The Science of the Total Environment 199 (1997) 165-172 The influence of skin moisture on the dermal absorption of propoxur in human volunteers: a consideration for biological monitoring practices Wim J.A. Meuling*, Agnes Ch. Franssen, Derk H. Brouwer, Joop J. van Hemmen Department of Occupational Toxicology, TN0 Nutn’tion and Food Research Institute, PO Box 360, 3700 AJ Zeist, The Netherlands Abstract A large number of workers in agriculture are exposed daily (through skin contact) to pesticides either directly during mixing and loadingor 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 (330°C) and environmentalrelative 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 wasobserved. The results indicate that the level of skin moisture influences the absorption of propoxur via the dermalroute, dramaticallyrangingfrom, on average, 13,33-63% of the ‘potentially absorbed dose’ which is excretedin urine asthe 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 doseand the dislodged doseafter 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. 0 1997 Elsevier Science B.V. Keywords: Dermal absorption;Biologicalmonitoring; Volunteer studies; Pesticides; Skin moisture;Relative humidity 1. Introduction Worldwide, a relatively large amount of chemi- cals (insecticides, fungicides, etc.) are used fre- *Corresponding author. Tel: + 31 30 6944793; fax: + 31 30 6944928; e-mail: meuling@voeding.tno.nl quently to prevent or to cure e.g. plants, crops, vegetables and ornamentals from all kinds of diseases. Therefore, exposure to these chemicals for workers during mixing/loading or handling of these substances is likely. In this respect, it is inevitable that even the smallest external expo- sure may lead to a degree of absorption into the body due to handling these substances.It has also 004%9697/97/$17.00 0 1997 Elsevier Science B.V. All rights resewed. PZZ SOO48-9697(97) 05492-2