Risk of herbicide mixtures as a key parameter to explain phytoplankton fluctuation in a great lake: the case of Lake Geneva, Switzerland

Abstract

Mixture risk assessment predictions have rarely been confronted with biological changes observed in the environment. In this study, long-term monitoring of a European great lake, Lake Geneva, provides the opportunity to assess to what extent the predicted toxicity of herbicide mixtures explains the changes in the composition of the phytoplankton community next to other classical limnology parameters such as nutrients. To reach this goal, the gradient of the mixture toxicity of 14 herbicides regularly detected in the lake was calculated using concentration addition and response addition models. A temporal gradient of toxicity was observed which decreased from 2004 to 2009. Redundancy analysis and partial redundancy analysis showed that this gradient explains a significant portion of the variation in phytoplankton community composition with and without having removed the effect of all other co-variables. Moreover, species that are significantly influenced, positively or negatively, by the decrease of toxicity in the lake over time are highlighted. It can be concluded that the herbicide mixture toxicity is one of the key parameters to explain phytoplankton changes in Lake Geneva.

Soil surface colonization by phototrophic indigenous organisms, in two contrasted soils treated by formulated maize herbicide mixtures

“…1 Thus, we support the necessity to re-evaluate the S-metolachlor toxicity by carrying on extensive soil studies on this molecule, in order to reconsider its use from an ecotoxicological point of view. The development of adapted ecotoxicological field tools to study phototrophic microorganisms seems a way to deepen in order to investigate the potential impairment of pesticides on soil and reach the ecosystemic level and the long time monitoring already used in aquatic study (Gregorio et al 2012). Furthermore, phototrophic microorganisms seem to be promising as pollution indicator, not especially by following specific communities but more by assessing the photosynthetic activity directly linked to the pigment biomass, as suggested by Bérard et al (2004).…”

Comparison of specific versus literature species sensitivity distributions for herbicides risk assessment

“…Predictive models have been developed for risk assessment of single substances and complex mixture at the community level de Zwart and Posthuma 2005; Van den Brink et al 2006;Gregorio et al 2012). These models are based on the species sensitivity distribution (SSD) as proposed by Posthuma et al (2002).…”

Modelling the effects of pulse exposure of several PSII inhibitors on two algae

“…Many of these herbicides belong to the triazines group and the phenylureas group (Gilliom, 2006;Gregorio et al, 2012), which act as photosystem II inhibitors (Knauert, 2008;Vallotton et al, 2008a). These types of herbicides are often measured at high concentrations because they are among the most important classes of herbicides used in the world (LeBaron et al, 2008;Sorensen et al, 2003;Stangroom et al, 1998).…”

“…These types of herbicides are often measured at high concentrations because they are among the most important classes of herbicides used in the world (LeBaron et al, 2008;Sorensen et al, 2003;Stangroom et al, 1998). In Switzerland, numerous triazines and phenylureas are also regularly detected at high concentrations in surface waters, such as lakes (Chevre et al, 2008;Gregorio et al, 2012) and streams (Chevre et al, 2006;Munz et al, 2013).…”