Effect of Lead on δ-Aminolevulinic Acid Dehydrase Activity in Red Blood Cells

The activity of δ-aminolevulinic acid dehydrase (ALAD) in red blood cells diminishes in lead poisoning. The variation of ALAD activity with the concentration of lead in the blood and the variation of ALAD activity with the concentration of δ-aminolevulinic acid in the urine are both exponential and the correlations inverse. In a study of ALAD in, inter alia, traffic workers, enzymatic activity proved normal. It may, therefore, be assumed that there is almost no risk of lead poisoning by air pollution in the area studied (center of a town with about 250,000 inhabitants). Determination of ALAD activity in erythrocytes is considered a suitable method for demographic studies of exposure to lead. The test is too sensitive for routine follow-up of the degree of lead intoxication in occupationally exposed workers.     

Lead exposure in highway toll-booth workers

Biomarkers of lead exposure (blood lead, BPb) and effect (erythrocyte protoporhyrin, EP, and activity of delta-aminolevulinic acid dehydratase, ALAD) were measured in 68 male toll-booth operators (aged 22-60 years) on the Zagreb-Karlovac motorway. Average values (arithmetic mean +/- standard deviation) were: 61.8 +/- 29.3 micrograms/L for BPb, 0.70 +/- 0.20 mumol/L erythrocytes for EP, and 50.6 +/- 9.8 U/L erythrocytes for ALAD. All were within the normal range determined for general population (BPb < 150 micrograms/L, EP < 1.62 mumol/L erythrocytes, and ALAD > 35 U/L erythrocytes). A significant positive correlation was found between BPb and EP (r = 0.367, P < 0.01) and an inverse correlation between BPb and ALAD (r = -0.271, P < 0.05) and for EP and ALAD (r = -0.381, P < 0.01). Significant correlations were found between BPb or ALAD and smoking index (r = 0.486, P < 0.01, and r = -0.322, P < 0.01, respectively), whereas BPb also significantly correlated with blood gamma-glutamyl transferase (GGT) activity, which may indicate hepatotoxic effect of alcohol consumption (r = 0.334, P < 0.01). Among standard spirometric tests, BPb inversely correlated with FEV1 (r = -0.251, P < 0.05) and Tiffenau index (r = -0.280, P < 0.05), whereas ALAD positively correlated with FEF75-85 (r = 0.261, P < 0.05) and Tiffenau index (r = 0.314, P < 0.01). Among standard hematologic tests, BPb positively correlated with MCV (r = 0.282, P < 0.05), EP inversely correlated with erythrocyte count (r = -0.253, P < 0.05), and ALAD positively correlated with MCHC (r = 0.306, P < 0.05) and inversely with MCV (r = -0.250, P < 0.05). Although PbB values in these workers are within occupational exposure limits, they are higher than in corresponding occupations in developed countries. This may be explained by greater exposure to lead in ambient air, tobacco (through mainstream and sidestream smoking) and alcohol in this population.     

Adverse effects in workers exposed to inorganic lead

This paper describes a retrospective cohort study comparing 60 workers occupationally exposed to inorganic lead and 60 matched controls. All subjects were assessed using data obtained from a specially designed Questionnaire for lead exposure and toxic effects assessment, physical examination, spirometry, ECG, and laboratory tests including blood lead level (BLL) and biomarkers of lead toxic effects. Muscle pain, droopiness, and work-related nasal symptoms were significantly more frequent in lead workers. The prevalence of lung symptoms was higher in lead workers than in controls, but not significantly (20 % vs. 6.6 %, respectively). Mean values of BLL and delta-aminolevulinic acid (ALA) were significantly higher in lead workers. The activity of delta-aminolevulinic acid dehydratase (ALAD) in lead workers was significantly lower than in controls. Abnormal of BLL, ALAD, and ALA were more frequent in lead workers, with statistical difference for BLL and ALAD. Inverse correlation was found between BLL and ALAD, and positive correlation between BLL and age, years of employment, and years of exposure. Inverse correlation was found between ALAD and age, years of employment, years of exposure, blood pressure, alcohol consumption, and years of alcohol consumption. Changes in spirometry correlated inversely with BLL. A positive correlation was found between BLL and erythrocyte count and haemoglobin concentration, whereas it was inverse for ALAD and haemoglobin concentration. A significant difference was found for BLL and ALAD, with a very high odds ratio (14.64 and 7.23, respectively) and high relative risk (4.18 and 3.08, respectively). Our data have confirmed the association between occupational lead exposure and deviation in specific biological markers of lead effect and between the role of occupational exposure in the development of adverse effects.     

Biological Response and Subjective Symptoms in Low Level Lead Exposure

Workers occupationally exposed to lead in the air of up to 60μg/cu m were examined for blood lead (Pb-B), urinary δ-aminolevulinic acid (ALA), erythrocyte ALA dehydrase (ALAD), hemoglobin, hematocrit, red blood cell count, and subjective symptoms.

The Pb-B and ALAD showed consistent increases and decreases, respectively, corresponding with the levels of Pb exposure, while other tests revealed no association with Pb. The range of Pb exposure as expressed by Pb-B was up to 50μg/100 gm. Subjective symptoms and urinary ALA are not likely to be increased at the Pb-B level of about 50μg/100 gm and less.     

Delta-Aminolevulinic Acid Dehydratase Activity of Erythrocytes and Liver Tissue in Man

The delta-aminolevulinic acid dehydratase (ALAD) activity of erythrocytes and of liver tissue was studied in subjects not occupationally exposed to lead. A considerable heterogeneity in the levels of ALAD activity of erythrocytes and of blood lead was confirmed in this group of subjects, an expression of the varying degree of absorption of lead that occurs in each individual who is exposed through pollution of the atmosphere and food. In the group of subjects studied, there was a correlation between the values of erythrocyte ALAD activity and the values of ALAD activity of liver tissue.     

Erythrocyte Protoporphyrin Test for Occupational Lead Exposure

? Determination of erythrocyte protoporphyrin levels was performed in workers who are occupationally exposed to lead. The level of erythrocyte protoporphyrin was easily measured with microsamples of blood by utilizing a fluorescent assay. The log of erythrocyte protoporphyrin level was closely correlated to blood lead level (r=.72) in lead-exposed workers. The erythrocyte protoporphyrin test is especially useful in the detection of mild increases in blood lead concentration under conditions of occupational exposure.     

Evaluation of genotoxic effects of lead in pottery-glaze workers using micronucleus assay, alkaline comet assay and DNA diffusion assay

Purpose

We investigated genotoxic effects of occupational exposure to lead acetate in pottery-glaze ceramic workers.

Methods

The study was carried out in 30 exposed workers and 30 matched controls, to whom several biochemical parameters—the blood lead (B-Pb; range: exposed, 41.68–404.77; controls, 12–52) and cadmium (B-Cd) level, the activity of delta-aminolevulinic acid dehydratase (ALAD), erythrocyte protoporphyrin (EP), the level of vitamin B₁₂ and folate in serum—were measured. The genotoxic effects were evaluated by the alkaline comet assay, the DNA diffusion assay and micronucleus test in peripheral blood lymphocytes.

Results

Subjects exposed to lead had significantly higher B-Pb level and, consequently, increased values of tail intensity (TI), frequency of apoptotic and necrotic cells, and frequency of micronuclei (MN). In contrast, their activity of ALAD, the level of vitamin B₁₂ and folate in serum were significantly lower compared to controls. Poisson regression analysis showed a significant correlation of profession, duration of exposure, smoking, level of cadmium in blood, ALAD and EP with primary DNA damage. A majority of primary damage repairs in a short period after exposure to a genotoxic agent. In addition, the influence of gender and level of vitamin B₁₂ and folate in serum MN frequency in exposed group was observed.

Conclusions

In this study, DNA diffusion and micronucleus test showed higher influence of tested parameters to DNA damage. The results indicate a need for concomitant use of at least two different biomarkers of exposure when estimating a genetic risk of lead exposure.     

Erythrocyte delta-aminolevulinic acid dehydratase genotype and other mechanisms affecting workers' susceptibility to lead.

In this study, the role of delta-aminolevulinic acid dehydratase (ALAD) variants in lead susceptibility was examined. The study subjects comprised 223 male workers, and the relationship between their blood lead level and erythrocyte ALAD activity or plasma/urine delta-aminolevulinic acid level was studied. Leukocyte specimens from 11 workers, whose erythrocyte ALAD activities were as low as one-fifth that of the other normal workers, were subjected to analyses of their ALAD and ALAD alleles. Further, the entire exon fragment of the ALAD gene was analyzed by polymerase chain reaction, and the reaction product was used as a target for direct DNA sequencing. Genomic DNA analysis revealed that all 11 workers had the ALAD allele, whereas the entire ALAD gene analysis failed to indicate other variants, except for the Rsa I site. The depletion in erythrocyte ALAD activity was not found to be caused by the ALAD allele.     

Studies on erythrocyte pyrimidine 5′-nucleotidase (P5N) test and its evaluation in workers occupationally exposed to lead

Summary An erythrocyte pyrimidine 5-nucleotidase (P5N) test was performed for 171 workers occupationally exposed to lead. Erythrocyte P5N activity was markedly inhibited by exposure to lead. Among several biological indicators (erythrocyte P5N, -aminolevulinic acid dehydratase (ALAD), protoporphyrin (PROTO), urinary -aminolevulinic acid (ALA), coproporphyrin (COPRO)), the P5N activity had the highest correlation with the concentration of lead in blood (r = – 0.77). A significant inhibition of erythrocyte P5N was found in groups of lead workers with blood-lead levels of more than 10 to 19 g/dl. This P5N inhibition started before any changes occurred in urinary ALA and COPRO. A 45 to 50% inhibition of P5N corresponded to the blood-lead value (50 g/dl) of the BEI recommended by ACGIH. In some lead workers, erythrocyte nucleotides (mainly CTP and UTP) were determined. The data indicated that a marked accumulation of these nucleotides had occurred, and their levels correlated negatively with P5N activity and positively with blood lead.     

Evaluation of lead exposure in workers at a lead-acid battery factory in Korea: with focus on activity of erythrocyte pyrimidine 5''-nucleotidase (P5N).

OBJECTIVE--To evaluate lead exposure among lead-acid battery workers in Korea, to evaluate in more detail the erythrocyte pyrimidine 5'-nucleotidase (P5N) test for lead exposure, and to evaluate the abnormal accumulation of erythrocyte pyrimidine nucleotides in the battery workers. METHODS--Activity of P5N and other biological variables were examined in 66 exposed workers in a lead-acid battery factory and in 26 non-exposed workers in Korea. RESULTS--At the factory the time-weighted average of 13 (72%) of 18 air samples for lead exceeded 0.05 (range 0.012-0.468) mg/m3. Blood lead concentration (PbB) in 39 of the 66 exposed workers was above 40 micrograms/dl, and the mean (SD) PbB in the exposed group was 45.7 (15.7) micrograms/dl. Compared with the nonexposed group, free erythrocyte protoporphyrin in the exposed group was significantly increased, whereas erythrocyte P5N activity and activity of erythrocyte delta-aminolevulinic acid dehydratase (ALAD) were significantly inhibited. Erythrocyte P5N activity had valid correlation biologically with PbB and with other biological variables, such as ALAD activity. In 28 exposed workers, the concentration of erythrocyte pyrimidine nucleotides (uridine 5'-diphosphate-glucose and cytidine 5'-triphosphate) correlated inversely with P5N activity and positively with PbB. CONCLUSIONS--These findings show that the depression of erythrocyte P5N activity by lead exposure results in the accumulation of erythrocyte pyrimidine nucleotides. In general, the standard analysis of PbB performed in laboratories around the world remains the most useful index of recent exposure. The results indicate that the erythrocyte P5N activity test provides supporting evidence of lead exposure and shows the effect of lead on nucleotide metabolism.     

Environmental and biological monitoring of arsenic in outdoor workers exposed to urban air pollutants

The aim of this study is to evaluate personal exposure to As in urban air in two groups of outdoor workers (traffic policemen and police drivers) of a big Italian city through: (a) environmental monitoring of As obtained by personal samples and (b) biological monitoring of total urinary As. The possible influence of smoking habit on urinary As was evaluated. We studied 122 male subjects, all Municipal Police employees: 84 traffic policemen and 38 police drivers exposed to urban pollutants. Personal exposure to As in air was significantly higher in traffic policemen than in police drivers (p=0.03). Mean age, length of service, alcohol drinking habit, number of cigarettes smoked/day and BMI were comparable between the groups of subjects studied. All subjects were working in the same urban area where they had lived for at least 5 yrs. Dietary habits and consumption of water from the water supply and/or mineral water were similar in traffic policemen and in police drivers. The values of total urinary As were significantly higher in traffic policemen (smokers and non smokers) than in police drivers (smokers and non smokers) (p=0.02). In the subgroup of non-smokers the values of total urinary As were significantly higher in traffic policemen than in police drivers (p=0.03). In traffic policemen and in police drivers total urinary As values were significantly correlated to the values of As in air (respectively r=0.9 and r=0.8, p<0.001). This is the first research in literature studying the exposure to As in outdoor workers occupationally exposed to urban pollutants, such as traffic policemen and police drivers. Personal exposure to As in the air, as well as the urinary excretion of As, is significantly higher in traffic policemen compared to drivers. These results can provide information about exposure to As in streets and in car for other categories of outdoor workers similarly exposed.     

Determination of delta-aminolevulinic acid dehydratase (ALAD) by enzyme immunoassay and its application to evaluation of lead exposure

Enzyme Immunoassay (EIA) technique using a glass bead was established in order to quantify the total amount of delta-aminolevulinic acid dehydratase (ALAD, EC 4, 2, 1, 24) including an inactivated enzyme and to determine the level of ALAD in erythrocytes of workers with moderate lead exposure. EIA was carried out by competitive antibody binding method in which the antigen (ALAD) was linked to a glass bead (O.D. 7 mm). A standard curve was fitted to the function y = A X B/(x-B) + C, where y is the enzymatic reaction product, x is the concentration of ALAD, and A, B and C are parameters. The coefficients of variation in the intra- and inter-assay were 3.7% and 6.5%, respectively. EIA-based amount of ALAD was 136.7 +/- 23 mg/l erythrocyte (mean +/- S.D.) in 66 workers. This ALAD amount was not found to be correlated with the lead level in the blood but correlated with the duration of lead-exposure. An especially good correlation (r = 0.453) was obtained with the inactivated portion of ALAD (EIA-based amount minus activity-based amount). On the other hand, the ratio of restored activity following heat treatment and addition of Zn and dithiothreitol to non-restored activity was well correlated with the lead level (r = 0.874), but not correlated with the duration of lead-exposure (r = 0.218). The inactivated portion of ALAD based on EIA accordingly may be considered a good indicator of the duration of lead exposure, and the activity-based amount of ALAD may be considered a suitable indicator of the extent of the present lead exposure.     

Lack of association of δ-aminolevulinic acid dehydratase genotype with cytogenetic damage in lead workers

Objective The objective of this study was to evaluate the correlations of genetic polymorphism of genotypes -aminolevulinic acid dehydratase (ALAD), blood lead levels (BLLs), zinc protoporphyrin (ZPP), sister chromatid exchanges (SCEs), and high SCE frequency cells (HFCs) in lead workers.Methods Three groups of lead workers were included in the study: high lead exposure group (26 workers), low lead exposure group (31 workers) and control group (30 controls who lived in an area uncontaminated by lead). Blood samples were taken from all subjects and analyzed for lead levels, ALAD genotype and SCE levels.Results Occupationally exposed workers had significantly higher BLLs, ZPP and hemoglobin levels than the controls. There were no differences among the three groups regarding percentages of ALAD 1-1 and ALAD 1-2 genotypes, but the ALAD 2-2 genotype was not detected in any of the three groups. There were no significant differences among the three groups for BLLs, ZPP and hemoglobin levels based on ALAD 1-1 and ALAD 1-2. Average SCE values in the high lead exposure group were significantly greater than those in the control group (6.2 vs 5.2 SCEs/cell, P<0.05). HFC analysis revealed a significantly higher HFC percentage (53.9%) in the high lead exposure group than in the low lead exposure group (16.1%) and the control group (10%). There appeared to be an interaction effect on HFC percentages between smoking and lead exposure. When multiple regression analysis was used, the factors that affected SCE levels were lead exposure and smoking, but ALAD genotypes did not have any significant effect.Conclusions A significant association existed between both SCE and HFC levels and lead exposure. However, different ALAD genotypes were not found to be associated with levels of blood lead and ZPP in the three groups.     

Relationship of blood lead levels to blood pressure in exhaust battery storage workers

Several researches has focused the hypothesis that low blood lead levels could be associated with an increased risk of hypertension. To assess the relation between occupational lead exposure and elevated blood pressure a group of 27 workers, age range from 27 to 62 years, mean (SD) 36.52 (+/- 8.16) yr; length of employment mean (DS) 2.97 (+/- 1.67) yr, were recruited as study subjects. The following variables were measured: blood lead concentration (BPb), delta-Aminolevulinic Acid Dehydratase (ALAD) activity, Zinc Protoporphirin (ZPP), creatinine, hematocrit, Body Mass Index (BMI) and Systolic Blood Pressure (SBP) and Diastolic Blood (DBP) Pressure. The results showed that long term occupational exposure was related to a slight increase of systolic and diastolic blood pressure among workers who had been exposed to higher level of lead with respect to workers exposed to lower level of lead. Furthermore, blood lead concentration (BPb) and ZPP resulted higher among workers exposed to higher level of ambient lead, while in the same group of workers ALAD activity resulted more inhibited. The authors concluded long term cumulative lead exposure can significantly increase blood pressure in low level Pb exposed workers.     

Behaviour of indicators of exposure and effect after cessation of occupational exposure to lead.

The behaviour of blood lead (PbB) and of some indicators of effect (erythrocyte protoporphyrin IX (EP), delta-aminolaevulinic acid dehydratase activity of erythrocytes (ALAD), and urinary delta-aminolaevulinic acid (ALAU)) were studied in subjects who had ceased working with inorganic lead for at least one year. Relations between these indices and chelatable lead (PbU-EDTA (lead in urine after injection of CaNa2 EDTA 1 g intravenously)), a test that is used to evaluate the lead deposits in the body, were also analysed. As a comparison, a group of subjects currently exposed was studied. In the workers with past exposure the PbB values were significantly lower, at the same PbU-EDTA levels, than those found in subjects at work. The relation between EP and PbU-EDTA shows that, corresponding levels of chelatable lead, the values of the erythrocyte metabolite are identical in the two groups. Considering the EP-PbB relation, however, at the same PbB levels the protoporphyrin values appear distinctly more altered in the subjects with past exposure. Similar results were obtained from a study of the relations between ALAD and PbU-EDTA and between ALAD and PbB. The relation between ALAU and PbU-EDTA, however, shows that, at the same PbU-EDTA levels the urinary metabolic in past-exposed subjects is distinctly lower than in subjects at work, while the relation between ALAU and PbB shows that, for similar blood lead values, the ALAU levels are identical. On the basis of the results obtained it is concluded that in subjects with past exposure, EP and ALAD can be used in establishing the persistence and extent of an "active deposit" of lead in the organism, while PbB is of very limited use.     

Relationship between delta-aminolevulinic acid dehydratase genotypes and heme precursors in lead workers

BACKGROUND: The objective of this study was to investigate the relationships between genotypes of delta-aminolevulinic acid (ALA) dehydratase (ALAD) and disturbances in the heme biosynthetic pathway by lead exposure. METHODS: The subjects were 192 male lead workers and 125 control subjects. Blood lead concentrations (Pb-B), plasma ALA concentrations (ALA-P), and ALAD genotypes were determined for all subjects. In lead workers, ALAD activity, ALA in urine (ALA-U), and erythrocyte zinc protoporphyrin (ZP) were also determined. RESULTS: The frequency of ALAD2 (minor type of ALAD allele) was calculated to be 0.087 in all subjects. No significant relationship was found between ALAD2 frequency and Pb-B levels in lead workers. ALAD1 homozygotes showed significantly higher levels of ZP and ALA-P in comparison with those of ALAD2 carriers at Pb-B levels more than 20 microg/dL and 40 microg/dL, respectively. CONCLUSIONS: ALAD1 homozygotes might be more susceptible than ALAD2 carriers to disturbances in heme metabolism caused by lead exposure.     

Individual variation in response to lead exposure: A dilemma for the occupational health physician

Subclinical lead poisoning with no clinical symptoms is a dilemma for the occupational health physician. He is supposed to assess when and how to treat workers at risk mainly by the results of biological monitoring. The aim of this study was to demonstrate different responses of biological indices in 50 lead-exposed workers who have been working in the same plant of lead pigment production factory. Twenty-one had normal, that is, permissible blood lead concentrations (PbB), erythrocyte protoporphyrin (EP), and aminolevulinic acid activity (ALAD) measured during regular periodic examinations (group 1). No differences between two measurements were found, although they were continuously working with lead. In 18 of the 50 workers (group 2). PbB and EP concentrations increased, whereas ALAD activity decreased: those parameters improved after a 3- to 6-month cessation of lead exposure. Seven of the 50 workers also had altered values of biological indices, but their condition improved spontaneously without cessation of lead exposure (group 3), while in the remaining four workers, elevated concentrations of biological indices did not change during the observation period. The reasons for such discrepancies and indications for chelation therapy are discussed. Am. J. Ind. Med. 31:631–635, 1997. © 1997 Wiley-Liss, Inc.     

Occupational exposure to agricultural chemicals: effect on the activities of some enzymes in the blood of farm workers

Objective: To determine the effect of different durations of exposure to agricultural chemicals on the activities of the blood enzymes δ-aminolevulinic acid dehydratase (ALAD), superoxide dismutase (SOD), and cholinesterase (ChE) in tobacco field workers. Methods: For this preliminary investigation, 8 volunteers (all smoked tobacco) who were working on a small tobacco farm were monitored over a period of 2 years along with a comparable urban unexposed group (n = 4). During the growing season between 1994 and 1996, dermal and respiratory exposure were determined and blood samples were drawn after the following durations of field work: (1) preexposure (0 DAY); (2) after 1 day of field work (1 DAY) – workers reentered fields at 24 h after spraying of acephate and maleic hydrazide; (3) after 30 days of field work (postspraying; 30 DAYS); and (4) Postexposure – no tobacco production. Standard analytical methods were used. Results: Activity of ALAD was depressed by 30% after 1 DAY and there was no further decrease in ALAD activity after 30 DAYS of field work. SOD activity, in contrast, declined by 29% and 50% after 1 DAY and 30 DAYS, respectively, as compared with 0-DAY activity and that of the urban control, which was similar to 0-DAY activity (P ≤ 0.05). Plasma ChE activity declined by 19% after both 1 and 30 DAYS of exposure/field work. The activities of all three enzymes were restored to urban control or preexposure levels during postexposure. Plasma Cd levels were high in the samples taken after 30 DAYS as compared with the preexposure levels. Respiratory nicotine exposure was highest after 30 DAYS of field work. Conclusion: This preliminary study suggests that erythrocyte SOD is a sensitive indicator of exposure to agricultural chemicals in tobacco field workers. Received: 18 May 1998 / Accepted: 31 October 1998     

Blood lead and erythrocyte delta-aminolevulinic acid dehydratase levels in Manchester taxi drivers.

Among 40 Manchester taxi drivers the mean blood lead was 1.10 mumol/1 (22.8 mug per 100 ml). The mean erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity among 34 of them was 30.1 units. No significant association was found between the blood lead levels and erythrocyte ALAD activity in these 34 men. No significant association was found between either blood lead elvels or erythrocyte ALAD activity and duration of service or weekly mileage as a taxi driver or with drinking or smoking habits, or age. The mean blood lead of those with homes in the north east quadrant of the city was higher than of those living elsewhere but the difference was not statistically significant. Although there was no correlation between blood lead levels and the source of domestic water, the mean blood lead of those with lead domestic plumbing was appreciably higher than the level of those with copper plumbing. There was no indication that, by virtue of their occupation, the taxi drivers were liable to greater lead absorption than their fellow-citizens.     

Lead and δ-aminolevulinic acid dehydratase in RBC's of urban mothers and fetuses

Environmental lead pollution may pose a health hazard to the mother and her fetus, but limited information concerning this problem is available. In this study, we examined erythrocyte δ-aminolevulinic acid dehydratase (ALAD) activity and erythrocyte lead levels in urban pregnant women and fetuses. The data show that the ratio of activated/nonactivated ALAD activity and erythrocyte lead are positively correlated in both the mothers and fetuses. The mean level of ALAD inhibition was found to be 28% in the mothers and 12% in the fetuses. The data also show that fetal erythrocytes have significantly higher levels of activated ALAD activity than maternal erythrocytes, and that a positive correlation exists between maternal and fetal erythrocyte lead levels. These results indicate that “normal” urban blood lead levels inhibit erythrocyte ALAD activity in the pregnant woman and fetus.