Wednesday, February 6, 2019 (10:00 am, Paris Time Zone)
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Betty CHAUMET (Irstea Bordeaux, France)
Diuron transfer and distribution mechanisms in the biofilm, linked with the toxic effects associated
In 2000, the Water Framework Directive required the return of rivers to good chemical and ecological status. In particular, it has classified 45 substances as priority for this assessment (Directive 2013/39/EU), including a large proportion of pesticides. Indeed, due to their massive use, these contaminants are now found in all compartments of the environment. In addition, given its ability to integrate contamination, biofilm is considered an excellent bioindicator for water quality assessment. It is at the base of the trophic chain in aquatic environments and is composed of microorganisms (microalgae, bacteria, fungi, etc…) embedded in a matrix of extracellular polymeric substances (EPS).
This work was focused on the analysis of mechanisms of pesticide transfer and distribution in biofilms related to toxic impacts. The study was carried out using a toxicokinetic approach whereby the bioaccumulation of diuron (a photosynthesis inhibitor herbicide) was monitored in the different compartments of the biofilm. The objective was to answer the following questions: how, where and at how fast diuron is accumulated in the biofilm and what is the toxic effect associated?
To understand the bioaccumulation mechanisms, two experiments were carried out. The first was to measure the influence of the flow velocity on diuron bioaccumulation (its distribution) in the biofilm and its toxic effect. The second focused on sorption mechanisms of diuron in biofilm through exposure to a diuron concentration gradient. These two experiments were carried out in channels in a thermo-regulated room.
This work has made it possible to highlight a very rapid bioaccumulation of diuron, according to a first-order kinetics. It has also been shown that along a gradient of concentration, diuron bioaccumulation in the biofilm was not linear. This fact was established through the coupling of toxicokinetic and toxicodynamic (TK-TD) approaches. Indeed, the combination of these two approaches established that different mechanisms were taking place during accumulation, such as continuous absorption by the cells and adsorption to the EPS matrix. In addition, the TK-TD approach has allowed the development of a prediction model that links the diuron concentration in the environment to the associated toxic effect from the diuron concentration in the biofilm.