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Use of re-exposures to examine the effect of watercress derived isothiocyanates on Gammarus pulex. Melanie Dixon. Why use re-exposures?. watercress farm & wash/pack house factory chalk stream headwater variable factory discharge ~8h per day weight/type products being washed. - PowerPoint PPT Presentation
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Use of re-exposures to examine the effect of watercress derived isothiocyanates on Gammarus pulexMelanie Dixon
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)
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
Hypothesis
• Gammarus pulex shows an increased sublethal response following repeated exposure to pure and watercress derived phenethyl isothiocyanate (PEITC).
Gammarus pulex (L.)
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
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
Results• response during 2h
exposure
• comparison of pairs separated: exposure & re-exposure
• pairs reforming after 24h in clean water
• ET50 values
Response during 2h exposure
Pairs separated
%
PEITC (1µl/l)Wash waterControlRe-exposures
0
20
40
60
80
100
0 15 30 45 60 75 90 105 120Time (mins)
Comparison of pairs separatedafter 2h (exposure/re-exposure)
Control Upper 95% CI
Control Lower 95% CI
0
20
40
60
80
100
Washwater 2
Washwater 4
WashWater 5
PEITC 3 PEITC 5
%
Pairs re-forming after 24h in clean water
0
10
20
30
40
50
60
70
80
Washwater PEITC Control
Mea
n %
pairs re-formed after 24h
pairs at exposure end
ET50 (95% CI) values
Mean81±9 mins
020406080
100120
Mean71±14 mins
Individual Tests
Min
ute
s
Washwater
020406080
100120140
PEITC
Mean ET50 (± SE)
Wash water
WW re-exp. PEITC
(1ug/l) PEITC re-exp.
0
20
40
60
80
100
Min
ute
s
• Environmentally relevant concentration used.
• Baseline sensitivity /variability in mate guarding phase.
• Potential pairs ‘lost’ during exposure; 3rd exposure possible?
Watercress (Nasturtium officianale (R.Br.))
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
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