Exposure to lead of the Belgian population

Summary According to the Council Directive of 29 March 1977 on biological screening of the population for lead, the blood-lead levels (PbB) were determined in samples of the Belgian population not occupationally exposed to this metal. Two campaigns of sampling were performed: the first one in 1979 (1678 samples analysed) and the second in 1981 (1000 samples analysed). Sampling was done in urban and industrial zones, as well as in areas where lead risk could be present. Concerning the urban and industrial areas, the results obtained seem to indicate that a particular lead risk does not exist for the adult population if we consider the reference levels of the CEE Directive. Moreover, the results of the second campaign of sampling showed a decreasing trend: the median PbB values dropped from 183 to 156 g/l in Brussels and from 192 to 139 g/l in Liège. This could be partly due to the limitation of the lead content of gazoline. On the other hand, the results of the surveys clearly demonstrated the existence of two areas where an obvious lead risk exists. In one of those, the lead risk is of industrial origin (lead smelter) and concerns mainly children: median PbB value 260 g/l, percentile 90 and 98 respectively 390 and 430 g/l. In the other one, the lead risk is from a hydric source and concerns adults and children: median PbB value 258 g/l, percentile 90 and 98 respectively 370 and 520 g/l.     

Behaviour of some indicators of biological effect in female lead workers

Summary The relationships between certain indicators of internal dose and of biological effect were studied in 93 adult women with varying degrees of exposure to lead (PbB levels ranging from 8 to 74 g/ 100 ml). The results were compared with those obtained in a group of 95 males with more of less similar exposure. In both groups a good correlation was found between PbB and ALAD, EP, CPU taken singularly and the trend of the indicators of effect, depending on PbB levels, was similar: the decrease in ALAD values was already clear at PbB levels which do not cause an elevation of EP and the erythrocyte metabolite increased earlier than CPU. Considering the same levels of internal lead load (measured by both PbB and PbU-EDTA) in women, EP values were higher than in the men. No significant difference was established between the two sexes regarding ALAD and CPU values, when considered at the same PbB levels. Validity of ALAD and EP in the females, as already shown in our previous studies on males, was moderate in predicting PbB levels 40 g/100 ml, while it clearly improved at PbB levels 50–60 g/ 100 ml. This indicates that for screening women of child-bearing age the two indicators of effect must be used with caution, since a value of 40 g/100 ml has been proposed as the permissible PbB limit.Abbreviations PbB blood lead (g/100 ml) - PbU-EDTA amount of chelatable lead excreted with 24 hours urine after administration of CaNa₂ EDTA (1 g intravenously) - ALAD -aminolevulinic acid dehydratase activity of erythrocytes (mU/ml RBC) - EP erythrocyte protoporphyrin (g/100 ml RBC) - ALAU urinary -aminolevulinic acid (mg/1) - CPU urinary coproporphyrin (g/1)     

Relationship between inhibition of erythrocyte pyrimidine 5′-nucleotidase activity and biological response for porphyrin metabolism in workers occupationally exposed to lead

Summary A rapid determination of erythrocyte pyrimidine 5-nucleotidase (P5N) activity in lead workers was carried out using a high-performance liquid chromatograph (HPLC). The P5N activity had a good negative correlation with the concentration of lead in blood (PbB) ranging from 16 to 96 g/dl (r = -0.82, n = 77). Further, the P5N was compared with other biological parameters: erythrocyte -aminolevulinic acid dehydratase (ALAD) activity, erythrocyte protoporphyrin (PROTO), urinary -aminolevulinic acid (ALA) and urinary coproporphyrin (COPRO).The correlation coefficients between P5N and ALAD, log PROTO, log ALA, and log COPRO were 0.59, –0.72, –0.65, and –0.61, respectively. On the other hand, the normal value of P5N obtained from 72 healthy subjects was 11.9 ± 2.1 units; ol uridine/h/g Hb (mean ± SD), indicating that the lower limit of 95% confidence interval for normal P5N was about 8 units. When P5N was cut off at 8 units in 77 lead workers, the validity (sensitivity + specificity) for PbB 40 g/dl, PbB 60 gg/dl, erythrocyte PROTO 150 g/dl RBC, urinary ALA 6 mg/l, and urinary COPRO 150 g/l was 1.66, 1.76, 1.57, 1.68, and 1.60, respectively. From these results, it was confirmed that the erythrocyte P5N test is suitable for the biological monitoring of exposure to lead in a wide range, and its activity is useful in predicting the disturbance of porphyrin metabolism induced by lead.     

An electroneurographic assessment of subclinical lead neurotoxicity

Summary While heavy exposure to inorganic lead is capable of inducing symptomatic neuropathy in man, the subclinical neuropathy due to low levels of occupational lead exposure remains to be proved. The reported results of electroneurographic studies on lead workers, however, have been controversial. In this study, 40 lead smeltery workers and 50 non-exposed referents were investigated. The air concentrations of lead at worksites were 0.25 to 42.5 mg/m³. The geometric means of PbB, PbU and -ALAU in lead exposed group were 40.03 g/dl, 71 g/l and 4.68 mg/l respectively, which were significantly higher (P < 0.001) than those (7.01 g/dl, 6.0 g/l and 1.81 mg/l respectively) in the reference group. There were no clinical symptoms or signs of nerve damage in either group. Alcoholism and diabetes were excluded in both groups. Nerve conduction velocity was measured by a DISA 1500 electromyograph in both groups. Eleven electroneurographic parameters, including motor nerve conduction velocity (MCV) and distal latency (DML) of median, ulnar and peroneal nerves as well as sensory nerve conduction velocity (SCV) and distal latency (DSL) of median, ulnar and sural nerves, showed statistically significant differences between the two groups. However, the results of electroneurographic measurements of each individual in the lead-exposed group were all within the normal range. There was no correlation between the bloodlead levels and the neurophysiological measurements except for the median MCV. No correlation was seen between the median MCV and the exposure duration. A reduction in MCVs of median and ulnar nerves and sural SCV was unexpectedly seen in eight lead workers after chelation therapy with CaEDTA, although their mean PbB decreased from 42.08 to 27.92 g/dl. No consistent findings in nerve conduction were found at these exposure levels.     

Free erythrocyte protoporphyrin as an indicator of the biological effect of lead in adult males

Summary The relationship between FEP and the indicators of dose (PbB, PbU, PbU-EDTA) was examined in a group of male subjects who had left lead-exposing jobs more than 12 months previously.In these subjects, FEP and PbB and FEP and PbU were correlated to a distinctly lower degree compared to previous findings in currently exposed subjects, although the correlations were still statistically significant. In the previously exposed subjects the erythrocyte metabolite displayed definitely higher values than those found in currently exposed subjects at the same PbB or PbU levels.A very close correlation was found between FEP and PbU-EDTA, as was found in exposed subjects. The regression curve assumed an identical profile in the two situations. From these results it may be concluded that FEP persists at high levels for a long time after cessation of exposure due to a direct inhibition of heme synthetase caused by lead released from the tissue deposits.It should be noted that FEP proved to be a valid test for predicting the amount of lead storage, even a long time after cessation of exposure.Abbreviations PbB blood lead (g/100 ml) - PbU lead in urine (g/l) - PbU-EDTA amount of chelatable lead excreted with 24 h urine after administration of Ca NA₂ EDTA (1 g intravenously) - FEP free erythrocyte protoporphyrin (g/100 ml RBC) - ALAU urinary delta-aminolevulinic acid (mg/l) - CPU urinary coproporphyrin (g/l)     

An effect of erythrocyte protoporphyrin on blood manganese in lead-exposed children and adults

Summary In one study in 2- and 3-year-old children (geom. average 143 g Pb/1) and in two studies in workers (geom. average 483 pg Pb/1 and 323 g Pb/1) manganese in blood levels increased with blood lead and with free erythrocyte porphyrin (FEP). The zero-order correlation between PbB and MnB disappeared when FEP was kept constant. The conclusion is drawn that the increase of MnB with increasing PbB is probably not due to simultaneous exposure, neither to direct interaction between Pb and Mn, but mediated through a relationship between Mn and porphyrin in erythrocytes.This study was supported by a grant from the Dutch Prevention Fund     

High medical consultation rates of lead workers after industrial dispute over lead effects

Summary Medical consultation rates were compared between a group of lead workers (346 males) and two groups of non-lead workers (317 and 329 males) in a newspaper company where a serious industrial dispute took place over health effects of lead three years before this study. The comparison was also made within the group of lead workers. Maximal blood lead concentrations (PbBs) ranged from 0.1 mol/kg to 3.6 mol/kg (74 g/ 100 g) with an average of 1.3 mol/kg in the past three years. Ages averaged 35 years in lead workers, and 34 and 30 years in non-lead workers, the ranges being 19-55 years in all.The consultation rate of lead workers was significantly higher than that of both the non-lead workers (P<0.001), when the number of workers who consulted physicians or dentists once or more for a year per 100 workers (general consultation rate) was compared. Disease-specific consultation rates were also higher in lead workers for seven categories of diseases and injuries such as hypertensive disease and peptic ulcers.When lead workers were divided into three groups by PbB or erythrocytes delta-aminolevulinic acid dehydratase (ALAD) levels, however, no significantly high rate was found in the higher PbB groups nor lower ALAD groups in terms of general and disease-specific consultation rates.It was concluded that the industrial dispute might have been a major cause of the high consultation rate of lead workers.     

Exposure to lead and cadmium of children living in different areas of North-West Germany: results of biological monitoring studies 1982–1986

Summary Between 1982 and 1986 several surveys were carried out to determine the levels of lead and cadmium in blood, urine, and shed deciduous teeth (incisors only) of children living in rural, suburban, urban, and industrial areas of North-West Germany. Blood lead (PbB) and blood cadmium (CdB) were measured in about 4000 children. In rural, suburban and urban areas the median PbB levels vary between 5.5 and 7 g/dl, with 98th percentiles varying between 10 and 13 g/dl. The median CdB levels are between 0.1 and 0.2 g/dl, with 95th percentiles between 0.3 and 0.4 g/l. Children from urban areas have significantly higher PbB levels than children from rural and suburban areas. Regarding CdB no differences could be detected. Children living in areas around lead and zinc smelters, particularly those living very close to the smelters, have substantially increased PbB and CdB levels. Children from lead worker families also have substantially increased PbB and CdB levels. The lead levels in shed milk teeth (PbT) were determined in about 3000 children. In rural, suburban and urban areas the median PbT levels are between 2 and 3 g/g, with 95th percentiles between 4 and 7 g/g. Children from urban areas have significantly higher PbT levels than children from rural and suburban areas. The highest PbT levels (on a group basis) are in children from nonferrous smelter areas. The median levels of lead in urine (PbU) are between 6 and 10 g/g creatinine, with 95th percentiles between 20 and 30 g/g creatinine. Children from polluted areas have higher PbU levels than children from less polluted areas. The median levels of cadmium in urine (CdU) are in the order of 0.1 g/g creatinine, with 95th percentiles being in the range of 0.5 and 1.0 g/g creatinine. Girls have higher CdU levels than boys. There are no differences between groups of children from different areas. Children from lead worker families have higher PbU and CdU levels than otherwise comparable children. The results of the present studies indicate a further decrease of PbB in children from North-West Germany since the CEC blood lead campaigns carried out in 1979 and 1981. The decrease of lead exposure also seems to be reflected by a decrease of tooth lead levels.The studies presented in this communication were supported by the Ministry of Work, Health and Social Affairs and the Ministry of Environment and Agriculture of Nordrhein-West-falen, FRG     

Urinary chlorophenols in sawmill workers

Summary The concentration of urinary chlorophenol was assayed for 230 sawmill workers. Information on the work tasks was obtained through questionnaires from occupational health centres. The workers were divided into three groups on the basis of the type of exposure: (1) those with skin absorption as the main route, (2) those with skin and respiratory route of equal importance and (3) those with respiratory tract as the main route. The concentrations of urinary chlorophenol were higher in workers with skin absorption as the main route (median concentration: 7.8 mol l^–1; range 0.1 to 210.9 mol l^–1) than in those with both routes of equal importance (1.4 mol l^–1; range 0.1 to 47.8 mol l^–1, P<0.001) or in those with mainly respiratory route (0.9 mol l^–1; range 0.1 to 13.3 mol l^–1, P<0.001). The urinary chlorophenol concentration was below 15 moll^–1 in all workers with the lungs as the main absorption route. In nine out of 112 workers whose main absorption route was the skin, the urinary chlorophenol values were above 50 mol l^–1. Six were loaders when the through-dipping method was used. In two of them urinary chlorophenol concentrations were as high as 170.8 and 210.9 mol l^–1, These results emphasize the need to develop and use simple methods of protection against skin contact with chlorophenols.     

Blood toluene as a biological index of environmental toluene exposure in the “normal” population and in occupationally exposed workers immediately after exposure and 16 hours later

Blood toluene was measured in a group of 100 workers occupationally exposed to a mean 8-h environmental toluene concentration of 128 g/l (34 ppm), and in a group of 269 normal subjects without occupational exposure to toluene. The mean blood toluene of the workers at the end of the shift and the following morning, after 16 h, was 457 and 38 g/l, respectively. The normal subjects had a blood toluene level of 1.1 g/l. On the basis of the highly significant correlation between blood toluene and occupational exposure, it can be calculated that environmental toluene exposure of 188 and 377 g/l (50 and 100 ppm) gives end-of-shift blood toluene levels of 690 and 1390 g/l, respectively. The corresponding blood toluene levels on the following morning are 50 and 100 /l, respectively.     

Blood styrene concentrations in a “normal” population and in exposed workers 16 hours after the end of the workshift

Summary Blood styrene was measured by a gas chromatography-mass spectrometry method in 81 normal people and in 76 workers exposed to styrene. In the normal subjects, styrene was also tested in alveolar and environmental air. Styrene was found in nearly all (95%) blood samples. Average styrene levels in the normal subjects were 221 ng/1 in blood (Cb), 3 ng/1 in alveolar air (Ca) and 6 ng/1 in environmental air (Ci). Styrene levels did not differ significantly between smokers and non-smokers, 95% of values being below 512 ng/1 in Cb, 7 ng/1 in Ca and 15 ng/l in Ci. In workers with an average exposure to styrene of 204 g/l, at the end of the workshift, mean blood styrene concentration was 1211 g/l. In blood samples collected at the end of the Thursday shift, styrene levels were significantly higher (1590 g/1) than those found at the end of the Monday shift (1068 g/l. A similar difference was found in samples taken the morning after exposure (60 and 119 g/l, respectively). Significant correlations between blood and environmental styrene were found both at the end of the shift and the morning after exposure (r=0.61 and 0.41, respectively). In workers occupationally exposed to styrene, 16 h after the end of the workshift, blood styrene (94 g/l) was significantly higher than that found in the normal subjects (0.22 g/l). The half-life of blood styrene was 3.9 h.     

Lead in deciduous teeth of children living in a non-ferrous smelter area and a rural area of the FRG

Summary Lead concentrations were measured in the deciduous teeth (incisors) of 302 children living in a lead-smelter area in the FRG (Stolberg, Rheinland) and of 86 children living in a nonpolluted rural area (Gummersbach, Bergisches Land). Blood lead levels were determined in 83 of the children living in the lead smelter area. On average, tooth lead levels of children living in the smelter area (mean: 6.0 g/g; range: 1.49–38.5 g/g) were significantly higher than those of children living in the rural area (mean: 3.9 g/g; range: 1.6–9.4 g/g). Blood lead levels were 6.8–33.8 g/100 ml (mean: 14.3 g/100 ml). Children of lead workers had on average higher tooth lead and blood lead levels than children of people who were not lead-workers. Tooth lead levels increased with increasing duration of residence in the lead-smelter area and with the degree of local environmental pollution by lead, as indicated by the lead content of the atmospheric dust fall-out around the children's homes. The correlation coefficient of tooth lead vs blood lead was 0.47. The intra-individual variability of tooth lead levels was low (r=0.86), and tooth lead levels of brothers and sisters were similar (r=0.75), suggesting that tooth lead may be used as a representative and reliable indicator of long-term lead exposure.This study was carried out at the request and with support of the Ministerium für Arbeit, Gesundheit und Soziales NW, Düsseldorf     

Biological and environmental monitoring of occupational exposure of pharmaceutical plant workers to methotrexate

Summary The exposure of 11 pharmaceutical plant workers to methotrexate (MTX) was studied. Personal air samples were taken during the different manufacturing processes: drug compounding, vial filling, and tablet preparation. The uptake of MTX was established by the determination of MTX in urine. MTX was analyzed using the fluorescence polarization immunoassay (FPIA), a method that is frequently used for monitoring serum levels in patients treated with MTX. The FPIA method was modified in such a way that MTX could be measured quickly and efficiently in air and urine samples. MTX was detected in air samples of all workers except for those involved in the vial filling process (range: 0.8–182 g/m³; median: 10 g/m³). The highest concentrations were observed for workers weighing MTX (118 and 182 g/m³). MTX was detected in urine samples of all workers. The mean cumulative MTX excretion over 72–96 h was 13.4 g MTX-equivalents (range: 6.1–24 g MTX-equiva g MTX-equivalents (range: 6.1–24 g MTX-equivalents). lents). A significantly lower background level of 10.2 g A significantly lower background level of 10.2 g MTX-equivalents was measured in urine of 30 control persons (range: 4.9–21 g MTX-equivalents).     

Relationship of air lead and blood lead for workers at an automobile battery factory

Summary Air lead and blood lead data, recorded over a period of 3 years for 972 employees at an automobile battery factory as part of a lead control program, were summarized and statistically analyzed. The air lead values were measured by mobile area samplers for approximately 2 years and then by personal samplers for approximately 1 year. Blood lead analyses were usually performed once a month for most of the workers.The trend in air lead levels was significantly upward in the 1st year and significantly downward in the 2nd year while the trend in blood lead levels was significantly downward in the 1st year and in the 3rd year. There were no other significant trends.To assess the relationship between air lead and blood lead, data were used whenever an air lead obtained by personal sampler was followed within 1 month by a blood lead on the same worker. The variables age, job tenure, and department identity were included in an analysis of covariance. Only air lead and departments were significant, accounting for 9% and 13% of the variance in blood lead, respectively. From these data 95% confidence limits were calculated for predicting blood leads from given air leads for an individual worker. These were 30–68 g/100 ml at 200 g/m³; 25–62 g/ 100 ml at 100 g/m³, and 22–60 g/100 ml at 50 g/m³.     

Current external and internal exposure to naphthalene of workers occupationally exposed to polycyclic aromatic hydrocarbons in different industries

Objectives: External and internal exposure to naphthalene was examined in the most important industries that are typically concerned with polycyclic aromatic hydrocarbon (PAH)-induced diseases (cancer). Furthermore, a control collective from the general population was investigated. Methods: External naphthalene was determined by personal air sampling (n=205). The internal exposure was examined by urinary metabolites 1-naphthol and 2-naphthol (n=277). Results: Highest median concentrations of naphthalene in air were found in converter infeed (93.2 g/m³) and coal-tar distillation (35.8 g/m³). Moderate and low levels were determined in coking plants (14.5 g/m³) and in the production of refractories (6.1 g/m³) and graphite electrodes (0.7 g/m³). Biological monitoring revealed concentrations of the sum of both metabolites [(1+2)-NOL] in smokers to be increased by 1.6–6.4 times compared with that in non-smokers at the same workplaces. Among non-smokers we found high median (1+2)-NOL levels in converter bricklayers (120.1 g/l), in coal-tar distillation workers (56.0 g/l) and in coking plant workers (29.5 g/l). (1+2)-NOL concentrations around 10 g/l were found in the production of refractories and graphite electrodes. There was a rough coherency between external and internal naphthalene exposure. In the controls, median (1+2)-NOL concentrations were 10.9 g/l in non-smokers urine and 40.3 g/l in smokers urine samples. Conclusions: Actual conditions of occupational hygiene at the workplaces investigated in this comprehensive study are better than those that current limit values of 50,000 g/m³ (TLV, TRK) seem to induce. It has become obvious that tobacco smoking is a crucial confounding factor in biological monitoring of naphthalene-exposed humans, making interpretation of occupationally increased naphthol excretions very difficult at low exposure levels.     

Internal exposure to organic substances in a municipal waste incinerator

Summary Fifty-three persons occupied in a municipal waste incinerator were examined with respect to their internal exposure to organic substances which may be produced during pyrolysis of organic matter. For this purpose the levels of benzene in blood, polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) in plasma, and mono- (MCPs), di- (DCPs), tri- (TCPs), tetra-(TECPs) and pentachlorophenol (PCP) and hydroxypyrene in urine were determined. For control purposes, 431 men and women were examined. Significantly higher values for the workers were found for the excretion of hydroxypyrene [median (m): 0.24vs 0.11 g/l; non-smokers], 2,4/2,5-DCP (m: 10.5 vs 3.9 g/l) and 2,4,5-TCP (m: 1.2 vs 0.8 g/l) and for the HCB level in plasma (m: 4.4 vs 2.8 g/l). For the concentrations of 4-MCP and 2,3,4,6/2,3,5,6-TECP, the controls had significantly higher concentrations in urine than did the workers in the incineration plant (m: 4-MCP 1.7 vs 1.2; 2,3,4,6/2,3,5,6-TECP: 1.2 vs 0.3 g/l). No significant differences between workers and controls were detected with respect to benzene in blood (m: 0.20 vs 0.28 g/l; non-smokers), 2,4,6-TCP and PCPs in urine (m: 0.85 vs 0.60 and 2.2 vs 2.2 g/l) or the levels of PCB congeners in plasma (m: 138, 153, 180: 5.6 vs 4.1 g/l). The elevated levels of hydroxypyrene, 2,4/2,5-DCP, 2,4,5-TCP and HCB in biological material may be related to the incineration of the waste. These elevations, however, are very small and are of interest more from the environmental than from the occupational point of view.     

Blood lead concentrations: Apparent reduction over approximately one decade

Summary Blood lead concentrations of male subjects presenting for preemployment examination during the period 1967–1969 have been compared with those obtained during the period 1978–1980. A statistically significant reduction of the geometric mean value from 20.2 g Pb/100 ml whole blood to 16.6 g Pb/100 ml whole blood has been found.     

Nitrous oxide in blood and urine of operating theatre personnel and the general population

Nitrous oxide (N₂O) was assayed in 676 urine samples and 101 blood samples provided after exposure by operating theatre personnel from nine hospitals. The blood and urine assays were repeated in 25 subjects 18 h after the end of exposure. For 80 subjects, environmental N₂O was also measured during intraoperative exposure. Mean urinary N₂O in the 676 subjects at the end of exposure was 40 g/l (range 1–3805 g/l); in 10 of the 676 subjects, urinary N₂O was in the range 279–3805 g/l (mean 1202 /l). The 98^th percentile was 120 g/l. Mean blood N₂O at the end of exposure, measured in 101 subjects, was 21 g/l (median 16 g/l, range 1–75 g/l). Blood and urine N₂O (1.5 g/l and 4.9 g/l, respectively) in 25 subjects, 18 h after exposure, was significantly higher than in occupationally non-exposed subjects (blood 0.91 g/l, urine 1 g/l). Environmental exposure was significantly related to blood and urinary N₂O (r = 0.59 andr = 0.64, respectively). Blood and urinary N₂O were significantly related to each other (r = 0.71), and were equivalent to about 25% of the environmental exposure level. The mean urinary N₂O of 1202 g/l in 10/676 subjects was not related to environmental exposure in the operating theatre. The highest urinary N₂O levels measured in these 10/676 subjects could be explained by an asymptomatic urinary infection.     

Human exposure to volatile halogenated hydrocarbons from the general environment

Summary The objective of this study was to assess individual human exposure to volatile halogenated hydrocarbons (VHH) under normal environmental conditions by means of biological monitoring, i.e. by the measurement of these compounds or their metabolites in body fluids, such as blood, serum, and urine. Blood samples of 39 normal subjects without known occupational exposure to these agents were examined for the occurrence of VHH. The following compounds were present in quantifiable concentrations in 60 to 95% of the blood samples examined: chloroform (median 0.2 g/l; range < 0.1–1.7 g/l), 1,1,1-trichloroethane (median 0.2 g/l; range < 0.1–3.4 g/l), tetrachloroethylene (median 0.4 g/l; range < 0.1–3.7 g/l). Trichloroethylene could be detected in 31% of all blood samples (median < 0.1 g/l; range < 0.1–1.3 g/l). In addition, the levels of trichloroacetic acid (TCA) were determined in serum and 24-h urine samples of 43 and 94, respectively, normal subjects. TCA was present in measurable concentrations in all serum and urine samples examined. The median of the TCA levels in serum was 21.4 g/l (range 4.8–221.2 g/l) and in urine 6.0 g/24 h (range 0.6–261.4 g/24 h). The results are discussed in relation to data from the literature on human exposure to VHH from the general environment, i.e. via air, food, and water. The upper normal limits calculated from the results of this investigation can be used to detect even minor excessive exposures to VHH.     

Increase in the amount of erythrocyte δ-aminolevulinic acid dehydratase in workers with moderate lead exposure

Summary The amount of ALA-D in human erythrocytes was determined directly by radioimmunoassay or calculated from the restored activity assayed in the presence of zinc and dithiothreitol, and a good correlation was observed between the RIA-based and the restored activity-based amounts.The RIA-based amount of ALA-D in the blood of 10 normal individuals (blood lead levels of 5.6 ± 2.3 g/100 ml: mean ± SD) and 19 lead-exposed workers (blood lead levels of 41.2 ± 10.2 g/100 ml) was 54.1 ± 11.8 g/ml blood and 92.3 ± 20.6 g/ml blood, respectively, indicating an apparent increase of the enzyme amount in lead-exposed workers.A significant increase in the amount of erythrocyte ALA-D calculated from the restored activity in lead-exposed workers was observed even in the low blood lead level of 10–20 g/100 ml, resulting in the range of blood lead level 20–40 g/100 ml. No significant difference was observed in hematocrit and hemoglobin content between lead-exposed and non-exposed groups. These observations suggested that the increase of erythrocyte ALA-D in lead exposure was not due to anemia, which might result in the increase of young erythrocytes in peripheral blood.This increase in the amount of ALA-D in human erythrocytes might be a result of the function to overcome the inhibition of the enzyme in bone marrow cells during lead exposure, and these findings may throw light on the danger to human health of low-level lead toxicity.Abbreviations ALA-D -Aminolevulinic acid dehydratase or 5-Amnoevulinic acid hydro-lyase, EC 4.2.1.24 - ALA -Aminolevulinic acid - Rc Reticulocyte - RIA Radioimmunoassay - DTT Dithiothreitol Supported in parts by Science Research Fund of the Ministry of Education, Science and Culture of Japan and by Research Grant of Fujiwara Foundation of Kyoto University