Organochlorine pesticides (OCPs) are a group of environmental contaminants that were banned in industrialized countries decades ago, but sut since they accumulate through the food chain and remain for a very long time in the human body, especially adipose tissue, they can still be found in a majority of people in most countries.

The most commonly known of these compounds is the pesticide DDT, which has gotten a renewed look due to mosquitoes that carry the Zika virus. Though DDT was banned in the US due to public concern, the United States Environmental Protection Agency (EPA) shows countries with mosquitoes related to malaria - which also carry Zika - how to effectively spray DDT inside homes.

No one was ever harmed by using DDT, including by accidentally using it as flour, so activists have instead insisted low-dose effects might be occurring over long periods of time. To make their case, they use correlations, such as cognitive impairment and chronic low-dose exposure to organochlorine pesticides. How can something that does not impact people at high levels - birds were fine, despite claims, humans were never harmed - be harmful at low doses? That kind of hormesis is where epidemiology and isolated curve matching comes into play.

Writing in Environmental International, a group at Uppsala University, which has already used correlations to suggest that environmental contaminants causes diabetes, atherosclerosis and stroke, have now used the same data set to claim shown that organochlorine pesticides

are related to future cognitive impairment.

The PIVUS study (Prospective Investigation of Uppsala Seniors) comprises around 1,000 70-year-olds in Uppsala who have been studied over a longer period of time. The researchers measured three different OCPs in plasma from the individuals and investigated who received a diagnosis of cognitive impairment over the coming 10-year period.

The results show that individuals with high levels of three OCPs (p,p'-DDE (a metabolite of DDT), transnona-chlordane and hexachlorobenzene) had about 3 times higher future risk of cognitive impairment than elders with low levels of OCP. These results are independent of factors such as sex, smoking, diabetes, exercise habits, alcohol intake, weight change and high blood pressure.

"Even though OCPs are well-known neurotoxins, our findings are surprising because current exposure levels of these chemicals are very low. However, our study subjects were the first generation with almost life-time exposure to these chemicals. Thus, we found evidence that low-dose, but chronic, exposure of OCPs can be harmful to the human brain," says Lars Lind, Professor of Medicine at Uppsala University.

Source: Uppsala University