This document discusses heavy metal contamination from tannery operations. During the liming process, which uses sodium sulfide and lime to dissolve hair and proteins from hides, heavy metals like arsenic, lead, and manganese are released from the hair into wastewater. Testing found these heavy metals present in hair, liming agents, and liming wastewater from cow, goat, buffalo and sheep hides. The wastewater from tanneries containing heavy metals is often discharged directly into aquatic environments, posing a threat to enter the food chain and groundwater and harm human health over time. The document recommends tanneries adopt alternative hair-saving liming processes like enzymatic treatments to prevent heavy metal pollution.

1. HAIR DISSOLVING LIMING IN TANNERIES ENHANCES HEAVY
METALS TO ENVIRONMENT
Md. Abul Hashem1*
, Md. Shahruk Nur-A-Tomal1
, Nil Ratan Mondal1
, Md. Aminur Rahman2
1
Department of Leather Engineering, Khulna University of Engineering & Technology (KUET),
Khulna-9203, Bangladesh
2
Department of Public Health Engineering, Zonal Laboratory, Khulna, Bangladesh
*Corresponding author E-mail: mahashem@mail.kuet.ac.bd, mahashem96@yahoo.com
Abstract
In tannery, liming is the first and indispensible chemical operation where conventionally
hide/skin is treated with sodium sulfide (Na2S) and lime (CaO) to dissolve keratins
(hair/wool, epidermis), non-structural proteins and to prepare for the next operations. Due to
having sulfhydryl (-SH) group in hair/wool; it acts as a good accumulator of heavy metals.
In hair dissolving liming, heavy metals content of hair/wool release into wastewater. In this
study, discharging of heavy metals was evaluated from the tanneries especially in hair
dissolving liming. Samples were analyzed from i) hair/wool of cow, goat, buffalo and sheep,
ii) conventional liming agents (Na2S and CaO) and iii) liming wastewater of cow, goat,
buffalo and sheep. Samples were acid digested; analyzed by atomic absorption spectroscopy
for the quantification of arsenic (As), cadmium (Cd), lead (Pb) and manganese (Mn).
Figure 1: Heavy metals content in (a) hair/wool and liming agents (b) liming wastewater
It was noticed that As, Pb and Mn in hair/wool, liming agents and liming wastewater were in
different concentrations nevertheless Cd was below detection limit (Fig. 1). Among the
heavy metals, amount of Mn was the highest level.
The heavy metals containing wastewater from the tanneries is directly discharged to aquatic
bodies where a fraction is adsorbed by soil/sediment. The presence of heavy metals in water
or soil can enter into food chain through various chemical or biological reactions or adsorb
heavy metals could be eluted into groundwater that could be a great threat for human health
in near future. To prevent heavy metals pollution, tanneries should follow an alternative hair
saving liming process e.g. enzymatic process.
As Pb Mn
0
15
30
45
60
75
90
105
120
135
150
(b) Sheep
Goat
Buffalo
Concentration(g/L)
Heavy metals
Cow
As Pb Mn
0
15
30
45
60
75
90
105
120
135
150
(a)
Na2
S
Buffalo
Sheep
Goat
CaO
Cow
Concentration(mg/kg)
Heavy metals