The influence of skin moisture on the dermal absorption of propoxur in human volunteers: a consideration for biological monitoring practices

A large number of workers in agriculture are exposed daily (through skin contact) to pesticides either directly during mixing and loading or indirectly due to contact. The aim of this study was to investigate the influence of skin moisture on the dermal uptake of the pesticide propoxur. The study was conducted in human volunteers under controlled temperature conditions (30°C) and environmental relative humidities of either 50, 70 or 90%. The study was approved by the Medical Ethics Committee. In this study a linear relationship between the environmental relative humidity and the level of skin moisture was observed. The results indicate that the level of skin moisture influences the absorption of propoxur via the dermal route, dramatically ranging from, on average, 13, 33–63% of the ‘potentially absorbed dose’ which is excreted in urine as the primary metabolite 2-isopropoxyphenol (IPP) at relative humidity levels of, on average, 50, 70 and 90%, respectively. The ‘potentially absorbed dose’ is defined as the difference between the applied dose and the dislodged dose after 4 h. It can be concluded that by assessing health risks of workers in agriculture exposed dermally to pesticides and e.g. in testing the efficiency of protective clothing under realistic conditions, the influence of the level of skin moisture on absorption of substances may be considerable and has to be taken into account.