SOLUBILITY OF LEAD AS LEAD(II) CHLORIDE IN HEPES-RINGER AND ARTIFICIAL SEAWATER (CA-ASW) SOLUTIONS

Total dissolved Pb was measured in a number of commonly used physiolog ical solutions by electrothermal atomization atomic absorption spectro metry (ETA-AAS). In HEPES-buffered solutions (pH 7.30) the concentrati on of total Pb in solution (''measured'' Pb) was only 77% of nominal P b up to 20 muM added Pb, where experiments were undertaken at room tem perature (22 +/- 1-degrees-C). However, test solutions equilibrated at 37 +/- 1-degrees-C contained 99% of added Pb up to 2 muM. Above this nominal concentration, percentage recoveries dropped to approximately 72% at a nominal concentration of 20 muM. Tris-buffered artificial sea water (CaASW) solutions (pH 7.60) contained more dissolved Pb compared to HEPES-buffered solutions at 22-degrees-C However, increasing the c alcium concentration in ASW appeared to increase precipitation of PbCl 2. Concentration-corrected dose-response relationships were plotted fr om previously published data on the effects of Pb on voltage-activated calcium channels of rat dorsal root ganglion (DRG) cells and Aplysia neurons. The plots suggest that the inhibitory effects of Pb on rat DR G cells may prevail at concentrations of Pb even lower than reported p reviously when measurements were made at 22-degrees-C. However, increa sing the temperature to 37-degrees-C resulted in closer agreement betw een measured and nominal dose-response curves. The measured dose-respo nse curves for the Tris-buffered ASW solutions closely followed those of the nominal up to 200 muM Pb. In ASW solutions containing 40 mM cal cium, PbCl2 was precipitated at Pb concentrations greater than 200 muM . (C) 1993 Intox Press, Inc.