Researcher Sarah Kimmins and her colleagues from Canada, South Africa and Denmark have shown how men exposure to DDT influenced the epigenome of their sperm and could adversely affect the health of their children.

The epigenome is the hereditary information that is passed on to the embryo at fertilization and can alter its development.

Exceptionally used as an insecticide for malaria control mainly in India and African countries, DDT (dichlorodiphenyltrichloroethane), now banned worldwide, is so stable it continues to poison the environment and move up the food web.

Over the years, researchers have linked DDT exposure to birth defects, infertility, cancer, and neurodevelopmental delays in the first generation. But little was known about the paternal modes of transmission from a biological point of view.

Published in the journal Environmental Health Perspectives, the study of the international team identified in two populations of indigenous men, Greenlandic Inuit and South African Vhavenda men, alterations in their sperm at specific DNA regions implicated in the development of diseases.

This first comprehensive epigenome study in men shows that similar mechanisms occurring in animals and linked to transgenerational negative health impacts such as cancer and altered neurodevelopment are likely to occur in humans.

An excellent collaboration between Sarah Kimmins, a researcher at the CRCHUM and a professor at Université de Montréal, and the teams of Dr. Jacquetta Trasler (Research Institute of the McGill University Health Centre), Christiaan de Jager (University of Pretoria, South Africa) and Gunnar Toft (Aarhus University Hospital, Denmark) enabled this major step forward to be taken. The first author, Ariane Lismer, is one of Kimmins’ former student at McGill University where the research work was carried out.

Different routes, same effects

Underrepresented in genomic studies, the two chosen populations of Indigenous men are exposed to DDT differently.

Greenlandic Inuit consume a traditional marine mammal diet consisting of whales, walrus, and seals and are indirectly exposed to p,p-DDE, a DDT breakdown product, through its bioaccumulation in the marine food chains.

South African Vhavenda men are exposed more directly as DDT is used for indoor residual spraying to control for mosquitoes responsible for the malaria transmission.

Using cutting-edge sequencing methods carried out on blood and semen samples from 47 men from Greenland and 50 from South Africa, the scientists identified DNA altered regions in association with DDT and p,p-DDE serum levels, likely to be transmitted by the sperm and to linger in the embryo.

In human studies, it is challenging to go beyond the association of an epigenetic alteration from an exposure and a change of function in the offspring, as it is often difficult to access tissues in the next generation that are matched to a father.

So, researchers overcome this limitation by using data sets from human preimplantation embryos and predicting whether altered regions in sperm persisted in the embryo and thus are implicated in epigenetic inheritance.

A global phenomenon

The impacts of DDT on human health are not restricted to regions of use given that DDT has been shown to be transported over long distances in the environment by weather patterns and ocean currents.

In parts of the world with no malaria, DDT contamination may still be observed due to slow degradation and accumulation in the food web.

The chemicals, though mostly originating in the south, accumulate in the Arctic and concentrate in animals high in the food web like whales, seals, polar bears. The northern Inuit populations in Canada are indirectly exposed to DDT as they rely on these types of food and eat them in considerable amount. It may impact the health of generations to come.

About the study 

“The Association between Long-Term DDT or DDE Exposures and an Altered Sperm Epigenome—a Cross-Sectional Study of Greenlandic Inuit and South African VhaVenda Men,” by Ariane Lismer et al., was published online Jan. 31, 2024, in Environmental Health Perspectives. The study received funding mainly from the Canadian Institutes of Health Research.

Science writing: Bruno Geoffroy