POPs are a group of chemical contaminants that humans can barely excrete and that degrade very slowly, therefore accumulating in our bodies and environment. Most POPs have been used as pesticides or are industrial residues; most POPs contaminate animal and human food webs.
Normally, the 'internal contamination' (within a person's body) by these chemicals is evaluated by checking for each pollutant separately, without analysing the mixture or 'cocktail' of POPs that is always found in a person. And when you look at each pollutant separately it is clear that the vast majority of the population has low concentrations of the POP, while only a small minority of the population has high concentrations of the pollutant. This is, when each POP is studied individually.
However, Miquel Porta, José Pumarega and colleagues at IMIM realised that nobody was looking at all POPs combined in the body of each individual person and, therefore, no-one had checked the assumption that the vast majority of the population had low levels of all POPs. The assumption turned out to be untrue.
The 'simple change' made by the researchers (which turned out to be quite radical) was to stop focusing on each POP separately and to focus on all POPs detected in each individual. And they thus discovered that the majority of individuals had at least one POP at high concentrations: specifically, 67% of participants in the study had one or more POPs at concentrations above the 90th. percentile (the 'top 10' or highest 10%).
They also discovered that a significant minority had several POPs each at high concentrations. In fact, 13% of the US population has 10 or more POPs at high concentrations; i.e., each POP is in a 'top 10' concentration (that is, at a concentration above the 90th. percentile).
The study analysed POP levels in 4,739 people included in the US National Health and Nutrition Examination Survey (NHANES). They calculated the number of POPs whose blood concentrations were greater than certain levels considered to be high.
"This pattern of many POPs at high concentrations is nine times more common in black people and four times less common in Mexican Americans than in the non-Hispanic whites. Therefore, the number of POPs at high concentrations is related to race (or ethnicity). We also found that the poorest people have more POPs at high levels, and such number of POPs at high concentrations also increases with age and the body mass index", explain José Pumarega, researcher at IMIM and at CIBER de Epidemiología y Salud Pública (CIBERESP) and Miquel Porta, head of the Clinical and Molecular Epidemiology of Cancer research group and Professor of Public Health at Universitat Autònoma de Barcelona (UAB) and main authors of the article, published in the journal PLoS One.