Plastics have transformed everyday life; usage is increasing and annual production is likely to exceed 300 million tonnes by 2010. In this concluding paper to the Theme Issue on Plastics, the Environment and Human Health, we synthesize current understanding of the benefits and concerns surrounding the use of plastics and look to future priorities, challenges and opportunities. It is evident that plastics bring many societal benefits and offer future technological and medical advances. However, concerns about usage and disposal are diverse and include accumulation of waste in landfills and in natural habitats, physical problems for wildlife resulting from ingestion or entanglement in plastic, the leaching of chemicals from plastic products and the potential for plastics to transfer chemicals to wildlife and humans. However, perhaps the most important overriding concern, which is implicit throughout this volume, is that our current usage is not sustainable. Around 4 per cent of world oil production is used as a feedstock to make plastics and a similar amount is used as energy in the process. Yet over a third of current production is used to make items of packaging, which are then rapidly discarded. Given our declining reserves of fossil fuels, and finite capacity for disposal of waste to landfill, this linear use of hydrocarbons, via packaging and other short-lived applications of plastic, is simply not sustainable. There are solutions, including material reduction, design for end-of-life recyclability, increased recycling capacity, development of bio-based feedstocks, strategies to reduce littering, the application of green chemistry life-cycle analyses and revised risk assessment approaches. Such measures will be most effective through the combined actions of the public, industry, scientists and policymakers. There is some urgency, as the quantity of plastics produced in the first 10 years of the current century is likely to approach the quantity produced in the entire century that preceded.
Keywords:
plastic, polymer, debris, endocrine disruption, phthalates, waste management
Many of the current applications and the predicted benefits of plastic follow those outlined by Yarsley and Couzens in the 1940s. Their account of the benefits that plastics would bring to a person born nearly 70 years ago, at the beginning of this ‘plastic age’, was told with much optimism:
It is a world free from moth and rust and full of colour, a world largely built up of synthetic materials made from the most universally distributed substances, a world in which nations are more and more independent of localised naturalised resources, a world in which man, like a magician, makes what he wants for almost every need out of what is beneath and around him (Yarsley & Couzens 1945, p. 152).
The durability of plastics and their potential for diverse applications, including widespread use as disposable items, were anticipated, but the problems associated with waste management and plastic debris were not. In fact the predictions were ‘how much brighter and cleaner a world [it would be] than that which preceded this plastic age’ (Yarsley & Couzens 1945, p. 152).
This paper synthesizes current understanding of the benefits and concerns surrounding the use of plastics and looks to challenges, opportunities and priorities for the future. The content draws upon papers submitted to this Theme Issue on Plastics, the Environment and Human Health together with other sources. While selected citations are given to original sources of information, we primarily refer the reader to the discussion of a particular topic, and the associated references, in the Theme Issue papers. Here, we consider the subject from seven perspectives: plastics as materials; accumulation of plastic waste in the natural environment; effects of plastic debris in the environment and on wildlife; effects on humans; production, usage, disposal and waste management solutions; biopolymers, degradable and biodegradable polymer solutions; and policy measures.
Degradable polymers have been advocated as an alternative to conventional oil-based plastics and their production has increased considerably in recent decades. Materials with functionality comparable to conventional plastics can now be produced on an industrial scale; they are more expensive than conventional polymers and account for less than 1 per cent of plastics production (Song et al. 2009). Biopolymers differ from conventional polymers in that their feedstock is from renewable biomass rather than being oil-based. They may be natural polymers (e.g. cellulose), or synthetic polymers made from biomass monomers (e.g. PLA) or synthetic polymers made from synthetic monomers derived from biomass (e.g. polythene derived from bioethanol) (WRAP 2009). They are often described as renewable polymers since the original biomass, for example corn grown in agriculture, can be reproduced. The net carbon dioxide emission may be less than that with conventional polymers, but it is not zero since farming and pesticide production have carbon dioxide outputs (WRAP 2009). In addition, as a consequence of our rapidly increasing human population, it seems unlikely that there will be sufficient land to grow crops for food, let alone for substantial quantities of packaging in which to wrap it. One solution is to recycle waste food into biopolymers; this has merit, but will ultimately be limited by the amount of waste food available.
Biopolymers that are designed to breakdown in an industrial composter are described as ‘biodegradables’ while those that are intended to degrade in a domestic composter are known as ‘compostable’. There are benefits of these biodegradable materials in specific applications, for example, with packaging of highly perishable goods where, regrettably, it can be necessary to dispose of perished unopened and unused product together with its wrapper. Song et al. (2009) show experimentally that degradation of biodegradable, as opposed to compostable, polymers can be very slow in home composters (typically less than 5% loss of biomass in 90 days). Degradation of these polymers in landfills is also likely to be slow and may create unwanted methane emissions. Hence, the benefits of biopolymers are only realized if they are disposed of to an appropriate waste management system that uses their biodegradable features. Typically, this is achieved via industrial composting at 50°C for around 12 weeks to produce compost as a useful product.
Some biopolymers, such as PLA, are biodegradable, but others such as polythene derived from bioethanol are not. A further complication is that degradable, as opposed to biodegradable, polymers (also called ‘oxo-biodegradable’, ‘oxy-degradable’ or ‘UV-degradable’) can also be made from oil-based sources but as a consequence are not biopolymers. These degradable materials are typically polyethylene together with additives to accelerate the degradation. They are used in a range of applications and are designed to break down under UV exposure and/or dry heat and mechanical stress, leaving small particles of plastic. They do not degrade effectively in landfills and little is known about the timescale, extent or consequences of their degradation in natural environments (Barnes et al. 2009; Teuten et al. 2009). Degradable polymers could also compromise the quality of recycled plastics if they enter the recycling stream. As a consequence, use of degradable polymers is not advocated for primary retail packaging (WRAP 2009).
There is a popular misconception that degradable and biodegradable polymers offer solutions to the problems of plastic debris and the associated environmental hazards that result from littering. However, most of these materials are unlikely to degrade quickly in natural habitats, and there is concern that degradable, oil-based polymers could merely disintegrate into small pieces that are not in themselves any more degradable than conventional plastic (Barnes et al. 2009). So while biodegradable polymers offer some waste management solutions, there are limitations and considerable misunderstanding among the general public about their application (WRAP 2007). To gain the maximum benefit from degradable, biodegradable and compostable materials, it is, therefore, essential to identify specific uses that offer clear advantages and to refine national and international standards (e.g. EN 13432, ASTM D6400-99) and associated product labelling to indicate appropriate usage and appropriate disposal.
Our intention when preparing this Theme Issue was to focus on the science surrounding all aspects pertinent to plastics, the environment and human health. There are some omissions from the volume, such as input from social scientists on how best to convey relevant information to influence littering behaviour, consumer choice and engagement with recycling. These omissions aside, to be of greatest value the science herein needs to be communicated beyond a purely scientific audience (see recommendations in ). This is in part the role of a Theme Issue such as this, and the final invited contribution to the volume examines the science–policy interface with particular reference to policy relating to plastics. Shaxson (2009) considers this interface from the perspectives of industry, the scientist and the policymaker. She emphasizes the need for policy relating to plastic to weigh societal and economic benefits against environmental and health concerns. This is a diverse subject area that will require a range of policies to focus at specific issues, including polymer safety, material reduction, reuse, recycling, biopolymers, biodegradable and compostable polymers, littering, dumping and industrial spillage. There are a range of appropriate measures (National Research Council 2008) including information and recommendations (e.g. WRAP 2009), regulations (such as the Canadian Government restrictions on BPA in baby bottles), taxes (such as land fill tax, which incentivizes the diversion of waste from landfill to recycling), standards (such as EN 13432 covering compostable plastics) and allocation of funds for research, innovation and capacity building. However, the diversity of issues leads to an equally complex policy environment. In the UK, for example, there is not one, but many relevant policy interfaces and numerous policies. These activities are shared among several government departments, driven by national pressures, international obligations and European directives. In such a complex environment, even robust and clearly delivered information from the scientific community does not always have the most appropriate effects on the policy process.
Shaxson presents evidence from case studies on policies relating to plastic litter in the marine environment and land-based plastic waste. She indicates that many plastic-related policy issues fall into what are defined as unstructured or badly structured problems—in essence, problems that lack consensus and clarity in the relevant policy question and in some cases lack clarity in the relevant knowledge base to inform any decision. Shaxson suggests such circumstances will require a reflexive approach to brokering knowledge between industry, scientists and policymakers, and that scientists will need to be prepared to make and facilitate value judgements on the basis of best evidence. From a UK perspective, she advocates using the science within this volume to help develop a ‘Plastics Road Map’, similar to the recently completed Milk and Dairy Road Map (Defra 2008) to structure policy around plastics, the environment and human health and suggests that this be facilitated by appropriate and broad debate among relevant parties.
Looking ahead, we do not appear to be approaching the end of the ‘plastic age’ described by Yarsley and Couzens in the 1940s, and there is much that plastics can contribute to society. Andrady & Neal (2009) consider that the speed of technological change is increasing exponentially such that life in 2030 will be unrecognizable compared with life today; plastics will play a significant role in this change. Plastic materials have the potential to bring scientific and medical advances, to alleviate suffering and help reduce mankind's environmental footprint on the planet (Andrady & Neal 2009). For instance, plastics are likely to play an increasing role in medical applications, including tissue and organ transplants; lightweight components, such as those in the new Boeing 787, will reduce fuel usage in transportation; components for generation of renewable energy and insulation will help reduce carbon emissions and smart plastic packaging will no doubt be able to monitor and indicate the quality of perishable goods.
In conclusion, plastics offer considerable benefits for the future, but it is evident that our current approaches to production, use and disposal are not sustainable and present concerns for wildlife and human health. We have considerable knowledge about many of the environmental hazards, and information on human health effects is growing, but many concerns and uncertainties remain. There are solutions, but these can only be achieved by combined actions (see summary ). There is a role for individuals, via appropriate use and disposal, particularly recycling; for industry by adopting green chemistry, material reduction and by designing products for reuse and/or end-of-life recyclability and for governments and policymakers by setting standards and targets, by defining appropriate product labelling to inform and incentivize change and by funding relevant academic research and technological developments. These measures must be considered within a framework of lifecycle analysis and this should incorporate all of the key stages in plastic production, including synthesis of the chemicals that are used in production, together with usage and disposal. Relevant examples of lifecycle analysis are provided by Thornton (2002) and WRAP (2006) and this topic is discussed, and advocated, in more detail in Shaxson (2009). In our opinion, these actions are overdue and are now required with urgent effect; there are diverse environmental hazards associated with the accumulation of plastic waste and there are growing concerns about effects on human health, yet plastic production continues to grow at approximately 9 per cent per annum (PlasticsEurope 2008). As a consequence, the quantity of plastics produced in the first 10 years of the current century will approach the total that was produced in the entire century that preceded.
We are indebted to James Joseph and Claire Rawlinson in the editorial office and Jessica Mnatzaganian in the journals production office at the Royal Society. Without their guidance and patience this volume would not have been possible. We also thank Dr J. P. Myers, Environmental Health Sciences, for his help in preparing text for the section on Green Chemistry.
One contribution of 15 to a Theme Issue ‘Plastics, the environment and human health’.
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