Organic Chemicals: Water Pollutants You Need To Know

Water pollution is a critical issue that poses a threat to both human health and the environment. It occurs when harmful substances, often in the form of chemical or biological contaminants, find their way into our precious water sources, including streams, rivers, lakes, and oceans. These contaminants can be naturally occurring or man-made, with chemical contaminants ranging from simple inorganic ions to complex organic molecules. Organic chemical water pollutants, such as pesticides, herbicides, pharmaceuticals, and industrial solvents, have aroused public concern due to their persistence, toxicity, and potential for adverse effects on living organisms. Understanding and addressing these pollutants are crucial steps towards safeguarding our finite drinkable water sources and the health of our ecosystems.

Chlorinated solvents

Some common chlorinated solvents include carbon tetrachloride (CT), tetrachloroethylene (PCE or perchloroethylene), trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA). These compounds are widespread groundwater contaminants, often found at industrial sites due to their extensive use in chemical production, metal degreasing, and dry cleaning. They tend to form dense non-aqueous phase liquids (DNAPLs) that sink through permeable groundwater aquifers until they reach a non-permeable zone. The slow dissolution of DNAPL masses into the surrounding groundwater creates a long-term source of contamination.

The release of chlorinated solvents into the environment can occur through various pathways, including improper disposal, spills, or leaks from industrial sites. Once released, these solvents are subject to natural microbial degradation, which can partially mitigate their environmental impact. However, their physical and chemical properties, such as low solubility and high density, contribute to their persistence in the environment.

The presence of chlorinated solvents in groundwater, especially drinking water sources, poses a potential threat to human health due to their mobility, longevity, and toxicity. They can enter the human body through inhalation or skin contact, leading to toxic effects. Some chlorinated solvents have also been linked to serious health hazards, including carcinogenic effects.

The widespread use of chlorinated solvents has led to their detection in various environments, including groundwater, surface water, and soil. In the United States, for example, a significant number of Superfund sites with groundwater contamination contained chlorinated solvents, highlighting the extent of their environmental impact.

Heavy metals

The toxic effects of heavy metals on living organisms are well-documented. Exposure to these metals has been linked to neurotoxicity, kidney damage, liver dysfunction, dermatological issues, and an increased risk of developing various cancers. They can also cause developmental issues, such as bone fragility and retardation. In fish, heavy metal contamination has been associated with malformations, fin loss, gill underdevelopment, and liver dysfunction.

The removal of heavy metals from water has become a critical goal in wastewater treatment. Conventional methods such as ion exchange, reverse osmosis, ultrafiltration, and chemical precipitation have been employed, but they often come with high operational costs and the generation of secondary pollutants. More recently, nanotechnology and biosorption techniques have emerged as promising alternatives for heavy metal removal, offering both cost-effectiveness and environmental benefits.

It is important to address heavy metal contamination in water to mitigate the potential health risks to humans, animals, and the environment. By understanding the sources and impacts of heavy metal pollution, we can develop effective strategies for their removal and work towards protecting our water resources and the health of all living beings that depend on them.

Pesticides

The physical and chemical properties of pesticides determine their interaction with water. Pesticides contain toxic materials that pose risks to both the environment and human health. Certain pesticides, such as atrazine, have been known to alter the genetic characteristics of frogs, even causing male frogs to develop female organs. Other pesticides, like organophosphorus compounds, are highly toxic to humans.

The persistence of pesticides in the environment is influenced by their half-life. Pesticides with longer half-lives remain in the environment for extended periods, posing threats to aquatic ecosystems and drinking water sources. Advanced oxidation processes (AOPs) and adsorption techniques have been employed to remove pesticides from water, converting them into non-toxic compounds or biodegradable intermediates.

While the uncontrolled application of pesticides in agriculture can lead to water pollution, there are ongoing efforts to mitigate their impact. The development of advanced treatment processes and the regulation of pesticide use aim to reduce the flow of pesticides into drinking water sources, protecting both the environment and human health.

Herbicides

Another removal strategy is mineralization through microbial metabolism, where soil microorganisms consume herbicide compounds and turn them into harmless substances like NH3, H2O, and CO2. In wastewater and drinking water treatment facilities, other methods such as UV photolysis, chemical oxidation, activated carbon adsorption, and microbial degradation are employed. The use of nanomaterials like TiO2 and ZnO has also been explored, as their small size and high surface area increase the interaction probabilities with target pollutants, accelerating their degradation.

Overall, herbicide pollution is a significant issue, and its impact on the environment and human health is a growing concern. While there are methods to remove herbicides from water, preventing their entry into water sources in the first place is crucial. This can be achieved through sustainable practices such as using natural alternatives to chemical herbicides.

PCBs

Polychlorinated biphenyls (PCBs) are organic chemical compounds with the formula C12H10−xClx. They are highly toxic and carcinogenic and were once widely used in industrial and consumer electronic products, such as carbonless copy paper, heat transfer fluids, and electrical equipment. PCBs were manufactured domestically from 1929 until their production was banned in 1979 due to their harmful effects on human and environmental health.

The process of degrading PCBs depends on their chemical makeup and their location in the environment. In the air, shallow water, or surface soils, sunlight plays a crucial role in breaking down PCBs. In soil or sediments, microorganisms such as bacteria, algae, or fungi biodegrade PCBs. To address PCB contamination in waterways, scientists must determine whether to dredge and remove contaminated sediments or leave them in place to naturally biodegrade.

The Stockholm Convention on Persistent Organic Pollutants, which entered into force in 2004, obliges countries to eliminate the use of PCBs in equipment and manage waste liquids and contaminated equipment. Despite the decline in PCB production since the 1960s, their longevity has kept them in use. As a result, everyone in the world is likely to have trace amounts of PCBs in their bodies.

Frequently asked questions