use of re-exposures to examine the effect of watercress derived isothiocyanates on gammarus pulex
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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 PresentationTRANSCRIPT
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Use of re-exposures to examine the effect of watercress derived isothiocyanates on Gammarus pulexMelanie Dixon
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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)
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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
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Hypothesis
• Gammarus pulex shows an increased sublethal response following repeated exposure to pure and watercress derived phenethyl isothiocyanate (PEITC).
Gammarus pulex (L.)
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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
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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
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Results• response during 2h
exposure
• comparison of pairs separated: exposure & re-exposure
• pairs reforming after 24h in clean water
• ET50 values
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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)
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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
%
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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
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ET50 (95% CI) values
Mean81±9 mins
020406080
100120
Mean71±14 mins
Individual Tests
Min
ute
s
Washwater
020406080
100120140
PEITC
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Mean ET50 (± SE)
Wash water
WW re-exp. PEITC
(1ug/l) PEITC re-exp.
0
20
40
60
80
100
Min
ute
s
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• Environmentally relevant concentration used.
• Baseline sensitivity /variability in mate guarding phase.
• Potential pairs ‘lost’ during exposure; 3rd exposure possible?
Watercress (Nasturtium officianale (R.Br.))
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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
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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