Pesticide mixture effects on bioaccumulation and toxicity in biofilms

Pesticides exert a significant risk to aquatic ecosystems, including biofilm communities composed of microorganisms (microalgae, bacteria and fungi) embedded in an extracellular matrix. Biofilms are at the basis of food webs.

They are good indicators for water quality assessment as they respond quickly to contamination, and pesticides are toxic to biofilms. Pesticide properties (logKOW and mode of action), influence their biological responses and bioaccumulation. However, the toxicity was mainly shown for single compound exposures, whereas pesticides always occur in mixtures.

Moreover, bioaccumulation is not always a linear function of exposure concentration, implying that concentration measurements do not provide an accurate risk indicator.

There is a need to understand mixture effects (competitive, additive or synergistic) of pesticides in biofilms, because the pollution linked to pesticides is considerable and continues to increase.

In order for current regulations to be as close as possible to the environmental reality and to consider the real toxic effect of pesticides on biofilms, it is essential to understand the inherent mechanisms. Testing all possible pesticide combinations is impossible. We therefore propose establishing a predictive model based on measurable and standardisable parameters.

This model will link the pesticide exposure in mixtures, to the bioaccumulation and the toxic effects in biofilms.