Weight gain and maturity in fetuses exposed to low levels of lead

The relationship between prenatal low-level lead exposure and fetal growth was evaluated in a sample of 4354 pregnancies in which the mean umbilical cord blood lead level was 7.0 micrograms/dl (SD = 3.3; 10th percentile, 3.4 micrograms/dl, 90th percentile, 10.9 micrograms/dl). Higher cord blood lead levels were significantly associated with gestations of slightly longer duration. Comparing infants with cord blood lead levels greater than or equal to 15 micrograms/dl to those with levels less than 5 micrograms/dl, adjusted risk ratios of 1.5 to 2.5 were observed for low birth weight (less than 2500 g) and for fetal growth indices that express birth weight as a function of length of gestation (e.g., small-for-gestational age, intrauterine growth retardation). The 95% confidence intervals of these risk ratios included 1, however, precluding rejection of the null hypothesis of no association. We conclude that the risk of adverse fetal growth is not increased at cord blood lead levels less than 15 micrograms/dl but that modest increases in risk may be associated with levels greater than or equal to 15 micrograms/dl.     

Occurrence of elevated protoporphyrin levels in relation to lead burden in infants

Simultaneous blood lead (PbB), erythrocyte protoporphyrin (EP), and hematocrit measurements were made semiannually in 232 normal infants from 6 to 24 months of age. The PbB averaged 7 (SD = 5) and ranged from 0 to 64 micrograms/dl. The incidence of elevated EP, a marker for deranged heme synthesis, was unrelated to PbB at levels below 15 micrograms/dl but was fourfold greater among the infants with PbB above 15 micrograms/dl. This relationship persisted even after eliminating the 31 (4%) anemic (hematocrit less than 33%) samples. The confounding effects of iron deficiency are discussed.     

Occupational lead exposure aboard a tall ship

To evaluate occupational exposures to lead in shipfitters cutting and riveting lead-painted iron plates aboard an iron-hulled sailing vessel, we conducted an environmental and medical survey. Lead exposures in seven personal (breathing zone) air samples ranged from 108 to 500 micrograms/m3 (mean 257 micrograms/m3); all were above the Occupational Safety and Health Administration (OSHA) standard of 50 micrograms/m3. In two short-term air samples obtained while exhaust ventilation was temporarily disconnected, mean lead exposure rose to 547 micrograms/m3. Blood lead levels in ten shipfitters ranged from 25 to 53 micrograms/dl (mean, 37.8 micrograms/dl); levels in three of these workers exceeded the upper normal limit of 40 micrograms/dl. Blood lead levels in shipfitters were significantly higher than in other shipyard workers (mean 10.0 micrograms/dl; p less than 0.001). Smoking shipfitters (mean, 47 micrograms/dl) had significantly higher lead levels than nonsmokers (mean, 32 micrograms/dl; p = 0.03). Lead levels in shipfitters who wore respirators were not lower than in those who wore no protective gear (p = 0.68). Four shipfitters had erythrocyte protoporphyrin (EP) concentrations above the adult upper normal limit of 50 micrograms/dl. A close correlation was found between blood lead and EP levels (r = 0.70). Prevalence of lead-related symptoms was no higher in shipfitters than in other workers. No cases of symptomatic lead poisoning were noted. These data indicate that serious occupational exposure to lead can occur in a relatively small boatyard.     

Prevalence and causes of anemia in the United States, 1976 to 1980

We estimated the prevalence of anemia in the United States from the results of the Second National Health and Nutrition Examination Survey ( NHANES II, 1976 to 1980). Reference ranges for Hb were first derived from 11,547 subjects in whom laboratory values for serum iron/iron-binding capacity, mean corpuscular volume, and erythrocyte protoporphyrin were all normal (greater than or equal to 16%, greater than or equal to 80 fl, and less than or equal to 75 micrograms/dl red blood cells, respectively). Using these reference standards, the prevalence of anemia (Hb values below the 95% reference range for age and sex) among the 15,093 subjects with complete laboratory results was highest in infants (5.7%), teenage girls (5.9%), young women (5.8%), and elderly men (4.4%). The pattern of laboratory abnormalities in anemic subjects indicated that iron deficiency predominated as a cause in infants and young women in contrast to inflammatory disease in the elderly.     

Blood lead levels of 4-11-year-old Mexican American, Puerto Rican, and Cuban children

Data from the Hispanic Health and Nutrition Examination Survey were used to estimate arithmetic mean blood lead and percent with elevated blood lead [25 micrograms per deciliter (micrograms per dl) or greater] for 4-11-year-old Mexican American, Puerto Rican, and Cuban children. The sample size was 1,390 for Mexican American children, 397 for Puerto Rican children, and 114 for Cuban children. Puerto Rican children had the highest mean blood lead levels (11.5 micrograms per dl), followed by Mexican American children (10.4 micrograms per dl) and Cuban children (8.6 micrograms per dl, P less than .05). Puerto Rican children had the highest percent with elevated blood lead (2.7 percent); 1.6 percent of Mexican American children had elevated blood lead; less than 1 percent (0.9 percent) of the Cuban children had elevated blood lead (P less than .05). Mexican American girls had a lower mean blood lead level than did boys: 9.7 micrograms per dl versus 11.0 micrograms per dl (P less than .05). For both Puerto Rican and Mexican American children, younger age indicated a higher risk of having elevated blood lead levels. Mexican American children who lived in poverty had higher mean blood lead levels than did Mexican American children who did not live in poverty--11.6 micrograms per dl versus 9.6 micrograms per dl (P less than .05). Despite advances in primary prevention of lead toxicity in children during the past 10 years, many Hispanic children are at risk of lead toxicity. Approximately 19,000 Mexican American 4-11-year-old children living in the Southwest and approximately 8,000 Puerto Rican children living in the New York City area had elevated blood lead levels (greater than or equal to 25 micrograms per dl) during 1982-84.     

Influence of alcohol on the behavior of dose and effect indicators in workers exposed to inorganic lead: unexpected behavior of ZPP]

A study was carried out on 65 male workers heavily exposed to lead in the ceramic tile manufacturing industry in order to assess the effects of alcohol on the biological indicators of lead (PbB, ALA-D, ALA-U, ZPP). All subjects selected for the study had PbB levels greater than or equal to 60 micrograms/dl, normal levels of serum iron and no haemoglobin disorders. The subjects were divided into three groups according to alcohol intake checked by anamnestic investigation, mean corpuscular volume (MCV) values and liver function parameters, as follows: Group A--27 subjects, controls, with daily alcohol intake less than 80 ml, MCV less than or equal to 95 mu 3, normal GGT, AST and ALT levels; Group B--20 subjects, heavy drinkers, with daily alcohol intake greater than or equal to 80 ml, MCV greater than 95 mu 3, occasionally high GGT, but normal AST and ALT values; Group C--18 subjects, heavy drinkers, with daily alcohol intake greater than or equal to 80 ml, MCV greater than 95 mu 3, abnormal GGT, AST and ALT levels. The length of lead exposure did not significantly differ in the three groups. The well-known effects of ethanol intake on PbB, ALA-D and ALA-U values were confirmed, with the following mean values in the three groups: Group A: PbB = 66.0 (micrograms/dl), ALA-D = 10.3 (mU/ml r.c.), ALA-U = 8.4 (mg/l); Group B: PbB = 68.3 (micrograms/dl), ALA-D = 6.7 (mU/ml r.c.), ALA-U = 9.1 (mg/l); Group C: PbB = 71.5 (micrograms/dl), ALA-D = 4.6 (mU/ml r.c.), ALA-U = 12.7 (mg/l).(ABSTRACT TRUNCATED AT 250 WORDS)     

Usefulness of red cell distribution width in association with biological parameters in an epidemiological survey of iron deficiency in children

The diagnostic usefulness of red cell distribution width (RDW) in association with usual biochemical and haematological parameters in detection of iron deficiency has been studied in a representative sample population of 384 children aged six months to six years in Reunion. Traditional parameters measured included serum ferritin (Fri), total iron binding capacity (TIBC), serum iron (SI), transferrin saturation (TSat), free erythrocyte protoporphyrin (FEP), mean corpuscular haemoglobin concentration (MCHC), mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV) and haemoglobin concentration (Hb). RDW is an index of the variation in red cell size (anisocytosis). This recently derived parameter is measured by some models of electronic cell counter. It is not usually used in epidemiological investigations. Of the children studied, 13.6% had Hb less than 11 g/dl. The Pearson correlation coefficients between circulating iron parameters (SI, TSat, TIBC) or iron storage parameters (Fri) and RDW, MCV, MCH and FEP were greater than with Hb. The best correlations were observed for RDW, MCV and MCH with all other parameters. In this study, the upper limit value of RDW was defined as 18% using a Technicon model H-6000 counter. Other iron deficiency criteria were also defined and found to be in agreement with the international reference values for children aged six months to six years; MCV less than 70 fl, MCH less than 22 pg, MCHC less than 32%, FEP greater than 35 micrograms/dl whole blood, SI less than 6 mumols/l, TIBC greater than 85 mumols/l, TSat less than 10% and Fri less than 12 micrograms/l. The combination of sensitivity and specificity was best for RDW and worst for MCHC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lead-induced anemia: dose-response relationships and evidence for a threshold.

We conducted a cross-sectional epidemiologic study to assess the association between blood lead level and hematocrit in 579 one to five year-old children living near a primary lead smelter in 1974. Blood lead levels ranged from 0.53 to 7.91 mumol/L (11 to 164 micrograms/dl). To predict hematocrit as a function of blood lead level and age, we derived non-linear regression models and fit percentile curves. We used logistic regression to predict the probability of hematocrit values less than 35 per cent. We found a strong non-linear, dose-response relationship between blood lead level and hematocrit. This relationship was influenced by age, but (in this age group) not by sex; the effect was strongest in youngest children. In one year-olds, the age group most severely affected, the risk of an hematocrit value below 35 percent was 2 percent above background at blood lead levels between 0.97 and 1.88 mumol/L (20 and 39 micrograms/dl), 18 percent above background at lead levels of 1.93 to 2.85 mumol/L (40 to 59 micrograms/dl), and 40 percent above background at lead levels of 2.9 mumol/L (60 micrograms/dl) and greater; background was defined as a blood lead level below 1.88 mumol/L (20 micrograms/dl). This effect appeared independent of iron deficiency. These findings suggest that blood lead levels close to the currently recommended limit value of 1.21 mumol/L (25 micrograms/dl) are associated with dose-related depression of hematocrit in young children.     

Hematological effect of supplementing anemic children with vitamin A alone and in combination with iron

Ninety-nine anemic children aged 1-8 y were divided into four groups. Each group was supplemented for 2 mo with vitamin A, iron, vitamin A plus Fe, or a placebo. Clinical, hematological, and Fe biochemical evaluations were performed at the beginning and end of the study. Vitamin A supplementation produced significant elevations in the serum levels of retinol, blood hemoglobin, hematocrit, erythrocytes, serum Fe, and percent transferrin saturation (%TS) and had no effect on total Fe binding capacity (TIBC) or serum ferritin. Fe supplementation did not affect serum retinol. However, it improved hematological and Fe nutrition indicators, including TIBC and serum ferritin. The simultaneous administration of vitamin A and Fe resulted in a better response of serum Fe and %TS than when the supplement consisted only of vitamin A or Fe alone. Vitamin A benefits hematological condition and Fe metabolism.     

Association between iron deficiency and low-level lead poisoning in an urban primary care clinic.

OBJECTIVES: The purpose of this study was to examine the association between iron deficiency and low-level lead poisoning. METHODS: Data were collected in an urban primary care clinic from 3650 children aged 9 to 48 months. Iron deficiency was defined as a red cell mean corpuscular volume (MCV) of less than 70 fL and a red cell distribution width (RDW) of more than 14.5 in children younger than 2 years, and an MCV of less than 73 fL and RDW of more than 14.5 in those 2 years or older. RESULTS: After adjustment for age, hemoglobin concentration, and insurance status, the odds ratios for iron deficiency predicting blood lead levels greater than or equal to 5 micrograms/dL and greater than or equal to 10 micrograms/dL were 1.63 (95% confidence interval [CI] = 1.29, 2.04) and 1.44 (95% CI = 1.004, 2.05). CONCLUSIONS: Iron deficiency is significantly associated with low-level lead poisoning in children aged 9 to 48 months.     

Exposure of the U.S. population to lead, 1991-1994.

Blood lead measurements were obtained on 13,642 persons aged 1 year and older who participated in Phase 2 of the Third National Health and Nutrition Examination Survey (NHANES III) from 1991 through 1994. NHANES III is a national representative survey of the civilian, noninstitutionalized U.S. population. The overall mean blood lead level for the U.S. population aged 1 year and older was 2.3 microgram/dl, with 2.2% of the population having levels >=10 microgram/dl, the level of health concern for children. Among U.S. children aged 1-5 years, the mean blood lead level was 2.7 microgram/dl, and 890,000 of these children (4.4%) had elevated blood lead levels. Sociodemographic factors associated with higher blood lead levels in children were non-Hispanic black race/ethnicity, low income, and residence in older housing. The prevalence of elevated blood lead levels was 21.9% among non-Hispanic black children living in homes built before 1946 and 16.4% among children in low-income families who lived in homes built before 1946. Blood lead levels continue to decline in the U.S. population, but 890,000 children still have elevated levels. Public health efforts have been successful in removing lead from population-wide sources such as gasoline and lead-soldered food and drink cans, but new efforts must address the difficult problem of leaded paint, especially in older houses, as well as lead in dust and soil. Lead poisoning prevention programs should target high-risk persons, such as children who live in old homes, children of minority groups, and children living in families with low income.     

Elevated blood lead in California adults, 1987: results of a statewide surveillance program based on laboratory reports.

California medical laboratories that test for blood lead are required to report results exceeding 1.21 mumols/L (25 micrograms/dl). Between April and December 1987, the California Department of Health Services received 3,077 blood lead reports from 34 laboratories for 1,293 civilian, non-institutionalized adults. Approximately 1 percent of all reports exceeded 3.87 mumols/L (80 micrograms/dl), 7 percent exceeded 2.42 mumols/L (50 micrograms/dl), and 21 percent exceeded 1.93 mumols/L (40 micrograms/dl). Individuals tested were overwhelmingly male (94 percent), disproportionately Hispanic surnamed (44 percent), and most often residents of Los Angeles County (81 percent). Workers in lead smelting, battery manufacturing, and brass foundries accounted for nearly 80 percent of reports. Construction, radiator repair, pottery and ceramics manufacturing, and gun firing ranges accounted for the remainder. All adults with reports of greater than or equal to 2.90 mumols/L who were contacted reported on occupational exposure. Approximately half were not in routine medical monitoring programs. Despite OSHA standards, elevated blood lead with the potential for serious acute and chronic lead poisoning in California adults remains a significant public health and major occupational health concern.     

The relationship between the level of lead absorption in children and the age, type, and condition of housing

A group of 184 preschool-aged children with pretreatment blood lead concentrations (PbB) greater than or equal to 50 micrograms/dl, who received inpatient chelation therapy, were followed prospectively as outpatients for 12 months after discharge. Of these, 160 were followed for 24-30 months. Serial PbB data were analyzed according to the type of housing to which each child was discharged. Following therapy, PbB stabilized by 3 months. Thereafter, highly significant differences (P less than 0.001) existed between those living in or visiting old houses in which lead-in-paint hazards had been abated according to local ordinances (m PbB = 38.5 micrograms/dl) and those discharged to "lead-free" public housing (m PbB = 28.8 micrograms/dl) or to recently, totally gutted and renovated old housing (m PbB = 28.7 micrograms/dl). During the period of study (1978-1982), no downward trend in PbB within housing groups was found during the first 12 months of follow-up. Of the 152 children discharged to old housing, 75 had 127 recurrences of PbB greater than or equal to 50 micrograms/dl. This emphasizes the need for close and prolonged follow-up in all cases. These data indicate that substantially improved methods of detection, classification, and abatement of lead hazards must replace traditional methods if lead exposure for young children in old housing is to be reduced to an acceptable level.     

Folacin and iron status and hematological findings in predominately black elderly persons from urban low-income households.

The folacin and iron status and hemotological parameters of 193 persons 60 years of age and older from urban low-income households were evaluated. Of the serum folacin values 30% were between 3 and 6 ng/ml and 8% were below 3 ng/ml. Of these subjects 60% could be classified as "high risk" (less than 140 ng/ml) and 11% as "medium risk" (140 to 160 ng/ml) based on red blood cell folacin concentrations. Serum iron was normal (greater than 50 micrograms/dl) for all subjects as was transferrin saturation (greater than 15%). Hematological indices showed a 14% incidence of anemia (hemaglobin less than 12 g/dl), and 32% incidence of leukopenia (leukocytes less than 4.8 X 10(3)). These findings demonstrate widespread folacin deficiency and no evidence of iron deficiency in these elderly people.     

Lead poisoning among household members exposed to lead-acid battery repair shops in Kingston, Jamaica

To investigate the risk of lead poisoning among household members exposed to 'backyard' battery repair shops (BBRS) in Kingston, Jamaica, environmental and blood lead (PbB) were measured at 24 households (112 individuals) with a BBRS worker or located at a BBRS premises and at 18 neighbourhood control households (74 individuals). Elevated PbB (greater than or equal to 25 micrograms per decilitre [micrograms/dl]) was common among subjects of all ages living at BBRS premises, especially among children less than age 12, 43% of whom had PbB greater than 70 micrograms/dl. Potentially hazardous soil and house dust lead levels were also common at BBRS premises, where 84% of yards had soil lead levels above 500 parts per million (geometric mean 3388 parts per million [ppm] at BBRS premises households with a BBRS worker). Geometric mean blood and environmental lead levels were significantly lower at control households, where less than 10% of subjects in all age groups had elevated PbB (maximum 33 micrograms/dl). Sharing a premises with a BBRS was a stronger determinant of household blood lead and environmental contamination than was the presence of a BBRS worker in a household. Blood lead levels were associated with soil and house dust lead levels in all age groups. We conclude that small battery repair shops, which have also been described in other developing countries, create a high lead poisoning risk for nearby residents.     

Assessment of marginal vitamin A deficiency in Brazilian children using the relative dose response procedure

Vitamin A status was determined using fasting plasma levels and the relative dose response (RDR) procedure before and 30, 120, and 180 days after administration of an oral massive (200,000 IU) dose of vitamin A. The study was carried out in Recife, Brazil among 93 children of 7 yr or less from low income families who attended two day-care programs. The RDR procedure is conducted by obtaining a fasting blood (A0), feeding 450 retinol equivalents and obtaining a second blood specimen after 5 h (A5). The RDR-(A5-A0)/A5 X 100. A single massive oral dose of vitamin A was given after conducting the base-line RDR test. The RDR procedure was repeated at 30, 120, and 180 days. Weight and height measurements were obtained at each observation and the bloods were analyzed for Hb, total protein, and serum iron, as well as vitamin A. Serum albumin was determined in 120- and 180-day bloods. Serum iron levels were improved 30 days after supplementation with the massive dose of vitamin A. The RDR procedure was found practical to apply in mildly undernourished children under nonclinical condition. In this group of low income children presumed to be habitually ingesting minimally adequate diets, a serum vitamin A level of 20 micrograms/dl or less invariably was associated with an elevated RDR test. Blood levels between 20 to 40 micrograms/dl were not consistently predictive of the RDR response. All elevated RDR tests reverted to normal after supplementation with vitamin A, presumably indirectly indicating a presupplementation inadequate vitamin A status. Hence, the RDR was a more sensitive indicator of inadequate vitamin A status than was only a serum level of vitamin A when blood levels were above 20 micrograms/dl.(ABSTRACT TRUNCATED AT 250 WORDS)     

Demographic risk factors associated with elevated lead levels in Texas children covered by Medicaid.

This is the first large population-based study of demographic risk factors for elevated lead in Texas children. It summarizes data on 92,900 children covered by Medicaid screened for blood lead during the first 6 months of 1993 in Texas. The highest percentage of elevated lead levels (14.3%) was in children 25-36 months of age, with slightly lower percentages in those younger (13% of 19-24 months) and older (12% of 37-48 months) with blood lead levels greater than 10 micrograms/dl. The group with the highest percentage of elevated blood lead levels was 2-4-year-old African American males (17.3%) making this subgroup 3.5 times higher than the group with the lowest percentage-white girls over age 4 (4.8%). Males had higher blood lead levels for all ages and ethnic groups. Three principal risk factors were found for excessive blood lead in children: ethnicity, gender, and age; this is consistent with the second National Health and Nutrition Examination Survey (NHANES II) and Phase I of the NHANES III results demonstrating ethnicity and income association with lead in children in the United States.     

Biological monitoring of lead exposure in high risk groups in Berat, Albania

STUDY OBJECTIVE: To determine blood lead concentrations in children living in an area with a battery plant in Berat, Albania. Another aim was to determine blood lead concentrations in mothers and cord blood levels in neonates from Berat and compare them with values found in Tirana. DESIGN: Cross sectional survey with a 10% random sample of children, and a 10% sample of mothers and newborn. SETTING: Hospitals, schools, and kinder-gartens in Berat and Tirana, Albania PARTICIPANTS: 129 preschool children, 373 school children, 151 mothers and their newborn. MAIN RESULTS: The mean observed blood lead concentrations in 84 preschool children living less than 2 km from the battery plant was 43.4 micrograms/dl (SD 23.0) and significantly higher than in 45 preschool children (mean 15.0 micrograms/dl, SD 3.5) living more than 2 km from the plant. Mean lead concentrations in 145 school children living close to the plant were 26.6 micrograms/dl (SD 14.4) compared with 16.0 micrograms/dl in 228 school children living at a greater distance. In 67% of the preschool children and 41% of the school children lead levels exceeded the WHO borderline level of 20 micrograms/dl, and 98% of preschool children, and 82% of school children had values greater than 10 micrograms/dl. Mean lead concentrations in cord blood of 151 newborn was 8.9 micrograms/dl (median 8.8, range 4.9-20.0 micrograms/dl), and 10.6 micrograms/dl in blood of their mothers (median 10.0, range 5.0-25.4 micrograms/dl). Mean lead concentrations in Tirana were 8.9 (newborn), and 7.0 micrograms/dl (mothers). CONCLUSIONS: Blood lead concentrations in children from Berat are comparatively high and abatement measures are needed.

 

     

Iron stores in pregnant Nigerians and their infants at term

Serum ferritin and blood haemoglobin were evaluated as indices of iron status in 65 pregnant Nigerians and in the cord blood of their full-term infants. All the mothers had taken iron and folate supplementation throughout pregnancy. The mean gravidity was 3.3 +/- 2.0. The mean cord ferritin concentration of 135.9 micrograms/l (77.6-238.2 micrograms/l) was 3.6 times the maternal level of 38.1 micrograms/l (17.3-83.8 micrograms/l). Parity had no effect on the haemoglobin or serum ferritin concentrations of the mothers or those of their babies. Maternal haemoglobin or serum ferritin concentrations correlated significantly (P less than 0.01) with cord levels, in babies with mothers of parity greater than or equal to 5. Infants of mothers with low iron stores (less than 20 micrograms/l) had significantly lower serum ferritin concentrations than infants of iron-replete mothers, which suggests variation in amounts of iron received during intrauterine growth. In order to ensure adequate iron stores in newborn infants, continual use of supplementary oral iron should be encouraged in pregnant Nigerians.     

Occupational lead poisoning in the United States: clinical and biochemical findings related to blood lead levels

Dose-response relationships between blood lead levels and toxic effects have been evaluated in 160 lead workers in two smelters and a chemicals plant. Blood lead levels ranged from 0.77 to 13.51 mumol/litre (16-280 microgram/dl). Clinical evidence of toxic exposure was found in 70 workers (44%), including colic in 33, wrist or ankle extensor muscle weakness in 12, anaemia (Hgb less than 8.69 mumol/litre (Hb/4) or 14.0 gm/dl) in 27, elevated blood urea nitrogen (greater than or equal to 7.14 mmol/litre or 20 mg/dl) in 28, and possible encephalopathy in two. No toxicity was detected at blood lead levels below 1.93 mumol/litre (40 microgram/dl). However, 13% of workers with blood lead levels of 1.93 to 3.81 mumol/litre (40-79 microgram/dl) had extensor muscle weakness or gastrointestinal symptoms. Anaemia was found in 5% of workers with lead levels of 1.93-2.85 mumol/litre (40-59 microgram/dl), in 14% with levels of 2.90 to 3.81 mumol/litre (60-79 microgram/dl), and in 36% with levels greater than or equal to 3.86 mumol/litre (80 microgram/dl). Elevated blood urea nitrogen occurred in long-term lead workers. All but three workers with increased blood urea nitrogen had at least four years occupational lead exposure, and nine had received oral chelation; eight of this group had reduced creatinine clearance, and eight had decreased renal concentrating ability. These data support the establishment of a permissible biological limit for blood lead at a level between 1.93 and 2.90 mumol/litre (40-60 microgram/dl).