Conversion Rate of Non-chelatable to Chelatable Lead after CaEDTA Injection: A Kinetic Study in Two Lead Workers

Diminution rate of body burden of chelatable lead (CPb) after injection of calcium disodium ethylenediamine tetraacetate (CaEDTA) was estimated at between 0.7 and 0.4% per week in two lead workers after termination of lead exposure. Hence, alteration in body burden of CPb during the week after a single injection of CaEDTA was simulated by two different equations. The first equation was (1 + a 1.30)6 (1 1.03k + a) A = 0.993A or 0.996A, where A = body burden of CPb just before CaEDTA injection; a = proportion of CPb converted from non-chelatable lead (NPb) to A during the 24 h after CaEDTA injection; k= proportion of 24-h mobilization yield of lead by CaEDTA to A; and 13= proportion of 24-h spontaneous urinary lead excretion to A. This equation was based on the assumption that the amount of lead converted to CPb during 24 h was proportional to the initial level of CPb. The second equation, i.e. (1 1.03k) (1 1.313)6A + {(1 1.313)6+ (1 1.3()5+ + (1 1.3(3) + 1} otA = 0.993A or 0.996A, assumed that the amount of lead converted to CPb during 24 h was nearly constant during a week after CaEDTA injection. The conversion rate (a) was obtained as a solution of each equation after determination of k and j3 according to our model. It was estimated that the amount of lead corresponding to 2% of body burden of CPb, i.e. 0.23 mg and 0.35 mg, was converted from NPb to CPb during the 24 h after CaEDTA injection in the two lead workers with blood lead concentrations of 44 ltg per 100 g and 6114 per 100 g, respectively. A previous model for estimating body burden of CPb from mobilization yield of lead by CaEDTA was amended in the light of this estimation.