Marine sediment can accumulate persistent hydrophobic organic contaminants, such as polychlorinated biphenyls, polycyclic aromatic hydrocarbons, dichloro-diphenyl-trichloroethane and heavy metals. The maintenance dredging operations for coastal ports and waterways consist mainly in removing sediments to improve the ship traffic. Sediment-bound pollutants can pose major concerns not only for marine environment but also for human health, showing combined effects that are still largely unknown on sediment-dwelling organisms, as well as the change in toxicity on weathering. New guidelines for the disposal of dredged materials have been prepared internationally and they can be used to classify sediment samples regarding their potential for toxicity and to identify contaminants. In the present work, the possible toxigenic effects of sediment on marine organisms were investigated using the sea urchin Paracentrotus lividus Lmk, which is worldwide considered as key model species to study marine environmental contamination. The first step consisted in the setting-up of a microcosm, in which adult P. lividus were incubated for two months in the presence of contaminated sediments, detecting chemical, physical and microbiological parameters. Eggs and sperma were then collected from these sea urchins exposed to the polluted sediments and then fertilized, checking three significant checkpoints in the sea urchin embryonic development by microscopic observations (i) fertilization success ii) first mitotic division (two blastomeres) iii) pluteus stage. Molecular effects was also detected on these embryos, following by Real Time qPCR the expression of fifty genes involved in different functional processes. Previous results showed a harmful effects of polluted marine sediment on P. lividus embryos. The proposed project represents a new initiative because to our knowledge microcosm studies are not available to study possible toxigenic effects of polluted sediment on marine invertebrates. Moreover, it can contribute to understand the cellular mechanisms that underlie the possible responses of benthic organisms to contaminated sediment exposure.