Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|AHR activation to ELS mortality, via VEGF||AdverseOutcome|
|AhR mediated mortality, via COX-2||KeyEvent|
Key Event Description
Increased early life stage mortality refers to an increase in the number of individuals dying in an experimental replicate group or in a population over a specific period of time.
Early life stage mortality occurs at any stage in development prior to birth/hatch and is considered embryolethal.
Early Life Stage Mortality refers to death prior to yolk sac adsorption and swim-up.
How It Is Measured or Detected
In birds it may be identified as failure to hatch or lack of movement within the egg when candled; heartbeat monitors are available for identifying viable avian and reptillian eggs (ex. Avitronic's Buddy monitor). In mammals, stillborn or mummified offspring, or an increased rate of resorptions early in pregnancy are all considered embryolethal, and can be detected using ultra-high frequency ultrasound (30-70 MHz; a.k.a. ultrasound biomicroscopy) (Flores et al. 2014). In fishes, mortality is typically measured by observation. Lack of any heart beat, gill movement, and body movement are typical signs of death used in the evaluation of mortality.
Domain of Applicability
All members of the subphylum vertebrata are susceptible to early life stage death (Weinstein 1999).
Evidence for Perturbation by Stressor
Exposure of embryos to 2,3,7,8-TCDD causes early life stage mortality in all studied species of fishes (Doering et al 2013).
Regulatory Significance of the Adverse Outcome
Poor early life stage survival is an endpoint of major relevance to environmental regulators, as it is likely to lead to population decline. Early-life stage, acute and chronic test guidelines have been established by the Organisation for Economic Co-operation and Development (OECD), U.S. Environmental Protection Agency (EPA) and Environment and Climate Change Canada (ECCC), and are currently used in risk assessments to set limits for safe exposures. Aquatic test guidlines are most prevalent and include OECD210, OECD229, EPA850.1400 and ECCC EPS 1/RM/28 for fish and OECD241 for frogs.
1. Flores, L.E., Hildebrandt, T.B., Kuhl, A.A., and Drews, B. (2014) Early detection and staging of spontaneous embryo resorption by ultrasound biomicroscopy in murine pregnancy. Reproductive Biology and Endocrinology 12(38). DOI: 10.1186/1477-7827-12-38
2. Weinstein, B. M. (1999). What guides early embryonic blood vessel formation? Dev. Dyn. 215(1), 2-11.
Doering, J.A.; Giesy, J.P.; Wiseman S.; Hecker, M. (2013). Predicting the sensivity of fishes to dioxin-like compounds: possible role of the aryl hydrocarbon receptor (AhR) ligand binding domain. Environmental Science and Pollution Research. 20 (3), 1219-1224.