2.1.1 uses
Silver is used as a plating or as an alloy for jewelry, flatware, dental amalgams and caps, electrical contacts, batteries, catalysts, coins, solders, brazing alloys, mirror backings, silvering of glass beads, etching ivory, as a catalyst in hydrogenation and oxidation, as an antimicrobial disinfectant in drinking water, to treat warts and burns, and as a photographic or radiographic emulsion. Silver is also used as a cloud seeding agent to promote rainfall.
Breath mints coated with silver, silver acetate anti-smoking lozenges, silver nitrate drops to prevent blindness in newborns exposed to gonorrhea, skin creams containing silver nitrate or silver sulphadiazine, and silver nitrate solutions for treating gum disease are the common medical or personal hygiene uses of silver (Anon. 1990, Anon. 1991, MRI 1975).
The reduction of silver salts by electromagnetic radiation is the basis of photographic and x-ray image capture. These are major industries that use large quantities of silver. The images are used for diagnostic purposes, information storage, transmission and aquisition, personal momentoes, scientific work and business advertising.
2.1.2 production
Canadian production declined for the fourth year in a row in 1992, to 1147 tonnes from 1261 tonnes the previous year (Keating 1992, Giancola 1994) In 1974 and 1975, of the over 1000 tonnes produced, most was refined silver, the remaining being silver ores and concentrates (Boyle 1968). In 1992 Canada was listed as the fifth largest producing nation in the world (Keating 1992, Giancola 1994), compared with being number one in 1974, at the time being responsible for 14% of the silver produced in the world, more than any other individual country. Forty percent of this came from Ontario and 15% from BC. Most of the silver production in the world is a by-product of lead-zinc, copper and gold mines; little is from silver-only mines (Boyle 1968).
2.1.3 consumption
Canadian consumption of silver was 341.5 tonnes in 1989, 464.0 tonnes in 1990 and 335.1 tonnes in 1991. Exports for 1991 and 1992 were 1070 tonnes and 1135 tonnes, respectively. In comparison, Canada's use of silver in 1974 and 1975 was just over 300 tonnes. However, Canada exported almost the entire production for those years as silver, or as ores and concentrates, and imported silver from the USA and Britain. The USA was the largest consumer at over 5500 tonnes in 1974, and 30% of this was used for photographic emulsions (George 1976, Keating 1992, Giancola 1994).
2.1.4 discharges
Silver is released to the environment as a waste product from mining and smelting activities (Anon. 1990). The 1993 summary report on the National Pollutant Release Inventory reports that in 1993 a total of 4.848 tonnes in 33 releases were made to the environment. This broke down to 0.203 tonnes in water, 3.016 tonnes underground and 0.011 tonnes on land. The facility with the largest reported release was Cominco Ltd. (Trail, British Columbia) with 3 reports of releases totalling 3 tonnes of silver; all released in the water. In New Brunswick one release was reported that was less than 1 tonne and in Quebec 3 reported releases totalled 0.962 tonnes. A total of 6 releases made as transfers to off-site locations totalled 26.376 tonnes. Most of this was in recovery, re-use and recycling (25.764 tonnes), and the remainder was in sewage (0.291 tonnes) and containment (0.324 tonnes). Of the 6 reports made, 5 were in Ontario where 25.764 tonnes was in recovery, re-use and recycling, 0.291 in sewage and 0.268 tonnes in containment with a total release of 26.320 tonnes. The other release was reported in Quebec with 0.056 tonnes reported for containment (Anon. Env. Can. 1995).
About 600 to 700 kg of AgI were released in cloud seeding over western Canada in 1977 (Chisholm) out of a total of about 3 tonnes worldwide (Klein and Mulvey 1978). In the USA about 25% of the annual consumption is estimated to be discarded annually. This discarded silver consists of about 10% unrecycled photographic silver sent directly to the water, 30% silver deposited in sewage sludge and 60% silver contained in combustible refuse and discarded appliances. An estimated 327 tonnes were released to the atmosphere with 54% from the iron and steel industry, 29% from the cement industry and 12% from burning coal (MRI 1975).
The total consumption of coal in the world in 1974 was about 3 billion tonnes. At an average silver content of 100 µg/kg, the amount of silver present was 300 tonnes. Only about half of the coal produced was burned to produce energy, resulting in only 10% of the silver (15 tonnes) being released to the atmosphere in fly ash. The total crude oil production of the world in 1976, 2.47 billion tonnes, contained only about 0.2 tonnes of silver; this is a relatively negligible source of silver release to the atmosphere (Bertine and Goldberg 1971 and McMullen 1976).
Silver thiosulphate complexes from waste photographic solutions are the main form in which the 500 or so tonnes of silver enter the environment each year in the USA. Probably 75% of this is trapped in sewage sludge (MRI 1975). The estimated total amount of silver released to the environment through anthropogenic activities around the world is 2500 tonnes annually; while smaller than the release of 11 000 tonnes due to natural weathering, this is still a significant amount (Klein and Mulvey 1978).