The situation is simple to describe: Almost all toxicity testing of pollutants is done on a chemical-by-chemical basis. Almost none of the testing involves multiple pollutants in combination (a chemical cocktail, a suite of pollutants, a toxic mix). Chemicals thrown together have a tendency to interact, producing new chemicals. This is particularly true when the chemicals are mixed with water, exposed to sunlight in the air, or dispersed within the complex chemistry of the soil. Toxicity testing while in these natural media is almost never done.
Here are a couple of facts: Newborn babies have, on average, 200 non-natural chemicals in their blood, including pesticides, dioxins, and flame retardants (Environmental Working Group: Body Burden – The Pollution in Newborns, USA 2005). Swedish rivers (not the dirtiest in the world) have, on average, 57 non-natural chemicals in their waters (Swedish Agricultural University, Uppsala, 2009). There are many similar studies.
Thus there is a big and poorly studied problem: Our environment carries a mixture of non-natural chemicals, which finds its way into us, and we don’t know how toxic it is. Call it the “chemical mixture toxicity problem,” or the “killer chemical cocktail.” That last one is over-dramatic, of course; it could be true nonetheless, we don’t know. That’s the problem.
This is not a new problem. Periodically somebody, scientists, government officials, gets perturbed about the ignorance. In this case, it’s the European Commission (the executive branch of the European Union) that commissioned a study by the University of Gothenburg (Sweden). The Swedish research team in collaboration with the University of London reviewed the literature on the subject of mixture toxicology, and ecotoxicology. The combined finding: The ‘cocktail effect’ of the combined chemicals is greater than the effect of the chemicals individually. One is tempted to say, “Duh,” but science needs evidence.
The study hit upon the biggest concern: “The combined exposure to chemicals from different sources used for example in agriculture and industry may have adverse effects on human health, even if each individual substance is below its own risk limit.” That is to say, most of what regulatory agencies test for – the risk limit of individual chemicals – is insufficient to understand the combined effects.
As part of the reaction to this study, the European Commission, through the Directorate General of the Environment, decided to fund further study of chemical mixture toxicity with a focus on endocrine disrupters – chemicals that affect the functioning of the human hormone system that could be responsible for declining sperm counts and quality, genital malformations, retarded sexual development and increased incidences of certain types of cancers.
“The number of chemical combinations that the Earth’s living organisms are exposed to is enormous,” says Thomas Backhaus, researcher at the Department of Plant and Environmental Sciences and co-author of the report. “Assessing every conceivable combination is not therefore realistic, and predictive approaches must be implemented in risk assessment. We need guidelines on how to manage the chemical cocktail effect so that we can assess the risks to both humans and the environment.”