PREGNANCY INCREASES MOBILIZATION OF LEAD FROM MATERNAL SKELETON

The question of the extent of lead mobilization from the maternal skel eton during pregnancy and lactation is one of the most outstanding pro blems of lead toxicity. We have undertaken a longitudinal cohort study in an urban environment of European female immigrants of child-bearin g age (18 to 35 years) to Australia whose skeletal lead isotopic compo sition has been determined to be different from that in their current environment. The cohort was to consist of 100 immigrants anticipated t o provide 20 pregnant subjects who would be compared with two groups o f control subjects: a matched immigrant nonpregnant control group and second-generation Australian pregnant control subjects. Pregnant subje cts also serve as their own controls for a comparison of changes durin g gestation with those before conception. High-precision lead isotopic compositions and lead concentrations are measured in maternal blood a nd urine prenatally, monthly during gestation, and post-natally for 6 months; they are also measured in infant blood and urine for 6 months; environmental measures are sampled quarterly for 6-day duplicate diet , house dust and water, and urban air and gasoline. Because of continu ing public health concerns about lead exposure; interim findings from this cohort are being reported. To date there have been 13 conceptions in immigrant subjects, with 7 births, in addition to 3 conceptions in the Australian control group, with 2 births. PbBs have been generally low, with a geometric mean of 3.0 mu g/dl, and have ranged from 1.9 t o 20 mu g/dl. Increases in PbB of similar to 20% during pregnancy have been detectable even in subjects with low blood lead levels, The skel etal contribution to blood lead level, based on isotopic measurements, has exhibited a mean increase (and standard deviation) of 31% +/- 19% with a range from 9% to 65%. Earlier studies that used lead concentra tions only have suggested that blood lead levels increased only during the second half of pregnancy. This increase in blood lead levels has also been observed in the present study. However, in two subjects the increases in total blood lead were also detected in the first 2 months of pregnancy. Changes in isotopic composition and blood lead during g estation for Australian pregnant controls were negligible. The ratio o f cord/maternal blood lead levels varied from 0.54 to 1.05, and the ra tio for the isotopic composition was 0.993 to 1.002. Results of this s tudy confirm that lead is mobilized from skeletal stores at an acceler ated rate during pregnancy and is transferred to the fetus. These resu lts also show that mobilization from longterm stores (i.e., bone) cont ributes significantly to blood lead levels during pregnancy. Furthermo re, exposure of the fetus to lead during pregnancy has implications fo r interpretations of neurobehavioral disorders attributed to only post natal exposure. Even after 800 days of residence in Australia, the con tribution of European skeletal lead to blood lead in nonpregnant subje cts can be on the order of 50%, but the current PbB may give no indica tion of the former high skeletal lead burden.