What are the Health Risks of Occupational Exposure to Adhesive in the Shoe Industry

The term “shoe” covers a wide range of products made from various materials. Organic solvents (OS) are components of various products such as the adhesives which are used in many industries. The shoe industry consumes large amounts of adhesives. This chemical risk assessment (CRA) is to validate the hypothesis of decreasing gradient of RA craft enterprises to industrial enterprises through the semi-industrial. The simplified methodology CRA of INRS was applied. For each chemical, a hazard class is assigned based on the sign, and then the potential exposure class is determined according to parameters “quantity and frequency of use”. Our RA process is complete with ambient measurements for solvents to which employees are most frequently exposed. Adhesives being constituted as solvent mixture, we have conventionally used an exposure index which is compared with the limit values. The simplified method CRA of INRS was chosen because it is one of the reference methods in RA established from the Kinney model. If these atmospheric samples and toxicology tests were made for the first time in the shoe industry in Sfax, they concerned a sample of companies of the three shoe manufacturing processes preceded by a preliminary RA with poststudy and inventory of products handled.


Introduction
The term "shoe" covers a wide range of products made from various materials. Boots, shoes, sandals, slippers, clogs, and others are made entirely or in part with leather, rubber, synthetic and plastic, cloth, rope, and wood [1]. Our study deals with the shoe industry, that is to say one based on traditional manufacturing methods. The rubber boots factory (or equivalent synthetic materials), which is one of the branches of the rubber industry, is excluded from this study [1,2].
Shoes, boots and leather sandals, felt, or other materials have been for century's hand. Quality shoes are still made entirely or partly in this way by craftsmen, but in all industrial countries, today the mass production predominates [2,3].
Organic solvents (OS) are components of various products such as paints, inks, pesticides, degreasers, solvents, and glues, which are used in many industries [1]. The shoe industry consumes large amounts of adhesives, diluents, and strippers OS bases. Consequently, the employees in this sector are likely to present particular nerve pathologies [2].

History of the shoe in the Sfax city
Sfax is an industrial and agricultural pillar of the Tunisian economy [4]. Among its industries, shoemaking is highly developed sector, which employ about 10000 employees or 10% the workforce of the nonagricultural professional environment which 6000 artisans' shoes located in the old city "the Medina." As in many cities, Sfax had a craft of the shoe. But in addition, Sfax was a shoe industry. The manufacture of the shoes to form Sfax "industrial" dates back to the nineteenth century. It was well structured in the Medina in the shoe area called "Souk Blaghgias." It consists of the main street shoes exhibition: The current street Mongi Slim known under its former name "Street of Bay." Until now, along this road for approximately 300 m shoe shops displaying their products. In the level one called "the Ally" in every store or in the neighboring streets were their own manufacturing facilities.
In 1960, after independence, observers were predicting the rapid decline and disappearance of the craft before the competition of the modern shoe industry. Now, after more than 30 years, this craft, far from having disappeared, has prospered and it feeds today, modern shoes, more than half of the Tunisian market. The artisan district of the boot has grown in the old town of Sfax; we hear all the noise of machines whose artisans are equipped to modernize the sensitive points of their manufacturing (Figure 1) [4].

Manufacturing processes of the shoe
The realization of a shoe includes several operations. Each step has been mechanized, but the manual production is used as reference. The introduction of new materials has modified manufacturing processes without changing the outline [1,2].
The manufacture of rods requires sorting and preparation of leather or other materials. The stems are cut with cutters on stitching presses (or burning). The various parties, including the linings, are then "assembled," that is to say, stitched or glued together. Perforation, eyeletting, or making buttonholes are the procedures carried out further.
In the lower part, the outer and inner soles, heels and welts are cut using cutters to moving blades or molding presses. It manufactures heels compressing leather or wooden slats. The assembly is then cut, formed, cleaned, and labeled.
The upper and lower parts of the shoe are then assembled and then stitched, glued, nailed, or screwed together. After that the shoes are shaped and smoothed by means of rollers. The finishing of the shoe includes waxing, staining, spraying, polishing, and packaging.
Among the raw materials used in manufacturing, adhesives, including adhesive solids and liquids and natural adhesive solutions prepared from organic solvents, represent the largest occupational hazards [3].

The basic products used in the shoe industry
In the industry of the adhesive and its derivatives, products intended for the manufacture of the shoe are divided into three groups [2,[5][6][7][8][9][10][11]: • Four groups of adhesive, • Primers, hardeners, and additives, • Solvents, thinners, and strippers. (Table 1) ▪ The polyurethane (PU) adhesive is used for assembling thermoplastic rubber soles (TR), rubber, polyvinyl chloride (PVC), leathers high in fat or synthetic fabrics requiring the use of high-performance adhesives.

Four groups of adhesive
▪ The polychloroprene adhesives (neoprene) are used for making coatings soles, fast repair, and bonding of natural materials (leather, rubber). They are made from synthetic resins dissolved in ketone solvents.
▪ The adhesives in aqueous emulsion (latex adhesives or white glues) may be natural or synthetic: • Natural latex adhesives are applied by machine gun or by hand. These are contact adhesives to attach soles, stitching, and lining.
• The synthetic latex adhesives are used for laying the ends and bonding liners.

Products Composition Use
Polychloroprene adhesives  The hot melt adhesive is a new generation of glue developed in order to reduce the use of solvents. It consists in applying on one of the faces to be bonded by a polymer melt temperature rise. It requires clock equipment which is expensive.

Primers, hardeners, and additives
▪ The halogenations operation of TR soles with new functions (rubber look and matt or transparent), must be strictly control any change of model. There are several formulas ready to use (one or two components) for receiving an additive to control the regular application on the soles. ▪ Catalysts, slow or fast, are used in polyurethane adhesives, polychloroprene or dispersion, as well as direct injection. They provide good resistance to the migration of fat leathers.

Solvents, thinners, and strippers
Beside adhesives preparations, there are other necessary preparations and complementary type of strippers, thinners, and solvents ( Table 2).

Applications and examples
The cleaning agent -PU soles: remove traces of mold release agent ; -PCV soles: remove surface plasticizer contained in PCV compounds The diluents -Dilute polychloroprene adhesives ; -Clean the machine to glue and brushes, spray guns stained with paint, screens for screen printing ink The solvents -Clean the rubber soles, spray guns stained with paint, screens for screen printing ink; -Dilute paints and glues.

Risks of the solvents and the adhesives on the health
According to their properties, the solvents can be used in the manufacture of the shoe, of: • Degreasing (cleaning soles, textiles…) • Additives and solvents (paints, varnishes, inks, adhesives…) • Stripping (removal of paints, varnishes, glues…) OS hydrocarbons are divided into eight main groups [12][13][14]. Six families are used in the manufacturing industry adhesives and footwear ( Table 3).
The intensive use of flammable liquids causes a high risk of fire, and the widespread use of presses and assembling machines has increased also the risk of accidents. The main danger to the health of workers is using toxic solvents, high concentrations of dust in the air, the risks due to ergonomic shortcomings, and noise from machinery.
OS can cause acute and chronic effects on the central nervous system. Benzene, which was once used in adhesives and solvents, has been replaced by toluene, xylene, hexane, methylethylketone (MEK), and methylbutylketone. The n-hexane and MEK can cause peripheral neuropathy and should be replaced by heptane or other solvents [2].
In many factories, there were outbreaks of a disease known as the "paralysis of the shoemaker" and characterized by clinical signs of a form of more or less serious paralysis. This is a flange type of paralysis, located in the upper and/or lower limbs resulting in deep tendon atrophy with areflexia, without altering the superficial or deep sensitivity. From the clinical point of view, this syndrome is due to an inhibition or a functional lesion of the lower motor neurons of the voluntary motor system (pyramidal system). Most often, it leads to a neurological regression with extensive proximodistal functional recovery [1,2].
Petroleum solvents Used as solvents in paints, adhesives and coatings: -Alkanes such as hexane (C6H14); -Cycloalkanes: The most used is cyclohexane (C 6 H 12 )

Alcohols
Very used as diluents inks, resins, varnishes, paints and glues. These are excellent dehydrating agents having good degreasing Action Example: isopropanol (or isopropyl alcohol).

Ketones
Mainly used as solvent paints, lacquers, varnishes, glues and adhesives. They are sometimes impregnated on wipes for small cleaning. They are good agents drying damp rooms.
The most commonly encountered are: acetone or MEK.

Acetates (esters)
Often mixed with other solvents, for example, in the curing products and halogenation
Examples: Trichloroethylene (degreaser leather, thinner glue) or dichloromethane (thinner adhesives and cleaner) Table 3. The families of solvents used in the manufacture of adhesives and shoes [13,15].
In the manufacture of shoes and boots, handling and leather processing can cause diseases by exposure to certain chemical substances mentioned above and in tanning and finishing. In addition, various chemicals can produce other diseases. Exposure to toxic solvents contained in adhesives and cleaning products, and to leather dust in the air is of particular concern. The use of benzene can cause thrombocytopenia (decreased number of red blood cells, platelets, and white blood cells in the blood) or pancytopenia. It has been almost eliminated from the footwear industry [3]. It was also found in some shoe factories cases of peripheral neuropathy due to n-hexane content in adhesives. This substance has also been largely replaced by less toxic solvents. Cases of electroencephalographic changes, liver damage, and behavioral alterations due to exposure to solvents have been reported in workers in the shoe industry [3].

Methods
The prevention of occupational risks, particularly chemicals, is based on the risk assessment (RA) according to the specified procedures. Thus, we realized an exposure assessment in making shoes in a sample of volunteer companies ( Table 4).
This chemical risk assessment (CRA) aims to validate the hypothesis of decreasing gradient of RC craft enterprises to industrial enterprises in passing by semi-industrial. The simplified assessment methodology for chemical risk (SAMCR) of National Institute of Research and Safety (INRS) [15] was applied only for strand "Health." For each chemical, a hazard class (HC) is assigned based on the sign, and then the potential exposure class is determined based on the parameters "amount and frequency of use."   The HC was determined only on the labeling. The allocation of HC to a preparation based on the analysis of the pictogram on the packaging ( Table 5). For preparations of glues or solvents "unidentified" (no information on the composition and/or the manufacturing company), it was decided that the assigned pictogram would be one that represents the greatest health risk and consequently the HC."  • Unidentified glue: The glue most dangerous to a symbol "Xn-Harmful" [5,11] for the health and attributed HC is "3." Thus, any unidentified glue the symbol "Xn-Harmful" and "3" class was assigned.
Adhesives being constituted as solvent mixture, an exposure index (I.exp) was used and compared with the limit values ( Table 6) [17,18]: Cn and EAVn are respectively the concentration and the average value of n pollutants exposure.
If I.exp is greater than 1, the limit value is considered outdated. Calculated from stationary sampling, this index is called pollution index (I.pol).
The potential risk score (PRS) process "industrial" 2 in case of danger class puts 13 chemical preparations to examine with high priority, including five of solvent preparations. For the HC "3," PRS do not exceed "10000," while with the hazard class "4" three of five solvent borne preparations pass a PRS 100000.
The situation of distinction for a process "semi-industrial" does not arise since we did not detect unidentified preparations. The preparations to consider with high priority are 2 solvents and 5 adhesives unidentified.
In the "artisanal" process, we have identified eight chemical preparations to examine with high priority: two solvents borne preparations and six adhesives.  Table 8. Inventory preparations "glues" used in the footwear industry and hazard class.

Atmospheric measurements
Measurements of atmospheric concentrations ( Table 9) show high levels especially in companies with semi-industrial process and type 1 craft.   Table 10. The steps of the shoe manufacturing (the welded Technique) and sources of pollution [11].
Exceedances of I.exp and/or I.pol are noted for exhibitors' positions including the upper part makers, smelters and finishing (Table 10) within three manufacturing processes ( Table 11).
All measurements in different companies show that exposure to OS varied from one process to another and from one position to another ( Table 12). The average atmospheric concentrations of hexane are particularly high, especially with the exposure average value (EAV) which overruns the position of the upper part maker, the sole maker, and finishing in all production processes except the process artisan type 2. The other solvents (acetone, cyclohexane, MEK, and toluene) are relatively high without exceeding the EAV.

Comments and discussion
Despite significant exposures to solvent-based preparations, an almost total lack of use of personal protective equipment such as gloves, masks, and goggles by the manipulators of the adhesives formulations and/or solvents was noted. The equipment of rooms by adequate ventilation is not rated very often, while the Tunisian regulations require companies to preserve human capital and implement a preventive political.  Semi-industrial footwear companies are craft enterprises working on a large scale with some mechanization, which paid their employees the number of parts produced per day (upper part makers and sole makers). They correspond to industrial companies that should be in IZ [19]. Another feature in this type of business is the presence of women in age mount positions rods and finishing [20]. Shoes manufacturing companies are increasing in the region with an extension to the new IZ south of the city of Sfax. The semi-industrial companies continue to invade Medina and especially the houses which are in most cases protected historical monuments.
The SAMCR of INRS was chosen because it is one of the reference methods in RA established from the Kinney model (mathematical model) [21].
If these atmospheric samples and toxicology tests were made for the first time in the shoe industry in Sfax, they concerned a sample of companies of the three shoes manufacturing processes (industrial, semi-industrial, and artisanal) preceded by a preliminary RA with a job and a study inventory of products handled.
Interest carcinogenic characteristics of certain preparations and especially their potential toxicity for reproduction must be taken, as a female presence in the shoe manufacturing sector increasingly important and cases of couple infertility [22] have been highlighted.

Conclusion
Identification and CRA are important steps in this process of prevention in the shoe industry. This detection was to (i) highlight the chemical preparations that are really harmful. This could be achieved by the inventory and prioritization of chemical preparations; and (ii) identify the nature of the manipulated chemical preparations. This identification was made by labeling of preparations. After this step, the semi-industrial process CRA is most at risk followed the industrial process and finally that of the artisanal process. When the study of exposure to workplace needs to know not only the average exposure over the EAV, but also to identify the polluting phases to determine the short-term exposure over the TLV.
Apart from the strengthening of health and safety measures in the shoe industry, two actions are to be undertaken in parallel: (i) the substitution of certain solvents by others in the manufacture of glues and derivatives seems necessary while maintaining the preparations use properties and (ii) a change in the Tunisian regulations on hygiene and safety, in particular, is necessary to mandate the RA in business.