The researchers call this the cocktail effect and investigated how five chemicals, including anti-bacterial agent triclosan found in personal care products and zinc pyrithione found in anti dandruff shampoos, acted in combination on ocean ecosystems along the Swedish coast.
According to Tobias Porsbring, who defended the work as his doctoral thesis last week, the mix of pharmaceutical and personal care chemicals in the ocean have a direct impact on the growth and reproduction of micro-organisms for example microalgae.
As these single cell organisms are the basis of the ocean food chain, any chemical, or collection of chemicals, which negatively affects this may damage the whole ocean ecosystem.
However, when calculating the environmental danger posed by a chemical its behaviour as part of a combination of chemicals is rarely taken into account.
“What we and others have observed is that even though chemicals are present at concentrations that are low enough to not provoke a discernible effect on their own they all add up to a clear combination effect,” he told CosmeticsDesign.com.
Therefore, taking only single chemicals into account may underestimate the actual environmental risk.
Porsbring described two models that can be used to estimate the cocktail effect of a number of chemicals as opposed to their single behaviour, that depend on whether the chemicals have the same mode of action or not.
Concentration Addition is a model that best describes the behaviour of chemicals that have the same mechanism of action, for example they bind to the same protein. Independent Action describes chemicals that don’t have the same mechanism of action.
However, Porsbring advises using the Concentration Addition model even if the mechanism of action of the chemicals is unknown, as it is slightly more conservative than other methods and the toxicity data needed to calculate it is easier to come by.
Household, industrial and agricultural chemicals
The five chemicals investigated in the research do not fully reflect those present in the ecosystem. Household chemicals, industrial chemicals from industrial sites, pesticides and herbicides will also be present but looking at more than five chemicals in combination can be difficult, explained Porsbring.
He also noted that most environmental mixtures are often made up of a few especially risky compounds and a background of additional chemicals.
“Hence, it is possible to lower the risks from environmental mixtures substantially, simply by identifying and focusing risk management towards a few ‘high risk’ compounds,” he said.
In this case, the cocktail effect should be taken into account when calculating what would be a safe level of these high risk chemicals.