Panel:
Based on Available Data, Can We Project an Acceptable Standard for Industrial Use of Asbestos?
BASED ON AVAILABLE DATA, CAN WE PROJECT A N ACCEPTABLE STANDARD FOR INDUSTRIAL USE OF ASBESTOS? ABSOLUTELY K. Robock Asbestos Institute for Occupational and Environmental Hygiene 0-4040 Neuss, Federal Republic of Germany and Institute for Hygiene and Occupational Medicine University of Essen 0 4 3 0 0 Essen, Federal Republic of Germany
It was not my choice to defend “absolutely” as the answer to this question. As a physicist, the term “absolute” makes me think of the Kelvin scale of temperature, which is based on “absolute zero” and is absolutely unattainable. With regard to this question, if we are to behave as responsible scientists, we can give only a valid answer that must be relative. Our knowledge of fiber concentrations in the past, when there was no control of dust levels, is not based on ideal data, and we can compare meaningfully only the relative concentrations in various sectors of the asbestos industry. Accordingly, by collecting the data available, including our own findings, and by reproducing conditions of the past as accurately as possible, we can arrive at a series of values that differ I ) . This is the only way in which a threshold by seven orders of magnitude (FIGURE level can be determined. In uncontrolled situations, from the 1920s to the 1950s. the highest concentrations had always been in the insulation industry (spraying and stripping), with mean values ranging from 50 to 500 fibers/ml but as high as 2000 fibers/ml.’-’ In decreasing order, the insulation sector was followed by the other branches of the asbestos industry, namely, the textile industry, mines and mills, and the asbestos cement industry. By controlled handling of asbestos and application of the best technical dust suppression methods available today, we have now achieved dust concentrations equal to or below 2 fibers/ml, in other words fiber concentrations two to four orders of magnitude less than had occurred previously. For hundreds of years, fiber concentrations within the general environment have been equal to or below lo-’ fibers/ml, or six orders of magnitude less than in the insulation industry in the past or three orders of magnitude less than the level in the present-day working environment (2 fibers/ml). Excessive cancer risks are observed only in groups of insulation workers and are confined to cigarette smokers. For cancer caused by exposure to radiation, a reduction in intensity of two orders of magnitude is (normally) sufficient to eliminate that risk! We have gone far beyond that, reducing the fiber concentration by up to four orders of magnitude. For those not familiar with logarithmic scales, I have plotted the relative fiber 2). On this scale, it is not concentrations on a conventional linear scale (FIGURE possible to mark the 2-fiber level or to distinguish between 2, 1, or 0.5 fiber/ml with 3 by use any degree of accuracy. The same conditions of the past are plotted in FIGURE of gravimetric values in grams per cubic meter. This method of presentation may also
205 0077-8923/79/033&0205 Sl.75/00 1979,N Y A S
Annals New York Academy of Sciences
206
10' INSULATION INDUSTRY
:
w3 *
TEXTILE INDUSTSY
c lo2 '
i
t
I
i
I
I I
I I
I
t
+
I
I
I '
loo
MILLS
I I
+ 10'
NINES
4 C PLANTS
.
In
+ I
:
I I ...........I.,.........I..........I...........I.........................
lo-' '
GENEQAL ENVIRONMENT
' lo-2~ FIGLIRE I . Asbestos dust concentrations (fibers/ml) in different branches of the asbestos industry and in the general environment (dotted line, 2 fibers/ml); logarithmic scale.
highlight the startling differences between previous occupational exposure and that of general environment. The risks of getting mesothelioma as reported by McDonald and McDonald4 and 4. Again, there is an excessive risk only for the group by Riittner' are shown in FIGURE of insulation workers who have been exposed to the highest fiber concentrations in the past and an insignificant, or nonexcessive, risk for workers in the other sectors of the asbestos industry. In addition, other unpublished results (Balangero Mine, Italy; Asbestos Cement Industry, Belgium, Germany, Austria, Switzerland, Colombia, and Israel) have demonstrated no excessive mesothelioma risk. According to Whitwell et u I . , ~Friedrichs's unpublished data reveal no significant difference in lung fiber concentration between the general population who suffer from mesothelioma and those who have no lesion (FIGURE5 ) . There was, however, a significantly higher concentration of fibers in lungs with asbestosis and/or mesothelioma in occupationally exposed asbestos cases (mainly insulation workers). The hypothesis of a "subasbestosis level" for fiber concentrations for mesothelioma is not supported by the evidence available. Therefore, on one hand, one fiber by itself cannot cause mesothelioma, and, on the other hand, factors other than asbestos cannot be excluded. In animal experiments (i.e., injection experiments), the unpublished data of Friedrichs (cited in Whitwell ef aL6)have demonstrated that a threshold of about lo7 fibers per animal is required for tumor induction to occur (FIGURE6). Again, this
Robock: Absolutely
207
observation emphasizes the fact that a single fiber by itself will not induce tumor formation and that a threshold for tumor induction does exist. Consequently, does the reader consider it right to compare asbestos with chemical carcinogens? Is it not imperative that we fill in the gaps in our knowledge about the mechanisms of how mesothelioma and other cancers are produced? For instance, when in the lung, the fiber itself may act only as an adsorber of carcinogenic substances present in inhaled air (e.g., in cigarette smoke), and, therefore, the fiber itself may not necessarily be carcinogenic. The differences in risk in the various segments of the asbestos industry are correlated with past dust concentrations. One can state, therefore, that a doseresponse relationship exists and that a threshold limit for tumor formation is operative. However, what is this threshold? I believe that the 2 fibers/ml value should be used 1). (see FIGURE My good friend, Professor Selikoff, has often suggested that the threshold limit value should be set at a level somewhere between past household exposure and 2 fibers/ml. Our measurements have shown that the household exposure value is between 5 and 30 fibers/ml (e.g., determined from clothing worn by asbestos workers); consequently, the threshold limit value may be between 2 and 5 fibers/ml.
1,on0
t
(
2.000)
5w
100
INSULATION INDUSTRY
TFYTlLE IIIOUSTRY
MINES/ MILLS
AC PLANTS
FIGURE2. Asbestos dust concentrations (fibers/rnl) in different sectors of the asbestos industry; linear scale.
Annals New York Academy of Sciences
208
gIm3 INSULATION INDUSTRY
10TEXTILE INDUSTRY
MINES 1IILLS
A C PLANTS
lom-
10
10
m ia ‘IEfICPAL
ENVIRONVENT
fC
FIGURE 3. Asbestos dust concentrations (g/m3) in different segments of the asbestos industry and in the general environment (dotted line, 0.1 mg/m’); logarithmic scale. Merorhelioma Risk [%1
FIGURE 4. Mesothelioma risk for the general population and for workers of the asbestos industry in general and the asbestos insulation sector.
Robock: Absolutely
209
F I B R E CONTENT ER LUNG
N
17
10
N
12
-
2
1
INVESTIGATED GROUPS
1:
NORWAL LUNGS
2:
NON-OCCUPATIONAL HESOTHELlOWA CASES
3:
ASBESTOSIS CASES
'I:
OCCUPATIONALLY CAUSED HESOTHELIOWA CASES
FIGURE 5. Fiber content per lung without and with occupational asbestos exposure (data from Friedrichs).
. _Tumor _ FIWJIBIICY
i
i
6
i
10
ti
U
16
Log Fibre Amount/A-
FIGURE 6. Tumor frequency dependency on fiber concentration (logarithmic scale) per injection and animal (data from Friedrichs).
210
Annals New York Academy of Sciences REFERENCES
1. 2.
3. 4.
5. 6.
HARRIES,P. G. 1976. Experience with asbestos disease and its control in Great Britain’s naval dockyards. Environ. Res. 11: 261-267. REITZE,W. B., W. J. NICHOLSON, D. A. HOLODAY & I. J. SELIKOFF. 1972. Application of sprayed inorganic fibre containing asbestos: occupational health hazards. Amer. Ind. Hyg. ASS.J. 3 3 178-191. ROBWK,K. Unpublished results. MCDONALD, J. C. & A. D. MCDONALD.1977. Epidemiology of mesothelioma from estimated incidence. Prev. Med. 6 426-446. RUTTNER, J. R. 1977. I n Proceedings of the Asbestos Symposium.: 86-89. Johannesburg. WHITWELL, F., J. SCOT & M. GRIMSHAW. 1977. Relationship between occupations and asbestos-fibre content of the lung in patients with pleural mesothelioma, lung cancer, and other diseases. Thorax 3 2 377-386.
Based on Available Data, Can We Project an Acceptable Standard for Industrial Use of Asbestos?
BASED ON AVAILABLE DATA, CAN WE PROJECT A N ACCEPTABLE STANDARD FOR INDUSTRIAL USE OF ASBESTOS? ABSOLUTELY K. Robock Asbestos Institute for Occupational and Environmental Hygiene 0-4040 Neuss, Federal Republic of Germany and Institute for Hygiene and Occupational Medicine University of Essen 0 4 3 0 0 Essen, Federal Republic of Germany
It was not my choice to defend “absolutely” as the answer to this question. As a physicist, the term “absolute” makes me think of the Kelvin scale of temperature, which is based on “absolute zero” and is absolutely unattainable. With regard to this question, if we are to behave as responsible scientists, we can give only a valid answer that must be relative. Our knowledge of fiber concentrations in the past, when there was no control of dust levels, is not based on ideal data, and we can compare meaningfully only the relative concentrations in various sectors of the asbestos industry. Accordingly, by collecting the data available, including our own findings, and by reproducing conditions of the past as accurately as possible, we can arrive at a series of values that differ I ) . This is the only way in which a threshold by seven orders of magnitude (FIGURE level can be determined. In uncontrolled situations, from the 1920s to the 1950s. the highest concentrations had always been in the insulation industry (spraying and stripping), with mean values ranging from 50 to 500 fibers/ml but as high as 2000 fibers/ml.’-’ In decreasing order, the insulation sector was followed by the other branches of the asbestos industry, namely, the textile industry, mines and mills, and the asbestos cement industry. By controlled handling of asbestos and application of the best technical dust suppression methods available today, we have now achieved dust concentrations equal to or below 2 fibers/ml, in other words fiber concentrations two to four orders of magnitude less than had occurred previously. For hundreds of years, fiber concentrations within the general environment have been equal to or below lo-’ fibers/ml, or six orders of magnitude less than in the insulation industry in the past or three orders of magnitude less than the level in the present-day working environment (2 fibers/ml). Excessive cancer risks are observed only in groups of insulation workers and are confined to cigarette smokers. For cancer caused by exposure to radiation, a reduction in intensity of two orders of magnitude is (normally) sufficient to eliminate that risk! We have gone far beyond that, reducing the fiber concentration by up to four orders of magnitude. For those not familiar with logarithmic scales, I have plotted the relative fiber 2). On this scale, it is not concentrations on a conventional linear scale (FIGURE possible to mark the 2-fiber level or to distinguish between 2, 1, or 0.5 fiber/ml with 3 by use any degree of accuracy. The same conditions of the past are plotted in FIGURE of gravimetric values in grams per cubic meter. This method of presentation may also
205 0077-8923/79/033&0205 Sl.75/00 1979,N Y A S
Annals New York Academy of Sciences
206
10' INSULATION INDUSTRY
:
w3 *
TEXTILE INDUSTSY
c lo2 '
i
t
I
i
I
I I
I I
I
t
+
I
I
I '
loo
MILLS
I I
+ 10'
NINES
4 C PLANTS
.
In
+ I
:
I I ...........I.,.........I..........I...........I.........................
lo-' '
GENEQAL ENVIRONMENT
' lo-2~ FIGLIRE I . Asbestos dust concentrations (fibers/ml) in different branches of the asbestos industry and in the general environment (dotted line, 2 fibers/ml); logarithmic scale.
highlight the startling differences between previous occupational exposure and that of general environment. The risks of getting mesothelioma as reported by McDonald and McDonald4 and 4. Again, there is an excessive risk only for the group by Riittner' are shown in FIGURE of insulation workers who have been exposed to the highest fiber concentrations in the past and an insignificant, or nonexcessive, risk for workers in the other sectors of the asbestos industry. In addition, other unpublished results (Balangero Mine, Italy; Asbestos Cement Industry, Belgium, Germany, Austria, Switzerland, Colombia, and Israel) have demonstrated no excessive mesothelioma risk. According to Whitwell et u I . , ~Friedrichs's unpublished data reveal no significant difference in lung fiber concentration between the general population who suffer from mesothelioma and those who have no lesion (FIGURE5 ) . There was, however, a significantly higher concentration of fibers in lungs with asbestosis and/or mesothelioma in occupationally exposed asbestos cases (mainly insulation workers). The hypothesis of a "subasbestosis level" for fiber concentrations for mesothelioma is not supported by the evidence available. Therefore, on one hand, one fiber by itself cannot cause mesothelioma, and, on the other hand, factors other than asbestos cannot be excluded. In animal experiments (i.e., injection experiments), the unpublished data of Friedrichs (cited in Whitwell ef aL6)have demonstrated that a threshold of about lo7 fibers per animal is required for tumor induction to occur (FIGURE6). Again, this
Robock: Absolutely
207
observation emphasizes the fact that a single fiber by itself will not induce tumor formation and that a threshold for tumor induction does exist. Consequently, does the reader consider it right to compare asbestos with chemical carcinogens? Is it not imperative that we fill in the gaps in our knowledge about the mechanisms of how mesothelioma and other cancers are produced? For instance, when in the lung, the fiber itself may act only as an adsorber of carcinogenic substances present in inhaled air (e.g., in cigarette smoke), and, therefore, the fiber itself may not necessarily be carcinogenic. The differences in risk in the various segments of the asbestos industry are correlated with past dust concentrations. One can state, therefore, that a doseresponse relationship exists and that a threshold limit for tumor formation is operative. However, what is this threshold? I believe that the 2 fibers/ml value should be used 1). (see FIGURE My good friend, Professor Selikoff, has often suggested that the threshold limit value should be set at a level somewhere between past household exposure and 2 fibers/ml. Our measurements have shown that the household exposure value is between 5 and 30 fibers/ml (e.g., determined from clothing worn by asbestos workers); consequently, the threshold limit value may be between 2 and 5 fibers/ml.
1,on0
t
(
2.000)
5w
100
INSULATION INDUSTRY
TFYTlLE IIIOUSTRY
MINES/ MILLS
AC PLANTS
FIGURE2. Asbestos dust concentrations (fibers/rnl) in different sectors of the asbestos industry; linear scale.
Annals New York Academy of Sciences
208
gIm3 INSULATION INDUSTRY
10TEXTILE INDUSTRY
MINES 1IILLS
A C PLANTS
lom-
10
10
m ia ‘IEfICPAL
ENVIRONVENT
fC
FIGURE 3. Asbestos dust concentrations (g/m3) in different segments of the asbestos industry and in the general environment (dotted line, 0.1 mg/m’); logarithmic scale. Merorhelioma Risk [%1
FIGURE 4. Mesothelioma risk for the general population and for workers of the asbestos industry in general and the asbestos insulation sector.
Robock: Absolutely
209
F I B R E CONTENT ER LUNG
N
17
10
N
12
-
2
1
INVESTIGATED GROUPS
1:
NORWAL LUNGS
2:
NON-OCCUPATIONAL HESOTHELlOWA CASES
3:
ASBESTOSIS CASES
'I:
OCCUPATIONALLY CAUSED HESOTHELIOWA CASES
FIGURE 5. Fiber content per lung without and with occupational asbestos exposure (data from Friedrichs).
. _Tumor _ FIWJIBIICY
i
i
6
i
10
ti
U
16
Log Fibre Amount/A-
FIGURE 6. Tumor frequency dependency on fiber concentration (logarithmic scale) per injection and animal (data from Friedrichs).
210
Annals New York Academy of Sciences REFERENCES
1. 2.
3. 4.
5. 6.
HARRIES,P. G. 1976. Experience with asbestos disease and its control in Great Britain’s naval dockyards. Environ. Res. 11: 261-267. REITZE,W. B., W. J. NICHOLSON, D. A. HOLODAY & I. J. SELIKOFF. 1972. Application of sprayed inorganic fibre containing asbestos: occupational health hazards. Amer. Ind. Hyg. ASS.J. 3 3 178-191. ROBWK,K. Unpublished results. MCDONALD, J. C. & A. D. MCDONALD.1977. Epidemiology of mesothelioma from estimated incidence. Prev. Med. 6 426-446. RUTTNER, J. R. 1977. I n Proceedings of the Asbestos Symposium.: 86-89. Johannesburg. WHITWELL, F., J. SCOT & M. GRIMSHAW. 1977. Relationship between occupations and asbestos-fibre content of the lung in patients with pleural mesothelioma, lung cancer, and other diseases. Thorax 3 2 377-386.
