Helena Joyce
Marine pollution is a pressing issue, encompassing various forms of trash and chemical contaminants. While plastic waste is a significant concern due to its longevity and impact on marine life, chemical pollutants from land-based sources, such as toxic chemicals, sewage, fertilizers, and petroleum products, also pose a grave threat to ocean health and marine ecosystems. Among these chemical pollutants, chlorine, a basic industrial chemical, stands out as a potential marine pollutant. With its solubility in water and high reactivity, chlorine is widely used in water treatment, manufacturing, and disinfection. However, its presence in the marine environment and its potential ecological effects raise questions about its role as a marine pollutant.
| Characteristics | Values |
|---|---|
| Definition of Marine Pollution | The introduction of substances or energy into the marine environment, resulting in harmful effects on marine life and ecosystems. |
| Sources of Marine Pollution | Land-based activities (80%), accidental spills, deliberate dumping, untreated effluent, atmospheric fallout, runoff from drains and rivers, agriculture, urban wastewater, stormwater, wastewater, fossil fuel burning, aquaculture, domestic waste, shipping and drilling, plastic waste, industrial waste, sewage, fertilisers, oil spills, and more. |
| Chlorine Characteristics | A basic industrial chemical, very soluble in water, highly reactive, used in water treatment and purification, wastewater treatment, manufacturing (plastics, paper, chlorinated lime), disinfection, bleaching, and more. |
| Chlorine as a Marine Pollutant | Chlorine is a component of seawater and is used in various marine-related applications, including water treatment and purification. However, it is also listed as a toxicant in some guidelines, and high concentrations can be toxic to marine life. |
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What You'll Learn
Chlorine's use in water treatment
Chlorine is the most commonly used chemical for the disinfection of water supplies. Chlorination is a chemical disinfection method that uses various types of chlorine or chlorine-containing substances for the oxidation and disinfection of what will be potable water sources. Chlorine is highly soluble in water and highly reactive.
The history of using chlorine for water treatment can be traced back to 1744 when it was first discovered in Sweden. However, the use of chlorine to remove odours from water only began in 1835. It was not until 1890 that chlorine was found to be an effective disinfectant, reducing the amount of disease transmitted through water. The first reported use of chlorination for water disinfection was in 1897 in Maidstone, Kent, UK, where bleach was used to disinfect a water main following a typhoid outbreak. Regular use in water treatment began around the beginning of the 20th century.
The three most common types of chlorine used in water treatment are chlorine gas, sodium hypochlorite, and calcium hypochlorite. Chlorine gas is greenish-yellow in colour and very toxic. It is heavier than air and will sink if released from its container. Its toxic effects make it an effective disinfectant, but it is also hazardous to humans. Exposure to high volumes of chlorine gas fumes can cause serious health issues, including death.
Chlorination is a popular method of disinfection and is used for water treatment worldwide. It is effective against bacteria and viruses, although it cannot inactivate all microbes. Some protozoan cysts are resistant to chlorine. Chlorination is a good option when protozoan cysts are not a significant concern, as it is inexpensive and effective in disinfecting other possible contaminants. The process is also relatively easy to implement compared to other water treatment methods.
During water treatment, chlorine can combine with naturally occurring organic matter to form disinfection byproducts (DBPs). While the levels of chlorine used for drinking water disinfection are unlikely to cause long-term health effects, DBPs can have negative health effects after regular, long-term exposure. Point-of-use filtration devices can be used to lower DBP levels in water.
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Chlorine's reactivity and persistence in water
Chlorine is a basic industrial chemical used in the manufacture of chlorinated organic and inorganic chemicals. It is a gaseous material that is very soluble in water and highly reactive. Chlorine is also used for pulp and paper manufacture, as an industrial and household bleach, a disinfectant, and in water and wastewater treatment.
Chlorine is a highly reactive element that does not persist for extended periods in water. However, its by-products persist for longer. Chlorine undergoes rapid chemical reactions in the atmosphere, with an atmospheric half-life of about 10 minutes and a lifetime of about 14 minutes. It reacts with organic compounds, mainly alkanes in polluted urban areas, to form hydrogen chloride and organochlorine compounds.
In water treatment, the intentional production of N-chloramines is used to extend the effectiveness of chlorination. After water treatment, the sum of free chlorine and combined chlorine is referred to as total residual chlorine (TRC). The toxicity figures are derived using measurements of TRC rather than free chlorine. The chemicals used for testing the effect of chlorine include chlorine gas (Cl2​) bubbled in water, sodium hypochlorite (NaOCl), or hypochlorous acid (HOCl).
Chlorine is a component of the minerals halite, sylvite, and carnallite and occurs as the chloride ion in seawater. It is used in water purification, as a bleaching agent, and in the processing of some foods. Chlorine is also used as a disinfectant in human drinking water treatment systems, swimming pool water systems, and sewage systems.
The use of chlorine in wastewater treatment and its presence in seawater as the chloride ion highlight its reactivity and persistence in water. While chlorine itself does not persist for long, its by-products and the need to maintain residual levels in certain applications demonstrate its impact on aquatic environments.
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Chlorine as a pollutant from wastewater treatment plants
Chlorine is a basic industrial chemical used in the manufacture of chlorinated organic and inorganic chemicals. It is also used for pulp and paper manufacture, as an industrial and household bleach, an antifoulant in cooling water, a disinfectant, and for water and
Wastewater treatment plants (WWTPs) typically focus on removing nutrients and suspended solids to safely dispose of effluent in a recipient aquifer. Chlorination is a common disinfection method used to treat wastewater, kill or inactivate microorganisms, and remove harmful substances. It is often the final step in the treatment process. Before chlorination, wastewater samples are analysed to determine the level of contamination and the required chlorine dose. Chlorine is then added to the wastewater, usually by spraying or mixing.
Chlorine reacts with organic and inorganic substances in the wastewater to kill microorganisms and oxidize contaminants. The reaction time depends on the characteristics of the wastewater and the concentration of chlorine. To ensure long-lasting disinfection, a certain concentration of chlorine must be maintained. Water quality monitoring equipment is used to continuously monitor chlorine residuals and other parameters to ensure water quality.
Chlorination is effective against bacteria and viruses, but some protozoan cysts are resistant to its effects. Reactions between ammonia and chlorine produce monochloramines, dichloramines, and trichloramines, collectively known as chloramines. These compounds are beneficial in the water treatment process due to their disinfection capacity, although they are less effective than chlorine. Chlorinated water can also be used to remove ammonia nitrogen, a common pollutant in industrial wastewater and sewage, by converting it into nitrogen or nitrogen compounds. Additionally, chlorinated water helps eliminate unpleasant odours and organic substances in wastewater through oxidation or chemical neutralization.
Overall, chlorine is a critical component of wastewater treatment, playing a vital role in microbial control and pollutant removal. However, it must be used with care, adhering to safety standards and regulations, to ensure its effective and safe application in protecting public health and the environment.
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Chlorine's contribution to algal blooms
Chlorine is a basic industrial chemical with a variety of applications, including water treatment. It is highly soluble in water and very reactive, with its by-products persisting longer than chlorine itself.
Algal blooms have become a significant challenge in water treatment globally. They are overgrowths of photosynthesising organisms, including algae and cyanobacteria. While not all algae or cyanobacteria are harmful, certain species are toxic to humans and animals when consumed or touched.
Organic chloramines, which form during the chlorination of drinking water, pose a significant threat to water quality. They are persistent, moderately chemically reactive, and toxic. The active chlorine (Cl+) in organic chloramines can lead to the formation of chlorinated phenolic compounds, which may cause oxidative or toxic pressure to bacteria or cells.
Studies have investigated the feasibility of using chlorine as an agent for disrupting algal biomass. Results show that chlorine is an effective agent for disrupting algal cells, with 90% of algal cells disrupted in 6 minutes at a 10 mg/L chlorine dose. However, the impact of chlorine on algal cell viability, surface morphology, and cell size is still being studied.
Additionally, increasing the level of chlorine in the water is a potential option for treating harmful algal blooms (HABs). Chlorine has the ability to remove dissolved toxins, but it is important to consider the specific toxins and disinfection by-products present in each system.
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Chlorine's presence in marine water quality guidelines
Chlorine (CAS 7782-50-5) is a basic industrial chemical used in the manufacture of chlorinated organic and inorganic chemicals. It is a gaseous material that is very soluble in water and highly reactive. Chlorine is also used for pulp and paper manufacture, as an industrial and household bleach, an antifoulant in cooling water, a disinfectant, and in water and wastewater treatment.
Although chlorine does not persist for extended periods in water, it is very reactive, and its by-products persist longer. It has been common practice to maintain a residual level of chlorine in wastewater plants, but recent awareness of the environmental effects of chlorine has resulted in moves to reduce this residual.
In water treatment, the intentional production of N-chloramines is used to extend the effectiveness of chlorination. After water treatment, the sum of free chlorine and combined chlorine is referred to as total residual chlorine (TRC). The toxicity figures were derived using measurements of TRC rather than free chlorine. The chemicals used for testing the effect of chlorine include chlorine gas (Cl2) bubbled in water, sodium hypochlorite (NaOCl), or hypochlorous acid (HOCl).
The default guideline values (previously known as 'trigger values') provided by the Australian and New Zealand Guidelines for Fresh and Marine Water Quality should be used in accordance with detailed guidance. These guidelines consider the toxicity of chlorine to aquatic organisms and aim to protect them from acute and chronic effects.
In China, there are also guidelines for chloride concentration levels in water, which include standards for surface water, drinking water, groundwater, agricultural irrigation water, and urban water supply. The United States Environmental Protection Agency (USEPA) has developed guidelines to assist states in revising water quality criteria, but there is no national standard due to the diverse nature of water ecosystems. Canada has guidelines for drinking water quality, which include considerations for chlorine dioxide, chlorite, and chlorate.
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Frequently asked questions
Marine pollution is a combination of chemicals and trash that comes from land sources and is washed or blown into the ocean. This pollution damages the environment, the health of organisms, and economic structures worldwide.
Chlorine is a basic industrial chemical used in the manufacture of chlorinated organic and inorganic chemicals. It is also used for water purification and wastewater treatment. While chlorine does not persist for extended periods in water, its by-products can remain longer and can be harmful to the environment and human health. Therefore, it is considered a marine pollutant.
Chlorine enters the marine environment primarily from land-based sources, such as industrial releases, wastewater treatment plants, and runoff from rivers and drains. It is also used in swimming pool disinfectants and algaecides, which can contribute to water contamination.
Chlorine is a highly reactive chemical that can have toxic effects on aquatic organisms. It can also form by-products that persist in the environment and contribute to water contamination. In marine water, chlorine can react with bromide and iodide, further impacting the ecosystem.
To reduce chlorine pollution, it is important to minimize the use of chlorine and properly treat wastewater before discharging it into the environment. Many countries have enacted regulations to limit or ban the use of disposable plastic items and reduce the residual level of chlorine in wastewater plants. Additionally, promoting alternative disinfection methods and sustainable waste management practices can help decrease chlorine pollution in marine ecosystems.
