Leather tanneries are an integral part of the textile industry. They are the sites where animal hides are processed and turned into functional leather. Leather tanneries have not only historically contributed greatly to the textile industry but have also offered increased revenue to numerous countries and have become the leading economic sector in many. However, with this increased revenue comes environmental degradation. During the leather tanning process, an excess of waste is produced which finds its way into waterways and the land, while simultaneously threatening the health and safety of workers and residents.
Leather Tanning Process
The process of leather tanning can be carried out by three methods including vegetable tanning; chrome tanning; and eco-friendly tanning. The most popular and accessible of these being chrome tanning with 80% of tanneries using this process. The objective of the tanning process is to transform animal skins into stable products, namely leather, and this involves stripping two out of the three outer layers of the hide, exposing the dermis to the “action agents” which convert the proteins into an insoluble mass known as leather (Iyer et al., 2006).
Vegetable tanning includes the use of tannins made of vegetables in the leather tanning process. The use of vegetable tannins was originally the most common way to produce leather but has since been dominated by chrome tanneries. This method is undoubtedly more environmentally sustainable compared to chrome tanning but is less cost and time-effective.
The chrome tanning process is performed according to the following steps: brushing and soaking to remove salt and dirt; liming in a solution of lime and sodium sulfide to loosen the hide; reliming to remove hair and start stripping layers of corium; deliming in ammonium sulphate and water to remove the sodium sulphide; and chrome tanning which involves pickling and drying to obtain stable leather.
The eco-friendly tanning process follows a similar process except instead of chromium, uses non-natural amino acids which produce comparable results with zero discharge of solid waste as well as all of its wastewater being non-toxic. This process allows limited maintenance of solid waste and wastewater due to higher biodegradability as well as the relief of no toxic outputs (Wu et al., 2020).
Environmental Impact of Tanneries
Every leather tanning method produces organic waste and sometimes chemical waste. The chrome tanning method in particular produces mass amounts of chromium waste which has a detrimental impact on the local water supply and the environment. This waste poses a risk of contamination to the local environment either through groundwater and waterway pollution or through air pollution if not properly disposed of, as is often the case.
Chrome tanning uses 69,000 tons of chromium annually in 1600 tanneries with up to 39% of that chromium ending up wasted. This can be in the form of solid waste, with some tanneries producing up to 5500 kg of solid waste each day; or as wastewater, with up to 150 L produced per hide (Syed et al., 2010). This excess chromium that is released in solid waste and/or wastewater has a very low biodegradability and high toxicity and often ends up back in the local water supply. This waste causes environmental challenges as it directly affects local organisms, the environment and may induce nitrification processes (Lofrano et al., 2013). Excess nutrients such as nitrogen promote nitrification in local waterways which cause these systems to become oxygen-starved and overproduce bacteria and algae while disrupting freshwater and/or marine life. Chrome tanneries contribute to severe water pollution and cause toxic chemicals to spread in groundwater across several municipalities.
Leather tanning produces so much waste that the US has chosen to outsource its labour and now has 95% of its tanneries operating overseas. This allows companies to avoid environmental oversight penalties. With the western world’s stricter water quality management regulations, these tanneries would have a difficult time abiding by water quality policies in their countries, as a result, many tanning companies turn to the global south to exploit their lack of regulations and cheaper labour. This is yet another example of the strain put on the global south by textile consumption in the global north. These tanneries have attempted to rectify the environmental impact by creating industrial districts to isolate the impact (Lofrano et al., 2013). However, having the bulk of the waste infiltrating into water systems, the chemicals and pollution still travel across boundaries.
Health Impact of Leather Tanneries
With these leather tanneries near or within densely populated areas, there are populations whose only access to water are these contaminated waterways. These residents must use this water to cook, drink, and bathe. Residents and workers are also frequently subjected to polluted air from tanneries. Respiratory infections and diseases are very common in these densely populated areas as a result of air pollution produced from burning tannery residual waste.
By being in direct contact with chromium – a carcinogenic substance, tannery workers experience extremely high rates of cancer as well as dermatological diseases, respiratory issues, and neurological disorders. Contamination with these toxic chemicals can occur through skin exposure, inhalation, and consumption. The use of contaminated water for agricultural purposes also increases the risk of the previously mentioned illnesses, diseases, and infections among residents. Moreover, this risk doesn’t end with the workers but is passed down to generations through pregnancy and childbirth, and increases the chances of pregnancy complications and the risk of stillbirths (Syed et al., 2010).
These issues are a call for a human health risk assessment in order to help reduce the risk of exposure to these chemicals. Sustainable and safer practices of leather tannery can be an option but are often also less affordable and less accessible. Solutions to avoiding chrome tanneries would be to convert back to vegetable tanneries if economically feasible or engage with more eco-friendly options. With limited research and practice of amino acids as an alternative, we need to support further research and encourage the practice of chrome alternatives. It is crucial to hold leather companies accountable for their production practices.
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