Design Life-Cycle

Texiera Andrews

Professor Cogdell

40A, Winter 2014

13, March 2014

Leather (Materials)

The goal for this research paper is to develop an understanding of how raw materials are mixed with chemicals during the leather manufacturing process, along with the economic, environmental, and human costs associated with leather goods. The entire life cycle for leather products, from the beginning to the end of the product’s life, involves an array of chemicals and materials. When we assess these materials throughout the full life cycle, we begin to see how much impact the materials have on our health and environment.

Leather is a material that comes from the hide (skin) of an animal. The most common domestic animal sources are livestock animals, including cows, pigs, sheep, and goats. Exotic leather is formed from the hides of wild animals, including crocodiles and snakes. The use of leather for clothing and shelter dates back to prehistoric times. In modern times, leather is widely used for a variety of products, from clothes and shoes to car seats and furniture. Products made of leather are generally considered more luxurious and upscale than similar products crafted of manmade materials. However, the use of leather is not without controversy, as many animal advocates take the position that it is cruel to produce goods using the skins of animals. The advocacy group People for the Ethical Treatment of Animals (PETA) launched a public campaign in 2012 to urge consumers not to purchase leather, and attempts to focus attention on the cruel treatment of animals farmed for their skins. “Most leather comes from developing countries such as India and China, where animal welfare laws are either non-existent or not enforced” (PETA). Other horrors discussed are the farming environments the animals are trapped in until they are slaughtered, and the inhumane ways in which they are slaughtered. Supporters of the use of leather counter that many hides are taken from meat farms and other food related industries, in order to make use of the entire animal. The meat industry is able to both profit from the use of the hides, and ensure that no part of the animal goes to waste.

Tanning is the chemical process for treating animal skins to produce leather. The process for tanning leather was invented in 1858 at a manufacturing scale, but has been seen in history as early as 7000 B.C. There are many steps that are performed when tanning leather. In the course of my research, I reviewed books on this topic and watched videos of the tanning process. While older methods of tanning used vegetable tanning and mineral tanning systems, modern tanning methods involve the extensive use of chemicals. The processes I examined took as long as two days of work, and the number of steps and multitude of chemicals used in large factories was quite alarming.

I compiled a list of chemicals and materials that were common and reoccurring, and identified about 48 chemicals and materials that are involved at some point in the leather tanning process. This number increased, however, when I started digging deeper into research studies and scientific evaluations from other countries on the use of leather tanning materials, and the effects these materials have on the environment. A paper by Dr. Javed Ahmas Chattha and M. Mobeen Shaukat notes that as many as 130 chemicals and materials were found to be used in a survey of 596 tanneries in Pakistan. This is alarming, due to the lack of regulations governing companies and factories in the developing world. Many of these chemicals have not been designated a health hazard, but others are considered to be extremely dangerous and damaging to humans and the environment. Some of these chemicals are dangerous in their raw state, others may become dangerous and hazardous when they are improperly disposed of.

The list begins with materials such as salt and lime. These are used in the early stages of cleaning and preserving the leather. Lime is introduced to the hide to help control swelling, and is necessary given that hide is raw flesh. Biocides are then added to help prevent the growth of bacteria; the hides are dipped or soaked in biocides, typically dithipcarbamates, a commonly used agriculture fungicide. Biocides are “chemicals used to suppress organisms that are harmful to human or animals health, or that cause damage to natural or manufactured materials.” (EC.Europa) The biocides, which are similar to antibiotics, end up back up in waste piles and can contaminate water supplies, posing a threat to both humans and animals. In recognition of this threat, regulations were introduced in the 1980s to address the problem of biocide waste, including mercury byproducts. Next, salts are used for curing the leather. This is to prevent water build up, and also helps with the swelling and bacterial contamination of the raw flesh. When looking deeper into the liming process, the chemical cyanide was cited in a few of the resources. I learned that cyanide, while a potentially deadly chemical, is also commonly used in a variety of manufacturing processes. This chemical, which has been used as a weapon of war in its gaseous state, can be harmful to the human central nervous system. Sodium hydroxide, also known as lye, is also frequently seen in the liming stages. It has many uses, and it commonly found in cleaning products, paint stripper, and products to straighten human hair. The toxic side of sodium hydroxide is that it can decompose proteins, is highly flammable, and it can cause chemical burns to flesh. This chemical is recommend to be stored is a safe container and can be destructive to the environment if improperly disposed of.  Chromium or chromium sulfate is also used as a major chemical component in modern leather tanneries. “As a leather industry standard, chrome tanned leather tends to be softer and more pliable than vegetable-tanned leather, has a higher thermal stability, is very stable in water and takes less time to produce” (Health Consultation Report). Chromium Sulfate (CrOHSO4) is created from chromate salts and is done through a process that involves mixing it with sulfur dioxide. Chromium is very effective in stable bonds of protein in the tanning process. Unfortunately, chromium has some of the most negative affects on the environment and those that are exposed to it.

The effects on the environment have been a main focus of the research done into leather tanning and manufacturing. This is due to the high levels of chromium that are being found in the environment during and after the leather tanning process. A great deal of industrial waste is associated with materials and the process of tanning. Waste is hazardous because the trimmings of finished material, left over chemicals, and used solutions are being dumped in the environment. These chemicals are then leaching into our water, soil and air. One thesis from the Process and Environmental Technology Department of Massey University estimated that “60000 tons of chrome tanning agents remain unutilized during the chrome tanning and might be discharged into the environment” (University of New Zealand).

Direct exposure to chromium is also a health risk; “when inhaled, chromium compounds are respiratory tract irritants, resulting in airway irritation, airway obstruction, and lung, nasal, or sinus cancer” (ATSDR). From direct contact with skin “dermatitis is related to the direct cytotoxic properties of chromium, while allergic contact dermatitis is an inflammatory response mediated by the immune system.” (ATSDR) An example from the Agency of Toxic Substances and Disease Registry website on the effects of chromium sulfate from a case study about leather tanning factory workers stated “A woman ingested 400 ml of leather tanning solution containing 48 grams of basic chromium sulfate (CrOHSO4). The patient died of cardiogenic shock, complicated by pancreatitis and gut mucosal necrosis and hemorrhage” (ATSDR). One of the studies I reviewed was conducted over a ten-year period by the U.S. Department of Health and Human Services on a former tannery in Arizona. The study disclosed many alarming problems with chromium waste, soil analysis, and high potential for human harm. (The tannery that was the subject of the study appears to no longer in production). The case study done on Pakistan tanneries states that “the mixing of chromium in poultry feed could produce serious human health problems. It is estimated that for a tannery producing on an average 10,000 kilograms of skins per day, a total of about 5,500 kilograms of solid waste would be produced per day” (A Case Study of Pakistan). As noted above, the tanning process involves a multitude of toxic chemicals that pose a risk to leather workers, and have negative effects on the environment in the recycling and dumping of waste chemicals in later stages.

In addition to the tanning process, I also examined the dying process. However, I found it more difficult to obtain detailed information about the processes that produce colored leather. While I was able to identify numerous types of dying processes, it is not readily apparent what chemicals and materials are associated with them. This lack of transparency is due to patents that firms hold on the dying processes, and the fact that many have extremely completed chemistry components. However, I was able to learn that “typically anionic acid dyes are used and this category consists of a number of chromophores which provide us with a wide range of colors and performances” (AAQTIC). The process by which a chemist has to mix these chemicals is said to be very challenging, and the right levels of toxicity must be reached in order for the leather to color properly. The main chemicals I found used in this stage of leather manufacturing are salt, carboxylic, and sodium chloride. In recent years, U.S. dye houses have had strict regulations enforced, and dyes must be water-soluble. For the safety of workers, orthotoluidine has been banned, as it causes cancer and liver damage, and contaminates the environment. For more detailed information on the chemicals utilized in the leather dying process, please refer to the chemical charts and formulas at the conclusion of this paper.

The chemical waste and byproducts noted above are not the only risk to human health and the environment. After the leather product is manufactured, there are unwanted pieces of leather left over. These clippings, as they are known, are shown in the image at the conclusion of this paper. Clippings are abandoned, or resold as feed for animals, or are used as inexpensive seating in poor villages and factory towns. Sadly, many of these clippings find their way into our oceans, landfills and water sources. While leather can decompose or break down, this takes fifty to one hundred years, and in the meantime the chemicals used to tan and dye the leather leach out into are environment. There are also examples of leather pieces as old as 5,000 years old, so clearly the idea of allowing leather to simply break down over time is not feasible. Leather can be repurposed and reused, which would be ideal, but the majority of leather clippings are discarded in landfills or burned.

Overall during this research project, I was amazed at the amount of research and environmental studies that have been conducted and are currently in progress examining the health and environmental implications of leather manufacturing. The research varies greatly depending on the country in question and the author’s area of interest/study. During the early stages, I noted that most studies cited about 48 chemicals, only a handful of which are being blamed for pollution. These numbers came from U.S. studies and companies. When I started reading reports from universities in other countries and health reports, I was shocked to see the number of materials/chemicals jump into the 130 range. This seemed to be related to the lack of regulations and concern for the well being of the workers or environmental contamination in the developing world. One thesis was 243 pages on just two chemicals. These two chemicals were the in chromium family. I also was surprised as how much material waste was linked to this industry. After evaluating the amount of chemicals and materials that are used during the leather textile process, my opinion on leather being natural has changed dramatically. While consumers may believe the marketing that real leather is a natural product and thus superior to synthetic leather, the reality is much more complex and troubling. Given the growing global demand for leather products, as well as the economic importance of this multi-billion dollar industry, the best solution may be to find healthier and more sustainable methods for producing leather goods or if possible try and cut down on global consumption it its entirety.

Bibliography

"ATSDR - ToxProfiles - Redirect." ATSDR - ToxProfiles - Redirect. Web. 08 Mar. 2014.

"Biocides - Chemicals - Environment - European Commission." Biocides - Chemicals - Environment - European Commission. N.p., n.d. Web. 08 Mar. 2014.

Cabeza, L. F., et al. "Processing of leather waste: pilot scale studies on chrome shavings of potentially valuable protein products and chromium." Waste Management 18.3 (1998): 211-218.

Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 20 Sept. 2012. Web. 08 Mar. 2014.

Chattha, Dr. Javed A., and Mobeen Shaukat. "An Assessment of Environmental Concerns in the Leather Industry and Proposed Remedies: A Case Study of Pakistan. "Environmental Expert.” Web. 8 Mar. 2014.

Covington, Tony. Tanning Chemistry: The Science of Leather. Cambridge: RSC, 2011. Print.

"Environmental Hazards of Leather." PETA. Web. 27 Jan. 2014.

Kite, Marion, and Roy Thomson. Conservation of Leather: And Related Materials. Oxford: Elsevier Butterworth-Heinemann, 2006. Print.

Kumar, Arvind. Industrial Pollution & Management. New Delhi: A.P.H., 2004. Print.

Lancaster, M. Green Chemistry: An Introductory Text. Cambridge: Royal Society of Chemistry, 2002. Print.

"Minimising the Environmental Impact of Chrome Tanning : A Thesis Presented in Partial Fulfilment of the Requirement for the Degree of Doctor of Philosophy in [the] Process and Environmental Technology Department in Massey University, Palmerston North, New Zealand." Minimising the Environmental Impact of Chrome Tanning : A Thesis Presented in Partial Fulfilment of the Requirement for the Degree of Doctor of Philosophy in [the] Process and Environmental Technology Department in Massey University, Palmerston North, New Zealand. DasGupta, Samir, 1996. Web. 08 Mar. 2014.

Page, Campbell, Jens Fennen, and Daniel Gagliardino. "Leather Dyes – Properties and Analysis Leather Dyes – Properties and Analysis." Http://www.aaqtic.org.ar/congresos/china2009/oralPresentation/1-25.pdf. Web. 8 Mar. 2014.

Watt, Alexander. The Art of Leather Manufacture. London: Lockwood, 1897. Print.

Leslie Lopez

998318668

Design 40A

Christina Cogdell

March 13, 2014

Leather Wastes and Emissions

In beginning my research for natural leather, I had high expectations. The practice of making leather has been one of the oldest human activities, so I figured that there would be a great abundance of information. My results were much more than I could fathom. I believe that the abundance of information that I found comes from not only the longevity of the process, but also from the great controversy behind it. Many, like myself, have always assumed that while there may be cruelty issues when it comes to the production of leather, that it has no real damaging effect on the environment since it is “natural”. In reality, this is quite the opposite. The process of producing leather results in waste emissions such as waterborne wastes, airborne wastes, solid waste, and in fact some actual useable products (Figure 1 has a specific details on the amount of input and output that occurs in this process (Joseph 681)). A major problem that contributes to most of this waste is the fact that the leather is chrome tanned. While some leather can be vegetable-tanned, chrome tanned leathers have “improved mechanical resistance, extraordinary dyeing suitability and better hydrothermal resistance” when compared with vegetable tanned leather (Swarnalatha 290). Chromium can enter the air, water, and soil in the common forms of chromium (III) and chromium (VI) through natural processes and human activities ("Chromium-Cr."). When it comes to the production of leather, both the concentration of chromium (III) and chromium (VI) are increased ("Chromium-Cr."). There are more immediate and obvious harms that can be seen when analyzing leather's production process. People who work in and around tanneries begin to have serious health risks. In Kentucky, a person can be five times more likely to have leukemia when living near a local tannery and in Sweden and Italy, a tannery worker can be 20% to 50% more like to get cancer due to the arsenic exposure ("Environmental Hazards of Leather."). In most developing countries where tanneries are located, tannery workers are often residents of the local community. The workers then suffer from a “double-edged problem”: as a resident, “they face surrounding environment problems directly”, and as a tannery worker, they “suffer from detrimental chemicals and wastes that are generated in the tannery itself” (Biswas 46). Tanneries in different part of the world produce different amounts of waste and are regulated quite differently. This will determine exactly how much damage is done to the surrounding environments and communities, including workers and residents.

 There is an abundance of waterborne waste throughout the life cycle of leather. While many believe that the production of leather starts at the tanner, its actual origin is much earlier. Hides arrive to a tannery as a by-product of meat (Cabeza 211), but we need to look back at farms, as to not overlook wastes that are produced from the raw materials. Raising the animals whose skin will later be used for leather creates a considerable amount of waste. Not only do these animals (usually cows and pigs) create 130 times more excrement than the human population (notably also without the benefit of waste treatment plants), but runoff from feedlots and dairy farms also create a major source of water pollution, reaching the point where the EPA has acknowledged that livestock pollution is the greatest threat to our waterways (“Environmental Hazards of Leather”). Once the hides reach the tanneries, the waste water is polluted by much different things. These pollutants includes things such as salt, lime sludge, sulfides, and acids, which can stabilize the collagen or protein fibers in the hides so that they actually stop biodegrading (“Environmental Hazards of Leather”) as well as allowing dyes to be resistant to degradation or fading (L.C. A. Oliveira 344). In the U.S. (as will be discussed in later paragraphs), regulation has improved and is continuously being developed in order to maintain waste. Especially when concerning water. However in other countries, the situation is far worse. Take for instance, Bangladesh, which is one of the poorest countries and has one of the lowest wages (Wages – Countries -List). Bangladesh (from a report from 2008) has about 313 tanneries and counting, in which 300 of them are currently in the city of Dhaka (Biswas 46). Waste is so poorly regulated in this country, so much that “22,000 cubic meters of environmentally hazardous liquid waste is emitted from them every day, flowing into the Buriganga River, Dhaka's main water way” (The America Tonight Digital Team).  It is completely eye-opening to see the huge amount of waste that is produce, not monthly, yearly or even weekly, but every single day. Not only that, but this waste is feeding right into their main waterway, polluting their drinking water. In the same Bangladesh city, there is a body of water centered around a local community that is ridden with waste. The children play in this water and residents say that the smell is also putrid, causing people to violently vomit ("Bangladesh: Toxic Tanneries."). Inside the tanneries, the beginning steps of producing leather, involve substances that can be found in wastewater. In the soaking process (removes blood, dung, and other dirt), “water, anti-septic and detergents that are used to clean skin and hides” are found in the wastwater (Biswas 50). Unhairing, liming (which swells up the flesh), de-liming (removes the lime from the previous process), batting (removing and excess hair), and tannings all use a multitude of chemical, which is not specified in this study (Biswas 50). In this same paragraph, Biswas also states that “workers do not touch the chemical directly”, but in my research I found a slideshow (The America Tonight Digital Team) that contradicts this statement. In Figure 2, you can clearly see how barefoot workers directly touch the chemicals and directly handle the hides. Since water is such a precious commodity, especially in these “developing” countries, research is continuously being done to bring more awareness to how much waste is being produced in these bodies of water and how harmful they can be.
Airborne waste is slightly more difficult to track as opposed to waterborne waste, but nonetheless, the results shows that this type of waste can be just as harmful. As mentioned before, arsenic, which is a chemical that is often used by tanneries, has been has “long been associated with lung cancer in workers who are exposed to it on a regular basis” ("Environmental Hazards of Leather."). This is only the tip of the iceberg. Joel Schwartz, who in his study analyzes the interesting topic of the correlation between air pollution and daily mortality (Schwartz 42), discusses how the fumes, dusts, and malodors can affect the lungs of workers (Biswas 48). Especially in developing countries, where factory settings are discarded in order to optimize profit, airborne waste can severely affect the workers and community. One example of poor management of airborne waste is in the Moti Tannery in Bangladesh (one note on my research is that the majority of information on poor waste management or poor regulation and upkeep of tanneries dealt with tanneries in Bangladesh). In this tannery, the structure is detrimental to any idea of proper management of airborne releases. On the main floor “there are no windows or extra doors apart from the main gate” and inside the only ventilation are the “two ventilators with adjuster fans (that do not even work)” (Biswas 48). This only allows for the airborne wastes to escape more easily and reach the surrounding communities faster. In a study done by Shen et. al. in Taiwan, benzene, toluene, xylene, and formaldehyde, which are common air pollutants in the industry, are often exposed to the workers in a vapor form, have poor solubility in water, and have a high toxicity (especially formaldehyde) which can often cause asthma, aplastic anemia, and leukemia, even cause abortion or fetus malformation in humans (Shen 997). In another case study, research was done on a leather upholstery company and the air emissions they produce in transportation. In Figure 3, you can see their chart that show the specific amounts for different emissions from each trial and in total. While they do not provide specific detail on how, this study states that after this study, the supply chain reengineered the system in order to reduce greenhouse emissions (Yazan 340). These wastes are only by one single supply chain, so to imagine that that amount of waste exponentially multiplies brings up the thought of how our air isn't completely toxic yet.

To begin on solid waste, I have to bring up some comments on my research. Solid waste throughout the life-cycle of leather was particularly hard to track in comparison of other types of waste. Most articles are very general in discussing solid waste, rarely divulging into the specific contents. In a very general sense, solid waste can be divided into 3 different categories. The total amount of solid waste from the life cycle of leather is about 1317 kg, from which “1040 kg is biodegradable and that was due to the slaughtering, tanning and finishing stages, 183 kg is non- biodegradable that was due to the tanning, finishing and electricity production stages and 95 kg is hazardous, mainly from the tanning and finishing stage of leather life cycle“(Joseph 679). The main types of solid waste that are commonly present in the beginning stages of production are the trimmings from the preparation of hides for processing, fleshings from the removal of excess flesh and fatty substances, lime trimmings from the removal of hair, and splits and shavings from the adjustment of hide thickness (Cabeza 212). As will be discussed later on (on the topic of creating useful by-products from waste), other forms of solid wastes as seen from the Yilmaz study are chromium-tanned shavings, vegetable-tanned shavings and buffing dust. Since buffing dust is so highly concentrated in trivalent chromium and other organic and inorganic compounds, its discharge from the tanneries can cause “severe groundwater contamination on land co-disposal and chronic air pollution during thermal incineration (Swarnalatha 290). Solid waste is usually sent straight to landfills, which as we know are growing rapidly. Because of this, we need to come up with strategies to put a stop or at least slow down the amount of waste production.

In the U.S., the Environmental Protection Agency (EPA) has kept a close regulation on waste. Under a federal law, the Resource Conservation and Recovery Act of 1976, there are steps that need to be taken in order to properly rid of hazardous waste. While these methods discuss what to do with present waste, the government has implemented legislation to attempt to limit future waste and toxic materials as much as possible. The RCRA has attempted to regulate and slow down the mass volume of solid waste that is produced. When it first passed, the RCRA implemented “an Office of Solid Waste within the EPA”, a “cradle-to-grave system for regulating waste”, and encouraged states to develop their own “solid waste control plans including provisions for closing open dumps” (Andersen 646). This is making baby steps towards better waste regulation. The EPA has also implemented some crucial steps in order to keep track of waste. According to the EPA, there is a life cycle to the manufacturing and upkeep of waste. There are fourteen steps in total, which could differ due to a number of variables. These steps include identifying waste, counting waste, determining generator status, obtaining EPA identification number, placing waste in accumulation unit, implementing LQG emergency procedure requirements, preparing contingency plan, implementing personal training,  contracting with hazardous waste transporter, following U.S. department of transportation procedure standards, preparing hazardous waste manifest, preparing appropriate notification and certification, sending waste off site for treatment, storage or disposal, and preparing biennial report (RCRA in focus: Leather manufacturing 7). In the U.S. we are slowing making our way towards progress, but we also need to focus on the fact that a massive amount of waste, and possibly the majority amount, is being produced in developing countries. In these countries, the tanneries are not under regulation and are rapidly offsetting the U.S.'s progress.

The massive amount of waste produced around the world from the production of leather is rising and as we've seen, waste management attempts are being made to prevent and manage the waste. While the waste that results from the production of leather has proven to be hazardous and to be accumulating more than we are reducing, there are studies that are being done to find some use with certain components of the waste. This way, we create a byproduct that can be used for other processes. Due to a relatively large specific surface of solid tannery waste (approximately 10 m2 g−1 (F. Langmaier)) it is possible to use this waste for decontamination of textile industry wastewater, which contains organic dyes. This method has been proposed (L.C.A. Oliviera 344) to remove methylene blue and reactive red textile dye from aqueous residues. There is another study in which the process of pyrolysis (heating carboneous material in an inert material) is being analyzed to turn the chromium-tanned shavings, vegetable-tanned shavings and buffing dust from leather into actual useful products (Yilmaz 437). What this study found was that this type of leather waste, by pyrolysis, could be converted into gas, which can be used for fuel; oil, which can be used as either fuel or as raw material for chemicals; ammonium carbonate; and carboneous reside, which can be burnt as fuel or safely disposed of (Yilmaz 437). Yet another method to make solid waste productive is to enhance it to make it suitable for mineral nutrition for mineral plants. The process involves taking the solid collagenic material from the solid waste of wet blue leather and enriching it with mineral P and K to produce NPK formulations and the results show that the “application of PK enriched-collagen formulations resulted in N contents in the vegetative parts and grains of rice plants which were equivalent or superior to those obtained with urea and commercial NPK formulations” (Nogueira 1064). Along with waste reduction, methods of making use of waste can at least put a dent in the amount of waste that leather produces.

Leather turned out to be a surprisingly interesting topic. I wrongly assumed that leather would be an almost harmless textile, when in fact, it resulted in being one of the most toxic things i've seen. Throughout the entire life-cycle, our water is being polluted, our air is being polluted, emissions are being put out into our environments and it is damaging our earth severely. Not only our earth, but our community as well. I have discovered that the waste and emissions that leather produces has blurred the lines between environmental and social. Adults and children alike are suffering the consequences that this industry has brought about. It is astounding, especially considering the fact that I still do not know the whole story. On a more positive note however, I believe that if on a global scale we can improve waste management and regulation, and if it kept consistently improving, and with new methods of transforming waste into by-products, this can be something that be fixed.

Bibliography 

Andersen, Roger W. "Resource Conservation and Recovery Act of 1976: Closing the Gap, The Gap."Wis. L. Rev. (1978): 633.

"Bangladesh: Toxic Tanneries." YouTube. 09 Oct. 2012. YouTube. <http://www.youtube.com/watchv=kT3xjfxMmoc>

Biswas, Salauddin. "The Effect of Working Place on Worker’s Health in a Tannery in Bangladesh." Advances in Anthropology 03.01 (2013): 46-53. Scientific Research Open Access. Web.

Cabeza, L.f., M.m. Taylor, G.l. Dimaio, E.m. Brown, W.n. Marmer, R. Carrió, P.j. Celma, and J. Cot. "Processing of Leather Waste: Pilot Scale Studies on Chrome Shavings. Isolation of Potentially Valuable Protein Products and Chromium."Waste Management 18.3 (1998): 211-18. ScienceDirect. Web.

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Covington, Tony. Tanning Chemistry: The Science of Leather. Cambridge: RSC, 2011. Print.

"Environmental Hazards of Leather." PETA. N.p., n.d. Web. 27 Jan. 2014.

F. Langmaier, verbal communication. Tomas Bata University in Zlin, Faculty of Technology, Zlin, Czech Republic, langmaier@ft.utb.cz.

Joseph, Kurian, and N. Nithya. "Material Flows in the Life Cycle of Leather."Journal of Cleaner Production 17.7 (2009): 676-82. Science Direct. Web.

Kite, Marion, and Roy Thomson. Conservation of Leather: And Related Materials. Oxford: Elsevier Butterworth-Heinemann, 2006. Print.

Kolomaznik, K., M. Adamek, I. Andel, and M. Uhlirova. "Leather Waste—Potential Threat to Human Health, and a New Technology of Its Treatment." Journal of Hazardous Materials 160.2-3 (2008): 514-20. National Center for Biotechnology Information. Web.

Kumar, Arvind. Industrial Pollution & Management. New Delhi: A.P.H., 2004. Print. 

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Nogueira, Francisco G.e., Isabela A. Castro, Ana R.r. Bastos, Guilherme A. Souza, Janice G. De Carvalho, and Luiz C.a. Oliveira. "Recycling of Solid Waste Rich in Organic Nitrogen from Leather Industry: Mineral Nutrition of Rice Plants."Journal of Hazardous Materials 186.2-3 (2011): 1064-069. ScienceDirect. Web,

Oliveira, Luiz C.a., Maraísa Gonçalves, Diana Q.l. Oliveira, Mário C. Guerreiro, Luiz R.g. Guilherme, and Rogério M. Dallago. "Solid Waste from Leather Industry as Adsorbent of Organic Dyes in Aqueous-medium." Journal of Hazardous Materials 141.1 (2007): 344-47. ScienceDirect. Web. 

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Swarnalatha, S., T. Srinivasulu, M. Srimurali, and G. Sekaran. "Safe Disposal of Toxic Chrome Buffing Dust Generated from Leather Industries." Journal of Hazardous Materials 150.2 (2008): 290-99. ScienceDirect. Web. 

The America Tonight Digital Team. "Slideshow: The surprising hell of Bangladesh's toxic leather tanneries." Aljazeera America. 4 Dec. 2013. <http://america.aljazeera.com/watch/shows/america-tonight/america-tonightblog/2013/12/4/bangladesh-s-toxictanneriesperhapshowhelllooks.html>.

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