PROTOCOL: Plastics in the food system: Human health, economic and environmental impacts. A scoping review

As of 2017, the running total of virgin plastics produced, since mass production of synthetic polymers began less than 70 years ago, was 8,300 million metric tons (Geyer, Jambeck, & Law, 2017); a fact that reflects the versatility of this remarkable group of materials which serve a vast range of important functions across various industries and sectors. However, there is growing evidence that the proliferation of plastic production and a reliance on these materials in the world economy, particularly in single-use or disposable forms, is leading to detrimental environmental and ecosystem impacts at local and global scales, with potentially negative implications for human health (Barboza, Dick Vethaak, Lavorante, Lundebye, & Guilhermino, 2018; UNEP, 2018). Packaging accounts for ~40% of all plastics produced since the 1950s, of which 41% is used specifically for food or beverages (Schweitzer et al., 2018). This statistic refers primarily to the latter stage of the food system in which food products are processed, marketed and transferred to consumers. However, plastics are also used extensively at other stages of the food system, for example in agricultural mulch, fishing nets and crates for transporting produce. Taken as a whole, the food system is likely to account for a much larger proportion of the world's reliance on plastics than its share in the use of plastic packaging alone. Within the food system, plastics play an important beneficial role in food transportation, preservation, hygiene and safety, increasing the lifespan of foods, the length of value chains and contributing to food and nutrition security (Claudio, 2012). Therefore, it is important that these beneficial functions are not overlooked in the public and policy debates concerning this material, its uses and impacts. However, recent decades have seen a correlation between substantial increases in plastic food packaging and upward trends in food waste (Schweitzer et al., 2018), suggesting that while plastic packaging can preserve food, in itself this might not be sufficient to reduce wastage. Recent calls to action on plastics are driven in part by observations that the widespread utilisation of single-use or disposable plastics, coupled with poor recycling rates and waste management is contributing to visible build ups of plastic across natural environments and oceans around the world. To illustrate this flow, of the total 6300 Mt of plastic waste produced by 2015, only 9% had been recycled or repurposed, with the remaining 91% either incinerated, placed into landfill or leaking into the natural environment (Geyer et al., 2017). The extent of the impacts of plastic pollution is still largely unknown and remains to be adequately explored. Among the evidence now beginning to emerge is that which reveals an increasing presence of microplastics, nanoplastics and synthetic polymers in marine food chains, food products and the air we breathe (Karami et al., 2017; Lusher, McHugh, & Thompson, 2013; Smith, Love, Rochman, & Neff, 2018; Tyree & Morrison, 2018). Not surprisingly, negative consequences for human and planetary health are also now being hypothesised and investigated (Barboza et al., 2018; Smith et al., 2018). These interlinking concerns around sustainability come in addition to toxicology research pointing towards potentially harmful effects that chemicals or additives used in plastics may pose for humans (Gray, Rasanayagam, Engel, & Rizzo, 2017; Rancière et al., 2015) as well as the suggestion that plastic packaging could be encouraging unhealthy diets (Relton, Strong, & Holdsworth, 2012). On a broader scale, it can be said that plastics are also linked to global warming and climate change, as around 99% of plastic monomers are derived from fossil fuels, the supply and demand for which contributes to greenhouse gas emissions (GHGs). Yet in agricultural production, evidence also suggests that plastic sheeting can deliver environmental benefits such as reduced GHG emissions (Petersen et al., 2013). Taking such trade-offs into account, there are growing calls for improved data and evidence to better understand and address the various effects of plastics, whilst developing alternatives — where necessary — for the functions they serve (Efferth & Paul, 2017; The Lancet Planetary Health, 2017). A major challenge for research investigating the role and impacts of plastics is to establish causal links between specific sectoral or industry flows and the impacts — both beneficial and harmful — that they might be having on natural environments, human health and wellbeing. Without a better understanding of these linkages, underpinned by a comprehensive and robust scientific evidence base, attempts to preserve the benefits and mitigate the harmful effects of plastics will be hampered. For this reason, we will conduct a systematic scoping review, looking at the impacts of plastics that are used specifically in or across the food system. This will be conducted in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Extension for Scoping Reviews, which advises that scoping reviews 'may examine the extent (that is, size), range (variety), and nature (characteristics) of the evidence on a topic or question' (Tricco et al., 2018). To do this, we will explore the food system's constitutive sub-sectors — from 'farm to flush' — to examine the extent (volume of research), range (variety of exposure-outcome relationships) and nature (study characteristics) of evidence for the impact of food system plastics on human health, food security and economics at the individual or household level and the environment. We characterise the exposure as plastic, including chemicals specifically emanating from the plastic exposure that are essential to its fundamental structure or functionality (i.e., phthalate plasticisers, or chemicals such Bisphenol A) used at any point, for any purpose, explicitly within the food system. Categories of plastics are defined by the Society of the Plastics Industry (SPI) resin identification codes and will include: polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, low-density polyethylene, polypropylene, polystyrene or styrofoam, miscellaneous plastics (includes: polycarbonate, polylactide, acrylic, acrylonitrile butadiene, styrene, fibreglass and nylon) (Sustainable Packaging Coalition, 2017). In accordance with the Food and Agricultural Organisation of the United Nations (FAO) we define the food system as 'the entire range of activities involved in the production, processing, marketing, consumption and disposal of goods that originate from agriculture, forestry or fisheries, including the inputs needed and the outputs generated at each of these steps' (Food and Agriculture Organization of the United Nations, 2013). Plastic in the food system is found in many different forms. For example, in agriculture plastic is used for mulching, growing tunnels, greenhouses and irrigation systems. In fishing, plastics are used in nets, lines and traps. Food and produce processing, storage and distribution use plastic in the form of packing crates, wrapping and food contact equipment. Packaging forms a crucial part of sales, marketing and consumption of goods. In addition, plastic food shopping bags, plastic crockery and cooking equipment are widely available at the consumer level. Finally, at the end of the food system with food disposal and waste management, plastic is used in pipes, compost storage containers, or in the black plastic bags thrown into landfill. The durability of plastic means that its use within the food system may have both short and long term effects. For example, plastic mulch used in agriculture may increase crop yields in the short term, but when the plastic begins to break down in the soil, it may have an impact on plant growth or the soil microbiota for years to come (Steinmetz et al., 2016). Estimates of biodegradation times in marine environments for different plastics range from around 20 years for a plastic shopping bag, to 50 years for a styrofoam cup, to 450 years for a plastic and to years for plastic fishing lines & 2018). 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