Non-relevance of acute dermal toxicity testing for assessing human health protection in the regulatory decision-making for agrochemical formulated products

Evaluation of the predictivity of Acute Oral Toxicity (AOT) structure-activity relationship models

Several public efforts are aimed at discovering patterns or classifiers in the high-dimensional bioactivity space that predict tissue, organ or whole animal toxicological endpoints. The current study sought to assess and compare the predictions of the Globally Harmonized System (GHS) categories and Dangerous Goods (DG) classifications based on Lethal Dose (LD50) from several available tools (ACD/Labs, Leadscope, T.E.S.T., CATMoS, CaseUltra). External validation was done using dataset of 375 substances to demonstrate their predictive capacity. All models showed very good performance for identifying non-toxic compounds, which would be useful for DG classification, developing or triaging new chemicals, prioritizing existing chemicals for more detailed and rigorous toxicity assessments, and assessing non-active pharmaceutical intermediates. This would ultimately reduce animal use and improve risk assessments. Category-to-category prediction was not optimal, mainly due to the tendency to overpredict the outcome and the general limitations of acute oral toxicity (AOT) in vivo studies. Overprediction does not specifically pose a risk to human health, it can impact transport and material packaging requirements. Performance for compounds with LD50 ≤ 300 mg/kg (approx. 5% of the dataset) was the poorest among all groups and could be potentially improved by including expert review and read-across to similar substances.

Increasing confidence in waiving dermal toxicity studies: A comparison of oral and dermal acute data with alternative approaches for agrochemicals and products

The refinement of OECD 402 study design and criteria under which the study can be waived has been welcomed in some regulatory regions but met with uncertainty in others. To address these human safety concerns, previously available in vivo acute oral and acute dermal toxicity data was evaluated from a total of 597 agrochemical active ingredients and products. It was identified that all active ingredients and 99.6% of products had an acute dermal classification equal to or less toxic than their acute oral classification, confirming that waiving the acute dermal study and basing the outcome on the acute oral toxicity result has no impact on human health assessment. Additionally, automated Acute Toxicity Estimate (ATE) calculations were conducted on 440 products to evaluate if the predicted dermal toxicity resulted in the same in vivo classification. 93% of ATE predictions provided excellent correlation to the in vivo result and 6.4% resulted in a more conservative prediction. It is therefore clear that the results of this investigation, should remove any regulatory concerns and that OECD 402 can be confidently eliminated in its entirety from testing requirements globally.

Compounded conservatism in European re-entry worker risk assessment of pesticides

We review the risk parameters and drivers in the current European Union (EU) worker risk assessment for pesticides, for example considering crop maintenance, crop inspection or harvesting activities, and show that the current approach is very conservative due to multiple worst-case default assumptions. As a case study, we compare generic exposure model estimates with measured worker re-entry exposure values which shows that external cumulative exposure is overpredicted by about 50-fold on average. For this exercise, data from 16 good laboratory practice (GLP)-compliant worker exposure studies in 6 crops were evaluated with a total number of 184 workers. As generic overprediction does not allow efficient risk management or realistic risk communication, we investigate how external exposure can be better predicted within the generic model, and outline options for possible improvements in the current methodology. We show that simply using averages achieves more meaningful exposure estimates, while still being conservative, with an average exposure overprediction of about 9-fold. Overall, EU risk assessment includes several numerically unaccounted "hidden safety factors", which means that workers are well protected; but simultaneously risk assessments are biased towards failing due to compounded conservatism. This should be considered for further global or regional guidance developments and performing more exposure-relevant risk assessment.