Assessing combined impacts of agrochemicals: Aquatic macroinvertebrate population responses in outdoor mesocosms

Abstract

Agricultural ditches host a diverse community of species. These species often are unwarrantedly exposed to fertilizers and a wide-array of pesticides (hereafter: agrochemicals). Standardized ecotoxicological research provides valuable information to predict whether these pesticides possibly pose a threat to the organisms living within these ditches, in particular macro-invertebrates. However, knowledge on how mixtures of these agrochemicals affect macro-invertebrates under realistic abiotic conditions and with population and community complexity is mostly lacking. Therefore we examined here, using a full factorial design, the population responses of macroinvertebrate species assemblages exposed to environmentally relevant concentrations of three commonly used agrochemicals (for 35days) in an outdoor experiment. The agrochemicals selected were an insecticide (imidacloprid), herbicide (terbuthylazine) and nutrients (NPK), all having a widespread usage and often detected together in watersheds. Effects on species abundance and body length caused by binary mixture combinations could be described from single substance exposure. However, when agrochemicals were applied as tertiary mixtures, as they are commonly found in agricultural waters, species' abundance often deviated from expectations made based on the three single treatments. This indicates that pesticide-mixture induced toxicity to population relevant endpoints are difficult to extrapolate to field conditions. As in agricultural ditches often a multitude (approx. up to 7) of agrochemicals residues are detected, we call other scientist to verify the ecological complexity of non-additive induced shifts in natural aquatic invertebrate populations and aquatic species assemblages.

Acute effect of low-dose thiacloprid exposure synergised by tebuconazole in a parasitoid wasp

“…Furthermore, pesticide exposure is poorly understood for many non-target invertebrate taxa, and it is needed that experiments simulate realistic exposure. Mesocosm experiments simulating natural community exposure to relevant pesticide combinations [41] are also encouraged.…”

Concerns and Threats of Contamination on Aquatic Ecosystems

“…"Measures of prevention and control are essential in improving the quality of water" and reducing the "costly treatment measures that are taken to treat water." Preventive measures and possible solutions to "control water contamination" are given as follows (Xiong et al 2015;Lan et al 2015;Xanthos and Walker 2017;Barmentlo et al 2018):…”

The choreography of chemicals in nature; beyond ecotoxicological limits

“…The results obtained with our mesocosm experiments show that when two different agrochemicals are added to the system e a binary mixture e the toxicity is predicted well by our lab-based knowledge. When more than two compounds are added simultaneously, though, the toxicity can no longer be forecast from lab results (Barmentlo et al, 2018a). When we our shifted our research focus to chemicals in combination with food availability, Barmentlo et al (2018b) saw that caged water fleas put out in ditches to which thiacloprid had been added were an incredible 2500 times more sensitive under field conditions than in the lab.…”