Highlights of the Scientific Opinion of EFSA on the testing methods for assessing of the effects of endocrine disruptors on human health and the environment

EndocrineHighlights prepared by Greenfacts of the report: The scientific criteria for identification of endocrine disruptors and appropriateness of existing test methods for assessing effects mediated by these substances on human health and the environment. A report adopted on 28 February 2013 and prepared on request from the European Commission.   


The Highlights of the report in 8 questions and 8 answers

 1. What were the questions asked to the Scientific committee? Three specific questions were posed by the Commission in the terms of reference, namely:

  1. What scientific criteria should be used to identify EDs?
  2. What is an adverse effect and how can it be distinguished from physiological modulation?
  3. Are existing toxicity testing methods appropriately covering the effects of endocrine active substances?

The opinion expressed is based on an evaluation of existing information, current insights and scientific activities on „endocrine disruptors‟, from European and other international parties which had to include the final report „State of the Art Assessment of Endocrine Disrupters‟(Kortenkamp et al., 2011)[1].  To this end, EFSA followed its specific Standard Operating Procedure detailing the steps necessary for establishing, updating or closing a scientific working group.

The declarations of interests of all short-listed experts were checked for absence of conflicts of interest before they could be invited to participate in the working group to contribute in their personal capacity, as an observer or as a hearing expert.

2. What is an endocrine active substance and what is endocrine disruption? The endocrine system plays a crucial role in maintaining human homeostasis and is often affected by exogenous stimuli. As an inter-related system, the endocrine system influences almost every cell, organ, and function of an organism. It regulates, with the use of numerous chemical messengers, various vital functions such as metabolism, growth and development, tissue function, or mood, from conception through adulthood and into old age. This includes for example the development of the brain and nervous system, the growth and function of the reproductive system, or the regulation of blood sugar level.

A range of synthetic as well as naturally occurring agents have been identified as interacting with the endocrine system. If the interaction of these exogenous substances with the endocrine system leads to adverse health effect in an intact organism or its progeny or (sub) populations, these substances are referred to as „endocrine disruptors‟(EDs). Overall, says the report, endocrine effects become adverse either by elicitation of a sub- (or supra-) normal response or persistence in a physiological state that is intended to be transitory.  Meanwhile, the point at which endocrine modulation becomes an adverse effect cannot be determined on the basis of an absolute response value, but on the basis of a relative response (compared to the control/background response). The SC is therefore of the opinion that, as adversity is a prerequisite for identifying a substance as an ED, it is necessary to determine a biological threshold between endocrine modulation and adverse effect.

In this report, the Scientific Committee (SC) defines an endocrine active substance (EAS)  as a substance having the inherent ability to interact or interfere with one or more components of the endocrine system resulting in a biological effect, but need not necessarily cause adverse effects. Therefore, the SC considers endocrine activity as a collection of modes of action, potentially leading to adverse outcomes (endocrine disruption), rather than a toxicological or eco-toxicological hazard in itself.

 3. What substances are capable of interfering with the hormone systems?  Many substances released into the environment through human activity are capable of interfering with the endocrine or hormone systems of animals and humans, which regulate the metabolism and function of the body. Such endocrine active substances (EASs) occur in a variety of chemical classes including synthetic drugs, pesticides, compounds used in industry and in consumer products, industrial by-products and pollutants, including some metals.

However, one should keep in mind that there is also a large number of EASs of natural origin occurring in plants consumed as food or feed, and also some secondary metabolites from fungi that may contaminate food and feed are known to express endocrine-like activity. Examples of naturally occurring EASs are oestrogenic compounds in soy (e.g. genistein and daidzein), mycotoxins (e.g. zearalenone) in cereals, goitrogens in cabbage with the potential to inhibit iodine uptake (glucosinates), and glycirrhizine in liquorice with the potential to disturb the mineralocorticoid system.

Furthermore, the endocrine system includes many additional signalling systems in humans and animals involving a vast number of hormonal or signalling factors, which are divided into 5 major classes: amino acid derivatives, small neuropeptides, large proteins, steroid hormones and vitamin derivatives. In addition, numerous peptide growth factors share actions with hormones. For this reason, hormonal aspects of metabolic regulation and neuro-development have also recently been included in the endocrine system.

 4. Are there specific criteria to define endocrine disruptive effects? As scientific criteria for an “adverse effect” in general have not been defined, specific criteria for endocrine disrupting effects, says the report, could not be identified to distinguish between substances that are endocrine disruptors (EDs) and other groups of substances with different modes of action. The SC concluded however that an endocrine disruptor is defined by three criteria:

  1.  the presence of an adverse effect in an intact organism or a (sub)population;
  2.  the presence of an endocrine activity (oestrogenic, androgenic, thyroid or steroidogenic) ;
  3. the presence of a plausible causal relationship between the two.

In general, but not always, transient, inconsistent and minor fluctuations at the biochemical and molecular level may be considered adaptive, i.e. non-adverse. On the other hand, changes at the cell-, organ-, organism-, or (sub)population-level resulting in pathology or functional impairment in vivo, as well as altered timing of development, may be considered adverse, says the report. And, in principle, no single assay is likely to provide all the information needed to decide whether a substance is an ED because of the need to provide both mechanistic and apical[2] information.  Therefore, expert judgement is required to assess on a case-by-case basis the (eco)toxicological relevance of changes at the molecular to individual and/or (sub)population level following exposure to an EAS.

 5. Are there threshold doses below which no endocrine effects are observed?  For most toxic processes, says the report, it is generally assumed that there is a threshold of exposure below which no biologically significant effect will be induced. According to the Kortenkamp report (see reference 1), the existence of dose thresholds cannot be proven or ruled out by experimental approaches, because all methods for measuring effects have their limits of detection which will obscure thresholds, if they exist. However, the presence of homeostatic and cytoprotective mechanisms, and the redundancy of cellular targets, mean that a certain degree of interaction of the substance with the critical sites or their occupancy must be reached in order to elicit a toxicologically relevant effect. Below this critical (threshold) level of interaction, homeostatic mechanisms would be able to counteract any perturbation produced by xenobiotic exposure, and no structural or functional changes would be observed. In certain developmental stages however, homeostatic capacity is limited and this will affect the sensitivity of the organism.

6. How is the potential hazard of a chemical to act as an endocrine disruptor evaluated?  The OECD  provides a “Conceptual Framework” which includes a guide to the data sources, to its test guidelines and standardised test methods available, under development or proposed for the evaluation of chemicals for EASs/EDs.  These tests include “in silico” tools[3], in vitro and in vivo screening assays and other mechanistic investigations.

The Scientific Committee reviewed the shortcomings in current tests and concluded from its work that a reasonably complete suite of standardised assays for testing the effects of Endocrine active substance (EAS) is (or will soon be) available for the oestrogenic, androgenic, thyroid and steroidogenic modalities in mammals and fish, with fewer tests for birds and amphibians. These tests allow to characterise the critical effect, severity, (ir)reversibility and potency aspects are part of the hazard of endocrine disruptors (EDs).

The report however considers important to recognise that standardised mechanistic assays for non -oestrogenic, androgenic, thyroid or steroidogenic (EATS) modalities relevant to mammals, fish and other vertebrates are not or not yet available and that a range of major taxa, e.g. reptiles or echinoderms have not yet been considered by OECD for any endocrine assay development.

 7. What are the recommendations of the Scientific Committee regarding testing of endocrine disruptors?  The SC identified the need for further development of screens and test methods and of testing strategies to generate adequate data for the identification and assessment of endocrine disrupting properties. This in particular with regard to non-EATS modalities that may be associated with adverse effects in humans or the environment, this in light of a number of general issues related to the testing of substances:

•   current mammalian tests may not cover effects that might be induced by exposure during fetal or pubertal development, but may emerge during later life stages even if fish lifecycle tests cover all relevant windows of exposure and can be expected to reveal the longer-term effects of developmental exposures at all stages of the lifecycle;

•   combined exposure to multiple EASs could occur in such a way that combined toxicity could arise;

•   the lack of consensus in the scientific community with regard to the existence and/or relevance of low-dose effects in connection with endocrine activity, endocrine disruption or other endpoints/modes of actions.

The evaluation methods should therefore, in principle, be fit for the purpose of establishing safe doses/concentrations of EDs if :

  1.  certain aspects (e.g. follow up of exposure in critical windows of susceptibility to later life stages) are addressed;
  2.  used with all available information in a weight-of-evidence approach.

The SC recommends as a follow up activity to clarify in a broader context the issues of biological thresholds and criteria for adversity, combined exposure to multiple substances.   The SC also underlines the need for the further development of tests.

 8. How to decide and inform on risk and level of concern related to endocrine disruptors? The SC is of the opinion that hazard characterisation (e.g. establishment of a health-/ecotoxicology-based guidance value) should be based on the effect leading to the lowest guidance value, irrespective of the mode of action. This would also protect against endocrine-mediated effects occurring at higher doses.

For the purpose of risk management decisions, says the report, risk assessment (taking into account hazard and exposure data/predictions) makes best use of available information. The opinion of the SC is thus that for their risk assessment, EDs can be treated like most other substances of concern for human health and the environment.  But, it adds that levels of concern are not determined exclusively by risk assessment but also by protection goals set by the risk management.

Reference : EFSA Scientific Committee; Scientific Opinion on the hazard assessment of endocrine disruptors: scientific criteria for identification of endocrine disruptors and appropriateness of existing test methods for assessing effects mediated by these substances on human health and the environment. EFSA Journal 2013;11(3):3132. Available online: www.efsa.europa.eu/efsajournal  © European Food Safety Authority, 2013

The Scientific Committee members: Jan Alexander, Diane Benford, Qasim Chaudhry, Anthony Hardy, Michael John Jeger, Robert Luttik, Ambroise Martin, Bernadette Ossendorp, Simon More, Alicja Mortensen, Birgit Noerrung, Joe Perry, Iona Pratt, John Sofos, Josef Schlatter, Kristen Sejrsen.

Correspondence: scientific.committee@efsa.europa.eu.

 Note: the “Highlights” of recent reports proposed by GreenFacts are not verified by its Scientific Board.

[1] see the GreenFacts Highlights of this report on : http://news.greenfacts.org/2012/10/endocrine-disruptors-updated-for-the-e-u-assessment-of-their-impact-on-health-and-the-environment/

[2] apical  effect : “observable outcomes in a whole organism, such as a clinical sign or pathologic state, indicative of a disease state that can result from exposure to a toxicant”

[3] “in silico” : In silico and non-animal test method approaches include molecular modelling tools; structure activity relationships (SAR) upon which physico-chemical read-across and chemical categories are based; predictive statistical models such as (Quantitative) Structure Activity relationships ((Q)SARs); databases; and expert systems.

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