Water's Solvent Nature: An Easy Target For Pollution

Water is a necessity for all living things, but it is also a finite resource. Known as a universal solvent, water has a unique chemical property that allows it to dissolve more substances than any other liquid on Earth. This property, which is related to its polar nature and molecular structure, makes water highly susceptible to pollution. Water's ability to readily dissolve and mix with various substances means that it easily picks up pollutants from farms, towns, factories, and other sources, leading to water pollution. This has significant implications for human health, the environment, and the availability of clean water sources.

Water is a universal solvent

Water is a polar molecule, with hydrogen and oxygen atoms that carry positive and negative charges respectively. This polarity gives water its unique solvent properties, allowing it to dissolve more substances than any other liquid. This property is why water is known as a "universal solvent".

Water's polarity leads to the formation of hydrogen bonds, which cause water molecules to stick together. This property is known as cohesion, and it is responsible for water's high surface tension. The high surface tension of water allows certain insects to stride on its surface, as their legs are strong enough to balance on the tensioned surface without breaking through.

The polar nature of water also means it has a net positive charge on the side with the two hydrogen atoms and a net negative charge on the oxygen side. This separation of electrical charge within a water molecule results in hydrogen bonds with other water molecules, mineral surfaces, and dissolved ions. Many minerals and pollutants readily dissolve in water because of the hydration shells formed by water molecules around ions.

Water's solvent properties are essential to every living thing on Earth. As water moves through the air, the ground, across the land, or through our bodies, it carries valuable chemicals, minerals, and nutrients. However, these same properties that make water a universal solvent also mean that it easily picks up toxic substances, causing water pollution.

Water pollution occurs when a substance enters a water body and degrades the water's quality to the point where it is harmful to humans, aquatic life, or the surrounding environment. Water pollution can be caused by a wide range of substances, including toxic chemicals, heavy metals, pesticides, and human or animal waste. It can also be caused by excess nutrients, high temperatures, or excess surface runoff into streams, which can stress aquatic life.

Water's polarity

Water is a polar molecule due to its composition of two hydrogen atoms and one oxygen atom (H2O), which form polar covalent bonds. While there is no net charge to a water molecule, the polarity of water creates a slightly positive charge on hydrogen and a slightly negative charge on oxygen, contributing to water's properties of attraction.

The polarity of water is caused by the difference in electronegativity between the oxygen and hydrogen atoms. The oxygen atom attracts electrons more strongly than the hydrogen atom, resulting in a partial negative charge near the oxygen and partial positive charges near the hydrogens. This unequal sharing of electrons makes water a polar molecule.

Additionally, water's polarity makes it a polar solvent, readily dissolving polar solutes. The partially positive hydrogen atoms of water attract the negatively charged atoms of the solute, while the partially negative oxygen of water attracts the positively charged atoms of the solute. This process dissociates the solute's covalent or ionic bonds, separating its atoms. However, water cannot dissolve non-polar solutes like oil or wax, as they lack an affinity for water and do not interact well with it.

The polarity of water also enables it to stick to and attract other polar molecules and ions, including many biomolecules such as sugars, nucleic acids, and some amino acids. This property is essential for various processes and techniques, including capillary action, which helps water reach the roots of plants and allows materials like paper towels and sponges to absorb water.

Groundwater pollution

Water is known as a "universal solvent", able to dissolve more substances than any other liquid on Earth. This means that it easily picks up and carries along valuable chemicals, minerals, and nutrients. However, this property also makes it vulnerable to pollution.

Common sources of groundwater pollution include leaking underground storage tanks for fuel, septic tanks, agricultural activity, and landfills. Underground fuel storage tanks, commonly found at gas stations, can corrode and leak, quickly contaminating local groundwater. Before 1988, these tanks were made of metal in the US, and while regulations now require leak detectors and protection from corrosion, over 30% of tanks still do not comply with EPA standards.

Agricultural activities, including farming and livestock production, are also major contributors to groundwater pollution. Fertilizers, pesticides, and animal waste contain nutrients and pathogens, such as bacteria and viruses, that can be washed into waterways during rainfall. Nutrient pollution, from excess nitrogen and phosphorus, is the top threat to water quality globally and can cause toxic algal blooms harmful to people and wildlife.

Other sources of groundwater pollution include radioactive waste from uranium mining, nuclear power plants, and military weapons production, as well as organic pollutants like polycyclic aromatic hydrocarbons (PAHs) and pesticides. These contaminants can persist in the environment for thousands of years, threatening groundwater resources and requiring costly remediation efforts.

Nonpoint source pollution

Water is known as a "universal solvent", able to dissolve more substances than any other liquid on Earth. This property makes water uniquely vulnerable to pollution.

Principal sources of NPS pollution include urban and suburban areas, agricultural operations, highway runoff, forestry and mining operations, marinas and boating activities, and atmospheric inputs. In urban areas, contaminated stormwater washed off parking lots, roads, and highways is a significant contributor to NPS pollution. This type of urban runoff is usually included under the NPS category, although it can become a point source if channelled into storm drain systems and discharged through pipes to local surface waters.

Agricultural operations account for a large percentage of NPS pollution in the US. The leaching of nitrogen compounds from fertilized agricultural lands, nutrient runoff from stormwater, and the entry of agrochemicals such as pesticides and fungicides into the environment through runoff and deposition are all examples of NPS pollution from agricultural sources. Farms with large livestock and poultry operations, often referred to as "concentrated animal feeding operations" or "feedlots", are also considered point source dischargers.

Water's surface tension

Water is known as a "universal solvent", able to dissolve more substances than any other liquid on Earth. This is due to its asymmetrical structure and polar nature, which results in a separation of electrical charge within the water molecule. This property makes it easily polluted.

The effects of surface tension can be observed in the beading of rainwater on waxy surfaces like leaves. Water adheres weakly to wax but strongly to itself, so it clusters into drops. Surface tension gives these drops their near-spherical shape, as a sphere has the smallest possible surface area-to-volume ratio. Surface tension is also responsible for the shape of water droplets and the phenomenon of capillarity, where water is pulled up in thin tubes due to the combination of cohesive and adhesive forces.

While surface tension is essential for giving water its unique properties, it is also a factor that makes water vulnerable to pollution. Water's ability to form hydration shells around ions, for example, enhances the solubility of many minerals and pollutants. Additionally, surface tension can be affected by temperature and salinity, decreasing as these factors increase. This understanding of water's surface tension and its role in solubility is crucial for addressing and mitigating water pollution.

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