Health and environmental impact
Health and environmental impact of leather tanning
The tanning process involves chemical and organic compounds that can have a detrimental effect on the environment. Agents such as chromium, vegetable tannins, and aldehydes are used in the tanning step of the process. Chemicals used in tanned leather production increase the levels of chemical oxygen demand and total dissolved solids in water when not disposed of responsibly. These processes also use large quantities of water and produce large amounts of pollutants.
Boiling and sun drying can oxidize and convert the various chromium(III) compounds used in tanning into carcinogenic hexavalent chromium, or chromium(VI). This hexavalent chromium runoff and scraps are then consumed by animals, in the case of Bangladesh, chickens (the nation's most common source of protein). Up to 25% of the chickens in Bangladesh contained harmful levels of hexavalent chromium, adding to the national health problem load.
Chromium is not solely responsible for these diseases. Methylisothiazolinone, which is used for microbiological protection (fungal or bacterial growth), causes problems with the eyes and skin. Anthracene, which is used as a leather tanning agent, can cause problems in the kidneys and liver and is also considered a carcinogen. Formaldehyde and arsenic, which are used for leather finishing, cause health problems in the eyes, lungs, liver, kidneys, skin, and lymphatic system and are also considered carcinogens. The waste from leather tanneries is detrimental to the environment and the people who live in it. The use of old technologies plays a large factor in how hazardous wastewater results in contaminating the environment. This is especially prominent in small and medium-sized tanneries in developing countries.
The UN Leather Working Group (LWG) "provides an environmental audit protocol, designed to assess the facilities of leather manufacturers,"for " traceability, energy conservation, [and] responsible management of waste products."
Alternatives
Untanned hides can be dried and made pliable by rubbing and stretching the fibers with a hide stretcher, and fatting. However, the hide will revert to rawhide if not periodically replenished with fat or oil, especially if it gets wet. Many Native Americans of the arid western regions wore clothing made by this process.
Smoke tanning is listed among conventional methods like chrome tanning and vegetable tanning. Impregnation of the hide's cells with formaldehyde (from smoke) offers some microbial and water resistance.
Associated processes
Leftover leather would historically be turned into glue. Tanners would place scraps of hides in a vat of water and let them deteriorate for months. The mixture would then be placed over a fire to boil off the water to produce glue.
A tannery may be associated with a grindery, originally a whetstone facility for sharpening knives and other sharp tools, but later could carry shoemakers' tools and materials for sale.
There are several solid and wastewater treatment methodologies currently being researched, such as the anaerobic digestion of solid wastes and wastewater sludge.
Tanwater
Tanwater was a special water treatment project initiated by Elmo tannery in Sweden in 1992. The aim was to reduce nitrogen effluent from the water treatment systems during the tanning of leather. Previously tanneries in Europe had only been able to reduce nitrogen in the water by up to a maximum of 30%. The "Tanwater" project aimed at reducing nitrogen waste by up to 80% and finally was able to achieve 89% nitrogen-waste reduction in the water. This was a major breakthrough for the tanning industry because nitrogen is a pollutant of groundwater.
Elmo tannery received a grant for the project from LIFE (The Financial Instrument for the Environment). LIFE finances environmental projects in the European Union. Elmo tannery, although producing leather predominantly for the car industry (upholstery leather), also produces leather for handbags and footwear. Since Elmo started this project there have been a number of tanneries that have followed in its steps of improving their water treatment systems in Sweden and Norway. Leather production processes:
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