Temperature and salinity effects on cadmium toxicity on lethal and sublethal responses of Amphibalanus amphitrite nauplii.

The official protocol of an ecotoxicological assay employing larvae of the crustacean Amphibalanus amphitrite as a model organism has recently been published by the Italian regulatory authority UNICHIM. Such assay is now one of the applicable tests for water quality assessment under Italian law. While specific temperature and salinity values are recommended by ecotoxicology bioassay protocols for test set up, little information is available on response changes in case of parameter variations. In particular, information is totally lacking for this innovative model organism. Under the standard test protocol, 20°C and 37‰ temperature and salinity, respectively, are required to be set in A. amphitrite bioassay. In order to evaluate the environmental relevance of the test, laboratory experiments simulating the effect on larval responses due to variations of temperature and salinity expected in field collected samples were carried out. The effect of temperature and salinity changes on different end-points, involving increasing sensitivity levels, has been investigated, with and without the presence of cadmium nitrate, Cd(NO3)2, as a reference toxicant, to determine the possible interactions between pollutants and environmental parameters fluctuations. Three end-points - mortality, immobilization, and swimming speed alteration - were measured in order to evaluate the impact of a wide range of temperature (5, 10, 15, 20, 25, 30, 35, 40°C) and salinity values (10, 20, 30, 37, 40, 50, 60, 70‰) on response variation after 24 and 48h of exposure. For each parameter, a Non-Effect Range (NER) - namely the limit values within which no effect related to environmental parameter changes is observed - has been defined. For both parameters, NER resulted to be wider for the less sensitive end-points - such as mortality and immobilization - and for shorter exposure time (24h). Later, the same end-points have been evaluated by exposing the same organisms to a reference toxic compound, Cd(NO3)2 (0, 0.2, 0.4, 0.8, 1.6, 3.2mg/L), within the detected NER both for temperature and salinity. LC50 and EC50 values have been calculated for each end-point after 24 and 48h. Cadmium toxicity was shown to decrease at higher salinity values and increase at higher temperatures. Obtained results offer a better bioassay characterization, and the possibility of a more realistic estimation of ecotoxicological assessments performed on field collected samples. Further studies are needed, especially to investigate the effects of simultaneous salinity and temperature changes on end-points.