Dermal in vitro penetration of methiocarb, paclobutrazol, and pirimicarb

Objectives—The dominant route of occupational exposure to pesticides in horticulture is dermal. However, preventive measures are seldom used when handling plant cultures recently treated with pesticides, thus causing significant dermal exposure and potential absorption. Assessment of exposure often depends on biological monitoring of blood or urine samples. The skin often acts as a temporary reservoir for chemicals before absorption. Failure to consider the lag time between dermal exposure and appearance of pesticide or metabolites in the general circulation may lead to false conclusions about assessment of exposure. Methods—In an experimental model in which in vitro static diVusion cells were mounted with human skin, dermal penetration of three extensively used pesticides (methiocarb, paclobutrazol, pirimicarb) was evaluated. Results—Pirimicarb and paclobutrazol had comparable rates of dermal penetration and lag times of around 18 hours. Methiocarb had a considerably shorter lag time. Dermal penetration continued for extended periods after exposure had ended. Conclusions—With lag times sometimes considerably longer than a normal working day, biological monitoring at the end of exposure may seriously underestimate the actual exposure. There may be implications for regulatory guidelines, which often require only 24 hour observation periods. (Occup Environ Med 2000;57:734–737)