The use of protozoa in ecotoxicology: Application of multiple endpoint tests of the ciliate E. crassus for the evaluation of sediment quality in coastal marine ecosystems

Despite an increasing number of surveys describing adverse effects of contaminated sediments on marine organisms, few studies have addressed protists. In this study, the free-crawling marine ciliate Euplotes crassus was evaluated as the test organism for the screening of sediment toxicity using sediments from both coastal and estuarine sites of the Venice Lagoon (Marghera harbour [MH], Valle Millecampi [MV], Murano island [MI] and Lido inlet [LI]). Two endpoints of high ecological value, mortality (Mry) and replication rate (RpR), were assessed in combination with the two sublethal biomarkers of stress, endocytotic rate (Ecy) and lysosomal membrane stability (NRRT). The results showed a significant inhibition of RpR, Ecy and NRRT paralleled by a small and insignificantly increased Mry of the exposed specimens. Our results thus demonstrate that only a combination of mortality and sublethal biomarkers was able to characterise an exposure-related stress syndrome. The suite of biomarkers described here was also able to detect and resolve a pollution-induced stress syndrome at an early stage of pollution. The contamination level of the sediments was assessed using chemical analysis, by estimating bioavailability and by computing a toxic pressure coefficient (TPC) to account for potential additive effects of different pollutants. The observed biological responses were consistent with the contamination levels in sediments, suggesting a high potential for using Protozoa in bioassays to assess environmental risk in coastal marine systems.