Plastic litter is encountered in aquatic ecosystems across the globe, including polar environments and the deep sea. To mitigate the adverse societal and ecological impacts of this waste, there has been debate on whether ‘biodegradable' materials should be granted exemptions from plastic bag bans and levies. However, great care must be exercised when attempting to define this term, due to the broad and complex range of physical and chemical conditions encountered within natural ecosystems. Here, we review existing international industry standards and regional test methods for evaluating the biodegradability of plastics within aquatic environments (wastewater, unmanaged freshwater and marine habitats). We argue that current standards and test methods are insufficient in their ability to realistically predict the biodegradability of carrier bags in these environments, due to several shortcomings in experimental procedures and a paucity of information in the scientific literature. Moreover, existing biodegradability standards and test methods for aquatic environments do not involve toxicity testing or account for the potentially adverse ecological impacts of carrier bags, plastic additives, polymer degradation products or small (microscopic) plastic particles that can arise via fragmentation. Successfully addressing these knowledge gaps is a key requirement for developing new biodegradability standard(s) for lightweight carrier bags.

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The evidence-policy interface is important for delivery of sustainable development policy. We examine one specific form of knowledge brokering, the temporary placement of academic research scientists in UK policy arenas. We argue that successful knowledge brokerage depends on establishing social processes critical to effective knowledge exchange. Merely facilitating proximity of academic and policy actors is insufficient. Cultural understandings are key conditions for knowledge brokerage in this context. Academics who are outsiders to the policy process need to become credible insiders in order to be effective in bringing an outsiders perspective into play. Background Research and policy impact Interest in creating impact from research has strengthened over several decades. Scientific collaborations between policy and academia increased during the 1970s and 80s (Denis & Lomas 2003). The need for effective science-policy interfaces became even more important in the face of the 'perfect storm' of climate change, resource depletion and food insecurity (Foresight, 2011). In the UK a further driver is the inclusion of 'impact' as a quality criterion in university research department quality assessment (REF 2014 1). Sustainable development (SD) is a particularly challenging context in which to consider policy impact. A Thomson Reuters Web of Science publications database search of article titles including the term 'sustainable development' from 2000-2015 revealed that SD is a concept employed by a vast range of experts and practitioners. For example, SD principles are considered in articles on hydrogeology, climate change, transport, steel-making, building design, energy, mining, education, food security energy and SD policy instruments. SD publications also cover a wide scalar range, from the modelling of blast-furnace operations to global population issues. Moreover, these diverse directions suggest a high degree of interdisciplinary and transdisciplinary policy and evidence activity (e.g. Brandt et al. 2013, Simon & Schiemer 2015). Although not all of this SD research activity aims to deliver knowledge at the policy interface, there is clearly a major challenge to find effective mechanisms that direct SD evidence into the policy world. The complex, value-laden and uncertain nature of SD has led to an emphasis on stakeholder involvement as key to the production of robust knowledge (Lang et al. 2012, Cornell et al. 2013, Hedlund-de Witt 2014). Less attention has been paid to how this knowledge informs policy and it is this latter aspect that forms the focus of this paper.