Plastic pollution of the aquatic environment is one of the major environmental issues of our times: the World's plastic consumption is ever increasing, and, due to poor waste management, most of this endless stream of plastic enters the waterways, ultimately reaching the seas and oceans. Marine litter is a very visible issue, but there is more than meets the eye: in fact, plastic items in the aquatic environment undergo a process of degradation, due to biotic and abiotic agents, originating millions of tiny fragments – microplastics. These microplastics have been shown to accumulate inside biota, and to adsorb persistent pollutants present in the water, potentially transferring them to the organisms ingesting the microplastics. Substituting traditional with biodegradable plastics (particularly in single-use applications) has been proposed as a solution to the plastic pollution problem. But is this a good idea for the marine environment? This study proposes an experimental plan aiming to answer this question, by comparing the performance in three main areas of two biodegradable polymers, polylactic acid (PLA) and polyhydroxyalkanoate (PHA), to the oil-based polyethylene (PE). The comparison focuses on: degradation in the marine environment and microplastic formation; persistent pollutant adsorption on microplastics; and toxicity on two important marine species (the mussel, M. edulis, and sea bass, D. labrax) of both microplastics and microplastics contaminated with pollutants.