Persistent organic pollutants (POPs) begin to accumulate in the tissues of mammals already during the foetal stage, according to new research from the University of Oulu, Finland. The animal-model study found that environmental toxins had built up in the tissues of sheep raised in clean organic production, and that the same substances were transferred in notable amounts to the developing foetuses’ adipose tissue.

Persistent environmental toxins, such as PCBs and DDT, remain in nature for long periods without breaking down. They can accumulate in the fatty tissues of organisms and bioaccumulate through the food chain. These substances were previously used in industry and as insecticides, and although their use is now strictly regulated, they remain widespread in the environment.

The study analysed tissue samples from 15 organic ewes and their lambs shortly after birth, searching for the most common POPs. Almost all of the substances investigated were detected in both adult sheep and lamb tissues. All the compounds identified were able to cross the placenta, and the transfer was so effective that concentrations in the lambs’ tissues averaged 30–103 per cent of those measured in the mothers.

Previous research in humans has shown that environmental toxins present in maternal circulation can pass through the placenta. What this study newly demonstrates is that, in sheep, compounds accumulated in the mother’s adipose tissue are transferred to the developing foetus in almost the same proportion.

Because placental structure in sheep differs from that in humans, no direct conclusions can be drawn regarding human exposure. However, concentrations of POPs in adult human adipose tissue are on average higher than in sheep, underscoring the need for further research.

‘The results illustrate the widespread distribution of persistent environmental toxins and the ways in which they infiltrate every part of our surroundings. In epidemiological studies, POP concentrations measured from umbilical cord blood after birth have been linked to obesity, metabolic syndrome and lower IQ. What remains for future research to determine is the extent of the health effects that POPs accumulated in adipose tissue may have on the foetus and on the child’s later health,’ summarises doctoral researcher Ella Vuoti.