The scientists led by Kristen Upson from the University of Washington evaluated data from the Women's Risk of Endometriosis study conducted among 18-49 year old women in western Washington State. They examined the relationship between the exposure of women to so-called OCPs (organochlorine pesticides) and the occurrence of endometriosis.

They found that two substances in the blood of more than 258 women suffering from endometriosis were higher than those of the control persons without endometriosis: Mirex and β-hexachlorocyclohexane (HCH), two substances no longer used either in the United States or in Europe. Their production and use have been prohibited in Europe by Annex I of Regulation (EC) No 850/2004 since 2003. HCH can be used only as an intermediate during manufacture of another product.

The substances detected were, however, were widely used in pesticides in the past. They belong to the so-called persistent organic pollutants - substances that remain in the environment and bioaccumulate in the food chain, with a risk of negative impacts on human health and the environment.

The researchers concluded that earlier intensive use of these substances may have had an influence on the health of women in reproductive years.

Endometriosis is an estrogen influenced, painful chronic condition in which the endometrial tissue appears outside the uterus. It can cause infertility. Several environmental toxins act similarly to natural hormones (so-called endocrine disruptors) and may have an impact on the development of this disease.

Source: http://ehp.niehs.nih.gov/1306648
http://chemicalwatch.com/17137/study-links-increased-endometriosis-risk-to-organochlorine-exposure

Kristen Upson, Anne Claire J. De Roos, Mary Lou Thompson, Sheela Sathyanarayana, Delia Scholes, Dana Boyd Barr and Victoria L. Holt (2013): Organochlorine Pesticides and Risk of Endometriosis: Findings from a Population-Based Case-Control Study. Environ Health Perspect. DOI: 10.1289/ehp.1306648