Trace element composition of bone

TRACE ELEMENTS IN LIVING BONE Trace element composition of bone 

The cations Sr and Ba concentrate in the vertebrate skeleton, and the amounts of these elements vary as a function of mineral stmcture. In vivo, strontium has been found to accumulate in bone by exchange onto crystal surfaces, and is rapidly washed out after exogenous strontium is withdrawn (Dahl et al. 2001). Incorporation of strontium into the crystal lattice as a substitute of calcium occurs at a low level in vivo, in contrast to the extensive lattice substitution of strontium for calcium in fossil bone. Strontium is not easily washed out of subfossil bone (Tuross et al. 1989), and the uptake of strontium into biological apatite was once proposed as a potentially useful chronometer analogous to fluorine uptake (Turekian and Kulp 1956). The combined uptake of strontium and fluorine into vertebrate calcified tissue may in no small part account for the existence of a fossil record. Both of these elements stabilize biological apatite, and add substantially to the crystal stability of apatite under acidic conditions (Curzon 1988). 

Strontium levels/Tissue Barium levels/Tissue Reference 

The amount of strontium and barium in bones and teeth differs by two orders of magnitude (Table 1). Human strontium and barium levels in bones and teeth exist in a bimodal literature that derives from an interest in the incorporation of °Sr in the 1950s, and a more recent group of studies that focus on strontium s effect on mineralization. A wide range in strontium content in human bone is reported in groups of studies that are fifty years apart, but, in general, modem human bone and enamel tends to have strontium content 200 ppm, while barium content is commonly reported at less than 10 ppm. The amount of strontium in a normal human diet ranges from 0.023 to 0.046 mmol/Sr/day (Marie et al. 2001), and when administered with calcium, strontium is adsorbed to a lesser extent (Milsom et al. 1987). 

Lead is another element of interest in a number of applications. Most of the ingested lead is stored in bone, and is difficult to remove once it is incorporated into the mineral phase. The half-life of lead in bone can be up to 20 years (Anderson and Danylchuck 1977, Drasch 1982). Lead is not distributed equally among the bones of the skeleton, although there seems to be a relationship among anatomical units within one skeleton that would allow an estimation of total skeletal lead burden (Wittmers et al. 1988). In a modern population of humans (n = 240) that had not been exposed to lead occupationally, the mean lead content in the femur was 3.86 mg/kg bone wet weight as compared to the temporal bone (5.59 mg/kg) and the pelvic bone (1.65 mg/kg) (Drasch et al. 1987). An occupationally exposed population had approximately ten to twenty times the amount of lead in bone compared to the unexposed population (Brito et al. 2000). 

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