An assessment of direct and indirect effects of two herbicides on aquatic communities

Abstract

Herbicides are often detected in watersheds at concentrations that are toxic to phytoplankton, potentially causing indirect effects on higher trophic organisms. The long-term effects of 5 applications over 30 d of binary mixtures of the herbicides diuron and hexazinone were assessed at "low" and "high" concentrations typically found in the environment, using mesocosms. Sixteen of 95 phytoplankton taxa, 3 of 18 zooplankton taxa, and 6 of 14 macroinvertebrate taxa responded negatively to contaminant exposures. Herbicide applications altered the phytoplankton community structure. Relative abundance of Cyanophyceae decreased following 5 applications from 52.1% in the control to 37.3% in the low treatment and to 25.9% in the high treatment, while Chlorophyceae increased to 50.6% in the low treatment and to 61.7% in the high treatment compared with the control (39.7%). Chlorophyceae had the greatest number of affected species (8), whereas 1 species within the Cyanophyceae was negatively affected on more than 1 sampling day. Further, chlorophyll a was reduced on 4 and 5 d out of the 8 total sampling days in the low and high treatments, respectively, compared with the control. These results highlight that integrating multiple taxa and contaminants with long-term exposures in ecological risk assessments of herbicides can facilitate the ability to make predictive and mechanistic generalizations about the role of herbicides in shaping patterns of species abundance in natural systems. Environ Toxicol Chem 2017;36:2234-2244. © 2017 SETAC.

Eutrophic status influences the impact of pesticide mixtures and predation on Daphnia pulex populations

“…In a previous mesocosm experiment performed with diuron, Hasenbein et al (2017) observed a decrease in phytoplankton richness and an increase in grazing-resistant algal species, which support our explanation. Moreover, the mesocosms treated with diuron, although did not show a statistically significant decrease in chlorophyll a concentration (Table 1), showed a significant reduction in the pH, conductivity, and dissolved oxygen concentration (Table S3), which indicate a reduction in the primary productivity and biomass.…”

Herbicides in surface water bodies - behaviour, effects on aquatic organisms and risk assessment

“…Studies of herbicide effects on outdoor ponds found no direct adverse effect on the invertebrate community, but indicated that long-term changes in macrophyte populations could cause longterm adverse effects on inverbrate community structure (Burdett et al, 2001). Similar findings were reported by Hasenbein et al (2017) in a study in which decrease in Daphnia magna abundance following herbicide application was determined. The authors concluded that the decline was a result of altered phytoplankton community structure.…”

Food web rewiring drives long-term compositional differences and late-disturbance interactions at the community level

“…Our systems were populated by several species with different sensitivities to the disturbances applied. The initial decrease in univariate descriptors of composition was mainly caused by the decline of sensitive species ( 25 , 29 – 31 ). Later, through recolonization (particularly of sensitive Ephemeroptera taxa, such as Cloeon sp .…”