Pollution Caused by the Tannery Industries in Bangladesh

Leather business has been clearly proclaimed as a successful money making business now a days, though a dark side is lying behind it. Along with money, it’s chaining a shocking future for us. The profit makers are willingly or unwillingly pushing the workers in a toxic environment which are making them sick in a gradual rate. Sometimes the chemicals used in these industries are really cheap and toxic. The surroundings of the industry are not congruent for living at all. The community situated close to the industry area is not safe from the pollution of water, soil or air. So it became necessary to take some ventures to surpass the state.

Leather is a substance created from imputrescible hides or skins to a putrescible, durable and flexible form. Again tanning is the process to make leather by treating those raw hides and skins. The place where the process is done is called tannery. The term "tannin" goes for the chemicals used in it. Many operations are involved to make it ready for using. Before tanning, the hides or skins have to pass through for unhairing, trimming, desalting, degreasing and soaking. The principle method for making leather is the same over years. Curing is for preserving the skin to stop them deteriorating by salting, chilling and freezing. The cured hides or skins are then soaked in water. The main work of liming is to remove hair of pelt through alkaline medium. The medium then has to be brought under slightly alkaline condition by deliming process. Bating and pickling are the last operations before chrome tanning.

There are varieties of tanning process like chrome tanning, vegetable tanning, Aldehyde tanning, Aluminum tanning and so on. But the revolution came with the chrome tanning. The main theme is chromium salts react with sodium hydroxide followed by dissolution of chromium tri hydroxide in sulphuric acid. The result of chromium salt in final discharge may bring toxins in the environment. The main pollutants found during leather processing include, NaCl and pesticides, strong alkalines and sulphides, inorganic residual compounds, dissolved matter and chromium salts. Chlorinated phenols are important compounds to be investigated due to the various mixtures used in the tanning industry and their exotoxicity potential. 

Hazards due to environmental contamination, depend on its oxidation state (i.e. hexavalent stage of chromium (Cr6+) is more toxic than the Cr+3 which precipitates at higher pH. Trivalent chromium is unable to enter into cells but Cr6+ enters through membrane anionic transporters. Intracellular Cr6+ is metabolically reduced to Cr+3. Cr6+ does not react with macro-molecules such as DNA, RNA, proteins and lipids. However Cr+3 and the reduction of intermediate Cr6+ are capable of coordinated covalent interactions with macro molecules. Tanning one ton of hide typically results in 20 to 80 cubic meters of wastewater with Chromium concentrations around 250 mg/L and sulfide concentrations at roughly 500 mg/L. Chromium pollution by tannery operations are ranked within the top ten pollution problems by the Blacksmith Institute.

While all hexavalent chromium compounds are being freed in the environment, they are considered carcinogenic to workers. The length of time for workers brings more risk for lung, nasal and sinus cancer. The Centers for Disease Control and Prevention found that the incidence of leukemia among residents in an area near one tannery in Kentucky was five times the U.S. average. Arsenic, a common tannery chemical, has long been associated with lung cancer in workers who are exposed to it on a regular basis. Studies of leather-tannery workers in Sweden and Italy found cancer risks ͞between 20% and 50% above [those] expected. Skin problems are common factor for workers. Again, chromic acid is a reason for eye damage, ulcers, kidney disease and asthma.

Formic acid is also introduced in tanning process. This acid is an inhibitor of the mitochondrial cytochrome oxidase causing histotoxic hypoxia. Formic acid is a weaker inhibitor than cyanide and hydro sulphide anions. The body burden of format in methanol poisoning is high enough to cause acidosis, and other clinical symptoms. This happens due to reactive oxygen in the molecule. By releasing Hydrogen from the acid chain, the oxygen becomes very much reactive.

Again the effluent of tanneries after tanning process causes serious damage to the nature. As tanneries don't have alternative drainage system, they release the tanning liquor in the local drain lines or sewerage. Flow of sewerage leads the liquor to the closest rivers or canals connected to it. As a result, rivers and canals are getting more polluted day by day. Dead fishes and insects are found often. Hence the air is getting polluted. Ecosystem related to these canals, are getting affected in many ways.

Tanning liquors are mixture of various acids and alkalies. In usual cases, some acids and alkalies remain unchanged after tanning process. As tanneries of Hazaribagh, didn't maintain any treatment process for tanning liquor, it went out raw in nature and caused terrible harm to environment and its beings.

Pollution can be minimized with the proper management of dismissal of effluent if the wastage is handled in an accurate course. The acidic and basic mixtures should be neutralized and the sulfides should be oxidized to sulfates. Chromium tanning liquors can be re-used so the chromium that contains can be recovered. Most first-world countries have strict environmental regulations to ensure that these chemicals are handled properly rather than being discharged, unfortunately, some developing nations don't. However, as chromium is the main culprit in the production, some methods of reducing the compounds can be applied such as coagulation and filtration.

The tanneries ruled the Hazaribagh area more than four decades. But as the pollution was exaggerating the government took the decision to shift the industries to Hemayatpur, Savar. The place is now called "leather polly". A good structure for reducing the pollution has been drawn carefully. Effluent tanning liquors are treated ETP (Effluent treatment plant). After treatment in this process, effluent of ETP has minimum chance to harm the surroundings. As a result the habitation will not face pollution close to the area.
 
Author: Maliha Chowdhury, Grad Student, Department of Leather Engineering, University of Dhaka.
 
 
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