# Assessment of Population Relevance of Endocrine-sensitive Apical Endpoints in Fish Chronic Studies Using Individual-Based Models

## TL;DR

This study uses population models to assess how chemical effects on individual fish might impact fish populations, focusing on endocrine-disrupting chemicals.

## Contribution

The study introduces an exposure-agnostic, molecule-independent approach to evaluate population-level impacts of endocrine-disrupting chemicals.

## Key findings

- A 20% reduction in fecundity or fertilization rate in stickleback led to population declines, while other species showed no such response.
- Effect magnitudes of 10% did not lead to population-level responses in any species.
- The study evaluates six endpoints across three fish species with different life histories.

## Abstract

Population models have long been thought of as a suitable
approach
for assessing the population relevance of chemical effects observed
on individuals in laboratory studies, although they have rarely been
applied in a regulatory context. We modeled potential population-level
responses of individual-level adverse effects induced by endocrine-disrupting
chemicals (EDCs). We imposed three effect durations (10-year, 3 months
summer, or winter) for six common EDC endpoints (fecundity, fertilization
rate, sex ratio: male and female skew, courtship and nesting behavior)
at four magnitudes of effect (10, 20, 50 and 90% reduction) using
individual-based population models for three fish species with differing
life histories: stickleback (Gasterosteus aculeatus), brown trout (Salmo trutta) and
zebrafish (Danio rerio). The suitability
of different assessment criteria for determining the significance
of population responses was evaluated. For all endpoints tested individually,
effect magnitudes of 20% did not result in any population-level responses
in each of the three species, except in the stickleback, where a 20%
reduction in fecundity or fertilization rate led to population declines
(in these cases, effect magnitudes of 10% did not result in population-level
responses). Once standardized, our “exposure-agnostic molecule-independent”
approach will enhance our understanding of population outcomes within
the regulatory hazard-based assessment of EDCs.