Ecotoxicological evaluation of Harbour sediments using marine organisms from different trophic levels |
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Authors: | Luigi Pane Elisabetta Giacco Christian Corrà Giuliano Greco Gian Luigi Mariottini Franco Varisco Marco Faimali |
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Institution: | (1) Department of Biology, University of Genova, Viale Benedetto XV 5, 16132 Genova, Italy;(2) CNR — ISMAR-Marine Technology Section, Via De Marini 6, 16149 Genova, Italy;(3) Multiproject S.r.l, Via del Carso 6/A, 34170 Gorizia, Italy |
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Abstract: | Background, Aim and Scope The toxicity of contaminated sediments should be evaluated considering the direct exposure of laboratory organisms to whole
sediments and the indirect exposure to elutriates or extracts (Tay et al. 1992, Byrne and Halloran 1999, Nendza 2002). The
alga Dunaliella tertiolecta is indicated for the use in toxicity bioassays because it is highly sensitive to several xenobiotics. Harpacticoid copepods
have been already used for toxicity testing and Tigriopus fulvus is a promising Mediterranean target-species in ecotoxicology (Todaro et al. 2001, Faraponova et al. 2003, Pane et al. 2005a).
In this study, the toxicity of sediments collected in harbour sites of the Northeastern Adriatic Sea was evaluated by growth
inhibition test with free living and alginate-immobilized Dunaliella tertiolecta and acute toxicity test with nauplii and adult Tigriopus fulvus with the aim of pointing out the importance to utilize model organisms from different trophic levels in sediment ecotoxicology.
Methodology Elutriates and whole sediments were tested on free living and immobilized (Pane et al. 1998) algal cells, and on laboratory
reared copepods. Free-living D. tertiolecta were exposed to diluted elutriates in a static, multi-well plate system. Naalginate immobilized D. tertiolecta were placed in polystyrene inserts fitted with polyester mesh bottoms and exposed to a thin layer (2 mm) of whole sediments
in multi-well plates (EPS 1992, Pane and Bertino 1999). Toxicity tests with copepods were carried out on Tigriopus fulvus nauplii (elutriates) and adults (whole sediments and elutriates). Same-aged nauplii useful for toxicity tests were obtained
by egg sac detaching and consequent hatching stimulation (Pane et al. 2006). Newborn nauplii (I–II stage) were exposed to
elutriates in multi-well plates provided with polystyrene inserts. Adult T. fulvus maintained in polystyrene inserts fitted with polyester mesh bottoms were placed in contact with a thin layer (2 mm) of whole
sediment placed on multi-well plate bottoms. All end-points were evaluated after 96 h.
Results In general, the effects increased with the increasing of elutriate concentration up to 50%; the stimulation or inhibition
of algal growth was statistically significant in comparison to the control. The inhibiting elutriates induced EC50 variations of algal growth ranging from 66.9% to 74.3%. The mortality of T. fulvus nauplii was always < 25% after treatment with 100% elutriates and < 10% after treatment with 50% dilution; no effect was
shown up with 25% dilution; therefore LC50 was not calculable. The effect of elutriates was negligible on adult copepods and LC50 values were never calculable; percent mortality always resulted in < 10% after treatment with whole sediments.
Discussion Both experimental systems gave substantially similar results after exposition to whole sediments and elutriates. During the
experiment with algal cells, the immobilization in Na-alginate and the employment of inserts which allowed the contact of
organisms with sediments and their easy counting were particularly useful. Likewise, the employment of inserts of adequate
mesh size in the tests with copepods allowed the contact of organisms with the sediment and made organism handling and counting
easy, as well as the evaluation of mortality. The methodology here described and the utilization of the proposed test-species
could have an importance also considering that the current trend in ecotoxicological research is towards finding the most
appropriate organism for specific areas of concern by using indigenous species (Mariani et al. 2006) and towards the major
significance of chronic and reproductive end-points.
Conclusions Based on the above results, it can be stated that the bioassay with Dunaliella tertiolecta could be a good estimation tool for the ecotoxicological assessment of marine sediments. The immobilization of algae in Na-alginate
was seen to be useful to evaluate the toxicity of whole sediments; the employment of polystyrene inserts allowed an improvement
of the procedures. T. fulvus nauplii and adults, as other harpacticoids such as Tigriopus japonicus (Yoon et al. 2006), satisfy the basic criteria for the employment of a standard species in marine bioassays. To date only
pelagic Acartia tonsa are utilized in the standardized procedure to evaluate the risk assessment of chemicals or wastewaters (ISO 1999). As, on
the contrary, the exposure of copepods to solid-phase contaminants it is not yet standardized, the employment of polystyrene
inserts improved the procedures for T. fulvus too. So, the rapidity and the possibility to solve practical problems could be the main attractive features of this technique
(Pane et al. 2005a) when applied to whole sediments.
Recommendations and Perspectives The methodology here developed being also applicable to long term and reproduction tests should be recommended because it
provides relevant information in comparison with other frequently applied, standardized biotests with crustaceans (ISO 1999).
The procedure has been shown to be easily applicable to selected marine organisms.
ESS-Submission Editor: Prof. Dr. Henner Hollert (henner.hollert@bio5.rwth-aachen.de) |
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Keywords: | Algal growth effects Dunaliella tertiolecta ecotoxicological evaluation harbours immobilization marine organisms sediments Tigriopus fulvus toxicity trophic levels |
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