Phil Botham

A 1-year toxicity study in dogs is no longer a scientifically justifiable core data requirement for the safety assessment of pesticides.

A review of publications on pesticides assessing the need for 1-year toxicity studies in dogs was performed. Four key peer-reviewed papers with different approaches investigated the value of a 1-year dog study in addition to a 3-month study. Despite different databases and approaches, each concluded with the recommendation to limit the testing of pesticides in dogs to a duration of 3 months. The combined weight of evidence presented in this review reinforces these independent conclusions. Therefore, the routine inclusion of a 1-year dog study as a mandated regulatory requirement for the safety assessment of pesticides is no longer justifiable and a globally harmonized approach should be taken to match the latest legislation of the European Union and the US EPA.

Feasibility of the extended one-generation reproductive toxicity study (OECD 443).

The extended one-generation reproduction toxicity study (OECD 443, adopted 28-July-2011) produces more information with fewer animals than the two-generation study (OECD 416), by including F1 neurotoxicity and immunotoxicity assessments, and omitting an F2 generation if there are no relevant F1 findings. This saves >1000 animals per compound. Feasibility studies based on draft OECD443 were conducted in industrial GLP laboratories in Europe and USA, using vinclozolin, methimazole and lead acetate. A fourth study was conducted with 2,4-dichlorophenoxyacetic acid (2,4-D) in response to a regulatory request for reproduction and developmental neurotoxicity data. The studies effectively profiled vinclozolin as an anti-androgenic developmental toxicant, methimazole as a developmental anti-thyroid agent, and lead acetate as a systemic and developmental toxicant. The 2,4-D study demonstrated the value of toxicokinetic data in dose setting and data interpretation. These results illustrate the variety of reproductive and developmental endpoints which can be captured in this complex but manageable study design. Time constraints for triggering further (F2) testing are summarized.

Guidance for the classification of carcinogens under the globally harmonised system of classification and labelling of chemicals (GHS).

The United Nations Conference on Environment and Development (UNCED) has developed criteria for a globally harmonised system of classification and labelling of chemicals (GHS). With regard to carcinogenicity, GHS distinguishes between Category 1 (‘known or presumed human carcinogens’) and Category 2 (‘suspected human carcinogens’). Category 1 carcinogens are divided into Category 1A (‘known to have carcinogenic potential for humans’), based largely on human evidence, and 1B (‘presumed to have carcinogenic potential for humans’), based largely on experimental animal data. Concerns have been raised that the criteria for applying these carcinogenicity classifications are not sufficiently well defined and potentially allow different conclusions to be drawn. The current document describes an attempt to reduce the potential for diverse conclusions resulting from the GHS classification system through the application of a series of questions during the evaluation of data from experiments with rodents; epidemiological data, which could lead to Category 1A, have not been considered. Answers to each question can lead either to a classification decision or to the next question, but this process should only be implemented in an environment of informed scientific opinion. The scheme is illustrated with five case studies. These questions are: (1) Has a relevant form of the substance been tested? (2) Is the study design relevant to human exposure? (3) Is there a substance-related response? (4) Is the target tissue exposure relevant to humans? (5) Can a mode of action be established? (6) Is the mode of action relevant to humans? (7) What is the potency?

Interlaboratory Validation of 1% Pluronic L92 Surfactant as a Suitable, Aqueous Vehicle for Testing Pesticide Formulations Using the Murine Local Lymph Node Assay

The mouse local lymph node assay (LLNA) has become the preferred test for evaluating the dermal sensitization potential of chemicals and requirements are now emerging for its use in the evaluation of their formulated products, especially in the European Union. However, despite its widespread use and extensive validation, the use of this assay for directly testing mixtures and formulated products has been questioned, which could lead to repeat testing using multiple animal models. As pesticide formulations are typically a specific complex blend of chemicals for use as aqueous-based dilutions, traditional vehicles prescribed for the LLNA may change the properties of these formulations leading to inaccurate test results and hazard identification. The objective of this study was to evaluate the effectiveness of an aqueous solution of Pluronic L92 block copolymer surfactant (L92) as a vehicle in the mouse LLNA across five laboratories. Three chemicals with known sensitization potential and four pesticide formulations for which the sensitization potential in guinea pigs and/or humans had previously been assessed were used. Identical LLNA protocols and test materials were used in the evaluation. Assessment of the positive control chemicals, hexylcinnamaldehyde, formaldehyde, and potassium dichromate revealed positive results when using 1% aqueous L92 as the vehicle. Furthermore, results for these chemicals were reproducible among the five laboratories and demonstrated consistent relative potency determinations. The four pesticide formulations diluted in 1% aqueous L92 also demonstrated reproducible results in the LLNA among the five laboratories. Results for these test materials were also consistent with those generated previously using guinea pigs or from human experience. These data support testing aqueous compatible chemicals or pesticide formulations using the mouse LLNA, and provide additional support for the use of 1% aqueous L92 as a suitable, aqueous-based vehicle.

Relevance of the 1-year dog study in assessing human health risks for registration of pesticides. An update to include pesticides registered in Japan.

Abstract Over 400 active pesticides are registered in Japan (4). The results of dog toxicity studies (usually, the 1-year study) were used by the Japanese regulatory authorities to establish the acceptable daily intake (ADI) for 45 pesticide active ingredients (about 9%). A retrospective review of ADIs established in Japan with dog studies as pivotal data for their derivation was performed: the ADIs were reassessed under the assumption that the 1-year dog study would not be available and an alternate ADI was derived based on the remaining toxicology database. In 35 of the 45 cases (77.8%) the ADI resulting from the absence of the 1-year dog study was no greater than twice the Japanese ADI, a difference considered not to be of biological significance. In 6 cases (13%) the resulting ADI was 2–5 times higher, which is considered of questionable biological relevance. On further evaluation of the database, three of these six cases were assessed as to clarify that there is no clear difference and for the other three additional studies to clarify that uncertain findings would have been required. In 3 of the 45 cases (7%) there may be a real difference within the ADI ratio of 2–5. Only in 1 case (2.2%) ADI was five times higher than that has been set. Accordingly, the absence of a 1-year dog study does not appear to influence the ADI derivation in a relevant manner in more than 98% of cases. For the four compounds with a real difference in ADI, consumer exposure would still be well below the alternative ADI. Therefore, a strong case can be made that the standard mandatory requirement to conduct a 1-year dog study, in addition to the 3-month study, is not justified and of no additional value in protecting human health. In addition, a substantial reduction in test animals could be achieved.