Elution of benzo[a]pyrene from carbon blacks into biomembranes in vitro

Elution of benzo[a]pyrene (BaP) from carbon blacks into phospholipid vesicles composed of dimyristoyl phosphatidylcholine (DMPC) or dipalmitoyl phosphatidylcholine (DPPC) was investigated. Samples of rubber-grade carbon blacks designated N-234, N-339, N-351, and N-375 containing exogenously adsorbed BaP were prepared by solvent extracting endogenous compounds from the carbon blacks and then readsorbing BaP at the desired concentrations. Concentrations of exogenous BaP on the carbon blacks were approximately 100-fold higher than normally occur on commercial carbon blacks, but the higher levels were used to improve the ability to detect elution of BaP into membranes. Elution of BaP from carbon blacks was studied using a fluorescence spectroscopic technique that allowed continuous monitoring of the elution process. Elution from N-234 was below detection limits of our system. Elution of BaP from N-339, N-351, and N-375 into DMPC and DPPC vesicles occurred in a biphasic manner. Elution occurred within 60 min of mixing carbon blacks with vesicles, although not all BaP was eluted from the particles. When the concentration of BaP adsorbed to N-375 was reduced, the rate and extent of elution were lowered. Extent of elution of of BaP in these experiments may be greater than that of endogenous BaP on commercial carbon blacks because of the considerably higher quantities of exogenous BaP present. Furthermore, solvent extraction of endogenous materials prior to readsorption of BaP may alter the adsorption characteristics. However, methods developed in these experiments will facilitate future studies of the bioavailability of endogenous BaP on carbon blacks, especially in terms of determining the experimental conditions under which elution may occur.