John M. Allen

Photochemical formation of singlet molecular oxygen (1O2) in illuminated aqueous solutions of p-aminobenzoic acid (PABA)

Evidence is presented for the photochemical formation of singlet molecular oxygen (1O2) in air-saturated buffered aqueous solutions of p-aminobenzoic acid (PABA) using sunlight-range illumination. This is significant because PABA is widely used as an active ingredient in sunscreen preparations that are applied to the surface of the skin and 1O2 is known to cause oxidative damage to cells via the formation and subsequent reactions of lipid peroxides. Furfuryl alcohol (FFA), a well known chemical trap for 1O2, was added to aqueous PABA solutions prior to illumination. The FFA was consumed when the solution was illuminated, but no loss of FFA occurred in the dark and loss by direct photolysis was negligibly slow. Further evidence for the formation of 1O2 in illuminated aqueous PABA solutions is provided by the results of experiments in which individual solutions containing PABA and FFA that were diluted with D2O exhibited an increased rate of FFA consumption due to the increased lifetime and concentration of 1O2 in this solvent.

Concentrations of contaminants in surface water samples collected in west-central Indiana impacted by acidic mine drainage

The results of analyses of surface waters collected from a variety of locations in west-central Indiana indicate extensive contamination by acidic mine drainage. These samples had pH values as low as 2.1 and total iron concentrations as high as 1200 mg1−1. The speciation of iron, expressed as the ratio [Fe(II)]/[Fe(III)] ranged from 0.08 to 8.27. Measured lead concentrations were as high as 811 mgl−1. In addition, the concentrations of nitrate and sulfate ions were as high as 359 and 624 mgl−1, respectively.

Sunscreens: The Molecules and Their Photochemistry

The alarming worldwide increase in skin cancer is a major cause of concern and the center of much research. In the USA alone one million new cases of skin cancer are reported each year, of which 10,000 cases ultimately lead to death.1 In countries like Australia and South Africa where the climate encourages the pursuit of outdoor activities, the incidence of skin cancer in the fair-skinned population is amongst the highest in the world.