Pesticides

Posted on June 6, 2016

Pesticides (also known as agrochemicals or plant-protection products) undergo a battery of tests to fulfil government regulatory agencies’ data requirements for health and safety. These include tests for eye and skin irritation, skin sensitisation, and acute oral, inhalation, and dermal toxicity as well as studies on reproduction and development, neurotoxicity, immunotoxicity, carcinogenicity, mutagenicity, and ecological effects.

Many of the required tests use animals. However, there is a global movement away from animal tests, which are increasingly being demonstrated to be unreliable or not relevant to humans,1–11 and towards non-animal toxicology testing approaches that better protect human health and the environment.

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Regulatory Landscape

In the EU and the UK, pesticide regulations require the use of non-animal methods where they are available, and lists of some of the accepted methods for each endpoint can be found in the data requirements.1–6

In the US, the Environmental Protection Agency (EPA) Office of Pesticide Programs has committed to making the transition towards the use of non-animal testing approaches, which will enhance the quality of risk assessment and ensure better protection of human health and the environment.7 The EPA offers companies the opportunity to provide robust scientific rationale to allow the waiving of tests that do not add value to the risk assessment process.8 In addition, in 2020, the EPA published a work plan9 (updated in December 2021) and two webpages10 summarising opportunities to reduce and replace animal use and testing metrics.

Eye Irritation/Corrosion

The use of non-animal methods to assess the eye irritation potential of pesticidal active ingredients and formulations may be allowed and even encouraged, depending on the regulatory region. In the EU and the UK, the regulation requires the use of non-animal methods when they are available.1,2 Additionally, guidance from the UK Health and Safety Executive warns that data from tests using animals may be rejected.3

In the US, the EPA Office of Pesticide Programs accepts the use of an alternate framework for evaluating the eye irritation potential of antimicrobial cleaning products and, on a case-by-case basis, other classes of pesticides and pesticide products.4 In addition, the EPA allows for the submission of in vitro data to address eye irritation data requirements and to support the registration of pesticide products and the registration review of registered pesticides.5 To broaden the use of reliable testing methods, the Science Consortium collaborated with the EPA, the European Commission’s Joint Research Centre, and others to review the available test methods and showed that in vitro and ex vivo methods are less variable and as or more human-relevant than the traditionally used rabbit eye test. The review also states that the rabbit test is not a reliable reference standard and that new methods should not be compared to the rabbit test to show their validity.6 The Science Consortium and the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) have also coordinated and funded the testing of agrochemical formulations using various in vitro and ex vivo methods to demonstrate how to use these methods to meet EPA testing requirements.7

Skin Irritation/Corrosion

There are multiple in vitro and in chemico skin irritation tests available that are applicable to pesticides (including formulations) and cover the full range of irritancy. In the EU and the UK, the regulation requires the use of non-animal methods when they are available.1,2 Additionally, guidance from the UK Health and Safety Executive warns that data from tests on animals may be rejected.3

In the US, the EPA, NICEATM, and others have partnered on a publication reviewing the reliability and relevance of the available test methods (publication forthcoming). In addition, the EPA allows for the submission of in vitro data to address skin irritation data requirements and to support the registration of pesticide products and the registration review of registered pesticides.4

Skin Sensitisation

In 2021, the Organisation for Economic Co-operation and Development (OECD) published a guideline outlining three defined approaches comprising combinations of in silico, in chemico, and in vitro approaches.1 The data produced by the defined approaches have been demonstrated to be as or more informative than the mouse local lymph node assay.2

In the EU and the UK, non-animal methods are required to be used in place of tests on animals when they are available and applicable.3,4 In the US, in 2018, the EPA instituted an agency-wide policy accepting the use of in vitro defined approaches for skin sensitisation testing of single chemicals (including agrochemicals),5 and in 2020, the agency applied the policy to the re-registration of six isothiazolinones by conducting a risk assessment using in vitro tests and an artificial neural network–based defined approach.6,7

Acute Systemic Toxicity

The Science Consortium partnered with NICEATM, the EPA, and others on the implementation of alternative approaches for acute systemic toxicity testing, including a publication outlining current regulatory requirements, data obtained from the currently required tests, data actually used and needed by regulators, and opportunities for the use of non-animal approaches to meet regulatory needs.1 The publication of this paper was an action item proposed at a 2015 workshop2 co-organised by the Science Consortium and was followed, in 2016, by a workshop3 focused on acute inhalation toxicity testing.

The GHS Mixtures Equation uses toxicity data from the individual ingredients in formulations to estimate the toxicity of end products without having to conduct additional testing.4 In the EU and the UK, the GHS Mixtures Equation is accepted for assessing acute systemic toxicity (oral, dermal, and inhalation) as well as eye and skin irritation and the skin sensitisation potential of pesticide formulations on a case-by-case basis, taking into account the likelihood of synergistic effects.5,6 In the US, in 2021, the EPA investigated the use of the GHS Mixtures Equation for the assessment of acute oral toxicity of formulations, and it concluded that the formula was useful to predict the toxicity of mixtures, particularly those with lower toxicity.7

Acute oral toxicity

Specific to predicting acute oral systemic toxicity, the EPA and NICEATM developed a computational model called the Collaborative Acute Toxicity Modeling Suite (CATMoS).8 The model is a free resource and can be implemented within the Open (Quantitative) Structure-activity/property Relationship App (OPERA).9

Acute inhalation toxicity

The EPA has accepted the use of a non-animal testing approach to support the re-registration of a fungicide known to be an irritant.10,11 The approach combined knowledge of the chemical’s physicochemical properties, exposure monitoring of agrochemical workers, and use of human dosimetry modelling to predict localisation within the human respiratory tract. It then used a reconstructed human tissue (MucilAir™, Epithelix Sàrl) representative of the respiratory region of interest to assess effects relevant to the human response. The EPA encourages registrants to meet with the agency to discuss the use of novel testing strategies that are not yet included in standard guidance.

A summary of the Science Consortium’s extensive work on respiratory toxicity testing can be found here.

Acute dermal toxicity

In the EU, acute dermal toxicity tests may be waived if the test substance has been shown to be corrosive to the skin.5 In 2016, the EPA issued guidance for waiving acute dermal toxicity tests of pesticide formulations12 based on a holistic assessment of other toxicity tests, and the guidance was extended to active ingredients13 in 2020.

Carcinogenicity

The Science Consortium, government, and industry are working to modernise carcinogenicity testing through the Rethinking Carcinogenicity Assessment for Agrochemicals Project (ReCAAP).1 Additional efforts are underway, including activities at the OECD2, to advance more human-relevant carcinogenicity assessments.3 In 2024, the OECD published our case studies, co-authored with Syngenta and Exponent, on using a weight of evidence approach for chronic toxicity and carcinogenicity assessments instead of the lifetime rodent bioassay. More information about this work and carcinogenicity testing can be found here.

Efforts to develop in vitro methods to assess carcinogenicity are ongoing. For example, cell transformation assays (e.g. the cell transformation assay based on the Bhas 42 cell line4) assess phenotypic changes to cells, which are associated with the initial stages of normal cells transforming into neoplastic cells. Data from cell transformation assays can be used in combination with other data streams to provide an indication of hazard or risk. In addition, in silico models – such as Lhasa Limited’s Kaptis, which is organised using relevant adverse outcome pathways (AOP) and networks – can be useful in determining the carcinogenic potential of a chemical.5 Lhasa Limited has also collaborated with the AOP-Wiki (established by the OECD) to develop Wiki Kaptis to improve the understanding of pathway connectivity within AOP networks.6

Ecotoxicity

Avian toxicity

For decades, the EPA has required data from both avian acute oral toxicity (OCSPP 850.2100) and avian dietary toxicity (OCSPP 850.2200) tests for the registration of pesticides. However, trends over the past 20 years have suggested that the avian sub-acute dietary test generally does not drive risk management decisions, and scientists from the Science Consortium and EPA conducted a detailed retrospective analysis to confirm this hypothesis. One-hundred-and-nineteen pesticides registered between 1998 and 2017 were evaluated, and the results demonstrate that the sub-acute dietary test conducted on birds is not used in risk management and can be removed without causing harm to the environment.1 This analysis was used to support the EPA’s guidance for replacing the avian sub-acute dietary test for pesticide registration with a science-based integrated assessment.2 The EPA now joins regulatory agencies in Australia, Canada, and the EU in avoiding the use of this test in favour of reliance on other scientific information. For more information on the Science Consortium’s work on avian toxicity, see here.

Aquatic toxicity

After conducting a retrospective data analysis, the EPA instituted a policy in 2020 to reduce the number of test concentrations – and therefore fish – used in fish bioconcentration tests.3

In 2023, the EPA published a paper with NICEATM demonstrating that it should be possible to assess potential acute risk of substances to fish using fewer than the three fish species currently required.4

Through the International Council on Animal Protection in OECD Programmes (ICAPO), the Science Consortium is co-leading a project (with the US) to reduce the number of fish used in aquatic toxicity tests by reducing the number of solvents used. In addition, through ICAPO, the Science Consortium is co-leading a project (with Austria) to develop guidance on integrated approaches to testing and assessment to assess the acute toxicity potential of a test substance to fish. For more information on the Science Consortium’s work on aquatic toxicity, see here.

Toxicity Tests Using Dogs

Many countries used to require both a 90-day (sub-chronic) study and one-year (chronic) study in dogs as part of the data requirements for registering pesticide active ingredients. Beginning in the late 1990s, numerous scientific articles1–10 have been published assessing the results of the one-year chronic test in dogs and supporting the conclusion that its elimination would not compromise human safety or protection.

In the US, the EPA removed the one-year study from its requirements in 2007.11 The EU passed legislation in March 2013 also eliminating the requirement for the one-year dog study. Following discussions between the Science Consortium and Health Canada staff, Canada eliminated its requirement in March 2016.12 Japan and South Korea eliminated their requirements in April 2018,13 and Brazil eliminated its requirement in July 2019. Australia, China, and India have indicated that they do not require the one-year test or that it can be waived when a robust scientific rationale is provided.

In addition to the one-year test, recent international collaborations have focused on the 90-day sub-chronic test in dogs, proposing a decision tree for when it is possible to waive the test, i.e. when sufficient information can be provided from existing information or in silico and in vitro methods to assess this endpoint.14

Training and Collaborations

The Science Consortium organises training opportunities to familiarise scientists and regulators with non-animal test methods. These sessions are led by in silico and in vitro method experts, such as the Institute for In Vitro Sciences and the Laboratory of Mathematical Chemistry. For example, several times each year, the Science Consortium sponsors a hands-on training at the Institute for In Vitro Sciences. In addition, the Science Consortium, the EPA, and others co-organise a webinar series on the use of new approach methods in risk assessment.

The Science Consortium participates in the Pesticide Program Dialogue Committee (PPDC), which is a federal advisory committee for the EPA Office of Pesticide Programs with members representing industry, growers, and the animal protection, environmental, and farmworker communities.

In the EU, the Science Consortium is a registered stakeholder with the European Food Safety Authority and meets with and provides comments to the European Commission as data requirements for pesticide active ingredients and formulations are updated. The Science Consortium also participates in member state competent authority meetings for biocides (which are regulated separately from plant protection products in the EU), in which data requirements are discussed and updated. The Science Consortium also works with the Commission, member state authorities, and industry representatives on a number of far-reaching regulatory initiatives, such as the Chemicals Strategy for Sustainability,1 to replace tests on animals with robust non-animal approaches.

Similarly, in India, the Science Consortium works with the Central Insecticides Board and Registration Committee and industry members, providing scientific recommendations on the implementation of effective, non-animal methods.

For a list of our publications, see here.