Pollution in the aquatic environment is erratic. Concentrations of chemicals are temporarily but greatly increased due to reoccurring or random events such as run off caused by rain fall, spraydrift, flooding, discharge of wastewater and shifts of tidal currents. These events may cause pollution that greatly exceeds the background environmental level of those chemicals. Assessing the environmental impact of such events is important but intermittent exposures are unfortunately not addressed in standard ecotoxicological testing and neither are latent effects that appear after the end of exposure.
Intermittent exposure was addressed and sugar kelp (Saccharina latissima, Linnaeus) was exposed to pulses of seven antifouling toxicants (chlorothalonil, DCOIT, dichlofluanid, diuron, irgarol, tolylfluanid, zinc pyrithione) and acute effects on photosynthesis were studied. All chemicals except zinc pyrithione were toxic to sugar kelp photosynthesis. Chlorothalonil and tolylfluanid caused photosynthesis inhibition that continued to increase even after exposure had ended. The carbon-concentrating mechanism of sugar kelp was also studied and found to be targeted by chlorothalonil, DCOIT, dichlofluanid and tolylfluanid.
Effects of pulsed exposures were further studied on sessile microalgal periphyton communities sampled on glass discs. The periphyton samples were exposed to a pulse of 1, 12, 24 or 96 hours of either irgarol (a PSII-inhibitor) or clotrimazole (a sterol-synthesis inhibitor) and the pigment composition of the community was evaluated using multivariate methods. The pigment fingerprint reflects taxonomic composition of the algal community as well as the physiology of the algae and these two aspects cannot be readily distinguished. Periphyton from a relatively unpolluted site suffered from inhibited growth and altered adaptations to the light regime in the bioassay during exposure to both toxicants. Effects of clotrimazole remained after exposure had ended. Periphyton from a site polluted by irgarol did not suffer from inhibited growth during irgarol exposure, but the light-adaptations were still disturbed. Periphyton from the irgarol polluted site were more affected by the clotrimazole exposure and effects lasted for a longer period after the end of exposure. Physiological effects on light-adaptations were in some cases evident despite that the periphyton were able to grow at the same rate as the controls. This is an example of an effect that would be hidden if only superior, integrating, endpoints are studied. In line with the community onditioning hypothesis and the Pollution-Induced Community Tolerance (PICT) concept the periphyton from the irgarol-polluted site reacted differently compared to the periphyton from the less polluted site. It is hypothesised that in a sequence of pulsed exposures the initial exposure shapes the community in a way that the impact of the second exposure depends on the relation of ecological mechanism of action of the toxicants. When they are similar, the community will have become more tolerant to the second exposure, through elimination of sensitive species and individuals. When the toxicants are dissimilar, however, the first exposure causes a decrease of genetic diversity in the community and thus a generally increased sensitivity to subsequent exposure and the second exposure would thus cause a larger toxic effect.
CONTENTS
SUMMARY
INTRODUCTION
- INTERMITTENT EXPOSURE
COMMUNITY ECOTOXICOLOGY
END POINTS - PHOTOSYNTHESIS AND COMMUNITY STRUCTURE
AIM OF THE THESIS
EXPERIMENTAL SETUP
- TESTED COMPOUNDS
SUGAR KELP PHOTOSYNTHESIS
PERIPHYTON COLONISATION, SAMPLING AND TRANSLOCATION
SWIFT
PIGMENT ANALYSIS HPLC
MULTIVARIATE STATISTICS
MOST SIGNIFICANT FINDINGS
- EFFECTS OF PULSED EXPOSURE TO SUGAR KELP PHOTOSYNTHESIS
COMMUNITY EFFECTS OF PULSED EXPOSURE
TRANSPLANTED PERIPHYTON
MICROCOSM PERIPHYTON AND FIELD-SAMPLED PERIPHYTON
CONCLUDING REMARKS AND OUTLOOK
ACKNOWLEDGEMENTS
REFERENCES
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