Quantification of Dermal Absorption of Pesticides from Dried Residues

  • James Clarke

Student thesis: Doctoral ThesisPhD


Pesticides must go through a rigorous risk assessment process to demonstrate that they are safe for use. One exposure scenario is that of the re-entry worker, who may enter a field soon after pesticide application and come in to contact with contaminated foliage. Following estimation of the potential dermal exposure, prediction of a systemic dose relies on applying a factor for dermal absorption. Currently, this value is obtained by carrying out in vitro diffusion cell testing of the concentrate and one or more representative spray dilutions. However, a worker is exposed to pesticide in a different form to those tested, a dried residue. The current work has developed an in vitro protocol to measure the absorption of pesticides from dried residues. This method is based on applying pesticides to an inert platform, creating dried deposits of pesticide, which are then transferred to a skin membrane and absorption measured in vitro using Franz diffusion cells.This method has been used to compare the dermal absorption of four compounds, from spray dilutions and their residues. In each case absorption was significantly less from the residue than the spray dilution. Further investigation of two of these compounds, found that absorption was affected by formulation and loading dose. Additionally, the effect of decontaminating the skin at different time points post-exposure found an effect on the total amount absorbed and that this effect may be more pronounced for the dried residue than the spray dilution. This work has provided valuable insight into an area of exposure science which is poorly documented. This novel method has the potential to be used to carry out more realistic risk assessments than those which may currently overestimate exposure of re-entry workers and hinder the passage of safe and effective products through the registration process.
Date of Award16 Nov 2017
Original languageEnglish
Awarding Institution
  • University of Bath
SponsorsBiotechnology and Biological Sciences Research Council & Syngenta Ltd
SupervisorRichard Guy (Supervisor)

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