2.DEFINITIONS

The following list includes terms, which are generally applicable to (eco)toxicological assays and studies, as well as specific terms used in the identification of endocrine disrupting properties.

Adaptive (non-adverse) effect: A biological effect that does not cause biochemical, behavioural, morphological or physiological changes that affect the general well-being, growth development or life span of an animal (Lewis et al., 2002).

Adverse effect: Change in the morphology / physiology (and pharmacology), growth, development, reproduction, or, life span of an intact organism, or a system or (sub)population, that results in an impairment of functional capacity, an impairment of the capacity to compensate for additional stress, or an increase in susceptibility to other influences (WHO/IPCS, 2009).

Adverse effect with population relevance (environmental assessment): A change in the morphology, physiology, growth, development, reproduction, or life span of an organism that results in an impairment of population stability or recruitment.

Adverse outcome pathway (AOP): A linear sequence of events from the exposure of research animals (or humans) to a potentially toxic substance that results in a molecular initiating event that may lead to early cellular events and, ultimately, an apical effect, e.g., an observable outcome / phenotypic effect (Ankley et al., 2010; OECD, 2013). In contrast to MoA (cf. Definition), AOPs are not substance-specific and therefore do not include metabolism considerations. AOPs can help address the biological plausibility of a MoA.

Apical endpoint: An observable outcome in a whole organism, such as a clinical sign or pathologic state, that is indicative of a disease state that can result from exposure to a toxicant (OECD (2012c), citing Krewski et al. (2011)). Further, OECD (2012c) refers to the definition provided within an ecotoxicology testing strategy: Traditional, directly measured whole-organism outcomes of exposure in in vivo tests, generally death, reproductive failure, or developmental dysfunction (Villeneuve and Garcia-Reyero, 2011). Alterations in apical endpoints can integrate the effects from multiple MoAs or AOPs. Specifically for the identification of endocrine disrupting properties, this implies that alterations of apical endpoints may or may not result from endocrine changes. For instance, the apical endpoint fecundity may also be affected by perturbations that are unrelated to the endocrine system (OECD, 2012a, b).

Biological plausibility: In accordance with Commission (2016) and ECHA and EFSA (2016), biological plausibility refers to the extent of evidence to support that a specific substance operates via a specific MoA. In Step V of the ECETOC 7SI-ED, specific criteria are presented for the assessment of the extent of evidence for the biological plausibility that adverse effects (Step III) and endocrine activity (Step IV) are linked by a specific endocrine MoA.

Coherence: The extent to which parameters and/or endpoint effects form a logical pattern across different lines of evidence (e.g. in vivo mammalian studies, in vivo non-mammalian studies, toxicokinetic studies, in vitro assays). A coherent pattern is observed when the recorded effects are manifestations of the same primary effect or MoA (e.g., with respect to endocrine disrupting properties, reduced testicular weight, testicular atrophy, reduced sperm numbers and reduced fertility).

Concordance (biological): The extent to which the pattern of primary events (indicators of MoA and apical effects) stands in accordance with broader biological knowledge (Meek et al., 2014a, b).

Consistency (within study): All parameters recorded in an in vivo study / in vitro or in vivo assay allow concluding on the same adverse effect(s) / type of activity / MoA. (When evaluating MoA in Step V of the ECETOC 7SI-ED, all outcomes match the hypothesised MoA.)

Consistency (amongst different studies): The same adverse effect / type of activity / MoA is recorded in different in vivo studies / in different in vitro and/or in vivo assays, as applicable. (When evaluating MoA in Step V of the ECETOC 7SI-ED, all outcomes match the hypothesised MoA.)

Diagnostic endpoint: A parameter that is determined in in vivo studies and that provides an indication for a MoA, but that does not necessarily constitute the observation of an adverse effect.

Endocrine activity: The interaction with one or more elements of the endocrine system (EFSA, 2013).

Endocrine disruptor: An exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub)populations (WHO/IPCS, 2002).

Endocrine MoA: A MoA leading to an observable adverse effect that can be attributed to an alteration in the endocrine system.

Mode-of-action (MoA): The biologically plausible sequence of substance-specific key events, starting with exposure and proceeding through the interaction of the substance or its metabolites with a cell, through functional and anatomical changes leading to an observed effect supported by robust experimental observations and mechanistic data (Sonich-Mullin et al., 2001; Boobis et al., 2009; Fenner-Crisp and Dellarco, 2016).

Relevance: The extent to which a study and its results can be generalised and applied to either humans or ecological species for a given purpose (e.g. the identification of an endocrine disrupting property).

Reproducibility: The extent to which a study can be reconstructed by the information (documentation) provided (e.g. in the publication or study report).

Systematic review: A review that involves a systematic search of the literature by using a detailed and comprehensive plan and search strategy agreed a priori, with the goal of reducing bias by identifying, appraising, and synthesizing all relevant studies on a particular topic (Uman, 2011).

Weight of evidence (WoE): An evidence-based approach, in which different pieces of available information are examined and weighted objectively (including strengths and weaknesses) and used collectively to reach a conclusion concerning a property of a substance that may not be evident on the individual data alone. While the WoE approach relies on all the available information, it is recognised that some studies have greater diagnostic precision than others in determining whether adverse effects will actually occur in living animals, populations, or humans. During WoE evaluations, the completeness and the consistency of the data, which support that a substance causes a specific adverse effect / activity / MoA, is assessed (in contrast to a collection of unrelated observations). A clear picture can only be obtained by considering all data (positive and negative) and by weighting the more relevant and higher quality pieces of information more heavily. For example, direct observation of an adverse effect in an intact animal has greater weight than the response of an in vitro assay in isolation.