Alberto Mantovani and Francesca Baldi – Istituto Superiore di Sanità in Rome, Italy, explain to us how the global issue of climate change is modifying our views on risks to the environment with comment on the main effects of chlorinated pesticides
Our world is facing climate change (some people call them “climatic crisis”) that are modifying our views on environmental risks. For instance, climate change is increasing the levels of exposure of aquatic organisms to UV radiation by reducing the thickness and duration of snow and ice cover, melting of glaciers and permafrost and increases in heavy precipitation. While UV radiation directly damages the health of environmental organisms, less recognised effects include the formation of micro-plastic pollutants, with bioaccumulation in food chains and increased toxicity of contaminants, such as pesticides and polycyclic aromatic hydrocarbons.
“Legacy” pollutants are manmade chemicals that can persist in the environment after banning and end of discharging. Top concern legacy pollutants have been produced at great amounts, bioaccumulate in food chains and show toxicological properties that can affect the current, as well as the next generations, such as endocrine disruption. The chlorinated pesticides identified as Persistent Organic Pollutants (POPs) under the Stockholm Convention share such features (2001 and successive updates): the most well-known is DDT, but the long list includes dieldrin, endosulfan, hexachlorobenzene, lindane and hexachlorocycloexanes and several others. Due to their lipophylicity, measuring such chemicals in adipose tissues and eggs of animals can indicate anthropogenic influences in remote ecosystems, e.g., the Arctic.
Despite their persistence, chlorinated pesticides are not eternal; after the ban, their presence in the environments and food chains have shown slow but consistent declining trends over decades, as stated, e.g., by their assessments as contaminants in feeds by the European Food Safety Authority. Moreover, a portion of pollutants is trapped (or “scavenged”) within some environmental comparts, such as permafrost.
Long-range atmospheric transport is a major pathway for delivering POPs to the water and terrestrial environments; atmospheric patterns can be altered and possibly increased, by global warming, which calls for updates of the models to predict and monitor POPs travelling. Snow and permafrost melting will provide an output of newly bioavailable molecules: deposition into sediments of rivers and seas will lead to uptake by food webs, including those relevant to our diet.
As melting accelerates under climate warming, the release of trapped chemicals may also increase, likely following a seasonal pattern, with possible pulses: the seasonal patterns of melting processes may also alter the exchange rates between air and seawater. Warming and continued decline in sea ice are also likely to result in shifts in food web structure, which in their turn, would modulate the deposition of pollutants in seafood, mainly large fatty fishes but also sediment-dwelling organisms such as shellfish. The direction and extent of the above-mentioned modifications are currently difficult to assess and more data on a range of trophic levels are needed to estimate the possible increased exposure of human diet, either globally and for specific populations, e.g., communities from the Arctic and sub-Arctic regions.
The potential for exposure is not the same for all chlorinated pesticides. For instance, DDT metabolites and hexachlorobenzene feature among the most persistent and bioaccumulating substances of the group; lindane is more toxic but definitely less persistent than its manufacturing by-product beta-hexachlorocycloexane.
One might say that the release of banned pesticides is the least of concerns related to climate change.
However, let’s consider the implications: from a social and economic standpoint, an increased presence in food and feedstuffs of toxic substances, for which legal limits exist, is a source of national and international alerts, calling for increased controls of raw materials by enterprises and public bodies, disrupting global trade and weakening the confidence of consumers. In an unlucky scenario, the widespread and increasing presence of pesticides residues in important and vulnerable food sources (e.g., seafood, milk from ruminants on pasture) might pose unpleasant choices to risk managers, such as salvaging food availability while weakening food safety standards. What would be the actual health risks? Significant uncertainties do exist. The current tolerable limits in feeds and foods for chlorinated pesticides are based on outdated data sets: after the ban, only limited research has been carried in order to update health-based guidance values. Yet, according to available data from independent research, the main effects of chlorinated pesticides include disruption of steroid and thyroid hormonal axes, altered development of neurobehavioral and/or immune functions, altered metabolism in liver and adipose tissue. Such effects are of top concern for the international risk assessment community and since the last decade, a major effort is ongoing to update toxicological testing to characterise such effects more properly.
In practice, we currently have a fairly accurate view of how many residues of chlorinated insecticides are in foods and feeds and also increasing data on human biomonitoring; conversely, we have many uncertainties to assess whether such exposure levels might pose a risk to the general population or vulnerable groups (unborn children, toddlers). Last, but not least, the mixture issue must be considered. These pollutants often occur together, in the same matrices (e.g., lipid-rich foods); while the individual levels are usually very low, many substances share toxicological modes of action and effects: for instance, DDT, its metabolite p.p. DDE and the persistent by-product of lindane, beta-hexachlorocyclohexane, all may exert estrogen-like actions. The available evidence call for a new risk assessment, where individual substances are grouped based on their toxicological properties. The release of currently trapped persistent pollutants may, therefore, be a real issue.
So what do we do? The global action against emissions that increase climate change must go on and for now, some specific actions can be envisaged: targeted monitoring of ecosystems for a timely identification of trends; updating of guidance values in environments, foods and feeds with the support of new research and modelling; considering the mixture issue for risk assessment; targeted monitoring of the most vulnerable food chain to prevent health risks. It may be useful to set “alert” (calling for attention and investigation in depth) and “action” (calling for risk mitigation) levels for the most prevalent chlorinated pesticides (including metabolites and by-products): this could facilitate the (sometimes-uneasy) job of risk managers.
In the area of Anthropocene, the assessment of the impact of environmental changes must include the assessment of their effects on presence, persistence, kinetics and toxicity of chemicals spread by human activities into the environment. The assessment has to be pursued with a “One Health” approach, linking ecosystems, feed and food production chains and human health.
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Istituto Superiore di Sanità – Roma, Italy
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