Articles of general interest-FL/ autoradiography study a procedure designed to provide a test solution containing DEHP in the physical state in which it would be likely to be encountered in blood stored in plastics bags. By immersing DEHP labelled with 14C in the carbonyl group in sterile mouse plasma. for 78 days at 22°C they achieved a concentration of 2.293 mg DEHP/ml. Intravenous injections of I ml of this plasma were given to adult male mice, which were anaesthetized and frozen for whole-body autoradiography after 1, 3, 9 or 24 hours or 7 days. Others, injected with the labelled DEHP 30 minutes after ligation of both renal pedicles, were subjected to autoradiography 1 or 3 hours after the injection. The responses of germ-free mice to these treatments were compared with those of conventional animals. In all the mice there was rapid accumulation of radioactive label in the kidney and liver, but not in other organs. This was demonstrated 1 hour after the injection, but by 3 hours considerable elimination into the urine, bile and intestine had occurred and elimination was virtually complete within 9 hours, except in the mice with ligated kidneys. These showed a more prolonged retention of radioactivity and a more scattered distribution in the blood and extracellular fluids. Attachment of DEHP to protein constituents of human plasma, with physical alteration, has been demonstrated by Stern et al. (ibid 1977, 41, 507), in further attempts to define the form of the DEHP
EVIDENCE
Cosr~rt. Tauicol. Vol. 17. No. I
actually encountered by patients given blood transfusions from PVC packs. In human plasma stored at room temperature for IO days in PVC packs plasticized with [14C]DEHP, they demonstrated that DEHP formed a non-particulate diffusion complex and that the extent of migration was determined not by the plasma lipid content but by the total protein concentration. In non-particulate solutions prepared by the careful addition of ethanolic DEHP to plasma, a large proportion of the DEHP was shown to be bound to the Q- and P-globulins. When the diffusion complex of [14C]DEHP was injected into the tail vein of rats, the second phase of 14C half-life in the blood was shorter than when a complex formed from an ethanolic or Polysorbate-80 solution was used, organ retention was reduced and excretion was more rapid, at least initially. When included in the perfusing fluid for an isolated rat-liver preparation, the protein diffusion complex of DEHP was metabolized and rapidly excreted in the bile. These findings provide further evidence that the physico-chemical reactions of DEHP with plasma are complex, and that when toxicity studies of this plasticizer are undertaken in connexion with its presence in transfused blood, the non-particulate complex, which is the actual blood contaminant, should be used, rather than other solubilized or particulate forms. [P. Cooper-BIBRA]
OF A SAFE
Toxicology cannot class toluene diisocyanate (TDI) as one of its success stories. In spite of considerable scientific interest, the mechanism underlying its toxic action still remains elusive (Cited in F.C.7: 1972, 10, 730; ibid 1976. 14. 218; ibid 1977. IS. 365). The inability of the toxicologiSt to define an acceptable atmospheric concentration of TDI is a more practical disappointment. Among recent additions to the TDI literature is a report by Wegman et al. (Br. J. ind. Med. 1977, 34, 196) on a follow-up of an earlier investigation of workers involved in the production of polyurethane. The original study (idem, J. occup. Med. 1974, 16, 258) demonstrated that exposure to TDI resulted in an acute reduction in pulmonary function. The same workers were re-examined 2 years later to assess the chronic effects of TDI. Only 63 of the 112 workers originally studied were still employed and therefore available for examination, but the pulmonary function of the retested and lost groups of workers was comparable in 1972 and there was little evidence of a selection bias in the restudied group. TDI levels at the workplace were determined five times during the 2 years between the two investigations and were found to be stable. The workers were divided into three groups of approximately equal size: those exposed to TDI levels in excess of 0.0035 ppm, those exposed to between 0.002 and 0.003 ppm TDI. and those exposed to levels below 0+)015 ppm.
89
LEVEL
OF TDI
Although the incidence of subjective symptoms of pulmonary disorder was similar in all three groups, the prevalence of coughing and phlegm increased with increasing exposure and there were variations in performance in pulmonary-function tests. The group exposed to the lowest levels of TDI had a 2-year change in forced expiratory volume (FEV) within t.he expected limits for a normal population, but in the other two groups, loss in FEV increased with increasing exposure. Even when all possible contributory factors were considered, including age, smoking habits and lung size, the differences between the groups were still significant, and it was concluded that a loss of pulmonary function occurred at TDI exposures of 0.0035 ppm with a possibility that exposures as low as 0.002 ppm were having some effect. Wegman er al. (1977, lot. cit.) stressed the importance of measuring the factory levels of TDI as well as length of work service in any prospective study of the effects of this particular monomer. If length of service had been adopted as the sole index of exposure, no significant correlation would have been found between exposure and reduction in FEV. These authors also noted the possible complications introduced by the welldocumented acute effects of TDI; at high exposures FEV decreases over every workshift, whereas at lower levels, acute loss occurs on the first day of a working week. Because of this, it was emphasized that lung function should be exam-
90
Articles of general interest--Ft/
ined immediately before commencement of work after at least a weekend away from the plant, to provide baseline measurements. The results presented in this study confirmed earlier indications (Cited in F.C.‘I: 1969, 7, 699) of a correlation between acute and chronic loss of FEV. It was suggested that workers who exhibit large acute pulmonary changes following TDI exposure should be frequently re-examined so that chronic changes in lung function may be detected at an early stage. In another study, the health of a number of workers in a TDI-manufacturing plant was monitored by Butcher er al. (Am. Rev. resp. Dis. 1977, 116, 411) over a 2.5year period. For purposes of comparison, the workers were divided essentially into three groups: those who had daily contact with TDI (group I). maintenance personnel who had intermittent contact (group II), and a group of non-exposed controls. All groups were comparable in atopic status, age, sex and race but were not matched for size or smoking habits. Before the start of TDI production (April 1973), and at roughly 6-monthly intervals, the immunological status and health of the workforce was evaluated. Of the 103 workers interviewed in April 1973, 89 subsequently undertook jobs entailing regular or intermittent exposure to TDI. Over the period of the study, the continuously monitored levels of TDI in the factory air often exceeded the present TLV of transient level being 0.02 ppm, the maximum 0.04 ppm. In the exposed group there was a significant increase (P < 0.01) in the prevalence of lower respiratory problems (cough, wheezing, shortness of breath), compared with the control group. In other respects, including the incidence of bronchitis and upper respiratory symptoms, immunoglobuhn levels, peripheralblood eosinophil counts and the average performance in pulmonary-function tests, TDI exposure had no discernible adverse effects. Unfortunately the results of the pulmonary-function tests were analysed only with respect to length of TDI exposure which. in the light of the conclusions drawn by Wegman et al. (1977, lot. cit.) may explain the apparent absence of a TDI-related effect. In spite of these largely negative results, a significant proportion of the workforce studied by Butcher et al. (lot. cit.) did develop sensitivity to TDI. For example, 13 workers demonstrated clinical sensitivity to the monomer and, of these, nine suffered an adverse bronchial response when challenged with TDI exposures from 0.005 to 0.02 ppm. Even in these sensitive individuals, the controlled TDI exposure did not result in any increase in the blood eosinophil
Cosrr~er. Tosicol.
Vol. 17. No. I
-.
count. Inhalation challenge with acetyl+methylcholine generated a bronchial response in eight of the 11 TDI-sensitive individuals who were tested, whereas only one out of ten non-sensitized subjects gave a similar positive response. This may have predictive value in the screening of workers for bronchial hyperreactivity before they enter jobs involving potential TDI exposure. An increasing incidence of TDI-specific IgE antibodies was detected using a radioallergosorbent (RAST) test. The first positive results, a single case in each of groups I and II, were found in March 1975. Although by April 1976 eight workers exposed to the TDI gave evidence of allergenicity, two workers of the control group were similarly affected. There was also an increase in the number of people who gave a positive response in a skin test with TDIhuman serum albumin (HSA) conjugate; a total of ten individuals of either group I or II exhibited positive but small reactions during the 3 years of observation, the first positive result occurring in March 1974. Somewhat surprisingly none of the workers who gave evidence of sensitivity to TDI in the RAST or patch tests were among the thirteen subjects who demonstrated clinical sensitivity to TDI. Wegman et al. (1977, lot. cit.) mentioned their use of personal as well as area sampling and drew attention to an earlier study in which this precaution had not been taken. Comparative air-sampling studies carried out by Butcher et al. (lot. cit.) confirmed the need to relate observed biological effects with individual levels of exposure rather than with levels deduced from area monitoring, by demonstrating a marked lack of correlation between the results of personal and area measurements. The monitoring programme used by Wegman et al. (1977, lot. cir.) does not seem entirely satisfactory, however, and it would be of value if their data could be confirmed and extended by a study involving the regular measurement of breathing-zone concentrations of TDI at intervals considerably more frequent than the five measurements in 2 years used as the basis for their reported study. In addition to providing further clues to safe exposure levels of TDI, these reports underline some of the pitfalls involved in such studies and some of the precautions that must be observed if meaningful results are to be obtained not only for TDI but also for other industrial chemicals. [J. Hopkins-BIBRA]
EVIDENCE
Cosr~rt. Tauicol. Vol. 17. No. I
actually encountered by patients given blood transfusions from PVC packs. In human plasma stored at room temperature for IO days in PVC packs plasticized with [14C]DEHP, they demonstrated that DEHP formed a non-particulate diffusion complex and that the extent of migration was determined not by the plasma lipid content but by the total protein concentration. In non-particulate solutions prepared by the careful addition of ethanolic DEHP to plasma, a large proportion of the DEHP was shown to be bound to the Q- and P-globulins. When the diffusion complex of [14C]DEHP was injected into the tail vein of rats, the second phase of 14C half-life in the blood was shorter than when a complex formed from an ethanolic or Polysorbate-80 solution was used, organ retention was reduced and excretion was more rapid, at least initially. When included in the perfusing fluid for an isolated rat-liver preparation, the protein diffusion complex of DEHP was metabolized and rapidly excreted in the bile. These findings provide further evidence that the physico-chemical reactions of DEHP with plasma are complex, and that when toxicity studies of this plasticizer are undertaken in connexion with its presence in transfused blood, the non-particulate complex, which is the actual blood contaminant, should be used, rather than other solubilized or particulate forms. [P. Cooper-BIBRA]
OF A SAFE
Toxicology cannot class toluene diisocyanate (TDI) as one of its success stories. In spite of considerable scientific interest, the mechanism underlying its toxic action still remains elusive (Cited in F.C.7: 1972, 10, 730; ibid 1976. 14. 218; ibid 1977. IS. 365). The inability of the toxicologiSt to define an acceptable atmospheric concentration of TDI is a more practical disappointment. Among recent additions to the TDI literature is a report by Wegman et al. (Br. J. ind. Med. 1977, 34, 196) on a follow-up of an earlier investigation of workers involved in the production of polyurethane. The original study (idem, J. occup. Med. 1974, 16, 258) demonstrated that exposure to TDI resulted in an acute reduction in pulmonary function. The same workers were re-examined 2 years later to assess the chronic effects of TDI. Only 63 of the 112 workers originally studied were still employed and therefore available for examination, but the pulmonary function of the retested and lost groups of workers was comparable in 1972 and there was little evidence of a selection bias in the restudied group. TDI levels at the workplace were determined five times during the 2 years between the two investigations and were found to be stable. The workers were divided into three groups of approximately equal size: those exposed to TDI levels in excess of 0.0035 ppm, those exposed to between 0.002 and 0.003 ppm TDI. and those exposed to levels below 0+)015 ppm.
89
LEVEL
OF TDI
Although the incidence of subjective symptoms of pulmonary disorder was similar in all three groups, the prevalence of coughing and phlegm increased with increasing exposure and there were variations in performance in pulmonary-function tests. The group exposed to the lowest levels of TDI had a 2-year change in forced expiratory volume (FEV) within t.he expected limits for a normal population, but in the other two groups, loss in FEV increased with increasing exposure. Even when all possible contributory factors were considered, including age, smoking habits and lung size, the differences between the groups were still significant, and it was concluded that a loss of pulmonary function occurred at TDI exposures of 0.0035 ppm with a possibility that exposures as low as 0.002 ppm were having some effect. Wegman er al. (1977, lot. cit.) stressed the importance of measuring the factory levels of TDI as well as length of work service in any prospective study of the effects of this particular monomer. If length of service had been adopted as the sole index of exposure, no significant correlation would have been found between exposure and reduction in FEV. These authors also noted the possible complications introduced by the welldocumented acute effects of TDI; at high exposures FEV decreases over every workshift, whereas at lower levels, acute loss occurs on the first day of a working week. Because of this, it was emphasized that lung function should be exam-
90
Articles of general interest--Ft/
ined immediately before commencement of work after at least a weekend away from the plant, to provide baseline measurements. The results presented in this study confirmed earlier indications (Cited in F.C.‘I: 1969, 7, 699) of a correlation between acute and chronic loss of FEV. It was suggested that workers who exhibit large acute pulmonary changes following TDI exposure should be frequently re-examined so that chronic changes in lung function may be detected at an early stage. In another study, the health of a number of workers in a TDI-manufacturing plant was monitored by Butcher er al. (Am. Rev. resp. Dis. 1977, 116, 411) over a 2.5year period. For purposes of comparison, the workers were divided essentially into three groups: those who had daily contact with TDI (group I). maintenance personnel who had intermittent contact (group II), and a group of non-exposed controls. All groups were comparable in atopic status, age, sex and race but were not matched for size or smoking habits. Before the start of TDI production (April 1973), and at roughly 6-monthly intervals, the immunological status and health of the workforce was evaluated. Of the 103 workers interviewed in April 1973, 89 subsequently undertook jobs entailing regular or intermittent exposure to TDI. Over the period of the study, the continuously monitored levels of TDI in the factory air often exceeded the present TLV of transient level being 0.02 ppm, the maximum 0.04 ppm. In the exposed group there was a significant increase (P < 0.01) in the prevalence of lower respiratory problems (cough, wheezing, shortness of breath), compared with the control group. In other respects, including the incidence of bronchitis and upper respiratory symptoms, immunoglobuhn levels, peripheralblood eosinophil counts and the average performance in pulmonary-function tests, TDI exposure had no discernible adverse effects. Unfortunately the results of the pulmonary-function tests were analysed only with respect to length of TDI exposure which. in the light of the conclusions drawn by Wegman et al. (1977, lot. cit.) may explain the apparent absence of a TDI-related effect. In spite of these largely negative results, a significant proportion of the workforce studied by Butcher et al. (lot. cit.) did develop sensitivity to TDI. For example, 13 workers demonstrated clinical sensitivity to the monomer and, of these, nine suffered an adverse bronchial response when challenged with TDI exposures from 0.005 to 0.02 ppm. Even in these sensitive individuals, the controlled TDI exposure did not result in any increase in the blood eosinophil
Cosrr~er. Tosicol.
Vol. 17. No. I
-.
count. Inhalation challenge with acetyl+methylcholine generated a bronchial response in eight of the 11 TDI-sensitive individuals who were tested, whereas only one out of ten non-sensitized subjects gave a similar positive response. This may have predictive value in the screening of workers for bronchial hyperreactivity before they enter jobs involving potential TDI exposure. An increasing incidence of TDI-specific IgE antibodies was detected using a radioallergosorbent (RAST) test. The first positive results, a single case in each of groups I and II, were found in March 1975. Although by April 1976 eight workers exposed to the TDI gave evidence of allergenicity, two workers of the control group were similarly affected. There was also an increase in the number of people who gave a positive response in a skin test with TDIhuman serum albumin (HSA) conjugate; a total of ten individuals of either group I or II exhibited positive but small reactions during the 3 years of observation, the first positive result occurring in March 1974. Somewhat surprisingly none of the workers who gave evidence of sensitivity to TDI in the RAST or patch tests were among the thirteen subjects who demonstrated clinical sensitivity to TDI. Wegman et al. (1977, lot. cit.) mentioned their use of personal as well as area sampling and drew attention to an earlier study in which this precaution had not been taken. Comparative air-sampling studies carried out by Butcher et al. (lot. cit.) confirmed the need to relate observed biological effects with individual levels of exposure rather than with levels deduced from area monitoring, by demonstrating a marked lack of correlation between the results of personal and area measurements. The monitoring programme used by Wegman et al. (1977, lot. cir.) does not seem entirely satisfactory, however, and it would be of value if their data could be confirmed and extended by a study involving the regular measurement of breathing-zone concentrations of TDI at intervals considerably more frequent than the five measurements in 2 years used as the basis for their reported study. In addition to providing further clues to safe exposure levels of TDI, these reports underline some of the pitfalls involved in such studies and some of the precautions that must be observed if meaningful results are to be obtained not only for TDI but also for other industrial chemicals. [J. Hopkins-BIBRA]
