Your Past - Tanneries - A potential cause of past pollution!

What did tanneries do?
Tanneries transformed raw skin and hides into finished leather by treating the skins with agents to make them resistant to heat and micro-organisms. It was and still is a complex process, involving three distinct processes. Tissue and hair is removed from the hide prior to tanning, commonly using arsenic sulphide, as well as soaking and washing to remove fat, salt and dirt. Next, the hides were pickled in sulphuric acid or, in later years, trivalent chromium and then finally dried, treated and dyed.

History
In the early 1800's, the tanning process was carried out in pits in the ground, with hides suspended over them. The process may have taken as long as 15 months, with the high likelihood that toxic effluent and chemicals simply leaked into the soil from the pit. At the end of the 19th century, chrome salt baths were introduced and from the early 20th century, synthetic organic tans were used. For most of the 20th century there was an increased use of heavier chemicals and elements, including phenols, cresols and naphthalene, formalin and formaldehyde, all very volatile and toxic products.

Waste Products
While some by-products, such as fat for rendering, were taken off site for further processing, earlier times saw very lax processes, inevitably causing spillage and run-off. The largest proportion of tannery waste is liquid effluent requiring treatment before discharge to a sewer, although where none existed, this simply ran into the soil or groundwater via sinks or slurry pits. Where solvents were used to separate slurry, separate waste streams of waste solvents would have been generated.

Likely contaminants
Wherever animal products are processed, the biggest concern is pathogens. While current health and safety practices are very strict, there was a virtual absence of measures in the past. While risks diminish over time, some, such as anthrax or tetanus could remain for decades. Many and varied chemicals have been used in the tanning process over the years. Prior to tanning, the following may be used: solvents (degreasing), lime, sodium and arsenic sulphate (hair removal), acid (removal of lime and PH balance), enzymes (removal of remaining hair). The tanning process could have used chromium sulphate and formaldehyde. A range of insecticides could have been used in tanneries after the Second World War and if hides were imported from outside Europe, banned or controlled substances, may well have been encountered. Compounds from waste streams could also have been absorbed into building walls, floors and ceilings and underlying soils. It is also possible that animal remains were buried on site and may not have been subject to checks for anthrax and other pathogens.

Where were they found?
Tanneries were usually sited close to water courses, as they required a good, clean supply of water. They were distributed widely throughout the UK, but with significant concentrations in the Pennines, Northampton, Glasgow, London, Merseyside and Humberside. The number of tannery sites reduced dramatically from the 1960's, largely as a result of foreign imports and increased use of synthetic foot soles for shoes.