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Biomedical subjects

M B Rabinowitz

Publications and source records attributed to M B Rabinowitz.

At least 19 recordsLinked to original sources
PubMed1995

Stable isotopes of lead for source identification.

Lead is unique among all the metals in having variations among mining districts in the relative abundances of its stable (non-radioactive) isotopes. Since first described in 1927, many applications have been reported, mostly for geological uses. More recently archeological, environmental, bio-kinetic and public health uses have been found. The abundances of the four stable isotopes are usually determined with specialized mass spectrometry using rapid mass scanning cycles or multiple collectors. The relative abundances are commonly expressed as 206/204, 206/207, and 206/208 atomic ratios. Precision of 0.5% for 206/204 and even better (0.03%) for the other pairs are obtainable. The three ratios co-vary strongly and depend on when the ore was formed. This provides a tracer for following a particular batch of lead, since the ratio can only change when the lead is mixed with a different lead. A major limitation of this method is that it is useful only to those problems where the potential sources are isotopically distinct and few in number. The covariance of the ratios usually allows for only two sources to be considered. Potential sources can often be ruled out.

Animals↗
PubMed1993

Relationships between serial blood lead levels and exfoliated tooth dentin lead levels: models of tooth lead kinetics.

Because bones and permanent teeth accumulate lead, exfoliated deciduous teeth have been utilized as retrospective markers of cumulative exposure in epidemiological surveys. In this paper we describe four models of lead uptake by the coronal dentin of shed primary teeth, each with different assumptions and ramifications. Each model is characterized by different relationships between blood lead at several ages and tooth lead. Values observed in our cohort of normal Boston children are most compatible with models positing the largest lead contribution coming at older ages (i.e., closer to age at exfoliation). Characteristics of models incompatible with our data include (1) lead deposition only during initial calcification and (2) no loss or resorption of lead.

Dentin↗
PubMed1991

Toxicokinetics of bone lead.

This article discusses bone as a source of lead to the rest of the body and as a record of past lead exposure. Bone lead levels generally increase with age at rates dependent on the skeletal site and lead exposure. After occupational exposure, the slow decline in blood lead, a 5- to 19-year half-life, reflects the long skeletal half-life. Repeated measurements of bone lead demonstrate the slow elimination of lead from bone. Stable isotope ratios have revealed many details of skeletal uptake and subsequent release. The bulk turnover rates for compact bone are about 2% per year and 8% for spine. Turnover activity varies with age and health. Even though lead approximates calcium, radium, strontium, barium, fluorine, and other bone seekers, the rates for each are different. A simple, two-pool (bone and blood) kinetic model is presented with proposed numerical values for the changes in blood lead levels that occur with changes in turnover rates. Two approaches are offered to further quantify lead turnover. One involves a study of subjects with known past exposure. Changes in the ratio of blood lead to bone lead with time would reflect the course of bone lead availability. Also, stable isotopes and subjects who move from one geographical area to another offer opportunities. Sequential isotope measurements would indicate how much of the lead in blood is from current exposure or bone stores, distinct from changes in absorption or excretion.

Bone and Bones↗
PubMed1986

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.

Child, Preschool↗
PubMed1985

Elimination kinetics of blood lead in workers with chronic lead intoxication.

Blood lead elimination half-lives were determined for 65 patients with occupational chronic lead intoxication who were removed from exposure, treated with intravenous EDTA, and followed for periods of up to 2,419 days. The median overall blood lead elimination half-life was 619 days in patients with normal renal function and 1,907 days in patients with renal impairment. Slow-phase elimination half-lives in patients followed for longer than 5 years ranged from 1,658 to 7,189 days. Blood lead concentrations declined during periods of chelation with a mean half-life of 7 days and rebounded to near prechelation concentrations following termination of chelation with a mean doubling time of 27 days. The overall blood lead elimination half-life was positively associated with length of follow-up (p less than 0.001), age (p = 0.04), and duration of exposure (p = 0.02), but was not associated with the initial blood lead concentration following cessation of exposure or the total amount of EDTA received.

Adult↗
PubMed1982

Temporal trends in the lead concentrations of umbilical cord blood.

Umbilical cord blood specimens from 11,837 births between April 1979 and April 1981 have been analyzed for lead by anodic stripping voltammetry. The mean was 6.56 +/- 3.19 (standard deviation) micrograms per deciliter of blood, and the range was 0.0 to 37.0 micrograms per deciliter. The mean decreased annually by 0.77 +/- 0.03 microgram per deciliter, about 11 percent. Lead concentrations were higher in infants born in summer than in infants born in winter (7.17 versus 5.99, probability less than .001). A Fourier model of the data is presented, and possible reasons for the decline are discussed.

Boston↗
PubMed1980

Effect of food intake and fasting on gastrointestinal lead absorption in humans.

The effect of food intake versus brief fasting on gastrointestinal absorption of lead was measured in five healthy men who were living in a metabolic unit and eating constant lead diets. Lead absorpiton was assessed by the difference between dietary intake and output of 1) lead tracers composed of nonradioactive isotopes which were ingested as a single dose either with food or during a 16-hr fast, 2) lead tracers ingested with meals for relatively long periods (2 to 124 days), and 3) total led in ingested foods. Absorption estimated by 1) was confirmed by increments in tracer concentrations in blood. Lead tracers were given as nitrate, cysteine complex, or sulfide. Absorption was 10.3 +/- 2.2% (SD) for food lead; 8.2 +/- 2.8% for tracers ingested with food; and 35 +/- 13% (P < 0.01) percent for tracers ingested without food. The increased absorption of lead when ingested without food should be considered when the hazards of exposure to lead are determined.

Adult↗
PubMed1977

Magnitude of lead intake from respiration by normal man.

Lead metabolism of five normal men was studied in a hospital metabolic unit in order to measure the daily intake of lead by respiration in urban adults. Subjects ingested a constant diet, and samples of blood, urine, feces, and diet were analyzed periodically for lead isotopic abundances by mass spectrometry. Three men were fed daily a stable isotope tracer of lead for 83 to 124 days in order to distinguish ingested from respired lead. Also, three men lived in rooms with filtered, low-lead air for 25 to 50 days in order to examine the response of blood lead levels to a change in airborne lead exposure. The quantity of respired lead intake was determined from the lead balance data, labeling of blood lead with a dietary lead tracer, and the response of blood lead levels and lead balances to exposure to low-lead air. The results indicate that these men absorbed a mean of 14 +/- 4 (S.D.) microgram/day of lead while exposed to the ambient levels of about 2 microgram/m3 of airborne lead. About twice this amount was absorbed from the diet.

Air↗