Residues of pesticide co-formulants in lettuce and parsley: Identification of decline processes using field trials in different cropping systems.

BACKGROUND: Although co-formulants constitute a substantial portion of the total plant protection product (PPP) mass applied to crops, data on residue formation and the behaviour of these substances on plants are scarce. In an earlier study we demonstrated that co-formulants commonly used in PPPs can form considerable residues, i.e., in the low to medium mg/kg range, but normally decline rapidly within few days. In the field trial reported here, we aimed to identify the major decline processes of co-formulants. Residues of co-formulants were therefore monitored in parsley and lettuce grown in an open field as well as under foil tunnels equipped with either an overhead or a drip irrigation system. RESULTS: Dissipation of three anionic surfactants was markedly faster when crops (parsley and lettuce) were exposed to natural rainfall or irrigation from above compared to drip irrigation. In contrast, the decline of three volatile organic solvents was not affected by rain or irrigation, but was dependent on the crop, with much shorter half-lives in lettuce than in parsley. Furthermore, dilution through plant growth contributed significantly to the reduction of residues over time. CONCLUSION: In this work we substantiate earlier findings on the magnitude and dissipation of residues of anionic surfactants and solvents representing the most important co-formulant classes. The chosen experimental setup allowed differentiation between decline processes and we confirm that foliar wash-off is a major dissipation process for anionic surfactants. For volatile organic solvents, dissipation appears to depend on the properties not only of the substance but also of the plant (surface). © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Magnitude and decline of pesticide co-formulant residues in vegetables and fruits: results from field trials compared to estimated values.

BACKGROUND: The application of plant protection products (PPPs) leads to the formation of residues in treated crops. Even though PPPs contain considerable amounts of co-formulants, regulation and monitoring of residues normally focus on the active substances (a.s.) only. For our study we selected four commonly used co-formulants (three anionic surfactants and one organic solvent) and investigated the formation and decline of residues in vegetables and apples under field conditions. The aims were to characterize the behavior of co-formulant residues on crops and to provide a basis for future investigations on consumer exposure. RESULTS: The development of robust and sensitive analytical methods allowed the quantification of residues in the low µg/kg-level. After treatment with PPPs, co-formulants were detected up to approximately 10 mg kg-1 in vegetables. In general, these residues declined fast with half-lives of a few days. Wash-off and volatilization were identified as important removal processes for anionic surfactants and the organic solvent, respectively. However, in specific crops (parsley and celery), organic solvent residues were still considerable (≈2 mg kg-1 ) 2 weeks after treatment. We further demonstrate that it is feasible to estimate co-formulant residues using publicly available data on pesticide a.s. CONCLUSION: To date no information on co-formulant residues in food is available. The findings from our field trials, as well as the presented approach for the prediction of residues, provide key elements for future consideration of consumer exposure to PPP co-formulants. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Toxic Responses Induced at High Doses May Affect Benchmark Doses.

To derive reference points (RPs) for health-based guidance values, the benchmark dose (BMD) approach increasingly replaces the no-observed-adverse-effect level approach. In the BMD approach, the RP corresponds to the benchmark dose lower confidence bounds (BMDLs) of a mathematical dose-response model derived from responses of animals over the entire dose range applied. The use of the entire dose range is seen as an important advantage of the BMD approach. This assumes that responses over the entire dose range are relevant for modeling low-dose responses, the basis for the RP. However, if part of the high-dose response was unnoticed triggered by a mechanism of action (MOA) that does not work at low doses, the high-dose response distorts the modeling of low-dose responses. Hence, we investigated the effect of high-dose specific responses on BMDLs by assuming a low- and a high-dose MOA. The BMDLs resulting from modeling fictitious quantal data were scattered over a broad dose range overlapping with the toxic range. Hence, BMDLs are sensitive to high-dose responses even though they might be irrelevant to low-dose response modeling. When applying the BMD approach, care should be taken that high-dose specific responses do not unduly affect the BMDL that derives from low doses.

The Current Dietary Risk Assessment of Chemicals in Food Underestimates the Actual Risk.

Dietary risk assessments (DRA) help determine safe exposure levels of toxic substances in food. Of these, Acceptable Daily Intake (ADI), derived from No Observed Adverse Effect Levels (NOAEL) of long-term toxicity studies, is compared to exposure estimates using lifetime-averaged food intakes. These estimates ignore intermittent high exposures exceeding the ADI; toxic effects of such exposures are considered irrelevant, on the assumption that toxic potency increases with exposure duration, which would be reflected by decreasing NOAELs. However, our statistical analysis of thousands of animal toxicology studies shows that NOAELs after short- and long-term exposure are similar if study design factors are considered. Thus, the short- and long-term potency effects of chemicals are similar. Hence, a short-term toxic effect is generally ignored in current DRA. It accounts for lifetime-averaged but not intermittent high food intakes and, therefore, must be revised. Additionally, there is no added value of long-term studies for ADI derivation.