Chromium tanning, management challenges and environmental legislation in Sub Saharan African tanneries

Abstract

Tanning of hides and skins are common practices in Sub-Saharan Africa. Tannery-based chromium wastes are sometimes crudely dumped in soils, thereby posing a risk to the population. This review paper was undertaken to understand chromium waste management and challenges on the continent. This covered chromium tanning technology, growth of the tanning industry, contemporary use of chromium tanning agent, leather tanning stages that generate chromium wastes and their management, the environmental legislation challenges. It also presents the unresolved debate about replacing chromium as a tanning agent, health effects and the future of tanneries in sub Saharan Africa. The challenges associated with tannery-based chromium waste management in Africa is also presented. From the information and data gathered we conclude that the management of chromium-based tannery waste is inadequate as these wastes continue to degrade soils ecosystems at crude dumpsites. There is a knowledge gap in the remediation of soil contaminated with chromium-based tannery waste.

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Proceedings of ICSMNR2018
15-17 October 2018, Polokwane, S.A JN Edokpayi, WM Gitari, EM Stam, SE Mhlongo (eds) ISBN 978-0-620-82267-1
38
Chromium tanning, management challenges and environmental
legislation in Sub Saharan African tanneries
RO Oruko 1*, JO Odiyo 2 and JN Edokpayi2
1Department of Ecology and Resource management, University of Venda, South Africa.
2Department of Hydrology and Water Resources, University of Venda, South Africa.
*Email of corresponding author: richardoruko@gmail.com
Abstract
Tanning of hides and skins are common practices in Sub-Saharan Africa. Tannery-based chromium
wastes are sometimes crudely dumped in soils, thereby posing a risk to the population. This review
paper was undertaken to understand chromium waste management and challenges on the continent.
This covered chromium tanning technology, growth of the tanning industry, contemporary use of
chromium tanning agent, leather tanning stages that generate chromium wastes and their
management, the environmental legislation challenges. It also presents the unresolved debate about
replacing chromium as a tanning agent, health effects and the future of tanneries in sub Saharan
Africa. The challenges associated with tannery-based chromium waste management in Africa is also
presented. From the information and data gathered we conclude that the management of chromium-
based tannery waste is inadequate as these wastes continue to degrade soils ecosystems at crude
dumpsites. There is a knowledge gap in the remediation of soil contaminated with chromium-based
tannery waste.
Keywords: Environmental legislation challenges, Remediation, Sub Saharan Africa tanneries, Tannery
based chromium waste.
1. Introduction
Chromium is the 21st most abundant element in the earth’s crust and exist in levels up to
100 ppm [1-2]. It is an essential micronutrient for living organisms. Cr (III) is an essential
trace element known for its particular role in the maintenance of normal carbohydrate
metabolism in mammals. [3]. Chromium III is widely used as major chemicals in leather
tanning because of its stability that helps protect raw skin from degradation by the
microbes, enzymes and environmental factors. However, it remains a subject of
environmental controversy and dispute because of its toxicity and hazardous nature in the
environment [2]. Environmental impacts of Cr (III) wastes from tanneries have been a subject
of extensive scientific and technical debate. Assumptions that complete oxidation of all forms
of Cr (III) to Cr (VI) will occur and that Cr (VI) will be completely reduced to Cr (III) if the
wastes are mixed with soil at crude dumpsites as commonly practised in Africa currently are
untenable and not based on scientific findings [2]. Thus, the need to review chromium wastes
disposal in the sub Saharan African tanneries and propose practical techniques for policy
makers and tannery managements to adopt in future.
2. Methods
Desktop review of one hundred and fifty-nine publications was undertaken; on topical
areas like historical evolution of chromium tanning technology, contemporary use of
chromium, growth of the tanning industry on the continent, the unresolved debate about
replacing it as a tanning agent, its wastes, their management and the environmental
legislation challenges in the sub Saharan African tanneries. It was supplemented with

Proceedings of ICSMNR2018
15-17 October 2018, Polokwane, S.A JN Edokpayi, WM Gitari, EM Stam, SE Mhlongo (eds) ISBN 978-0-620-82267-1
39
administration of questionnaires to more than seven key informants in the sector from
selected countries in the continent to generate and correlate more data.
3. Result and Discussion
Historically leather tanning came about either by accident or by trial and error as man
discovered methods of preserving and softening leather by treating raw animal skins with
smoke, oils, minerals and bark extracts from plants [4]. Infogalactic states that, the first use
of animal skins is attributed to Australopithecus habilis was roaming East Africa some two
million years ago [5]. They used skins structures believed to have been warmed by fire
which created a curing effect. This dried the skins slowly. The other earliest tanning methods
were based on the use of vegetable and alum but in the nineteenth century, these tanning
techniques were later supplemented with chrome tanning. This method is still in use today
and accounts for about 80-90% of all tanning done globally [6]. Chrome tanning became
the tanning method for modern footwear and fashion leathers. It produces soft, supple,
beautiful and fine leathers [7]. The technique was discovered in 1858 by Knapp. The first
commercial chrome tanned leather was produced in 1884 by Augustus Schultz of New York
[8,9].
The main reaction between chrome and collagen fiber takes place when the positive
charged chrome tanning agent bind with negative charged collagen carboxyl group by
coordinate bond to fix the structure of collagen fiber and to give tanning effects, such as
thermostability, chemical resistance and flexing endurance as shown in Figure 1.
Figure 1. Cross link between hydrated chromium ion and carboxyl group of the collagen
[10].
In most African countries, commercial chrome leather industries were established as
export-based industry of semi-processed raw hides and skins with no consideration given to
linking them to the development of a finished leather and leather products industry [11].
African leather industry development can therefore be categorized into three levels:
developed – Egypt, Morocco, Tunisia and South Africa; Fairly developed – Eastern and
Southern African countries including Ethiopia and Zimbabwe; Relatively under-developed –
most of West African countries [12]. Figure 2 gives their regional distribution and total
numbers in the continent.
Tanneries found in Africa range from modern and well-equipped commercial ones to
the small and outdated ones known as artisanal tanneries, respectively [13,14]. Most
tanneries in the continent face a lot of challenges that range from lack of space (to install
waste management facilities), technical expertise, adequate capital (to build up individual
wastewater treatment plants), poor quality of raw materials, market access, political

Proceedings of ICSMNR2018
15-17 October 2018, Polokwane, S.A JN Edokpayi, WM Gitari, EM Stam, SE Mhlongo (eds) ISBN 978-0-620-82267-1
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changes and civil unrest. Other challenges include the importation of second-hand tannery
products such as footwear and counterfeit footwear. Inadequate infrastructure and
transportation, lack of foreign direct investment (FDI), inadequate infrastructure and
processing equipment and facilities. These challenges often lead to the generation of toxic
waste [11-14].
Figure 2: Regional distribution of tanneries in Africa [14].
To overcome these challenges, requires joint efforts of governments and tannery owners.
There are also environmental concerns associated with the discharge of unused chromium
effluent and the safe disposal of solid waste containing the metal ion. This has also brought
the debate on how to replace chromium with other safe tanning agents like zirconium and
titanium, but they have low shrinkage temperature in comparison to chromium. Some expert
believe it is hardly feasible to reproduce all the features of chrome tanning with another
material. They argue that the mechanism of chrome tanning has not been understood to the
required level of resolution to help the development of alternatives [15, 16]. Therefore,
there might be a need for a review to find areas for tanners and research institutes to
collaborate and carry out more detailed studies. This could help with the development of
the most appropriate tanning agent to replace chromium.
70% of the key informants and the reviewed literature confirmed that, the two most
polluted waste streams in a tannery are the beam house wastes and the tan yard wastes.
Beam house waste is highly alkaline and usually has high organic contents. The tan yard
wastes are highly acidic and contain high concentrations of chromium [9]. The forms of wastes
generated range from chrome sludge, splits, wet blue shavings, trimmings, crust trimmings,
buffing dust, vegetable tanning extracts, mineral acids, alum, fatliquors, acid dyes, solvent
coatings, pigments, and sodium chloride. In addition to dirt, manure, fleshings, grease,
residual hair, proteins, oils, unfixed tan liquors and accidental spillover of chromium
chemicals [9]. These wastes often end up in the environment without proper treatment.
The current waste treatment technologies employed in Africa include landfilling, open
dumping, incineration, composting and occasional recycling (Figures 3-4). The tannering
0
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150
200
250
300
350
400
450
North Africa Eastern
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Central
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Southern
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West Africa
No of Tanneries
Regions of Africa

Proceedings of ICSMNR2018
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waste is either packed in sacks or crudely dumped in the open spaces as shown in Figure 4.
Combustion of chromium containing wastes (Figure 3) can lead to the oxidation of trivalent
chromium into hexavalent chromium, which is considered a carcinogenic compound [17]. This
poss a direct health risks to tannery workers and other people living or working in close
proximity to the tannery.
Figure 3: Tannery wastes crudely dump in sacks and burnt in the open space and kiln in a
tannery in Kenya (Oruko, 2017).
Figure 4. Dried chromium cake dump inside a tannery compound in Kenya (Oruko, 2018).
During precipitation events rain water percolates into the dumped tannery waste
leading to the formation of highly toxic leachates which often infiltrate through the soil and
contaminate groundwater. There is also a possibility of the oxidation of Cr (III) to Cr (VI)
during disinfection of Cr- contaminated water for human consumption. This poses a threat to
public health. Large areas around such dumpsites are also rendered unsuitable for living
and other activities [18].
Landfills remain the prefered disposal method globally for most solid wastes, but well
managed landfills are not available in many African countries. Chromium wastes end up,
polluting the ecosystems like soils and endangering human health. Therefore, a number of
tanneries have been closed in a number of countries in Africa for failure to meet wastewater

Proceedings of ICSMNR2018
15-17 October 2018, Polokwane, S.A JN Edokpayi, WM Gitari, EM Stam, SE Mhlongo (eds) ISBN 978-0-620-82267-1
42
sewer acceptance limits, odour nuisance and polluting small water courses [13, 19].
Although some governments have closed polluting tanneries but there are weak policies in
place on how to remediate such sites. Sustainable bioremediation techniques may be
required for contaminated sites in future. This is necessary due to the fact that those sites
continue to pose a health risk to tannery workers who grow food crops like kales, spinach
and tomatoes on them as shown in Figure 5.
Figure 5. Spinach and Kales grown next to tannery dumpsites in South Africa and Kenya
respectively (Oruko, 2018).
Despite the many difficulties faced in implementing tannery pollution control in Africa,
important regulations and pollution prevention measures have been introduced, especially
in Ethiopia, Kenya, Namibia, Tanzania, Tunisia, Zambia and Zimbabwe [12]. Some
legislations have a check on the quality of treated effluents; while others on the quality of
the recipient water bodies; some specify the permissible levels of impurities to be dis-
charged per day into the recipient water body, whereas in some cases specifications are
linked to the total amount of waste water discharged. Some countries have also made
regulations related to production, import and sale of leather products with regard to
hazardous substances. These legislations face challenges like low parameters values that
seems impossible to reach. Their imposition by politicians who have no knowledge of
environment problems, lack of capability to manage and implement the norms and lack of
structures and experts to control and implement environmental laws need the attention and
review of policy makers [13, 20]. In some cases, industries are encouraged to keep their
plants operating as laws requiring treatment of wastes sometimes result in low production
capacity that does not enable them to compete with other industries globally.
In developed countries, leather industries have invested time and resources in
conforming to environmental protection laws. This has been achieved mainly by relocating
most tanneries to tanning districts where centralised treatment plants are constructed, thus
achieving economies of scale [14]. The reviewed literature and response from 45% key
informants show that the tanning sector in Africa is finding it difficult to comply with
environmental regulations, when there is strict enforcement of norms. They face challenges
in cost effectiveness. Therefore, there may be a need in future for the governments to work
with tanners and other stakeholders to address these shortcomings in the sector.

Proceedings of ICSMNR2018
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4. Conclusion
The tanning sector in Africa is still faced with numerous challenges which are summatable
if all the relevant stakeholders from the government, private enterprise and tanneries
owners work together. The management of chromium waste from tanning industries is
inadequate on the continent. The waste will continue to degrade soil and water ecosystems
at crude dumpsites. Thus, the need for policy makers and tanners to come up with sustainable
management and remediation strategies for chromium contaminated sites.
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