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Use of re-exposures to examine the effect of watercress derived isothiocyanates on Gammarus pulex Melanie Dixon.

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Presentation on theme: "Use of re-exposures to examine the effect of watercress derived isothiocyanates on Gammarus pulex Melanie Dixon."— Presentation transcript:

1 Use of re-exposures to examine the effect of watercress derived isothiocyanates on Gammarus pulex Melanie Dixon

2 Why use re-exposures? watercress farm & wash/pack house factory chalk stream headwater variable factory discharge ~8h per day weight/type products being washed Watercress farm outfall (Spring 08)

3 Isothiocyanates glucosinolates occur naturally; watercress and other crucifers enzyme released when plant wounded isothiocyanates produced as secondary metabolites important in defence of plant against herbivorous invertebrates Parabolic screen above outfall

4 Hypothesis Gammarus pulex shows an increased sublethal response following repeated exposure to pure and watercress derived phenethyl isothiocyanate (PEITC). Gammarus pulex (L.)

5 Method Development selection of test organism; depletion of G. pulex acute juvenile test sublethal endpoint, precopular separation time constraints, degradation rate G. pulex precopular pairs

6 Method prepare wash water or PEITC solution expose pairs for 2h return to clean water count pairs re-formed re-expose for 2h in fresh wash water

7 Results response during 2h exposure comparison of pairs separated: exposure & re-exposure pairs reforming after 24h in clean water ET50 values

8 Response during 2h exposure Pairs separated % PEITC (1µl/l) Wash water Control Re-exposures 0 20 40 60 80 100 0153045607590105120 Time (mins)

9 Comparison of pairs separated after 2h (exposure/re-exposure) Control Upper 95% CI Control Lower 95% CI 0 20 40 60 80 100 Wash water 2 Wash water 4 Wash Water 5 PEITC 3PEITC 5 %

10 Pairs re-forming after 24h in clean water

11 ET50 ( 95% CI ) values Mean 81±9 mins 0 20 40 60 80 100 120 Mean 71±14 mins Individual Tests Minutes Washwater 0 20 40 60 80 100 120 140 PEITC

12 Mean ET50 ( ± SE ) Wash water WW re-exp. PEITC (1ug/l) PEITC re-exp. 0 20 40 60 80 100 Minutes

13 Environmentally relevant concentration used. Baseline sensitivity /variability in mate guarding phase. Potential pairs lost during exposure; 3 rd exposure possible? Watercress (Nasturtium officianale (R.Br.))

14 Conclusions re-exposures could be successfully carried out re-exposures resulted in slight (not statistically significant) increase of impact on most occasions transient impact? Watercress in flower

15 We gratefully acknowledge the support of the Vitacress Conservation Trust and use of facilities at the National Oceanographic Centre and Environment Agency Biological Effects Laboratory. Vitacress Salads Ltd, Hampshire, UK


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