COMPARATIVE ABSORPTION OF LEAD FROM CONTAMINATED SOIL AND LEAD SALTS BY WEANLING FISCHER-344 RATS

A 44-day dosed feed study was performed to compare the bioavailability of lead from contaminated soil versus two lead salts and the effect o f soil on gastrointestinal absorption of ingested lead. Male Fischer r ats (approximately 4 weeks of age) received lead, 17, 42, or 127 ppm, in the form of lead acetate, lead sulfide, lead-contaminated soil, or combinations thereof in the diet for 7, 15, or 44 days, Control soil w as added to the diets of some animals to determine how it might alter lead bioavailability, Blood Delta-aminolevulinic acid dehydratase (Del ta-ALAD) and blood, bone, kidney, and liver lead were determined in gr oups of animals at each time-point, Blood Delta-ALAD was inhibited in a dose-dependent manner and to the greatest degree in the lead acetate and lead acetate/control soil groups, followed by the lead sulfide an d lead-contaminated soil groups, Bone and tissue lead levels increased in a dose-dependent manner and were greatest in animals receiving lea d acetate and significantly less in animals receiving lead sulfide and lead-contaminated soil. Blood lead levels were generally greatest by 7 days and stabilized at lower levels thereafter, Bone lead concentrat ion-time patterns did not demonstrate the biphasic change seen with ti ssues and continued to increase in most treatment groups through the c ourse of the study, The presence of soil in the diet clearly attenuate d the absorption of lead acetate, but had little effect on the absorpt ion of lead sulfide. Results of these studies confirm previous observa tions that lead absorption is highly dependent on the form of lead ing ested and the matrix in which it is ingested, More important, these st udies demonstrate that lead in soil may be significantly less availabl e than estimated by current default assumptions and that the presence of soil may decrease the availability of lead from lead salts on which the default assumptions are based. Results presented here also demons trate that the weanling rat may represent an appropriate model that co uld be used to obtain relatively rapid and economical estimates of the availability of lead in complex matrices such as soil. (C) 1996 Socie ty of Toxicology.