Ferskvandsinvertebraters bevægelsesadfærd som biomarkør for pesticideksponering og effekt

Ferskvandsinvertebraters bevægelsesadfærd som biomarkør for pesticideksponering og effekt

Summary and conclusions

Aim

Drift in stream invertebrates is induced upon exposure to comparatively low concentrations of pesticides. Increased drift in aquatic invertebrates in running water may lead to a decline in population size. The present project was initiated to investigate the feasibility of quantifying drift related changes in locomotory behaviour in the laboratory rather than using the current approach employing mesocosm or field studies. The aim of the project was to develop and implement a computer automated video tracking system for quantification of the effects of pesticides on locomotory behaviour in stream invertebrates.

Methods

The locomotory behaviour of the freshwater amphipod Gammarus pulex and the isopod Asellus aquaticus placed in petri dishes was recorded by using a state-of-the-art video tracking system (EthoVision Pro, Noldus Information Technology, Holland) during exposure to pesticides. In order to evaluate the relative sensitivity of the behavioural response, the effect of the pesticides on mortality was investigated.

Pesticides

Pesticides were selected in collaboration with the Danish Environmental Protection Agency based on criteria for use in Denmark, biological activity and occurrence in surface water. Studies were performed using the pyrethroid insecticides cypermethrin and esfenvalerate, the organophosphate insecticide dimethoate and the strobilurin fungicide azoxystrobin. In order to obtain realistic concentration-response relationships, methods were developed to determine the real pesticide concentrations during exposure by using liquid chromatography coupled to mass spectrometry (LC-MS).

Experiments

The video tracking system was used for three types of experiments, i.e. for studying the background behaviour in uncontaminated water, for testing the acute behavioural toxicity of pesticides and for studying the ability of the animals to recover following a transient pesticide exposure. Investigations of acute behavioural toxicity included effect studies of cypermethrin, esfenvalerate, dimethoate and azoxystrobin in adult G. pulex, of cypermethrin in juvenile G. pulex, and of esfenvalerate in adult A. aquaticus.

Results

The video tracking experiments using the pyrethroids cypermethrin and esfenvalerate on both adult G. pulex and A. aquaticus and on juvenile G. pulex unambiguously show that during exposure to low, environmentally realistic concentrations of pyrethroids the animals display a maximum flight response. This avoidance behaviour is maintained as long as possible, being followed by immobilisation at higher exposure concentrations. Immobilisation appears to be irreversible; immobilised G. pulex and A. aquaticus are still immobile 24 hours after transfer to uncontaminated water. G. pulex displays avoidance behaviour at lower pyrethroid concentrations than A. aquaticus while A. aquaticus is more sensitive as far as immobilisation is concerned. No marked differences in the acute behavioural response of juvenile and adult G. pulex were noted. Dimethoate and azoxystrobin did not affect the locomotory behaviour of G. pulex even at high exposure concentrations.

Conclusions

The method for automated behavioural monitoring implemented in the present project has the potential for generating results that may be utilised for evaluating risks related to contamination by or discharge of pesticides into stream ecosystems. The video tracking system is capable of generating cost-effective concentration-response data on behavioural toxicity, and could be employed by environmental authorities as a screening tool. The video tracking system facilitates combination exposure studies where experimental animals are exposed to mixtures of pesticides. Following future method validation in the field, the system may be applied in relation to monitoring in streams.