Ferrous sulfate adsorption by activated charcoal

Although activated charcoal is thought to not appreciably adsorb iron salts, previous in vitro work indicates some adsorption of iron. This study characterized the adsorptive capacity of activated charcoal for ferrous sulfate at 3 pH environments. Langmuir adsorption isotherms were determined with a fixed amount of iron in the reaction vessels. Activated charcoal USP (20, 40, 60, 80, 100, or 120 mg) was placed in plastic tubes to which were added 1 of 3 different simulated gastrointestinal fluids (pH = 1.5, 4.5, or 7.5) and 1.49% ferrous sulfate in water. The reaction vessels were agitated and immersed in a water bath at 37 C for 30 min. Each series was performed in triplicate. Following temperature eQuilibration filtration yielded an aliquot that was assayed for iron by atomic absorption spectrophotometry. Adsorptive capacities (mean +/- SD) of activated charcoal for ferrous sulfate (mg elemental iron/g charcoal) at pH 4.5 (102.96+/-4.49) and pH 7.5 (100.94+/-19.02) were higher (P<0.01) than at pH 1.5 (-0.01+/-0.26). At pH 1.5 iron was not appreciably adsorbed by activated charcoal. Activated charcoal adsorbed ferrous sulfate to a greater extent at pH environments where iron is typically absorbed from the gastrointestinal tract. These results indicate that activated charcoal may prove an effective therapy for acute iron poisoning and further investigation is warranted.