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Home The River Basin People and the River Governance Resource Management
The Limpopo River Basin
Climate and Weather
Water Quality
 Principles of Water Quality
 Human Impacts to Water Quality
 Agricultural Impacts
 Industry and Mining
 Heavy Metals
Persistent Organic Pollutants
 Water Temperature
 Case Study: Upper Olifants River
 Water Quality Fitness for Use
Ecology and Biodiversity
Sub-basin Summaries



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Water Quality: Persistent Organic Pollutants  

Of all the pollutants released into the environment every year by human activity, persistent organic pollutants (POPs) are among the most dangerous. POPs are either used as pesticides, in industry, or generated unintentionally as by-products of various industrial/combustion processes.

POPs are toxic, causing an array of adverse effects, including death, disease, and birth defects among humans and animals. Effects may include cancer, allergies and hypersensitivity, damage to the central and peripheral nervous systems, reproductive disorders, and disruption of the immune system. Some POPs are also considered to be endocrine disrupters, which, by altering the hormonal system, can damage the reproductive and immune systems of exposed individuals as well as their offspring; endocrine disrupters can also have developmental and carcinogenic effects.

These stable compounds can persist for years or decades before breaking down. They circulate globally through a process known as the 'grasshopper effect'. POPs released in one part of the world can, through a repeated (and often seasonal) process of evaporation and deposition, be transported through the atmosphere to regions far away from the original source.

POPs are also problematic because they concentrate in living organisms through bioaccumulation.  Though not soluble in water, POPs are readily absorbed in fatty tissue where concentrations can become magnified by up to 70,000 times the background levels. Fish, predatory birds, mammals, and humans are high up the food chain and so absorb the greatest concentrations. When they travel, POPs travel with them. As a result of these two processes, POPs can be found in people and animals living in remote regions such as the Arctic, thousands of kilometres from any major POPs source (World Bank 2008).

9 new chemicals were recently added to the list of POPs at the COP4 Meetings in Geneva, so now we have the "Dirty 21" (instead of the "Dirty Dozen").

The agricultural use of POP-containing pesticides such as aldrin, DDT, Dieldrin and heptachlor has been prohibited in South Africa (UNDP-GEF 2008).

POPs are covered by the Stockholm Convention on Persistent Organic Pollutants (, which is a "global treaty to protect human health and the environment from chemicals that remain intact in the environment for long periods, become widely distributed geographically, accumulate in the fatty tissue of humans and wildlife, and have adverse effects to human health or to the environment. (Stockholm Convention 2010)" 

Further information on major POPs and guidance on risk assessment and site remediation methods can be found on the POPs Toolkit

Discarded barrels that were used to contain Persistent Organic Pollutants (POPs) can become a source of contamination.
Source: ©iStockphoto/Urbanija 2006
( click to enlarge )



Explore the sub-basins of the Limpopo River

Explore the interactions of living organisms in aquatic environments

Examine how the hydrologic cycle moves water through and around the earth

Tour video scenes along the Limpopo related to The River Basin Theme