Exposure to Toluene Di-isocyanate and Respiratory Effects in Flexible Polyurethane Foam Industries in Western India.

BACKGROUND: Flexible foam industry largely uses 2,4 and 2,6 Toluene di-isocyanate as main raw materials and chronic exposure to its result in occupational asthma. The exposure to di-isocyanates might be higher due to the usage of obsolete technology, hand-mixing methods and working in confined spaces with insufficient local exhaust ventilation systems in developing countries. Exposure studies in flexible foam industries have not been done in developing countries.
OBJECTIVE: The present cross-sectional study was conducted to evaluate toluene di-isocyanate (TDI) exposures and respiratory health of the workers working in the seven flexible polyurethane foam industries located in Western India during 2010-2013.
METHOD: A total of 128 personal air samples collected and evaluated for total TDI concentration using improved Occupational Safety and Head Administration method number 42. Then 194 workers were covered for complete clinical examination and spirometry for assessing respiratory health.
RESULTS: In all, 17.83% of air samples exceeded the ACGIH TWA-TLV of 0.005 ppm for TDI. Though only 11 (5.6%) workers had respiratory complaints, the spirometry revealed that 19 (9.8%) and four (2.1%) had restrictive and obstructive type of pulmonary function impairment, respectively.
CONCLUSION: The TWA concentration of TDI exceeded at raw material storage, mixing, foaming, block cutting and curing areas in four out of seven industries even in the presence of local exhaust systems. The respiratory health effect is less when compared to exposure to TDI, suitable preventive and control measures were suggested based on the study findings to the stakeholders to prevent the increase of respiratory health effects. Copyright:

INTRODUCTION

Occupational exposures to isocyanates occur during the production of flexible and rigid polyurethane foams.[12] There is good evidence to indicate that isocyanates cause chemical bronchitis or pneumonitis, isocyanate asthma, causes non-specific airways disease including chronic bronchitis.[3456] Further asthma can occur at low concentrations of isocyanates, the higher the exposure greater the risk.[7] Other chemical agents such as amines used as a catalyst in the manufacture of polyurethane foam are also reported to cause the respiratory symptoms.[7] The studies reported that despite low airborne isocyanate concentrations, it was possible to demonstrate biological uptake of isocyanates through biological monitoring suggesting that absorption can also occur via dermal or other routes of exposure.[89] A spirometric change suggestive of bronchial obstruction of a mild degree is also reported in the earlier study.[10]

The isocyanates and di-isocyanates are used in manufacturing a wide range of products such as synthetic rubber, synthetic textile fibres, glues and adhesives, anti-corrosive chemicals, wire and cable insulation, paints, lacquers, ink and varnishes, leather finishes, etc.[111213] The major part of the world's isocyanate production is shared by the two isocyanates namely toluene di-isocyanate (TDI) and methylenediphenyl di-isocyanate (MDI). TDI is used as one of the raw materials for the production of flexible polyurethane foams. Polyurethane foam is produced when polyol is made to react with isocyanate (TDI in case of flexible polyurethane foam and MDI in case of rigid foam), catalyst, surfactant, colouring agent and blowing agents in a chilled condition. The density of the foam produced varies from 13 to 80 kg/m3. Once the foam is produced and attained the required size, it is cut into big blocks and kept for curing for 18 hours or above. The fully dried or cured blocks are cut by horizontal and vertical cutting machines into various sizes as per customer requirement, packed and transported to respective destinations.

In flexible foam industries, the reaction between TDI and polyol being exothermic, the TDI becomes airborne during mixing and foaming process and workers might be exposed to high concentrations of TDI.[14] In developing countries such as India, the process in the manufacturing of flexible foam involves hand mixing of chemicals, working in confined spaces, absence of efficient local exhaust ventilation and mostly obsolete technology. So the exposure is often more than the permissible limit of ACGIH TLV-TWA of 0.005 ppm.[15] Further, in the absence of regulatory standards such as permissible exposure limits in India, there is a necessity to evaluate TDI concentrations and its effect on the respiratory system of workers in flexible foam industries. Thus the present study was undertaken to evaluate TDI concentration in different work areas; to assess the respiratory health of the workers exposed to TDI and to suggest suitable preventive and control measures to reduce exposures to the stakeholders.

MATERIALS AND METHODS

This study was conducted during 2010-2013 in seven flexible foam industries located in Ahmedabad, Gandhinagar, Sabarkantha and Mahesana districts of Gujarat and Silvassa area of Western India. The study protocol included exposure assessment of TDI and the health monitoring of the workers. The project was approved by the Institutional Ethics Committee of Indian Council of Medical Research-National Institute of Occupational Health, Ahmedabad meeting held on 10 June 2008 with reference no. NIOH/EC/SK/2008/1514/1554; Agenda No. 3.

Exposure assessment of TDI

A total of 128 air samples were collected and evaluated for total TDI concentration. The modified OHSA 42 method was applied for sampling and analysis of TDI. An external standard calibration curve in the range of 0.5-9.0 ng/ml has been prepared for 2, 4- and 2, 6-Toluene Di-IsocynatoPolyurea (TDIP). The concentrations of 2, 4- and 2, 6-TDIP in air samples were determined using the external standard calibration curve.

The airborne TDIs samples were collected through the SKC 225-9002 filter cassettes (sampling media coated with 1, 2-Pyridyl Piperidine 1-2 mg) fitted to personal air samplers at the flow rate of 0.5 l/min for the entire work shift of 6-8 hours in different process areas of seven flexible foam industries. The airborne TDI is converted into TDIP by reacting with 1, 2-pyridyl piperidinecoated on the filter paper. The collected air samples-filter cassettes were end-capped and transported in an ice pack with proper labelling and kept in the refrigerator until analysis.

The TDIP present in the sampled filters were extracted with 2 ml of 90:10:: ACN: DMSO mixture. An aliquot of 20 μl were injected into Shimatzu 10 ATVP services HPLC-Fluorescence instrument (excitation@ 270 nm and emission @340 nm) using autosampler as per OSHA method number 42. The HPLC conditions employed for the analysis of 2, 4 and 2, 6-TDIs are shown in Table 1.

Table 1

HPLC conditions employed for the analysis of 2, 4- and 2, 6-TDI

Column used	Luna CN 5 u 100 A Phenomenex, 250 × 4.6 mm ID
Column oven temperature	40°C
Column flow rate	1.0 ml/min
Mobile phase	Acetonitrile: 0.05 M Ammonium acetate, (pH 6.1) buffer: 32:68
Injection volume	20 µL
Detector	RF-Fluorescence Detector (Excitation @240 nm and Emission @ 370 nm)
Run time	15 min

The reliable quantitation limit for the 2, 6-TDI and 2, 4-TDI in air samples were 0.32 and 0.36 parts per billion (ppb), respectively. The reliable quantitation limit for total TDI (2, 6 TDI + 2, 4 TDI) is 0.68 ppb that is equal to 0.00068 parts per million (ppm). The total TDI values found below the reliable quantitation limit of 0.68 ppb (0.00068 ppm) were reported as below detection limit (BDL). The total TDI values found below LOQ of 0.00068 ppm were divided by 2 for statistical analysis. The TDIP concentrations were converted into TDI using the conversion factor of 0.3479 and finally expressed as milligrams of TDI. This concentration of total TDI in milligram was divided by the volume of air samples in cubic meters to get the total TDI concentration in mg/m3.

Health monitoring

A total of 194 randomly selected workers out of 300 employed in the selected polyurethane foam manufacturing units were monitored in the study. After explaining the purpose of the study, the informed written consent was obtained in vernacular language (Gujarati and Hindi). The information regarding demographic, occupational and clinical history was collected on a pre-designed and pre-tested proforma through interview of the subject. This was followed by a complete clinical examination with special emphasis on respiratory system. The spirometric parameters of the subjects were measured using Spirovit SP- 10 (M/s Schiller AG, Switzerland) following standard protocol. For categorizing the pulmonary function impairment, a cut-off of 80% of predictive FVC and 70% of FEV1/FVC ratio was taken to label it restrictive or obstructive impairment, respectively.[16] For the analysis, the smoking habit was dichotomized into ever smoker (included current smokers and ex-smokers) and never smoker. Statistical analysis was carried out using the statistical software package “Epi Info 5” (World Health Organization, Geneva) and included calculation of proportion and percentages and application of tests of significance such as ANOVA.

RESULTS

A total of 128 air samples were analysed for total TDI including 124 air samples in the study area and 4 samples outside the industry. The correlation coefficient (r2) values of 2, 4- and 2, 6-TDIP for external standard calibration curves were 0.999581 and 0.999795, respectively. The HPLC conditions employed for the analysis of 2, 4- and 2, 6-TDI is shown in Table 1.

The time-weighted average (TWA) value of total TDI found in seven flexible foam industries is given in Table 2. The mean total TDI concentration varied from BDL of 0.00068 ppm to a maximum of 0.1225 ppm. The average TDI value found from all the production areas is 0.0015 ppm for industry 1, (0.0357 ppm) for industry 2, (0.0232 ppm) for industry 3, 0.0022 ppm for industry 4, 0.003 ppm for industry 5, 0.0010 ppm for industry 6 and 0.0012 ppm for industry 7. Thus, except for industry 2 and industry 3, the average total TDI concentration was within the TWA-TLV of 0.005 ppm.[15] The reason might be due to poor local exhaust system or of lower capacity especially over the foam production area as well as poor general ventilation in raw material storage and mixing area and block cutting areas.

Table 2

Total TDI values of the foam industries and control areas

Industries	n	Mean	Std. Deviation	Minimum	Maximum	Std. Error of Mean
1	10	0.0015	0.0011	BDL	0.0034	0.0004
2	10	0.0357	0.0264	0.0014	0.0978	0.0084
3	11	0.0232	0.0383	BDL	0.1225	0.0116
4	6	0.0022	0.0016	BDL	0.0041	0.0007
5	37	0.0030	0.0067	BDL	0.0350	0.0011
6	25	0.0010	0.0015	BDL	0.0041	0.0003
7	25	0.0012	0.0027	BDL	0.0116	0.0005
TOTAL	124	0.0065	0.0172	BDL	0.1225	0.0015
Control area - outside industry	4	0.0002	0.0002	BDL	.0004	0.0001

The TWA values of total TDI found in different process areas in all seven industries is given in Table 3. In industry 1, the highest exposure was found in raw material storage, mixing area and foam production, that is, foaming area, whereas lowest exposure (BDL) was found in the curing area. In industry 2, the minimum TWA concentration of total TDI was found in the curing area and the maximum concentration was found in the block cutting machine area. In industry 3, the total TDI found was BDL in the curing area, the maximum was in foam production and raw material storage, and mixing areas that were exceeded the ACGIH TWA-TLV of 0.005 ppm. In industry 4, the concentration was BDL in the packing area, whereas maximum concentration was found both in the foaming area and block cutting area. In industry 5, the concentration has exceeded the ACGIH TWA-TLV value at foaming area, whereas in all other departments namely raw material storage/mixing area, curing area, horizontal and vertical cutting machine area, peeling area, finished block storage area, packaging/despatching area, administration office and outside industry-security gate it was BDL for total TDI. In industries 6 and 7, higher concentration was found in raw material mixing area and foaming area, however, in all other work areas it was BDLs.

Table 3

Process-wise total TDI values in foam industries

Work Area	n	Total TDI-TWA (ppm)	Std. Deviation	Minimum	Maximum	Std. Error of Mean
Raw material storage and mixing area	15	0.0045*	0.0069	BDL	0.0235	0.0018
Foam production (foaming area)	37	0.0139*	0.0236	BDL	0.1225	0.0039
Block cutting machine area	23	0.0091*	0.0233	BDL	0.0978	0.0049
Curing area	17	0.0005	0.0007	BDL	0.0024	0.0002
Horizontal and vertical cutting machine area	24	0.0004	0.0008	BDL	0.0029	0.0002
Packing-despatching area	8	0.0001	0.0002	BDL	0.0005	0.0000
TOTAL	124	0.0065	0.0173	0.0000	0.1225	0.0016

BDL=below detection limit-< 0.00068 ppm for total TDI. * TDI values exceeding ACGIH TLV TWA value of 0.005 ppm

The TDI value exceeding the ACGIH TLV recommended limit in four industries and different processes is shown in Table 4. Twenty-three air samples exceeded the recommended TLV limits of 0.005 ppm for total TDI.[15] It was observed the TWA values of total TDI had exceeded the TLV limits in foam production, block cutting and raw material storage and mixing areas. Out of the 23 samples exceeding TWA TLV levels maximum[15] were from the foaming process area followed by 4 each from block cutting and storage and mixing areas.

Table 4

Higher than the recommended levels of TDI in industries and processes (n=23)

Characteristics		Values > ACGIH TLV
Industry	Processes
2	Foam production, block cutting and raw material storage and mixing	9
3	Foam production, raw material storage and mixing	5
5	Foam production	7
7	Foam production	2

The health monitoring was carried out in 194 subjects, which comprises 184 (94.8%) males and 10 (5.2%) females. The mean age of the workers was 29.26 ± 9.27 years and the mean duration of exposure was 6.73 ± 5.6 years. 31.9% of workers were involved in the loading and unloading of finished products. Workers who were operating the vertical, horizontal and circular cutting machines followed this. Only 24 (12.4%) of the workers were engaged in the foaming process. Table 5 depicts the indicators of respiratory health. Only 11 (5.6%) subjects had respiratory complaints such as cough, sputum production and complaint of breathlessness while remaining did not report any symptom at the time of the study. The spirometry revealed that 87.1% of the subjects were not having any pulmonary impairment while 9.8% and 2.1% had a restrictive and obstructive type of pulmonary function impairment, respectively. Only one subject had combined type, that is, both obstructive and restrictive type of impairment while one subject did not cooperate for performing the procedure. When the mean FVC and FEV1 values (indicators of respiratory function) were compared between foam production workers and office staff, a significant reduction in FVC (P = 0.005) and FEV1 (P = 0.028) was observed among production workers. This suggests that exposure to TDI results in affects the respiratory function. However, when controlled for factors like age, duration of exposure and smoking habits the difference in mean FVC and FEV1 values between foam production workers and the office staff was found statistically non-significant (P > 0.05).

Table 5

Respiratory health indicators in the study population (n=194)

Respiratory health indicators	Number (%)
Respiratory symptoms
Present	11 ( 5.6)
Absent	183 (94.4)
Pulmonary function impairment
Obstructive impairment	4 (2.1)
Restrictive impairment	19 (9.8)
Combined impairment	1 (0.5)
No impairment	169 (87.1)

DISCUSSION

The present study carried out in polyurethane foam units of Western India reveals that in some of the units the TWA for total TDI in some of the units was higher than the recommended TLV. It is interesting to note that in our study even in the presence of local exhaust ventilation (LEV) system at foaming areas, the TWA values have exceeded the ACGIH TLV-TWA of 0.005 ppm in the foaming area in four industries out of seven studied. Earlier studies in the polyurethane foam industry also reported exposure to TDI at the workplace. A similar study measured TDI exposures and reported air concentrations of TDI isomers in the range of 0.2-58.9 μg/m3.[10] The highest concentrations of TDI were found in the workstations of the maintenance workers (9.9-41.5 μg/m3) and paper folders (0.3-58.7 μg/m3). Lower concentrations of TDI were found in the samples collected from the work stations of foaming head operators (0.6-11.3 μg/m3) and cutting machine operators (0.2-6.5 μg/m3).

In this study, the total TDI concentrations found in flexible foam industries varied from BDL of 5.0-255 μg/m3. The wide variations in the average total TDI concentrations in our study may be due to many factors such as wide variation in efficiency and capacity of local exhaust ventilation systems over the foaming area, more or less number of foaming cycles during the study period, general ventilation and open spaces existing in these industries. An earlier study evaluated TDI concentrations in 100 air samples and reported varied concentrations of 53-81 μg/m3.[17] Similarly, another study has also reported low and varied airborne concentrations of TDI in moulded polyurethane products, insulation materials and spray painting operations.[8]

In the present study, only 11 (5.6%) workers had respiratory symptoms. This may be attributed either to the healthy worker effect on the job or to effective control technology in the industry. Further, only 2.1% had shown obstructive pattern on spirometry.

Limitation of the study: However as we could not perform the bronchodilator test, the chronicity of this obstructive pattern could not be ascertained. The biological monitoring for TDI metabolite (toluene diamine (TDA)), which is more specific indicator to show the effect and absorbed dose, could not be performed in this study due to the limited resources.

Thus to conclude, this study is some polyurethane foam industries, the TWA of TDI exceeded the ACGIH TWA-TLV of 0.005 ppm. The processes such as foaming, block cutting, raw material storage and mixing areas reported higher values of TDI suggesting a risk of developing respiratory ill health in workers involved in these processes. However, the study did not show any alarming level of respiratory ill health among workers that can be due to better control measures at the workplace. Based on the results of the study suitable recommendations that include environment management guidelines, emergency procedures to be followed during spills and leaks, first aid tips, health management guidelines and suitable personal protective equipment for workers handling TDI (ACS, 2013) were suggested to stakeholders.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Ministry of Environment, Forest and Climate Change, Govt. of India.

Conflicts of interest

There are no conflicts of interest.