PROTOCOL: Plastics in the food system: Human health, economic and environmental impacts. A scoping review
Year: 2019
Type: article
Abstract: 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 bottle and up to 600 years for plastic fishing lines (Statistica & Grant, 2018). This means that the use of plastics within the food system may continue to have an effect on the environment, human health and well-being, long after their intended function has passed. In this sense, the responsibility for these plastic products, and the impact that they have, must also endure. Please note: For the purposes of this review, we use 'impacts' and 'outcomes' interchangeably. human health. individual/household food security and economic factors. the natural environment. Given the interdisciplinary nature of this review, we expect heterogeneity among the specific outcomes considered in the literature, and therefore heterogeneity in the associated mechanisms and pathways to impact. For this reason, our logic model (Figure 1) encapsulates the major anticipated relationships between exposures and outcomes whilst also providing the necessary flexibility for more defined pathways to be informed by the literature. Logic model for this systematic scoping review on the impact of plastics used within the food system on human health, individual and household food security and economic factors and the natural environment [Color figure can be viewed at wileyonlinelibrary.com] To maintain clarity, the three ultimate impact domains are considered as distinct outcome areas, though we acknowledge that the three domains are interlinked and often interdependent (Pan American Health Organization, 2013). We reflect these bi-directional relationships in the 'Broader Interactions' of Figure 1. The logic model depicts the relationship between the exposure (plastics in the food system) and the three ultimate impact domains. It encompasses potential direct outcomes (i.e., plastics in the food system directly leading to an ultimate impact domain), as well as intermediate outcomes that we reasonably hypothesise as being on the pathway to impact (i.e., plastics in the food system leading to impacts on a relevant population that exists prior to an ultimate impact domain). The grey arrows indicate these relationships that we seek to elucidate. Our assumptions regarding intermediate outcomes are stated in Figure 1. We anticipate that existing literature could describe a relationship between any of the listed plastic types, used at any point of the food system, and a direct impact on human health. Studies considering this relationship will have to include human populations, demonstrating either a harmful effect or association (including contributing to illness, disease, physical or congenital abnormalities or physiological disruptions), a beneficial effect or association (including protection or promotion of health and the prevention of illness or disease), or null effect or association. The arrow from exposure direct to human health demonstrates this element of our enquiry. Specific human health impacts that have been considered in the more general literature on plastics are intestinal damage and tissue abrasion from plastic particles themselves (Revel, Châtel, & Mouneyrac, 2018) and impacts via chemicals leached from the plastics on endocrine dysfunction, diabetes, and reproductive problems for example (Thompson, Moore, vom Saal, & Swan, 2009). In order to qualify for our scoping review, studies will have to demonstrate that the plastic, including chemicals leached from the plastic, originated from a specific human use within the food system, which is not always the case. Research has also considered the role of plastic food packaging in the protection of human health. For example, foodborne diseases (i.e., Salmonella) caused 420,000 deaths in 2010 (World Health Organization, 2015). Plastic packaging can help to protect human health by keeping food sterile and safe for consumption (Claudio, 2012), hence, studies showing a change in pathogen/bacterial content associated with food system plastics would be included in our review along the food safety pathway to human health. Mechanisms, by which the relationship between plastics and human health exist include ingestion, dermal exposure or inhalation of plastic or plastic chemical additives (Revel et al., 2018; Thompson et al., 2009). In addition to the direct impacts on human health, we anticipate that certain studies will demonstrate effects or associations with intermediate outcomes, inferring a subsequent impact on human health as shown in Figure 1. An important intermediate outcome, as mentioned above, is food safety or contamination (World Health Organization, 2019). Some studies may demonstrate the presence (or absence) of known harmful bacteria and toxicants in foodstuffs or drink as a final outcome. If a food system plastic is implicated in this effect on the food or drink then we will reasonably assume the potential for onward effects on human health. Similarly, we will also consider studies that assess the presence (or absence) of plastic particles or associated chemical additives in food or drink items as an intermediate step on the pathway to human health outcomes. Between food safety and human health, we will consider one further intermediate step — the presence of plastic particles or associated chemical additives within the human body. Studies may not be able to provide evidence of an associated disease state given the potential difficulties in studying this pathway from food system plastics to proven disease, however, we wish to include crucial intermediate outcomes so as to fully capture the range of potential human health impacts. Regardless of the specific outcome, each study will need to demonstrate that the plastic exposure originated specifically within the food system. As a hugely complex and intricate field, our consideration of the impacts of plastics on food security and economics is focused on selected factors that do not attempt to describe all potential pathways or relationships between exposures and outcomes. Our key interest in this impact domain is individual and household level food and nutrition security, and selected economic factors including changes in income, food expenditure, total expenditure and household food provisioning and food waste. We anticipate that literature could describe a direct effect or association with the use of plastics in the food system on these outcome areas, which could be of a beneficial or harmful nature (Figure 1). Due to the complexity of determinants of food and nutrition security and household economics, we are aiming to capture a range of intermediate outcomes that will be useful in examining this relationship. These include factors such as food availability, food access, food utilisation, food stability, crop or produce yield, livestock growth and welfare, soil contamination, soil temperature, soil moisture and nutrient content, nutrient leaching, pest or weed control, pesticide or fertiliser use, water-use, energy-use, plant growth, livestock health and other related beneficial, harmful or null effects or associations. We provide this range of outcome measures as a guide in advance of our screening process but a key focus of our scoping review is to gather the range of outcome indicators used in these fields and therefore we will remain flexible in updating our list of intermediate outcomes as we proceed. Our assumptions in linking these 'intermediate' outcomes to the impact domains are stated in Figure 1. For example, plastic plays an important role in hygiene and preservation of food, in both transport and storage phases of the food system (Claudio, 2012). Logically, if plastic increases the hygiene and safety of food, along with its ability to travel undamaged, and its capacity to be stored for longer durations in the home or locally (Our Food: Public Health Impacts of Packaging), then plastic may increase food availability by increasing trade and transport possibilities, increasing food access in hard-to-reach regions, and increasing food stability and food utilisation — since people can store, process and preserve food safely, guarding themselves against shortages. These components are known as the 'Four Pillars of Food Security' (Bokeloh, Gerster-Bentaya, & Weingärtner, 2005) and will be considered as 'intermediate' outcomes in accordance with general consensus on the building blocks of food security. We also include factors such as crop/product yield and post-harvest losses in the 'intermediate' outcomes under the assumption that changes at this level will have an effect on the income of agricultural families (Food and Agriculture Organization of the United Nations, 2014). Due to their multifactorial nature, we anticipate that studies may not follow through to looking at the impacts of plastic on household economy or income and therefore we include these intermediate outcomes in order to broaden our understanding of the potentially beneficial impacts of plastics. The health of the natural environment is multifaceted. It can be framed in terms of climate change, biodiversity, species health and population counts, ecosystem services and natural resources (OECD, 2003). We anticipate that literature could describe direct impacts of plastic used in the food system on any of these impact areas. This is shown in the Impact Domain column of Figure 1. The grey arrow indicates our line of exploration direct from exposure (plastics in the food system) to outcome (impact on the environment). Due to the range of indicators that can be used to describe the natural environment, pathways from exposure to outcome will be similarly diverse. An example of the direct impacts of plastic is harm caused to marine species through ingestion and entanglement, leading to tissue abrasion, gut obstruction, dermal wounds and deaths (Duncan et al., 2017; Law, 2017). It has also been shown that the most common plastics used in the world are releasing greenhouse gases, methane and ethylene, into the air when exposed to ambient solar radiation. This includes plastics on the land and in the sea, no longer in use, but contributing to gas emissions and therefore to climate change (Royer, Ferrón, Wilson, & Karl, 2018). However, plastic sheets used to cover manure in the agricultural sector have also been shown to reduce the amount of methane released into the atmosphere, demonstrating an environmentally protective effect (Petersen et al., 2013). We aim to capture any measurable environmental changes that occur as a result of food system plastics. As shown in Figure 1, we will also include impacts on the 'intermediate' outcomes such as the presence of plastic particles or chemical additives in soil, air and water (both freshwater and marine) samples. As essential components of the natural environment, any effects on soil, air or water constitute impacts on the environment in themselves. However, in our logic model, these are placed as 'intermediate' outcomes to their in broader of the natural environment, including and plant the of and We anticipate that studies may consider effects at this intermediate level being able to direct links to ecosystem damage or global warming for example, we wish to include in our review in order to capture the range of environmental impacts. we wish to include as an intermediate outcome, the presence of plastics or associated chemical additives within as we this as a crucial step on the pathway from plastic exposure to damage or disease These studies will have to demonstrate changes or a change in exposure in order to demonstrate impacts than and research of the impacts of our reliance on plastics has the 20 years and from different fields of study such as agricultural production, food materials environmental health and public health Due to increases in research and the of the the evidence for the impact of food system plastic is An understanding of the state of research across these specifically on the impact of plastics used within the food system, will for research that can to action and among food system In the research studies have been for example studies examining the impacts of plastic marine on of plastic mulch on crop yield and land of mulch on plant growth, and of plastic packaging on contamination et al., & 2018; & 2018; & 2018). These are a of the more recent and with many more it is essential that we build a and comprehensive of the research that has been in order to specific where there is a need for systematic reviews or policy literature reviews exist that at the impacts of plastics in marine environments, on the soil ecosystem and on human health & 2018; Law, 2017; et al., 2018). These reviews are crucial for on the impacts of plastics within specific outcome areas, plastic is considered and from different industry In addition, these reviews are not conducted We aim to to this understanding by linking impacts to a specific of plastic food system and its in order to increase we aim to broaden the consideration of impact domains to into account the human health, food security and economic and environmental impacts of plastics. not have impacts of specific uses of plastics in the food system, for example, a review of agricultural plastic on soil (Steinmetz et al., 2016). These of reviews are useful in to our understanding of the impacts of specific uses of plastics they are in both at the exposure and outcome and can not address our of the research on the impacts of plastics within the food system. The effect that our reliance on plastic is having on our and on our health has been a growing public in recent around the world are to reduce plastic across including the food and to disposal and recycling 2018). in the form of and on the production, and of bags have been the to such in in in and in 2018). A on plastic bags was in in 2017, with for and though the of this remains 2017). include a on plastic and for in the 2018). In order to that are in or the use of plastics, and are robust in from the plastics a is 2018). Our scoping review will to providing an for food system by a of existing evidence to the impacts — beneficial, harmful and null — of plastics used in the food system on human health, individual and household food security and economics and the environment. This scoping review is by the is the range and nature of the evidence on the human health, individual and household food security and economics, and environmental impacts of plastics used within the food system, including the extent to which research has been the range of exposure-outcome relationships considered and study in this field, since there evidence or to the impacts of plastics in the food system and where is there a need for further research or to conduct systematic reviews within the of the human health, individual and household food security and economics, and environmental impacts of plastics in the food The for our scoping review is informed by the Extension for Scoping Reviews (Tricco et al., 2018) and will examine the range and nature of the evidence for the impact of plastics used within the food system on human health, food security and economics at the individual or household and the environment. will be conducted in by and and by will be screening at and We an via an with screening to each along with example as to the of these and was through and We then of selected that by or by and on to after each on to the in and will be by including for will be of screening and rates will be through screening of at a a of is will then be with by for data purposes will be for and in the We will include all and studies point with a with or study of illness, or (including and (including and and studies in which the outcome is a of illness, or studies in which there is no group or will be as will studies that do not a of illness, or studies will be Studies of the impact of plastics in the food system on human health may to human in any including and in areas. Studies conducted between will be will be This is to into account the nature and of food coupled with increases in plastic production and associated waste since (Geyer et al., 2017). on can be found further in this will be Studies looking at the impact of plastics used in the food system on food safety, nutrient content and contamination or related outcomes will not include a human the study population will of food or drink samples. Studies investigating plastics used within the food system and their subsequent presence (or in the human may to human in any including and in areas. The will be to intermediate outcome Studies of the impact of plastics in the food system on individual or household food security and economics may to human at the individual or household level in any including and in areas, from to Studies that consider food security or economics on a broader such as at industry or will be Food availability, food access, food utilisation and food Studies of the impact of plastics used in the food system on the of food security may to human at the individual or household level in any including and in areas, from to Studies that consider these outcomes at a broader such as at industry or will be yield, soil contamination, soil temperature, soil moisture and nutrient content, nutrient leaching, pest or weed control, pesticide or fertiliser use, water-use, energy-use, plant growth, livestock health and other
Source: Campbell Systematic Reviews
DOI: 10.1002/cl2.1033
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: diamond
Award: G2810484033
OpenAlex ID: W2963649472