Field evaluation of the EPA (kenaga) nomogram, a method for estimating wildlife exposure to pesticide residues on plants

Abstract

Abstract-The Kenaga nomogram was developed by the U.S. Environmental Protection Agency (EPA) in the mid 1970s and has since been used prior to the registration of a pesticide to estimate the maximum potential pesticide residue level on plant material in the food chain of wildlife. The objective of this study was to evaluate the nomogram using field data. Six pesticides representing a variety of pesticide classes were applied to 15 plant species. Five of the six nomogram categories were tested with plant parts representing differences in surface morphology (i.e., glabrous vs. pubescent leaves). The sixth category was a mixed-grass community seeded with three grass species. Pesticide residue levels were determined the day of application and up to 32 d afterward. While the linear nomogram model does not represent the data as well as other models, relatively few data points (10%) collected on the day of pesticide application exceeded the nomogram predictions. The one systemic pesticide tested had degradation rates similar to nonsystemic pesticides in most categories. Present nomogram categories were significantly different from each other in most cases. However, the forage category should be combined with the leaves and leafy-crop category and have higher estimated residue levels than the Kenaga nomogram. A considerable amount of variation occurs in the level of pesticide residue on plant materials even under controlled experimental conditions and therefore nomogram values should be used as an estimate only until actual field residue data are available. The nomogram, with modifications, appears to be a reasonable regulatory device if careful thought is given in selecting the plant category for making residue estimates.

A new tool for the evaluation of crop residue trial data (day-zero-plus decline)

“…For many years estimates of residues on vegetation used in initial tiers of environmental risk assessment have been based on simple empirically derived relationships between application rate and residue levels (Hoerger and Kenaga 1972;Fletcher et al 1994;Pfleeger et al 1996). It is assumed that provided the interval between application and measurement is short, the measured residues provide a good measure of the volume of spray intercepted by the part of the plant that is of interest when normalized for application rate.…”

Analysis of a database of pesticide residues on plants for wildlife risk assessment

“…The assumption underlying the concept of RUD, that residues on plants are proportional to the dosage of pesticide, is supported in 36 of 41 studies in which this could be tested, but as much variance is unexplained as is explained by the linear model. Pfleeger et al [14], who evaluated five of the nomogram categories by spraying pesticides on 15 crop species, concluded that a quadratic model was always a better fit for the relationship between application rate and residue concentration. The discrepancy between the two results may come from the fact that the authors used six rates to test their model, whereas the studies reported here rarely tested more than three application rates.…”

“…Despite the extensive use and importance of the nomogram in making regulatory decisions, few efforts have been made to validate this approach. Some studies examining the ability of the nomogram to predict correctly the residues on alfalfa [12,13] and other crops [14] show that residues occasionally exceed the original upper limit values. Of greater relevance, however, is testing the validity of the concept of RUD, because this is the basis for extrapolation of expected environmental concentrations across different application rates.…”

“…Of greater relevance, however, is testing the validity of the concept of RUD, because this is the basis for extrapolation of expected environmental concentrations across different application rates. The evidence published so far suggests that the relationship between application rate and residue concentration may not be linear [12,14]. Those authors also suggest that differences resulting from use of the wrong model may be minimal.…”

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

“…The EC guidance reviews recent work on estimating residues on vegetation and insects (Luttik, 1992;Fletcher et al, 1994;Pfleeger et al, 1996;Brewer et al, 1997;Fischer and Bowers, 1997;Edwards, 1998;Joerman, 1998). In the past the majority of data concern pesticide residues on plants and residues on insects have been derived from these.…”