1.1. Identity, physical and chemical properties. Copper is a reddish-brown, ductile and malleable metal. It belongs to group IB of the Periodic Table. In compounds found in the environment it usually has a valence of 2 but can exist in the metallic, +1 and +3 valence states. Copper is found naturally in a wide variety of mineral salts and organic compounds, and in the metallic form. The metal is sparingly soluble in water, salt or mildly acidic solutions, but can be dissolved in nitric and sulfuric acids as well as basic solutions of ammonium hydroxide or carbonate. Copper possesses high electrical and thermal conductivity and resists corrosion. 1.2. Analytical methods. The wide range of copper species, inorganic and organic, has led to the development of an array of sampling techniques, preparation and analytical methods to quantify the element in environmental and biological samples. Contamination of the samples with copper from air, dusts, vessels or reagents during sampling and preparation is a major source of analytical errors, and 'clean' techniques are essential. Colorimetric and gravimetric methods for the measurement of copper are simple to use and are inexpensive; however, their usefulness is limited to situations where extreme sensitivity is not essential. For measurement of low concentrations of copper in various matrices, atomic absorption spectrophotometric (AAS) methods are the most widely used. A dramatic increase in sensitivity is obtained by the utilization of graphite furnace atomic absorption spectrophotometry (GF-AAS) rather than flame AAS. Depending upon sample pretreatment, separation and concentration procedures, detection limits of about 1 μg/litre in water by GF-AAS and 20 μg/litre by AAS have been reported and levels of 0.05-0.2 μg/g of tissue have been detected by GF-AAS. Greater sensitivities can be achieved through the use of emission techniques such as high temperature inductively coupled argon plasma techniques followed by atomic emission spectroscopy (ICP-AES) or a mass spectrometer (ICP-MS). Other more sensitive and specialized methodologies are available such as X-ray fluorescence, ion-selective electrodes and potentiometric methods, and anodic stripping and cathodic stripping voltametry. 1.3. Sources of human and environmental exposure. Natural sources of copper exposure include windblown dust, volcanoes, decaying vegetation, forest fires and sea spray. Anthropogenic emissions include smelters, iron foundries, power stations and combustion sources such as municipal incinerators. The major release of copper to land is from tailings and overburdens from copper mines and sewage sludge. Agricultural use of copper products accounts for 2% of copper released to soil. Copper ores are mined, smelted and refined to produce many industrial and commercial products. Copper is widely used in cooking utensils and water distribution systems, as well as fertilizers, bactericides, fungicides, algicides and antifouling paints. It is also used in animal feed additives and growth promoters, as well as for disease control in livestock and poultry. Copper is used in industry as an activator in froth flotation of sulfide ores, production of wood preservatives, electroplating, azo-dye manufacture, as a mordant for textile dyes, in petroleum refining and the manufacture of copper compounds. 1.4. Environmental transport, distribution and transformation. Copper is released to the atmosphere in association with particulate matter. It is removed by gravitational settling, dry deposition, washout by rain and rainout. Removal rate and distance travelled from the source depend on source characteristics, particle size and wind velocity. Copper is released to water as a result of natural weathering of soil and discharges from industries and sewage treatment plants. Copper compounds may also be intentionally applied to water to kill algae. Several processes influence the fate of copper in the aqueous environment. These include complex formation, sorption to hydrous metal oxides, clays and organic materials, and bioaccumulation. Information on the physicochemical forms of copper (speciation) is more informative than total copper concentrations. Much of the copper discharged to water is in particulate form and tends to settle out, precipitate out or be adsorbed by organic matter, hydrous iron, manganese oxides and clay in the sediment or water column. In the aquatic environment the concentration of copper and its bioavailability depend on factors such as water hardness and alkalinity, ionic strength, pH and redox potential, complexing ligands, suspended particulate matter and carbon, and the interaction between sediments and water. The largest release of copper is to land; the major sources of release are mining operations, agriculture, solid waste and sludge from treatment works. Most copper deposited in soil is strongly adsorbed and remains in the upper few centimetres of soil. Copper adsorbs to organic matter, carbonate minerals, clay minerals, hydrous iron and manganese oxides. The greatest amount of leaching occurs from sandy acidic soils. In the terrestrial environment a number of important factors influence the fate of copper in soil. These include the nature of the soil itself, pH, presence of oxides, redox potential, charged surfaces, organic matter and cation exchange. Bioaccumulation of copper from the environment occurs if the copper is biologically available. Accumulation factors vary greatly between different organisms, but tend to be higher at lower exposure concentrations. Accumulation may lead to exceptionally high body burdens in certain animals (such as bivalves) and terrestrial plants (such as those growing on contaminated soils). However, many organisms are capable of regulating their body copper concentration.