5 Types of Products That May Undergo Chronic Toxicity Testing for Safety Evaluation
Product safety cannot always be evaluated solely by observing effects following a single exposure. Some substances may be used or encountered repeatedly over long periods.
Under these circumstances, certain toxic effects may only become apparent after prolonged exposure. Chronic toxicity testing is one approach that can be used to characterize the potential effects of repeated, long-term exposure to a test substance.
OECD Test Guideline 452 describes chronic toxicity studies as investigations designed to characterize the toxicity profile of a substance in a mammalian species following prolonged and repeated exposure. The guideline primarily focuses on rodents, with an exposure period generally lasting 12 months.
However, not every product requires chronic toxicity testing. The need for testing should be determined according to the substance, intended use, exposure route and duration, existing toxicological information, and applicable regulatory requirements.
Here are five categories that may be considered for long-term toxicity evaluation.
Table of Content:
- Pesticides
- Pharmaceutical Products or Drug Candidates
- Food Additives and Food-Related Substances
- Industrial Chemicals
- Ingredients or Chemicals Used in Consumer Products
Pesticides
Pesticides are among the product categories that may require comprehensive toxicological evaluation. They include:
- insecticides;
- herbicides;
- fungicides;
- rodenticides; and
- other pesticide categories.
Depending on their intended use, active ingredients may present the potential for repeated exposure. Therefore, safety assessments may need to consider not only acute effects but also potential effects associated with prolonged exposure.
Chronic toxicity testing can provide information about biological responses occurring during extended repeated exposure. Parameters may include clinical observations, body weight, hematology, clinical chemistry, organ evaluation, and histopathology.
OECD guidance on repeat-dose toxicity specifically discusses the analysis and evaluation of toxicity studies involving pesticides and other chemicals. These data may subsequently contribute to a broader risk assessment according to the product and regulatory context.
Pharmaceutical Products or Drug Candidates
Pharmaceutical products may also require evaluation of effects associated with long-term exposure. Some medicines are intended to be administered for months or years.
Consequently, pharmaceutical development may need to evaluate whether repeated exposure produces effects that are not evident during shorter studies. Long-term toxicity studies may help investigate:
- potential target organs;
- dose-response relationships;
- hematological changes;
- biochemical changes;
- tissue or organ alterations; and
- persistence or reversibility of selected effects when appropriately designed.
However, there is no single study duration appropriate for every pharmaceutical product. Molecular characteristics, clinical indication, intended duration of treatment, pharmacokinetics, previous toxicological data, and regulatory guidance all influence study design.
For example, a review of biotechnology-derived pharmaceuticals discusses six-month toxicity studies in the regulatory assessment of certain products intended for chronic use. Therefore, chronic toxicity testing should form part of a scientifically designed safety strategy rather than being applied identically to every pharmaceutical product.
Food Additives and Food-Related Substances
Certain food additives may be consumed repeatedly over extended periods, making exposure duration an important consideration in their safety assessment. These substances may include selected:
- colorants;
- sweeteners;
- preservatives;
- emulsifiers;
- stabilizers; and
- other technological additives.
Toxicological evaluation may also be relevant to certain food contaminants and naturally occurring food constituents. Research comparing subchronic and chronic studies of food additives, contaminants, and natural constituents demonstrates how long-term toxicity data may contribute to establishing points of departure such as NOAELs and LOAELs for risk assessment.
Through chronic toxicity testing, researchers can evaluate whether particular biological effects emerge or progress during prolonged exposure. However, additional studies should only be performed when scientifically and regulatorily justified, taking existing evidence into consideration.
Industrial Chemicals
Industrial chemicals are another category that may require long-term toxicity evaluation when repeated exposure is plausible. Exposure may occur during manufacturing, handling, occupational activities, environmental release, or the use of downstream products.
Relevant substances may include certain:
- industrial raw materials;
- solvents;
- coating chemicals;
- manufacturing materials;
- specialty chemicals; and
- other chemical compounds.
The exposure route is particularly important when designing toxicity studies. OECD TG 452 recognizes oral, dermal, and inhalation exposure routes, with study conditions selected according to the relevant route and toxicokinetic characteristics of the test substance.
Chronic toxicity testing can therefore provide information on biological changes that may not become apparent during shorter exposure periods.
Ingredients or Chemicals Used in Consumer Products
Selected ingredients or chemical substances used in consumer products may also require long-term toxicological evaluation. This does not mean that every finished consumer product automatically requires a chronic animal study.
Toxicological assessment often focuses on relevant ingredients or substances based on hazard characteristics and expected exposure scenarios. The National Research Council has discussed the broad need for toxicity information across chemicals used in pesticides, cosmetics, pharmaceuticals, food, and commercial applications, while also emphasizing the need to prioritize testing resources.
Before selecting chronic toxicity testing, several questions should therefore be considered:
- Is repeated exposure expected?
- How long could exposure occur?
- What is the relevant exposure route?
- What exposure level is expected?
- What toxicological information already exists?
- Are particular organs or effects of concern?
- What do applicable regulations require?
Answering these questions helps ensure that long-term studies are conducted because they provide necessary scientific information rather than simply as a routine procedure.
What Is Evaluated During Chronic Toxicity Testing?
A chronic study does not simply determine whether a substance causes mortality. OECD TG 452 incorporates multiple observations to characterize biological responses during prolonged exposure.
These may include:
- clinical signs;
- body-weight changes;
- food consumption;
- hematology;
- clinical chemistry;
- urinalysis;
- organ weights;
- gross pathological examination; and
- tissue histopathology.
Together, these observations can help identify potential target organs, dose-response patterns, and the characteristics of adverse effects. Therefore, chronic toxicity testing provides information that differs from studies designed primarily to evaluate short-term exposure.
How Long Does Chronic Toxicity Testing Take?
The term chronic should be distinguished from acute, subacute, and subchronic toxicity. Under OECD TG 452, chronic toxicity studies in rodents generally involve an exposure period of 12 months.
The actual study design, however, should follow the guideline relevant to the substance, regulatory context, and research objective. OECD TG 453 separately addresses combined chronic toxicity and carcinogenicity studies.
Under this design, the chronic phase normally lasts 12 months, while the carcinogenicity phase may extend to approximately 24 months. Therefore, chronic toxicity and carcinogenicity testing should not be treated as synonymous, even though both may involve long-term exposure.
Why Is Long-Term Exposure Important?
Exposure duration can influence a substance's toxicity profile. An effect that does not appear after a single or short exposure may potentially develop following repeated exposure.
Toxicological responses depend on multiple factors, including dose, exposure route, frequency, duration, metabolism, and biological characteristics. Fundamental toxicology references such as Hayes' Principles and Methods of Toxicology emphasize dose, biological variability, transformation, and timing as central considerations in understanding toxic effects.
Long-term evaluation may therefore provide additional information when a substance is expected to be used or encountered repeatedly.
Does Every Product Need Chronic Toxicity Testing?
No, the decision to conduct chronic toxicity testing should be based on scientific and regulatory needs. Depending on the substance and intended purpose, existing toxicological data, weight-of-evidence approaches, in vitro methods, shorter-duration studies, or other accepted approaches may provide appropriate information.
OECD guidance also emphasizes selecting appropriate methodologies to meet data requirements while reducing animal use whenever scientifically possible and appropriate. Therefore, the testing strategy should first consider the research objective, existing evidence, required endpoints, and applicable regulatory framework.
Evaluate Long-Term Product Safety Through Toxicity Testing
Could your product or substance involve repeated exposure over an extended period? Don't rely solely on short-term exposure data when evaluating its safety profile.
Toxicity Testing can provide scientific data to support safety evaluation using an appropriate study design and relevant parameters. Contact IML Testing & Research today and discuss your chronic toxicity testing requirements and appropriate testing strategy with our team!
Author & Editor: Lina
References
OECD. (2018). Test No. 452: Chronic Toxicity Studies. OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publishing, Paris.
OECD. (2014). Guidance Document 116 on the Conduct and Design of Chronic Toxicity and Carcinogenicity Studies, Supporting Test Guidelines 451, 452 and 453. OECD Publishing.
OECD. (2018). Test No. 453: Combined Chronic Toxicity/Carcinogenicity Studies. OECD Guidelines for the Testing of Chemicals, Section 4.
Hayes, A. W., & Kruger, C. L. (Eds.). (2014). Hayes' Principles and Methods of Toxicology. 6th ed. CRC Press.
Hayes, A. W., & Kobets, T. (Eds.). (2024). Hayes' Principles and Methods of Toxicology. CRC Press.
Klaassen, C. D. (Ed.). Casarett & Doull's Toxicology: The Basic Science of Poisons. McGraw-Hill.
Batke, M., et al. (2020). Comparison of points of departure between subchronic and chronic toxicity studies on food additives, food contaminants and natural food constituents. Food and Chemical Toxicology, 146, 111784.
Clarke, J., et al. (2008). Duration of chronic toxicity studies for biotechnology-derived pharmaceuticals: Is 6 months still appropriate? Regulatory Toxicology and Pharmacology, 50(1), 2–22.
Rhomberg, L. R., et al. (2007). Issues in the design and interpretation of chronic toxicity and carcinogenicity studies in rodents: Approaches to dose selection. Critical Reviews in Toxicology, 37(9), 729–837.
