What Chemicals and Pollutants Affect Water Quality?
- differences in geology
- distance to the sea
- downstream progression of water from headwaters.
- where discharge from ground water carries elevated carbon dioxide;
- where higher temperatures decrease the amount of gas that can dissolve in the water;
- where the decomposition of natural organic matter (e.g. dead plants and leaves) depletes oxygen;
- where the balance between plant photosynthesis and respiration alters the balance of carbon dioxide and oxygen;
- where changes in water turbulence affect how rapidly dissolved gases exchange with the atmosphere;
- where different vertical water layers form in lakes (stratification), preventing gas exchange with the atmosphere;
- or even where altitude changes the amount of gas available (think of how climbers have to use breathing equipment because of the “thin air” on top of high mountains).
The effects of pollution
Want to keep
Cardiff University online course,
The Challenge of Global Water Security
In other words, he considered human activities as a key source of pollution, while also linking his definition to legal standards. Others have since extended this definition to suggest that pollution occurs where contaminants disrupt normal environmental processes. Substances classed as pollutants include:“the introduction by people, into the environment, of substances or energy liable to cause interference with legitimate uses of environment”.
1. Organic wasteThis is a dominant source of pollution around the world. It’s still a very major issue in urban regions of the less developed world where untreated or partially treated sewage enters freshwater ecosystems. As well as the dissolved pollutants, organic wastes often contain solid particles of waste and pathogenic organisms such as bacteria. Organic wastes can also arise from processes such as leather tanning, pulp and paper manufacture, wood processing, food processing, agricultural wastes such as cattle slurry or discharges from intensive pig or poultry units. Major problems arise when the microbial decomposition of large organic concentrations depletes oxygen concentrations faster than they can be replenished. At worst, this can lead to a complete lack of oxygen, particularly in sediments.
2. NutrientsPhosphates and nitrates used as agricultural fertilisers can subsequently leach into rivers and lakes downstream, dramatically increasing fluxes above natural background concentrations with consequences for algal production (‘cultural eutrophication’) and water supply or safety.
3. MetalsMetals such as lead, nickel, cadmium, zinc, copper, mercury or aluminium enter freshwater ecosystems from a wide range of industrial processes, water leaching from landfills, some agricultural processes, and from activities such as mining. Gases such as chlorine, ammonia and methane, and anions, such as cyanides, fluorides and sulphites are also considered as pollutants.
4. Alkalis and acidsThese pollutants are often the result of industrial processes but can also appear from the formation of acid rain caused by sulphur and nitrogen oxides formed by fossil fuel combustion. Acid rain can have a direct effect on water ecosystems by making the waters too acidic for life. It can also leach metals such as aluminium from soils, causing additional ecological impact in acidified waters.
5. Complex organic compoundsComplex organic compounds include pollutants referred to as ‘xenobiotic substances’ or Persistent Organic Pollutants (POPs). These compounds include pesticides, herbicides, PCBs, a range of hydrocarbons, solvents, surfactants, dioxins, phenolic compounds, flame retardants (eg PBDE). Arising from a wide variety of industrial, agricultural, transport and domestic sources.
6. Oil and petroleum productsThese pollutants are often the result of spillages or accidents at extraction sites or during transportation. They’re also part of a cocktail of pollutants entering water courses from road runoff.
7. Pharmaceutical chemicalsA group of substances that are receiving increasing attention where they arise from human uses or domestic livestock treated either curatively or preventatively for a wide range of conditions. Painkillers, anti-inflammatory drugs, chemotherapeutic agents, endocrine disrupting substances, anti-depressant drugs, anti-helminthic treatments (for parasitic worms, dominantly from livestock), antibiotics or their metabolites are all now widespread in surface waters among hundreds of chemicals in this group.
8. PlasticsPlastic pollutants vary in size (macro, micro and nano) and are currently attracting attention. They can have detrimental physical effects on organisms e.g. entanglement or obstruction, may be toxic in their own right, and can transport other pollutants.
9. Inert solidsSolid particles of a wide range of size fractions from silts and clays to sand and gravel can enter freshwater ecosystems from agriculture, forest operations, mining, construction, urban landscapes or as part of sewage wastewater. They affect organisms by inflicting physical damage, occluding surfaces, blocking pore spaces on the beds of lakes or rivers, and reducing the transport of oxygen rich water.
10. Heat and lightHeat and light are also considered increasingly as pollutants, for example where warm-water effluents enter surface waters from industry or power station coolants, or where artificial light at night (ALAN) disrupts a wide range of organism behaviours.
The Challenge of Global Water Security
Our purpose is to transform access to education.
We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.
We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.