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Mapping and development of alternatives to chlorinated lubricants in the metal industry (KLORPARAFRI)

9 Exposure assessment in the working environment of selected components in non-chlorinated lubricants

• 9.1 Introduction to chapter 9
• 9.2 Substances in focus
• 9.3 The exposure scenario
• 9.4 Dermal exposure
  • 9.4.1 Worst case dermal exposure calculated by EUSES EASE model
  • 9.4.2 Dermal absorption calculated by various skin absorption models
• 9.5 Exposure by inhalation
• 9.6 Discussion of exposure results and risk characterization
  • 9.6.1 Introduction
    • 9.6.1.1 Tributyl phosphate (TBP) (CAS No. 126-73-8)
    • 9.6.1.2 Phenol isopropylated phosphate (3:1) (ITAP) (CAS No. 68937-41-7)
    • 9.6.1.3 Sulphurized 2,4,4-Trimethyl pentene (CAS No. 68515-88-8) and di-tert-dodecyl pentasulphide (CAS No. 31565-23-8)
• 9.7 Conclusion

9.1 Introduction to chapter 9

The health and environmental screening of proposed non-chlorinated lubricants and the health and environmental assessments of components typically found in non-chlorinated lubricants focus on the inherent properties of chemical substances and products. The use of the lubricants is not considered.

In order to also consider the use of the lubricants and thereby the health risk involved when using the non-chlorinated lubricants in the working environment, exposure assessments have been performed for four substances. Together these substances represent two groups of components typically found in non-chlorinated lubricants for heavy-duty metal working with the main function as extreme pressure additives (EP additives).

The exposure assessment and evaluation of the health risk in the working environment for the use of non-chlorinated lubricants are very much performed at a screening level and only provide an indication of the health risk involved by use of the products.

The exposure assessments only consider exposure in the working environment. Exposure of the specified substances may also occur in other spheres – for instance by diffuse exposure via the environment. Exposure in other spheres than the working environment is not considered in this project.

Chapter 9 describes the method and results of the exposure assessments and discuss the results.

9.2 Substances in focus

Organic phosphorous compounds and alkyl sulphides (polysulphides) are considered to be the two most critical substance groups found in non-chlorinated lubricants with respect to potential adverse health effects in the occupational environment. This evaluation is based on the health assessments performed in this project on components in non-chlorinated lubricants. Both organic phosphorous compounds and polysulphides are typically entering non-chlorinated lubricants primarily as EP additives. The inherent health and environmental properties of the substance groups are discussed in chapter 7.

Exposure assessments in the working environment have been performed for two organic phosphorous compounds and two polysulphides. The substances selected for the exposure assessments are the organic phosphates; tributyl phosphate (TBP) (CAS No. 126-73-8) and phenol, isopropylated, phosphate (3:1) (ITAP) (CAS No. 68937-41-7), and the polysulphides sulphurized; 2,4,4-trimethyl-pentene (CAS No. 68515-88-8) and di(tert-dodecyl) pentasulphide (CAS No. 31565-23-8). The health assessment of the four substances is described in sections 7.5.4 and 7.7.4, respectively. The choice of these four substances were determined by the availability of physical/chemical and health data for the individual substances. The selected substances demonstrated the best data platform.

9.3 The exposure scenario

Today, chlorinated lubricants are used at Danfoss A/S for metal forming operations, such as extrusion, stamping and deep drawing in stainless steel. Exposure conditions at Danfoss A/S during these forming operations are used as scenarios in the exposure assessment.

The relevant exposure routes for chemicals in the working environment are skin contact and inhalation.

At Danfoss A/S, metal forming operations are performed by machines in machining rooms, which are generally fenced from the working areas.

The degree of dermal exposure to the lubricant may vary depending on the type of forming operation. However, in general dermal exposure occurs during continuous surveillance and regulation and mounting of the machines, cleaning and renovation of used tools, and control of finished work pieces. This may imply skin exposure of hands and underarms, in addition to drip on shoulders and hair. The oil is heated to 70 –80°C during some of the forming operations. Thus, dermal exposure to metal forming lubricants occurs through non-dispersive use with direct and extensive handling.

Hot vapours may be generated during intentional heating of the lubricant to 70 – 80°C to adjust the viscosity, but also during friction heating generated at the metal surface under the forming operations. There is no data on the temperature at the metal surface under the forming operations. However, presumably it may reach the decomposition point of the substances in focus which are informed to be > 200° C. Decomposition products of TBP may be toxic fumes of phosphor oxides (31). There is no information on decomposition products of ITAP, while decomposition products of the polysulphides may be toxic fumes of hydrogen sulphide and sulphur oxides (30).

Metal forming operations do not give rise to mechanically produced mist (aerosols). Mist may be formed by condensation of hot vapour. However, the exposure to mist during metal forming is considered to be very limited. Exposure to lubricants by inhalation of vapours and mist occurs in the machining room during surveillance and regulation, shift of tools and manual emptying of boxes containing finished work pieces.

9.4 Dermal exposure

A worst-case assessment of dermal exposure is calculated for the four substances in focus by use of the EUSES EASE model (77). The use pattern is non-dispersive use and direct and extensive handling.

In addition, skin absorption estimates of the four substances are, if possible, calculated using three different skin absorption models. The models used are SkinPerm (78), DermWin (79) and the method described by Sartorelli (80).

9.4.1 Worst case dermal exposure calculated by EUSES EASE model

The calculated worst case dermal exposure for metal working lubricants with direct and extensive handling using the EUSES EASE model lies in the range of 1- 5 mg/cm²/day (3). The estimated exposure area (hands and underarms) is 2700 cm² and the average human body weight is 70 kg. Thus, the calculated exposure of the total lubricant will be approximately 39 – 193 mg/kg bw/day. The calculated worst case range of dermal exposure for the four substances in focus are stated below in table 9.1.

Table 9.1 Calculated worst case dermal exposure concentrations for four non-chlorinated lubricant EP-additives estimated by the EUSES EASE model (77).

9.4.2 Dermal absorption calculated by various skin absorption models

Skin absorption estimates of the four substances are, if possible, calculated using three different skin absorption models. The models used are SkinPerm (78), DermWin (79) and the method described by Sartorelli (80).

All three models are developed based on data set for a limited number of substances. Thus, the sensitivity of the models varies depending on the physical/chemical characteristics of the chosen substances. In addition, all three models are based on skin absorption of substances in aqueous solution. This is indeed not an optimal absorption model for components in metal forming lubricants as they are most often mineral oil based. However to our knowledge, there are no skin absorption models available at present, which are developed on the basis of substances in oil-based solutions. The three skin absorption models underestimate the skin absorption of substances with very low water solubility.

A scenario with an exposure time of 8 hours/day and an exposure area (hands and arms) of 2700 cm² is used in the three models. Mean average human body weight is 70 kg.

The calculated total absorption in/through the skin for the four substances in focus are stated in table 9.2. The Sartorelli model is not suitable for calculation of skin absorption for substances with a Log Pow above 6. Thus a skin absorption estimate calculated by the Sartorelli model is only available for tributyl phosphate (TBP) having a Log Pow below 6 (16).

Table 9.2 Calculated total dermal skin absorption for four non-chlorinated lubricant EP-additives using three different skin absorption models. Log Pows marked with an asterisk ( * ) are estimated by EpiWin (81). A ( - ) indicates that the absorption model is not applicable for the specific substance.

9.5 Exposure by inhalation

The EUSES EASE model (77) has been used to calculate the vapour concentrations of the substances in focus in the working environment during conditions as described in the exposure scenario. An operating temperature of approximately 80° C are used in the model. Decomposition products are not considered.

Below in table 9.3 are stated the vapour concentrations at a process temperature at 80°C calculated by the EASE method in addition to the saturated vapour concentrations of the four substances in focus.

Table 9.3 Vapour concentrations and saturated vapour concentrations at a process temperature on 80°C for four EP additives in non-chlorinated lubricants for metal forming. * Estimated by EPIWIN (81) and EUSES/EASE (77)

9.6 Discussion of exposure results and risk characterization

9.6.1 Introduction

A risk characterization has been performed in the working environment for the four substances in focus – two phosphorous compounds (TBP, CAS No. 126-73-8 and ITAP, CAS No. 68937-41-7) and two polysulphides (sulphurized 2,4,4-trimethyl pentene, CAS No. 68515-88-8 and di(tert-dodecyl) pentasulphide, CAS No. 31565-23-8).

The risk characterization has been performed by comparison of the calculated exposure levels by dermal contact and inhalation and the NOAEL, LOAEL or NOAEC for critical health effects of the four substances by repeated exposure. Critical health effects of a substance is the effects observed on health at the lowest dose/concentration levels. NOAEL is an abbreviation for the “no observed adverse effect level” while LOAEL is the “lowest observed adverse effect level”. NOAEC is the “no adverse effect concentration”

9.6.1.1 Tributyl phosphate (TBP) (CAS No. 126-73-8)

Dermal exposure

The worst case dermal exposure scenario for tributyl phosphate (TBP) estimated by EASE is 0,4 – 29 mg/kg bw/day (table 9.1), while the calculated skin absorption estimates for TBP using three different skin absorption models range from 0,42 – 5,01 mg/kg/day (table 9.2). It can be concluded that there is reasonable consistency between the magnitude of the skin absorption estimates in the three models. There is also a reasonable consistency between the magnitude of the skin absorption estimates and the worst case dermal exposure calculated by EASE. Thus the calculated worst case exposure seems to be a reasonable estimate of the internal exposure of TBP by skin contact.

Exposure by inhalation

The calculated vapour concentration of TBP at 80°C is in the range of 554 - 1110 mg/m³, while the saturated vapour concentration (SVC) of TBP at 80°C is 153 mg/m³ (table 9.3). The SVC is the theoretical maximum in a steady state environment and will rarely, if ever, be achieved in practice in an industrial situation. The actual vapour concentration of TBP is therefore likely to be lower than the SVC. Thus the worst case vapour concentration of TBP in the working air calculated by EASE is obviously an overestimate. The contribution from aerosols to the inhaled exposure is considered to be very limited and is, thus not included in the exposure assessment.

Risk characterization

There are no data on the health effects of TBP by repeated dermal exposure. Available data on effects by repeated oral exposure, indicate that the critical effects seem to be effects on the peripheral nerve system, effects on the seminiferous tubules, effects on reproduction (reduced pup weight) and possible carcinogenicity in the urine bladder. It should be emphasized that the importance of these results to humans are not thoroughly assessed. Health effects by repeated exposure of TBP assessed as critical are summarized below in table 9.4. The studies and results mentioned are also described in the health assessment of TBP in section 7.7.4.2 (studies A, B, C, D and E).

Table 9.4 summarizes critical health effects of tributyl phosphate (CAS No. 126-73-8) by repeated exposure.

Effects on peripheral nerve system and seminiferous tubules are observed at 400 mg/kg bw/day, whereas effects on reproduction (pup weight) and carcinogenic effects are observed at lower exposure levels. LOAEL for effects on pup weight was 15 mg/kg bw/day while NOAEL for neoplastic lesions in the urine bladder was 9 mg/kg bw/day for males and 12 mg/kg bw/day for females, respectively. Comparison of these effect levels with the calculated worst case dermal exposure level for TBP (0.4-29 mg/kg bw/day) indicates that a worst-case dermal exposure scenario to lubricants containing TBP (CAS No. 126-73-8) at a common lubricant concentration levels implies a risk of adverse effects on health.

In a 4-month inhalation study with rats exposed to TBP, effects on cholinesterase activity and liver were observed at 13,6 mg/m³. The vapour concentration of TBP at 80°C will never exceed the SVC at the same temperature. Thus the theoretical maximum vapour concentration of TBP will be 153 mg/m³. In reality, the vapour concentration will be considerably lower than SVC. Comparison of the theoretical maximum vapour concentration of TBP (153 mg/m³) with the effect level of 13.6 mg/m³ indicates that the vapour concentration of TBP at 80°C may reach levels during metal forming operations implying a risk of adverse effects on health.

9.6.1.2 Phenol isopropylated phosphate (3:1) (ITAP) (CAS No. 68937-41-7)

Dermal exposure

The worst case dermal exposure scenario for ITAP estimated by EASE is 0,4 – 29 mg/kg bw/day (table 9.1), whereas the skin absorption estimate using two skin absorption models ranges from 0 to 0,5 µg/kg/day (table 9.2). There is considerable inconsistency between the magnitudes of the calculated skin absorption estimates and between the skin absorption estimates and the worst case dermal exposure estimate. The calculated water solubility of ITAP is very low (2,58 x 10-5 mg/l). The suitability of the skin absorption models for calculation of skin absorption of non-water soluble substances is limited. The calculated skin absorptions are underestimations. The actual internal exposure of ITAP by skin contact are presumably somewhere between the worst case dermal exposure calculated by EASE and the estimated skin absorption.

Exposure by inhalation

As illustrated in table 9.3, the calculated vapour concentration of ITAP at 80°C is in the range of 0 – 1,88 mg/m³, while the saturated vapour concentration (SVC) of ITAP at 80°C is 0,12 mg/m³. As mentioned for TBP, the SVC is the theoretical maximum in a steady state environment and will rarely, if ever, be achieved in practice in an industrial situation. The vapour exposure of ITAP is therefore likely to be lower than the SVC. The contribution to exposure by inhalation from aerosols is considered to be very limited.

Risk characterization

Two 4-weeks dermal exposure studies of triisopropylated phenyl phosphate (ITAP) (CAS No. 68937-41-7) with rats indicate that the critical health effects by repeated dermal exposure are slight inhibition of plasma cholinesterase activity in both sexes and effects on adrenals in males. The lowest NOAEL for inhibition of plasma cholinesterase was 200 mg/kg/day, while the NOAEL for adrenal effects in male rats was 100 mg/kg/day. Studies in hens and epidemiological studies are inconclusive with respect to toxicity of ITAP to the peripheral nerve system. The critical health effects of ITAP are summarized below in table 9.5. The studies and results are also described in the health assessment of ITAP in section 7.7.4.1 (studies A, B, C and D).

Table 9.5 Critical health effects of triisopropylated phenyl phosphate (ITAP) (CAS No. 68937-41-7) by repeated exposure.

Comparison of the lowest NOAEL from a 4-week dermal exposure study with rats (100 mg/kg bw/day) with the worst case dermal exposure estimate of 0.4-29 mg/kg bw/day for ITAP (table 9.1) indicates that the rise of adverse health effects in the working environment due to dermal exposure of lubricants containing ITAP should be considered limited. Dermal exposure from vapour concentrations of ITAP contribute to the dermal exposure. However, this contribution is considered to be negligible compared to direct dermal contact.

Available inhalation data for ITAP from studies in hens indicate that inhalation of ITAP in aerosol form may cause harmful effects on the nervous system. However, the contribution from aerosols generated during metal forming operations is considered to be very limited. An estimated NOAEC for the effect was 0,12 mg/m³. This indicates that the risk of harmful effects on health caused by inhalation of ITAP vapours and aerosols is considered to be minimal at expected concentrations during metal forming.

9.6.1.3 Sulphurized 2,4,4-Trimethyl pentene (CAS No. 68515-88-8) and di-tert-dodecyl pentasulphide (CAS No. 31565-23-8)

Dermal exposure

As can be seen from table 9.1, the worst case dermal exposure range of the polysulphides estimated by EASE is 1,2 - 58 mg/kg bw/day, whereas the skin absorption estimates using two skin absorption models ranges from 0 to 5,0 x 10^-2 mg/kg bw/day for sulphurized 2,4,4-trimethyl pentene and from 0 to 7,3 x 10^-5 mg/kg bw/day for di-tert-dodecyl pentasulphide (se table 9.2). There is considerable inconsistency between magnitudes of the skin absorption estimates, and between the skin absorption estimates and the worst case dermal exposure. The calculated water solubility of the two polysulphides are very low (7,825 x 10^-3 mg/L and 5,36 x 10^-8 mg/L). The suitability of the skin absorption models for calculating skin absorption of non-water soluble substances is limited and underestimates the skin absorption. The actual internal exposure of the polysulphides by skin contact is presumably somewhere between the worst case dermal exposure estimate and the skin absorption estimates.

Exposure by inhalation

As summarized in table 9.3, the calculated vapour concentration for sulphurized 2,4,4-trimethyl pentene (CAS No. 68515-88-8) at 80°C is 298 – 596 mg/m³, while the saturated vapour concentration (SVC) at 80°C is 810 mg/m³. Thus the calculated vapour concentration of sulphurized 2,4,4-trimethyl pentene is possible in the working environment under metal forming operations.

For di-tert-dodecyl pentasulphide (CAS No. 31565-23-8), the calculated vapour concentration at 80°C is 0 – 2.08 mg/m³ while the saturated vapour concentration (SVC) at 80°C is 0.05 mg/m³, as can be seen from table 8.3. The SVC is the theoretical maximum in a steady state environment and will rarely, if ever, be achieved in practice in an industrial situation. The actual vapour exposure of di-tert-dodecyl pentasulphide is therefore lower than the SVC.

Risk characterization

Limited health data are available for polysulphides, especially data by repeated exposure. Sensitization by skin contact seems to be one effect of some polysulphides. Systemic effects by repeated exposure includes decreased body weight gain and effects on the blood and immune system. Four sub-chronic dermal toxicity studies in rats and rabbits have been conducted with either sulphurized 2,4,4-trimethyl-pentene (CAS No. 68515-88-8) of sulphurized 2-methyl-1-propene (CAS No. 68511-50-2). The predominant effect observed was dermal irritation at the site of the test material. The lowest reported NOAEL for systemic toxicity in a 13-weeks rat study was 50 mg/kg bw/day for sulphurized 2-methyl-1-propene (CAS No. 68511-50-2). The critical health effects of polysulphides are summarized below in table 9.6. The studies and results are also described in the health assessment of polysulphides in section 7.5.4 (studies A, B and C).

Table 9.6 Critical health effects of polysulphides by repeated exposure.

Comparison of the worst case dermal exposure estimates on 1,2 - 58 mg/kg bw/day for sulphurized 2,4,4-trimethyl pentene and di(tert-dodecyl) pentasulphide calculated by EASE with the estimated NOAEL on 50 mg/kg/day for systemic toxicity by dermal exposure of another polysulphide, sulphurized 2-methyl-1-propene (CAS No. 68511-50-2) indicates that repeated dermal exposure to some polysulphides may involve a risk of adverse effects on health.

In addition, data indicates, that some polysulphides exhibit a sensitizing potential by repeated skin contact.

Available inhalation data for sulphurized 2,4,4-trimethyl pentene from a single study in rats indicate that inhalation of the substance may cause systemic effects (reduced body weight gain) below 15 mg/m³. The maximum vapour concentration of sulphurized 2,4,4-trimethyl pentene at 80°C was calculated to be 596 mg/m³, which is well below the calculated SVC on 810 mg/m³. The maximum vapour concentration of di-tert-dodecyl pentasulphide at 80oC was 2.08 mg/m³ which is considerably above the SVC for this substance at 0.05 mg/m³. Comparison of the NOAEC < 15 mg/m³ with maximum vapour concentrations at 80oC of 596 mg/m³ for sulphurized 2,4,4-trimethyl pentene indicates that there is a risk of harmful effects on health caused by repeated inhalation of vapours of sulphurized 2,4,4-trimethyl pentene during metal forming operations. As the possible vapour concentration of di(tert-dodecyl) pentasulphide at 80°C (the SVC at 0.05 mg/m³) is considerably below 15 mg/m³, the risk of adverse health effects caused by inhalation of ditert-dodecyl pentasulphide during metal forming operations is considered very limited.

9.7 Conclusion

Exposure assessments and risk characterization in working environment have been performed at a screening level for two phosphates representing the substance group phosphorous compounds and two polysulphides representing the substance group polysulphides. Both substance groups typically occur in non-chlorinated lubricants as extreme pressure additives and are considered to be the most critical substance groups in non-chlorinated lubricants regarding health effects. This evaluation is based on the results of the health and environmental assessment of components in non-chlorinated lubricants described in chapter 7.

Dermal exposure

The results of the exposure assessments and risk characterizations indicate that worst-case dermal exposure to lubricants containing tributyl phosphate (TBP) (CAS No. 126-73-8) at common lubricant concentrations involve a risk of adverse effects on health, while the risk of adverse health effects due to dermal exposure of lubricants containing phenol isopropylated phosphate (3:1) (ITAP) (CAS No. 68937-41-7) at common lubricant concentrations should be considered limited.

Worst case dermal exposure estimates of polysulphides indicates, that repeated dermal exposure to some polysulphides may involve a risk of adverse effects on health including skin sensitisation. However, the actual dermal exposure levels in the working environment are presumably lower than the worst case estimations as the exposure time and especially the exposure area are lower. Further, the dermal exposure to metal forming lubricants can easily be reduced substantially by use of personal protection equipment, in particular, gloves.

Exposure by inhalation

Regarding exposure by inhalation, the results of the exposure assessments indicate that the vapour concentration of TBP at 80°C may reach levels during metal forming operations implying a risk of adverse effects on health. The risk of harmful effects on health caused by inhalation of ITAP vapours is considered to be minimal at worst case estimated vapour concentrations.

Based on worst case estimates of the vapour concentration at 80°C, there is a risk of harmful effects on health caused by repeated inhalation of sulphurized 2,4,4-trimethyl pentene (CAS No. 68515-88-8). The risk of adverse health effects caused by inhalation of di-tert-dodecyl pentasulphide (CAS No. 31565-23-8) at 80°C is considered to be very limited.

The exposure assessments do not consider exposure from decomposition products of the four substances in focus formed due to friction heating at the metal surface during forming operations. Decomposition products of phosphorous compounds may be toxic fumes of phosphor oxides, while decomposition products of polysulphides may be toxic fumes of hydrogen sulphide and sulphur oxides. Thus decomposition products of phosphorous compounds and polysulphides may involve an additional risk of adverse health effects.

In addition, only exposure in the working environment is considered in the exposure assessments. Exposure from other spheres – most probably diffuse exposure via the environment - may involve an additional exposure.

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Version 1.0 October 2005, © Danish Environmental Protection Agency