Adverse effect

Change in the morphology, physiology, growth, development, reproduction or life span of an organism, 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 (OECD, 2019[1]).

Adverse Outcome Pathway (AOP)

An Adverse Outcome Pathway describes a logical sequence of causally linked events at different levels of biological organisation, which follows exposure to a stressor and leads to an adverse health effect in humans or wildlife. (OECD, n.d.[2])

Bioassay or effect-based method

Bioassays or effect-based methods “are bioanalytical methods using the response of whole organisms (in vivo) or cellular bioassays (in vitro) to detect and quantify the effects of groups of chemicals on toxicological endpoints of concern. (Brack et al., 2019[3]) See also: in vivo tests and in vitro tests

Biological organisation

Levels of biological organization: Atom, molecule, cell, tissue, organ, organ system, organism (individual), population, community (Villeneuve and Garcia-Reyero, 2010[4]).

Contaminants of emerging concern (CECs)

A vast array of contaminants that have only recently appeared in water, or that are of recent concern because they have been detected at concentrations significantly higher than expected, and/or their risk to human and environmental health may not be fully understood. Examples include pharmaceuticals, industrial and household chemicals, personal care products, pesticides, manufactured nanomaterials, microplastics, and their transformation products. Also commonly known as micropollutants or emerging pollutants.

EATS modalities

Estrogen, Androgen, Thyroid and Steroidogenesis modalities are the most studied endpoint for endocrine disruption. The OECD added in its revised document modalities for invertebrates: Juvenile Hormones (Jh) and ecdysteroids (Ec) (OECD, 2018[5]).

Endocrine active substance

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 (EFSA, 2013[6]).

Endocrine disruptor or endocrine disrupting chemical (EDCs)

“An [endocrine disrupter] is 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.” And, “a potential [endocrine disrupter] is an exogenous substance or mixture that possesses properties that might be expected to lead to endocrine disruption in an intact organism, or its progeny, or (sub)populations” (IPCS, 2002[7]). Also known as endocrine disrupting chemical or endocrine disrupting substance.

Endocrine system

The chemical coordinating system in animals, that is, the endocrine glands that produce hormones (Jacsó, 2002[8]).


The recorded observation coming from an in chemico method, an in vitro assay or an in vivo assay (OECD, 2011[9]).

Effect-based monitoring / methods (EBM)

Bioanalytical methods using the response of whole organisms (in vivo) or cellular bioassays (in vitro) to detect and quantify the effects of groups of chemicals on toxicological endpoints of concern (Brack et al., 2019[10]).

Effect-directed analysis

“A tool for identifying predominant toxicants in complex, mostly environmental mixtures combining effect testing, fractionation and chemical analysis”; “Designed to direct chemical analysis toward those chemicals that actually cause hazards mostly indicated by laboratory in vitro and in vivo bioassays” (Brack, 2011[11])

Hazard-based decision-making

Decision-making in chemicals management that “focuses on addressing the inherent hazards of chemicals through substitution or other approaches, rather than calculating an acceptable level of risk” (UNEP, 2019[12])


“The traditional definition of a hormone is a molecule produced by an endocrine gland that travels through the blood to produce effects on distant cells and tissues” (UNEP WHO, 2013[13]).

Indirect effects

“Indirect effects in ecotoxicology are defined as chemical- or pollutant-induced alterations in the density or behaviour of sensitive species that have cascading effects on tolerant species in natural systems” (Fleeger, 2020[14]).

In vitro test

The technique of performing a given experiment in a test tube, or, more generally, in a controlled environment outside of a living organism (OECD, 2018[15]).

In vivo test

Experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research (OECD, 2018[15]).

Legacy chemical

Chemicals that are banned or restricted, but still appear in environment as legacy compounds.


A combination of two or more chemicals (liquid or solid) that do not react with each other (OECD, 2018[15]).

Mixture effect

Temporal co-exposure to any combination of two or more compounds that may jointly contribute to actual or potential effects in a receptor population (OECD, 2019[1]).

Non-monotonic dose response

Adverse effects of chemicals that exhibit greater or even opposite effects at low doses compared to those observed at high doses. This means that traditional toxicology, which hinges on the premise that high-dose toxicity testing will proportionally inform us about low-dose exposures, does not hold (Vandenberg et al., 2012[16]).

Recycled water

Former wastewater that has been treated to remove solids and certain impurities. It is only intended to be used for non-potable uses (e.g. irrigation, dust control, fire suppression); with more advanced treatment, it can be used for indirect potable reuse (i.e. discharged into a water body before being used in the potable water system). Also known as reclaimed water (OECD, 2009[17]).

Risk-based decision-making

An approach to decision-making in chemicals management based on patterns of exposure to a chemical. “This includes identifying use patterns that may create widespread exposure across a population, or intense exposure for a subset of the population.” (UNEP, 2019[12])

Substance-by-substance approach

Risk approach for testing water quality based on detection of above-threshold levels of single chemicals.

Trophic levels

The classification of natural communities or organisms according to their place in the food chain. Green plants (producers) can be roughly distinguished from herbivores (consumers) and carnivores (secondary consumers) (United Nations, 1997[18]).


[11] Brack, W. (ed.) (2011), Effect-Directed Analysis of Complex Environmental Contamination, Springer Berlin Heidelberg, Berlin, Heidelberg,

[3] Brack, W. et al. (2019), “Effect-based methods are key. The European Collaborative Project SOLUTIONS recommends integrating effect-based methods for diagnosis and monitoring of water quality”, Environmental Sciences Europe, Vol. 31/1,

[10] Brack, W. et al. (2019), “Effect-based methods are key. The European Collaborative Project SOLUTIONS recommends integrating effect-based methods for diagnosis and monitoring of water quality”, Environmental Sciences Europe, Vol. 31/1,

[6] EFSA (2013), “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, Vol. 11/3,

[14] Fleeger, J. (2020), “How Do Indirect Effects of Contaminants Inform Ecotoxicology? A Review”, Processes, Vol. 8/12, p. 1659,

[7] IPCS (2002), Global Assessment of the state-of-the-science of Endocrine Disruptors, International Programme on Chemical Safety, Geneva.

[8] Jacsó, P. (2002), McGraw Hill dictionary of scientific and technical terms,

[1] OECD (2019), Pharmaceutical Residues in Freshwater: Hazards and Policy Responses, OECD Studies on Water, OECD Publishing, Paris,

[15] OECD (2018), Guidance Document on Good In Vitro Method Practices (GIVIMP), OECD Series on Testing and Assessment, No. 286, OECD Publishing, Paris,

[5] OECD (2018), Revised Guidance Document 150 on Standardised Test Guidelines for Evaluating Chemicals for Endocrine Disruption, OECD Series on Testing and Assessment, No. 150, OECD Publishing, Paris,

[9] OECD (2011), Report of the Workshop on Using Mechanistic Information in Forming Chemical Categories, OECD Environment, Health and Safety Publications Series on Testing and Assessment No. 138 ENV/JM/MONO(2011)8.

[17] OECD (2009), Alternative Ways of Providing Water. Emerging Options and Their Policy Implications.

[2] OECD (n.d.), OECD Series on Adverse Outcome Pathways, OECD Publishing, Paris,

[12] UNEP (2019), UNEP Guidance on Risk Reduction Tools for Chemicals Control, United Nations Environment Programme, Nairobi.

[13] UNEP WHO (2013), State of the Science of Endocrine Disrupting Chemicals 2012: Summary for Decision-Makers, United Nations Environment Programme and the World Health Organization.

[18] United Nations (1997), Glossary of Environment Statistics, Studies in Methods, Series F, No. 67, United Nations, New York.

[16] Vandenberg, L. et al. (2012), “Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses”, Endocrine Reviews, Vol. 33/3, pp. 378-455,

[4] Villeneuve, D. and N. Garcia-Reyero (2010), “Vision & strategy: Predictive ecotoxicology in the 21st century”, Environmental Toxicology and Chemistry, Vol. 30/1, pp. 1-8,

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