Accounting for Differing Exposure Patterns between Laboratory Tests and the Field in the Assessment of Long-term Risks of Pesticides to Terrestrial Vertebrates

Abstract

Long-term risks of pesticides to birds and mammals are currently assessed by comparing effects thresholds determined in chronic laboratory studies to exposure levels expected to occur in the field. However, there is often a mismatch between exposure patterns tested in the laboratory tests (exposure levels held constant) and those experienced by animals in the field (exposure levels varying over time). Three methods for addressing this problem are presented and discussed. Time-weighted averaging (TWA) converts a variable field exposure regime to a single value that can be compared directly to the laboratory test results. Body-burden modeling (BBM) is applied to both laboratory and field exposure regimes allowing a straightforward comparison of body residue levels expected for each situation. Temporal analysis (TA) uses expert judgment to decide if the length of time exposure exceeds a toxicity threshold is long enough to cause biologically significant effects. To reduce uncertainty in long-term assessments, the conduct of specialized laboratory tests in which test subjects are administered a time-varying exposure that mimics what occurs in the field should be considered. Such tests may also be useful testing the validity of each of these assessment methods.

A toxicokinetic model for thiamethoxam in rats: implications for higher-tier risk assessment

“…In general, without quantification of the parent compound, the data are unsatisfactorily nonspecific (Barton et al 2006), as such data may not be representative of the kinetics of the relevant metabolite at the target site (Rubach et al 2011). Fischer (2005) recently suggested that for modern pesticides, that generally do not bioaccumulate, a TK model capable of realistically modelling metabolic processes and the site of toxic action needs to be developed. However, after oral dosing of rats, up to 90 % of the applied thiamethoxam at 100 mg kg −1 bw is readily eliminated as parent compound in the urine (Maienfisch et al 2001).…”

Estimating the Exposure of Birds and Mammals to Pesticides in Long-term Risk Assessments

“…(Furthermore, the subjects are exposed to fixed concentration levels throughout the test period. See Fischer (2005) on allowing for different exposure patterns in laboratory and field.) For mammals, there is a wider range of 'long-term' toxicity tests including a 90-day dietary test and multi-generation reproductive studies.…”

Improved Approaches to Assessing Long-term Risks to Birds and Mammals

“…Improvements in problem formulation and ways in which temporal and spatial factors might be incorporated into long-term risk assessments are suggested. Fischer (2005) discusses accounting for differences between exposure patterns tested in the laboratory tests (exposure levels held constant) and those experienced by animals in the field (exposure levels varying over time). Three methods for addressing this problem are presented and discussed.…”