ABC: microAlgae, Bivalves and Crustaceans as model organisms to assess transfer and effects of emerging contaminants through a marine food chain

Thousands of different natural and synthetic chemical compounds continuously enter aquatic ecosystems. Some of these compounds are emerging contaminants that include for instance agrochemicals, pharmaceuticals and personal care products, nanoparticles, per- and polyfluorinated compounds and plasticizers. The present PhD thesis evaluated the effects of BPA analogues - a group of emerging contaminants - currently used to replace bisphenol A (BPA) which is largely used in polycarbonate plastic production, as well as in the production of thermal papers and food packaging. These new compounds are considered safer than BPA, even if they share a similar chemical structure. In this regard, the first chapter of the thesis (Chapter One) is a comprehensive review concerning BPA analogues, their presence in aquatic ecosystems and their biological effects on marine species. The first aim of this research project was to assess the effects of BPA analogues on three different marine model species with a relevant ecological and economic value, and representative of three trophic levels, namely the microalgae Phaeodactylum tricornutum as a primary producer, the clam Ruditapes philippinarum as a primary consumer and the crab Carcinus aestuarii as a secondary consumer. In this project, we tested three different BPA analogues: bisphenol AF, bisphenol F and bisphenol S, which are the currently main substitutes for BPA. The effects of a mixture of these three BPA analogues were also evaluated as a more realistic scenario. The selected concentration was 300 ng/L for each single compound, while the mixture included 100 ng/L of each of the three components (300 ng/L in total). The second aim of this research project was to improve knowledge concerning the potential bioaccumulation and transfer of BPA analogues through the marine food chain. For this reason, a brief marine food chain was simulated in laboratory conditions using the previously mentioned species. This project has been divided into two parts. In the first part (Chapter Two), each of the previously described marine species has been individually exposed to the three BPA analogues and their mixture. In the second part (Chapter Three), two trophic experiments were conducted, exposing clams or crabs to BPA analogue-contaminated diets. In detail, the lower trophic level was subject to waterborne exposure to BPA analogues and then provided as food for the upper trophic level. Several biomarkers regarding the antioxidant system, oxidative damage, immune system, epigenetic mechanisms and physiology were measured in each experiment. In addition, we evaluated the bioaccumulation of BPA analogues in the three species after exposure to contaminated seawater or contaminated food. Indeed, it is known that aquatic organisms can bioaccumulate contaminants from water or sediments and may transfer these contaminants to predators that forage on them. Overall, the results obtained (Chapter Four) demonstrate that BPA analogues can cause toxic effects on all three tested species. In particular, BPA analogues were able to cause ROS-mediated toxicity increasing oxidative stress and oxidative damage in all the species, following both waterborne and foodborne exposures. Moreover, we observed alterations in the immune system and some physiological parameters. Such results agree with those of initial studies and demonstrate that these compounds can cause alterations similar to those already reported for BPA. As for bioaccumulation, it was observed that BPA analogues were bioaccumulated mainly following waterborne exposure. Lastly, the mixture of the three BPA analogues seems to be the worst experimental condition tested, in which synergic interactions between the three components probably occurred. In conclusion, based on the results reported in this thesis, it seems that BPA analogues are not harmless substitutes for BPA, being able to affect several biological parameters in the three marine species tested.