How Environmental Factors Disrupt Hormones in Fish and Frogs

Jenn Hoskins
25th March, 2024

How Environmental Factors Disrupt Hormones in Fish and Frogs

Image Source: Natural Science News, 2024

Key Findings

  • Study finds that artificial light at night (ALAN) may disrupt hormones in aquatic animals
  • Current definitions of endocrine disruptors (EDs) may be too narrow, overlooking non-chemical sources
  • The study suggests redefining EDs to include natural and non-traditional disruptors for better ecosystem protection
Endocrine disruptors (EDs) are chemicals that can interfere with the hormonal systems of both humans and wildlife, potentially leading to harmful effects on development and reproduction. These substances are a growing concern in the Anthropocene—the current geological epoch marked by significant human impact on the planet's ecosystems and geology. The Leibniz Institute of Freshwater Ecology and Inland Fisheries has recently conducted a study[1] that sheds light on the complexity of endocrine disruption, particularly in aquatic vertebrates like fish and amphibians. Surface waters are the primary repository for EDs, where they pose a significant risk to the creatures that inhabit these environments. Traditionally, EDs have been categorized into four main groups based on their effects on hormonal pathways: estrogenic, androgenic, thyroidal, and steroidogenesis—collectively known as EATS modalities. These modalities are the focus of validated tests used for regulatory purposes. However, the study indicates that this categorization may be too narrow, as it does not account for non-EATS modalities or natural sources of disruption, such as plant decomposition products or parasitic infections. One particularly novel finding of the study is the identification of artificial light at night (ALAN) as a potential ED. ALAN disturbs natural circadian light rhythms, which are crucial for the regulation of biological processes in many organisms. This disturbance suggests the need to broaden the definition of EDs, which currently focuses only on exogenous substances—those that originate outside an organism. The research builds on previous studies that have shown the sensitivity of certain species to EDs. For example, zebrafish, a common model organism in toxicology, have been used to demonstrate how thyroid hormones (THs) are crucial for early vertebrate development and how environmental pollutants that disrupt the TH system can cause significant developmental issues[2]. Eye development in zebrafish, directly regulated by THs, has proven to be a sensitive indicator of endocrine disruption, with effects being partly reversible after a short recovery period. The study also emphasizes the importance of improving in vitro assays to test for endocrine disruption. Traditional 2D cell cultures often do not accurately mimic the complex structure and function of glandular tissues like the thyroid. A recent advancement is the development of a thyroid organoid-on-a-chip (OoC) device, which better represents the thyroid's follicular architecture and functions, enhancing the predictive power of such assays[3]. Furthermore, the study highlights the lack of global mandatory screening for EDC levels in water resources. While bioassays are commonly used to assess acute toxicity, they are not standardized worldwide. The existing framework for identifying single-compound EDCs includes a set of bioassays for EATS pathways, but there is a need for more comprehensive testing strategies. Recommendations from the study suggest using internationally validated in vitro bioassays, ensuring cell viability, and evaluating the recovery of water sample preparation methods[4]. In conclusion, the study from the Leibniz Institute of Freshwater Ecology and Inland Fisheries calls for a re-evaluation of the current WHO definition of EDs and suggests that future research and regulation should not only focus on minimizing anthropogenic EDs but also consider the broader range of natural and non-traditional disruptors. By acknowledging the coevolutionary processes that have involved natural EDs without resulting in a loss of biodiversity, we can better adhere to the 'One Health' principle, which recognizes the interconnection between the health of people, animals, and the environment. This holistic approach is crucial for developing effective strategies to mitigate the impact of endocrine disruptors and protect the health of our planet's ecosystems.

EnvironmentEcologyMarine Biology

References

Main Study

1) Endocrine disruption in teleosts and amphibians is mediated by anthropogenic and natural environmental factors: implications for risk assessment.

Published 25th March, 2024

https://doi.org/10.1098/rstb.2022.0505

Related Studies

2) Reversibility of Thyroid Hormone System-Disrupting Effects on Eye and Thyroid Follicle Development in Zebrafish (Danio rerio) Embryos.

https://doi.org/10.1002/etc.5608

3) Thyroid-on-a-Chip: An Organoid Platform for In Vitro Assessment of Endocrine Disruption.

https://doi.org/10.1002/adhm.202201555

4) Towards regulation of Endocrine Disrupting chemicals (EDCs) in water resources using bioassays - A guide to developing a testing strategy.

https://doi.org/10.1016/j.envres.2021.112483


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