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Ng CA, von Goetz N. The global food system as a transport pathway for hazardous chemicals: the missing link between emissions and exposure. Food is a major pathway for human exposure to potentially hazardous chemicals [ National Research Council NRC ] and may contain a wide variety of chemicals that enter at many points along the value chain. Chemicals are used to increase efficiency and yield during production pesticides, hormones, antibiotics , may be applied to increase stability surface treatments, preservatives, packaging ingredients and compatibility emulsifiers during processing, or may inadvertently end up in food because they are present in the environment, particularly if they are persistent under environmental conditions.
Thus, even chemicals that have been largely banned, such as dichlorodiphenyltrichloroethane DDT and polychlorinated biphenyls PCBs , continue to be regularly detected in foods Schecter et al. Chemicals that are intentionally applied to food are relatively strictly regulated in most countries [e. MRLs have also been set for a small number of environmental pollutants e. As the complexity of our food system grows, it becomes increasingly difficult to consistently monitor the presence of contaminants in food.
As set out in the landmark report, Exposure Science in the 21st Century , exposure science will play a critical role in supporting policies that ensure the safety and sustainability of the food supply NRC However, in order to use exposure data to craft control and regulatory measures, exposures must be adequately linked to the sources of the chemical s in question, and in our current food system, sources can be far removed both geographically and via many processing steps from the site of exposure. Our food system is increasingly globalized. Food trade increased in value from billion USD in to 1.
At the same time, trade has shifted from fresh foods and agricultural raw materials to more complex, processed food products Ercsey-Ravasz et al. At each of these steps, the number, identity, and concentration of chemicals may also be influenced by environmental and regulatory differences between countries and regions. One approach to understanding chemical fate in foods and subsequent human exposure is through the use of models.
Two types of models are typically developed for this purpose: bioaccumulation models and human exposure models. Bioaccumulation models attempt to trace chemical accumulation from the environment through the food web into different foods Streit Although sophisticated models exist that combine the global distribution of chemicals as driven by processes in the air, water, and soil with key predator—prey interactions Breivik et al.
Human exposure models, in contrast, often rely on measured levels in the foods of interest, which are combined with consumer data on consumption, body weight, age, and sex. At present, the most sophisticated models for human exposure to chemicals via food also take into account the packaging Oldring et al. Although a few countries have instituted mandatory country-of-origin labeling, it usually only applies to specific sectors e.
Therefore, food origin is typically not addressed within human exposure models. Because bioaccumulation models focus on chemical transfer from the source to the surrounding environment and local organisms without incorporating human-mediated transport i. What is missing between the two approaches is an explicit consideration of the industrial food web through which the majority of people now obtain their food.
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In this work, we argue that a fully integrated approach is needed to investigate how the distribution of chemicals in the environment influences the exposure of consumers within the context of the modern food system. Only by explicitly accounting for the sources of different chemicals in foods can we predict human exposure to the myriad of health-relevant chemicals they contain, despite limited analytical resources, and conduct sound risk assessments and effective risk abatement strategies.
Here, we present a conceptual framework to further the science of human exposure to chemicals via one of the most important, and complex, exposure pathways—the global industrial food web. The distribution of chemicals in the environment depends on their emissions, physicochemical properties, and environmental transport processes. Thus, chemical emissions into environmental compartments may be determined by levels of industrial activity e.
Once released, the chemical properties themselves—in particular, volatility, partition coefficients, and degradation rates—are key.
Finally, mechanisms of transport, such as advection with wind or ocean currents, shape the way contaminants move on a global scale. During crop production or growth of livestock, intentionally applied chemicals include pesticides, growth stimulants, and therapeutic drugs. For example, because of climatic conditions, insecticide use in Spain is much more common than in Germany or Switzerland, where more herbicides are used EuroStat At the same time, environmental contaminants—in particular, persistent pollutants—may enter foods by transfer from air, water, or soil.
DDT was banned from agricultural use in most industrialized countries in the s and s Rogan and Chen POPs generated within the technosphere, such as PCBs, may enter the environment through different pathways.
Although PCBs were banned in the s, they continue to be released from electrical transformers and building materials produced before the ban Kohler et al. This continued release gives rise to regional hotspots throughout the world He et al. Because of the movement of these currents, longitudinal dispersion of chemicals is generally faster than latitudinal transport.
Transport across the equator, for both air and water currents, is particularly slow.
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Therefore, global-scale chemical fate models typically assume relatively rapid distribution of chemicals within latitudinal bands and much slower transport across the equator Scheringer Several multimedia bioaccumulation models have been developed to link chemical emissions and environmental distribution with accumulation in human food chains.
Other authors subsequently extended the model by linking it to a more complex fate model CoZMo-POP2 to consider the effects of non—steady-state emissions patterns Breivik et al. However, in both cases it was assumed that concentrations in the diet came from the local environment of the exposed population.
The USEtox model Rosenbaum et al. However, food trade flows are not explicitly included in this model, and the description of the environment has no spatial resolution Henderson et al. One of the best examples of combining a spatially explicit chemical fate model with food production and consumption data is the study by MacLeod et al. The authors showed that a spatially explicit approach is essential for chemicals for which the ingestion pathway is dominant that is, for which the chemicals accumulate from the air into food and are subsequently ingested and for those chemicals with relatively low environmental mobility, where the proximity of the site of food production to the source of the chemical becomes more important such as benzo[ a ]pyrene.
However, that study assumed that all foods were produced in North America, and the authors did not account for any regional variation in the foods consumed. Therefore, models are already in place that can address spatially explicit emissions and chemical fate and bioaccumulation. However, these models fail to account for the transport of chemicals via food trade, which may follow pathways that differ from the distribution of chemicals in the environment via natural processes like advection with air and water.
Additional data or methods of parameterization will be needed to adequately link these models to spatially resolved descriptions of consumption. Once a chemical has gone through the processes of emission, environmental distribution, and accumulation in a given food matrix, it enters, together with the food, another complex set of processing steps embodied in the industrial food system, which, being global, may occur in different places.
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Over the past 30 years, there has been a marked shift in traded commodities away from fresh foods and basic agricultural staples towards more meat, processed foods, and high-quality, off-season, or exotic foods Ercsey-Ravasz et al. Global food trade has more than doubled in the last three decades, supported in large part by increasing wealth, with rises in trade relationships and trade value following increasing GDP, and outpacing both global population and global crop yield Dalin et al.
With this globalization and industrialization, food chains are becoming longer and more complex. For processed foods, cross-contamination can occur at any step, and production origin data alone are not sufficient Kruse Given this complexity, it is extremely difficult to determine the origin of particular foods LeBlanc et al.
Unlike environmental chemicals that can be traced back to the origin of foods, the use of food additives a broad category that includes nutritional additives, processing agents, preservatives, and sensory agents can not only vary according to the region where processing takes place owing to regional legislation, culture, or know-how but also depend on product type and company procedures. Some toxicologically relevant compounds, such as polycyclic aromatic hydrocarbons PAHs , are imparted to foods during processing methods such as smoking or adding smoke flavor Gomaa et al.
Such chemical transfer can depend on the specific procedures used but is also dependent on packaging and shelf life. For example, acrylamide levels in coffee are lower when vacuum roasting is used than when conventional roasting methods are employed Anese et al.
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Packaging itself can release substances such as fluorinated compounds or plasticizers Bhunia et al. These substances can also be introduced by specific processing steps such as the handling of meat with PVC gloves Tsumura et al. Thus, for effective modeling of chemical fate in food, the processing, packaging, and storage of foods need to be considered. A number of models are available for the optimization of food processing or storage; examples include models for the melting and crystallization of fats Himawan et al.
Exposure models that take into account processing-induced changes to chemicals in food are scarcer. For pesticides, where the influence of processing on pesticide concentrations must be evaluated as part of the registration procedure [ European Parliament EP ], a fate model was proposed for pesticides applied to potatoes; this model includes a fixed processing factor and the effects of storage in the calculation of daily intake Juraske et al. In addition, processing factors are specific to a single substance of interest and do not account for other substances formed during processing.
The U. However, even if these approaches work well for packaging, they remain somewhat isolated because only migration of chemicals from packaging material is considered: Moerman and Partington showed that often, the same chemicals are also released from processing containers Moerman and Partington and therefore add to the concentration in a packaged food.
Hence, for all steps in the food system production, processing, storage, and packaging , efforts are underway to understand which chemicals can contaminate food and under what circumstances, but the models are not comprehensive. For some chemicals, the integration of all steps is not necessary e. For those chemicals, only an integrated assessment can deliver suitable information for designing the most effective intervention strategies or for extrapolation of analytical data.
The origins of many foods have changed in recent years, with developing countries exploiting new markets in Europe and North America e. At the same time, food markets have become more integrated and global and are now dominated by a few large international trading companies Hazell and Wood Current exposure assessments for food-borne chemicals mostly rely on the combination of chemical concentrations in food with data on the consumption of foods by a certain population [ European Food Safety Authority EFSA , ].
Concentrations for a limited number of chemicals are available from the open literature and dedicated surveys. This assumption is mostly valid, but the food basket analyzed needs to be representative for the studied population, requiring large data sets specific to a region.
Because substance concentrations vary among regions owing to environmental factors [e. Consequently, data gaps or inconsistent data sets are very common. Nevertheless, because of global trade, the same food may be consumed in different regions.