Reproducibility and Relevance: Important Elements of Chemical Testing


We wish to reside in a world the place the chemical substances that enhance our high quality of life are secure to make use of. We wish to make sure the safety of our households, our most weak communities, and the setting. We can not do that underneath the present regulatory system, nonetheless, as a result of predicting the toxicity of chemical substances depends closely on decades-old animal checks.

Two rats with blue background

The excellent news is that there have been large developments within the strategies we will use to check chemical substances and predict their potential toxicity to us and our surroundings. Now greater than ever, we’re capable of harness dependable and related instruments—that don’t use animals—to raised perceive chemical results extra rapidly. Using these instruments will permit us to maintain our world safer than ever earlier than.


Reproducibility is outlined because the extent to which constant outcomes are obtained when an experiment is repeated.

It’s important that the strategies we use to check chemical substances are high-quality and produce constant outcomes. If you happen to can not repeat a consequence, the science isn’t sound.

Take a look at strategies developed within the 21st century have undergone rigorous examination to find out if they’re reproducible earlier than they’re used or accepted by regulatory companies. This isn’t the case, nonetheless, for animal checks that had been developed many many years in the past. Lately, analyses have been carried out to evaluate the reproducibility of animal checks, and the outcomes are alarming.

Examples of animal checks demonstrating lack of reproducibility

Carcinogenicity checks are carried out to foretell whether or not a chemical will trigger most cancers in people. Within the animal check, rats and mice are uncovered to a chemical each day for 18 to 24 months. They’re then killed, and their our bodies are dissected to search for cancerous tumors. An evaluation of 121 repeated most cancers checks in rats and mice confirmed that outcomes had been reproducible solely 57% of the time.1

Eye irritation checks are carried out to foretell whether or not a chemical will irritate the human eye. Developed in 1944, the animal check makes use of rabbits and has many demonstrated flaws.2 An evaluation of 491 chemical substances assessed at the least twice within the rabbit eye check confirmed that research predicting delicate or reasonable irritation had been reproducible, respectively, solely 33% or 16% of the time! As well as, there’s a 10% likelihood that chemical substances initially labeled as extreme irritants, when examined once more, can be re-classified as non-irritants.3

Skin sensitization checks are carried out to foretell the potential of a chemical, by repeated publicity, to trigger an allergic human pores and skin response. Within the animal check, mice are uncovered to chemical substances for 2 or three days earlier than they’re killed. A examine analyzing virtually 90 chemical substances, for which multiple check in mice had been carried out, confirmed that the outcomes are reproducible solely 62% of the time (underneath essentially the most broadly used classification system).4

Acute oral toxicity checks are carried out to foretell what’s going to occur to people following short-term publicity to a chemical. Within the check on rats, the premise is to find out the quantity of an ingested chemical that causes 50% of the rats to die. A examine analyzing virtually 2,500 chemical substances confirmed that checks utilizing rats to evaluate acute oral toxicity are reproducible solely 60% of the time.5

Skin irritation checks are carried out to foretell whether or not a chemical will irritate human pores and skin. The animal check is carried out utilizing rabbits and was developed in 1944. An evaluation of virtually 1,000 chemical substances assessed at the least twice within the rabbit pores and skin check confirmed that research predicting delicate or reasonable irritation had been reproducible lower than 50% of the time.6

Endocrine disruption checks are carried out to foretell whether or not a chemical impacts the hormonal, or endocrine, system of people. Most of the present checks depend on the usage of giant numbers of animals, and a few have been assessed for his or her reproducibility. An evaluation of 235 chemical substances within the uterotrophic check, which assesses the estrogenic system in feminine rats, confirmed that the check was reproducible solely 74% of the time.7 Equally, a examine of 25 chemical substances within the Hershberger check, which assesses hormonal results in male rats, confirmed that the examine was reproducible solely 72% of the time.8

What benefits do non-animal checks present over animal checks?

In distinction to animal checks, non-animal checks are often reproducible 80% to greater than 90% of the time. For instance, two human cell–based mostly checks developed to evaluate eye irritation (EpiOcularTM and SkinEthic) are reproducible 93% and 95% of the time, whereas one other eye irritation check (LabCyte) is reproducible 87% of the time. Strategies that assess essential facets of pores and skin allergy potential, named kDPRA and ADRA, have been proven to be reproducible 88% and 100% of the time!

  • Non-animal checks will be based mostly on human cells to raised replicate human biology and supply details about how a chemical causes toxicity in people.
  • Non-animal checks will be quicker than animal checks and, due to this fact, extra knowledge on extra chemical substances will be produced extra quickly.
  • Using non-animal strategies permits for the examine of mixtures, not solely of single chemical substances. Learning mixtures offers a extra reflective image of how people are uncovered to chemical substances in actual life and isn’t possible to undertake with prolonged animal checks.
  • Opposed outcomes in people can rely upon genetic background, physiology, pre-existing illness situations, way of life, life-stage, and co-exposure—none of which is explored when counting on checks on animals. As non-animal strategies are additional developed, patient-tailored testing may permit for extra personalised well being research.


  1. Gottmann E, Kramer S, Pfahringer B, Helma C. Knowledge high quality in predictive toxicology: reproducibility of rodent carcinogenicity experiments. Environ Well being Perspect. 2001;109(5):509-514.
  2. Clippinger AJ, Raabe HA, Allen DG, et al. Human-relevant approaches to evaluate eye corrosion/irritation potential of agrochemical formulations. Cutan Ocul Toxicol. 2021;40(2):145-167.
  3. Luechtefeld T, Maertens A, Russo DP, Rovida C, Zhu H, Hartung T. Evaluation of draize eye irritation testing and its prediction by mining publicly obtainable 2008-2014 REACH knowledge. ALTEX. 2016;33(2):123-134.
  4. Dumont C, Barroso J, Matys I, Value A, Casati S. Evaluation of the Native Lymph Node Assay (LLNA) variability for assessing the prediction of pores and skin sensitisation potential and efficiency of chemical substances with non-animal approaches. Toxicol Vitr. 2016;34:220-228.
  5. Karmaus AL, Mansouri Ok, To KT, et al. Analysis of variability throughout rat acute oral systemic toxicity research. Toxicol Sci. 2022;188(1):34-47.
  6. Rooney JP, Choksi NY, Ceger P, et al. Evaluation of variability within the rabbit pores and skin irritation assay. Regul Toxicol Pharmacol. 2021;122:104920.
  7. Kleinstreuer NC, Ceger PC, Allen DG, et al. A curated database of rodent uterotrophic bioactivity. Environ Well being Perspect. 2016;124(5):556-562.
  8. Browne P, Kleinstreuer NC, Ceger P, et al. Improvement of a curated Hershberger database. Reprod Toxicol. 2018;81:259-271.

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