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RSC Advances Review pesticide, has a signicantly higher sorption rate for PLA and polybutylene succinate (PBS) when compared with PE, PP, PVC and polystyrene (PS).159 The diversity of the dynamics of sorp- tion–desorption of co-contaminants to MPs derived from bio- based polymers may play a signicant role in their bioaccessibility and consequent toxicity to organisms. However, there is currently no information on whether the bio- accessibility of co-contaminants adsorbed to biobased MPs will be enhanced or reduced. The release of leachates from the polymer matrices can be of signicant importance (see Section 4) and lead to further meaningful toxicological effects in organisms, which can be chemical-led rather than particle induced. For instance, Boyle et al.160 demonstrated that PVC-MPs release lead (Pb) additives to freshwater media, which were bioavailable [the fraction of an ingested compound that is absorbed by the digestive system150] and toxic to zebrash. In seawater, leachates from common fossil fuel-based polymers signicantly enhanced toxicity to sea urchin embryos (PVC products) and clam larvae (PE plastic bags),130 while inhibiting the settlement of barnacle cyprids [higher toxicity on leachates from PVC, low-density polyethylene (LDPE) and PC].128 In the work of Bejgarn et al.,119 the only in vivo assessment of the effects of leachates from biobased plastics in a marine organism, the authors showed that PLA did not induce any toxic effects in Nitokra spinipes at tested concentrations. However, substances released from a biodegradable plastic bag (50% corn starch and 50% aliphatic polyester) showed increased toxicity aer weathering processes,119 indicating that environmental stressors such as the UV irradiation (weathering) on plastic materials can play an important role in the leachates release and toxicity to organisms. In the assessment of ecotox- icological effects of leachates from biobased plastics in fresh- water organisms, Zimmermann et al.161 showed that PLA leachates (extracted from a MP concentration of 122 mg L1) did not induce any toxicity on reproduction nor in the survival of adult water eas. However, in parallel treatments, water eas exposed directly to MPs that did not incur any extraction procedure showed a decrease in their reproduction rate (EC50 1⁄4 122 mg L1).161 These results indicate that particles may induce physical effects beyond chemical toxicity, even though at an order of magnitude highly exceeding environmental relevant concentrations. In an in vitro assessment from the same authors,148 leachates from PLA showed a strong baseline toxicity, similar to leachates from PVC and polyurethane (PU), but once more at concentrations exceeding expected ones in the environment. These early assessments on the toxicity of leach- ates from biobased plastics indicate that even though indi- vidual additives may not be considered toxic for aquatic organisms (see Section 4, Table 1), complex mixtures of addi- tives released in the environment may induce toxicity, which may be enhanced by weathering processes of the materials. Currently the effects of leached chemicals from the matrices of biobased products on aquatic organisms are largely unknown, and this topic requires further investigation to provide high quality data for the assessment of the realistic environmental risks of biocomposites. 5. Improvement of the performance of biocomposites used in marine applications 5.1 Composites and biocomposites design and fabrication The European directive (2008/98/EC) on waste management denes the role of the designer as fundamental to the devel- opment of a more eco-sustainable product. The load/ degradation scenario of an object needs to be addressed a pri- ori to dene the structural design boundary conditions. Preliminary design can be improved by detailed numerical analysis to obtain relevant safety factors during the overall design process.61 Aer the design stage, the mechanical performance of biocomposite materials is dependent on manufacturing techniques. There is a need to investigate conventional and unconventional manufacturing processes to limit misalignments of the bres, waviness, formation of voids and interfacial problems that lead to porosities and bre/matrix debonding. A systematic tuning of the manufacturing parame- ters should always be considered, knowing that mechanical properties can drop very quickly due to aws and void content.162 For example, a 1% voids inclusion within conven- tional composites can reduce tensile, exural and interlaminar shear strengths by 10 to 20%. The following section aims to highlight the latest advances in the fabrication of bio- composites for marine applications. In particular, some aspects related to design, surface coatings, material treatments, and alternative manufacturing processes are highlighted for future biocomposites development. 5.2 Designconsiderations Both engineering and nature are adept at creating functional components, sometimes achieving the same result in terms of mechanical properties, but adopting different design strategies. Biological composites and usual engineering materials can be grouped together under the concept of architectured mate- rials.163 From an engineering point of view an architectured material is an object, made of organised matter that responds to external stimuli to perform certain functions. The way in which material is organised and combined with other materials provides their functions and effectiveness. It is up to scientists, whether they are chemists, mechanical, electrical or process engineers to cooperate to develop new structural designs and improvements of biocomposites through micro- and macro- structures. The majority of so called ‘semi-green’ or ‘green’ composites have maximum tensile strengths and stiffness in the ranges of 100–200 MPa and 1–4 GPa,164 restricting their use for primary, load-bearing components. One way to overcome lower performance is to use designs based on the repetition of a unit cell (or scaffolds) of known geometry and properties. In this way the properties of the resulting materials can be measured according to different boundary conditions, then compared to nite element methods (FEM) and predictive modelling since properties of the unit cell are known a priori.165 In addition, investigation to compare manufactured structures 32932 | RSC Adv., 2021, 11, 32917–32941 © 2021 The Author(s). 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