Bekæmpelsesmiddelforskning fra Miljøstyrelsen, 102 – Effekter af pulseksponering med pyrethroider på vandløbsinvertebrater - med særlig fokus på lambda-cyhalothrin

Effekter af pulseksponering med pyrethroider på vandløbsinvertebrater

Summary

Aim

Drift is one of the key phenomena observed in relation to short-term pesticide pulses in freshwater streams. During these events a diverse range of stream invertebrates are carried along with the current and disappear completely or partially from the contaminated stretch of the stream. The main aim of the project was to link laboratory studies of the sublethal effects of pyrethroide insecticides on locomotory behaviour with drift studies under more environmentally realistic conditions in stream microcosms. The hypothesis was that if this link could be established, the cost-effective laboratory studies could be utilized to extrapolate directly to effects in natural streams.

Methods

The locomotory behaviour of stream invertebrates placed in glass petri dishes in the laboratory was quantified by using a computerized video tracking system before, during and following various kinds of pulse exposures to pyrethroids, especially lambda-cyhalothrin. The effects on locomotory behaviour were compared with the effects of lambda-cyhalothrin on drift and the effects in a multi-species system in outdoor stream microcosms.

Experiments

In the laboratory, behavioural toxicity tests were performed using the pyrethroids esfenvalerate, alpha-cypermethrin, cypermethrin, lambda-cyhalothrin and tau-fluvalinate, and lambda-cyhalothrin was selected as model pyrethroid. The influence of pulse duration and water temperature on the behavioural response was investigated. Finally, an experiment with lambda-cyhalothrin in combination with glyphosate, which is commonly occurring in Danish streams, was performed.

Pulse exposures using the crustaceans Gammarus pulex and Asellus aquaticus, the stonefly Leuctra nigra, the mayfly Heptagenia sulphurea, the caddisfly Sericostoma personatum and the snail Ancylus fluviatilis were performed in the laboratory. The long-term effects of pulse exposure to lambda-cyhalothrin were investigated in recovery studies lasting three weeks using G. pulex and A. aquaticus. The effects on interspecific interactions were investigated in a study of the predator-prey-relationship between G. pulex and L. nigra.

Two types of experiments were carried out in the stream microcosms: Drift and effects on a multi-species system. In the drift experiments, the immediate drift response in G. pulex, L. nigra, H. sulphurea, A. fluviatilis and S. personatum during and following pulse exposure to lambda-cyhalothin was studied in semi-natural stream microcosms.

In the multi-species studies, the long-term effects of exposure to lambda-cyhalothrin were investigated to elucidate both direct and indirect effects. This study included G. pulex, L. nigra, H. sulphurea and A. fluviatilis. The study lasted 10 days, with daily measurements of drift. Furthermore, the breakdown of organic matter and change in algal biomass was determined in order to clarify indirect effects of pyrethroid exposure.

Results

In the table below, a comparison of the laboratory and stream microcosm results based on NOEC (no observable effect concentration) and LOEC (lowest observable effect concentration) values is given. The LOECs for L. nigra (1 ng l^-1), G. pulex (10 ng l^-1), A. aquaticus (10 ng l^-1) and H. sulphurea (100 ng l^-1) are all within expected environmentally realistic levels.

Table 1. Extrapolation from laboratory to stream microcosms. NOEC and LOEC lambda-cyhalothrin-concentrations (ng l^-1) for hyperactivity (Hyper), hypoactivity (Hypo) and immobilisation (I) in the laboratory and for drift (D) in the stream microcosms after 90 minutes of exposure.

	Laboratory				Stream microcosm


Species	NOEC	LOEC_Hyper	LOEC_Hypo	LOEC_I	NOEC_D	LOEC_D


Leuctra nigra	0.1	-	1	10	-	1
Gammarus pulex	1	10	1000	1000	1	10
Asellus aquaticus	1	10	100	1000	no data	no data
Heptagenia sulphurea	10	100	10000	10000	10	100
Sericostoma personatum	10000^a	-	-	-	1000^a	-
Ancylus fluviatilis	10000^a	-	-	-	1000^a	-

a: Highest concentrations tested in the laboratory and in the stream microcosms.

In the laboratory as well as in the stream microcosms, the rank ordering of the sensitivity of the species towards lambda-cyhalothrin was:

L. nigra > G. pulex > H. sulphurea > S. personatum > A. fluviatilis

The laboratory results indicate that the five pyrethroids investigated have the same qualitative effects on locomotory behaviour (hyperactivity and immobilisation) as well as very comparable effect concentrations in G. pulex. In general, hyperactivity is observed at 10 ng l^-1. At 100 ng l^-1 G. pulex is not capable of maintaining the hyperactivity, and at 1000 ng l^-1 immobilisation is observed.

Conclusions

Based on the results of the present report it is concluded:

1) that both the observed effect concentrations as well as the rank ordering of the species sensitivities towards lambda-cyhalothrin can be extrapolated directly from laboratory studies of locomotory behaviour to studies of drift in the more environmentally realistic stream microcosms. Once the relation between the changes in locomotory behaviour in the laboratory and drift in the microcosms has been documented for the individual species, the laboratory studies may replace the stream microcosm studies. Consequently, this applies to the species studied in the present project.

2) that alpha-cypermethrin, cypermethrin, lambda-cyhalothrin and tau-fluvalinate all markedly affect the behaviour of G. pulex at a concentration of 10 ng l^-1, while esfenvalerate causes behavioural changes at 1 ng l^-1. All of the pyrethroids studied consequently have effects at concentrations which are barely quantifiable; for comparison, the requirements for the detection limit in the analytical techniques used for monitoring pesticides in freshwater is 10 ng l^-1.

3) that brief pulse exposure to lambda-cyhalothrin results in delayed effects on behaviour and survival in freshwater invertebrates; effects which may be observed for 2-3 weeks after the pulse exposure has ceased.

4) that predator-prey-interactions are affected at environmentally realistic pulse exposures to lambda-cyhalothrin.

5) that pulse exposure to lambda-cyhalothrin results in marked indirect effects on the growth of the algal biomass and the breakdown of organic matter, indicating that environmentally realistic exposure of stream invertebrate communities to lambda-cyhalothrin may lead to effects at the ecosystem level, beyond the direct effects on specific species and populations.

The results of the project demonstrate that the methods utilized complement each other, i.e. the cost-effective laboratory studies can be employed for rapid screening of potential effects of pesticides on the locomotory behaviour of freshwater invertebrates in order to establish effect concentrations and rank ordering of species sensitivities. These data may be utilized in e.g. the planning of stream microcosm experiments. Concurrently, observations from more complex stream microcosm studies, such as effect studies at the community level, may be elucidated by subsequent laboratory studies of locomotory behaviour, recovery and interspecific interactions.