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

 



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Water Quality: Heavy Metals  

Metals can be present in the environment either as ions, complex molecules, or in combination with other metals or particulates as colloids and precipitates (Ashton et al. 2001). 

There are several factors that determine how toxic a metal is to the biological receptors and how far a metal can travel from its source. Toxicity depends on the type of metal, the chemical interactions of the metal with other metals and the presence of organic compounds which may increase the bioavailability and spread of the toxic metal (Davies and Day 1998).  The flow rate and volume of water, the physical make-up of sediments, water temperature, oxygen, pH and salinity also impact: (1) how toxic a metal is in a given environment (Davies and Day 1998); (2) speciation (the proportion of metals in different forms); and, (3) the mobility (Ashton et al. 2001).

Heavy metals include cadmium, copper, nickel, zinc, chromium, arsenic, mercury, lead, etc. Many of the metals present in the aquatic system are in suspension or are absorbed onto particulate matter, rather than being in solution as free ions (Ashton et al. 2001). Metals absorbed onto particulates can travel long distances along water courses and be detected downstream of the source. 

Mining

Heavy metals are persistent in the environment and can be bioaccumulated in aquatic organisms. Mining is one of the primary sources of metal contamination in the Limpopo River basin. The water quality impacts related to mining, with specific reference to metals, are shown below for impacted sub-basins. Sub-basins that have no record of water quality impacts related to heavy metals from mining are excluded from the table below.

Heavy metal water quality issues associated with mining for sub-basins in the Limpopo River basin.

Sub-basin

Type of Mining

Water Quality Issues

Motloutse

Base metals, smelters

Copper, nickel

Shashe 1

Gold, base metals, smelters, alluvial gold

Bismuth, copper, nickel, mercury 

Mzingwane 1

Gold, base metals, small-scale

Arsenic, cobalt, mercury, nickel

Mwenezi

Small-scale, other (emerald)

Chromium

Marico

Base metals, smelters, other

Chromium, lead, zinc

Crocodile 1

Gold, base metals, smelters, other

Copper, chromium, iron, lead, manganese, silver, zinc

Laphalala 1

Base metals, other

Lead, tin,

Theuniskloof 1

Base metals, other

Iron, manganese

Mogalakwena

Gold, base metals, smelters, other

Antimony, tin

Sand

Small-scale

Copper, mercury, nickel,  zinc

Nzhelele

Other

Lead, nickel

Riet & Little Olifants 1

Base metals, smelters

Copper, iron, manganese

Middle Olifants

Gold, base metals, other

Chromium, copper, iron, manganese, tin, zinc

Steelpoort

Base metals, smelters

Chromium, copper, iron, manganese, molybdenum, vanadium

Selati 1

Gold, base metals, smelters, other

Antimony, arsenic, cadmium, copper, iron, manganese, mercury, zinc

Middle Letaba and Great Letaba 1

Gold, base metals, small-scale, other

Antimony, arsenic, iron, mercury, tin

Shingwedzi

Gold, small-scale

Arsenic, mercury

1- Sub-basin names may be slightly different than those found in the source document.
Source: Ashton et al 2001.
Effluent from metal mines must be contained in hydrologically isolated waterbodies.
Source: Vogel 2005
( click to enlarge )

Industry and Other Sources

Metal contamination can also originate from industrial activities as well as from urban storm water runoff from roads, parking areas and other impervious surfaces, ending up either in waste water treatment plants, or directly in the river. Toxic metals are also associated with some pesticides (Heath and Claasen 1999).

Sources of metal pollution from industry.

Metal Source
Cadmium Laundrettes, electroplating workshops, plastic manufacturing, pigments, enamels, paints
Chromium Alloys, preservatives, dying and tanning activities, metal coatings
Copper Electronics, plating, electrical wires, paper, textiles, rubber, printing, plastic
Iron Galvanizing, electroplating, polishing
Lead Fuel additive, batteries, pigments, roofing, fishing weights
Zinc Domestic wastes, galvanizing, batteries, paints, fungicides, textiles, cosmetics, pulp, papermills, and pharmaceutics
Nickel Alloys, electroplating, nickel-cadmium batteries, laundrettes, paints
Mercury Dental practices, clinical thermometers, glass mirrors
Source: Moletsi et al. 2004

 



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