Sperm count

https://www.theguardian.com/science/2017/jul/29/infertility-crisis-sperm-counts-halved

https://www.tandfonline.com/doi/abs/10.1080/14647273.2021.1917778

https://www.centreformalepsychology.com/male-psychology-magazine-listings/is-sperm-quality-deteriorating-worldwide-find-out-what-the-experts-are-saying

https://www.nytimes.com/2017/08/16/health/male-sperm-count-problem.html

https://metro.co.uk/2022/11/16/sperm-count-decline-is-a-global-crisis-threatening-humanity-17767054/

They saw this coming for decades but early on most of the evidence was coming from fertility clinics so sceptics could dismiss it as they claimed it was an observer bias. Now it's not so easy to dismiss.

https://www.news.com.au/lifestyle/health/health-problems/study-explains-why-sperm-rates-have-dropped-50-per-cent/news-story/7eab2f14b2cc012fb23799f4283b03e6