs.. (Copyright; User:Leyo via Own work based on: M. Van den Berg et al. (2006). "The 2005 World Health Organization Reevaluation of Human and Mammalian Toxic Equivalency Factors for Dioxins and Dioxin-Like Compounds". Toxicological Sciences 93 (2): 223–241. DOI:10.1093/toxsci/kfl055. PMID 16829543.)

    These compounds are classified as human carcinogens. In certain concentrations, PCB exposure can manifest as chloracne. Chronic exposure to PCBs can cause liver and central nervous system damage. Lastly, PCBs can cause reproductive issues as well.


    This page titled 2.3.1: Chemical Contamination of Water is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Elizabeth Gordon.