The Concern About POPs

The Concern About POPs

Of all the pollutants released into the environment every year by human activity, persistent organic pollutants ( POPs) are among the most dangerous . POPs are either used as pesticides, in industry, or generated unintentionally as by-products of various industrial/combustion processes.

POPs are toxic, causing an array of adverse effects, including death, disease, and birth defects among humans and animals . Effects may include cancer, allergies and hypersensitivity, damage to the central and peripheral nervous systems, reproductive disorders, and disruption of the immune system. Some POPs are also considered to be endocrine disrupters , which, by altering the hormonal system, can damage the reproductive and immune systems of exposed individuals as well as their offspring; endocrine disrupters can also have developmental and carcinogenic effects.

These stable compounds can persist for years or decades before breaking down . They circulate globally through a process known as the ‘ grasshopper effect’ . POPs released in one part of the world can, through a repeated (and often seasonal) process of evaporation and deposition, be transported through the atmosphere to regions far away from the original source.

POPs are also problematic because they concentrate in living organisms through bioaccumulation . Though not soluble in water, POPs are readily absorbed in fatty tissue where concentrations can become magnified by up to 70,000 times the background levels . Fish, predatory birds, mammals, and humans are high up the food chain and so absorb the greatest concentrations. When they travel, POPs travel with them. As a result of these two processes, POPs can be found in people and animals living in remote regions such as the Arctic, thousands of kilometers from any major POPs source.

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Grasshopper effect

Persistent and volatile pollutants – including certain pesticides, industrial chemicals and heavy metals – evaporate out of the soil in warmer countries where they are still used, and travel in the atmosphere toward cooler areas, condensing out again when the temperature drops. The process, repeated in “hops”, can carry them thousands of kilometres in a matter of days.

Canada’s cold climate puts it at the receiving end of this process, with measurable concentrations of DDT, toxaphene, chlordane, PCBs, and mercury found in both the Great Lakes and the Arctic. Ingested by fish and other species, the chemicals travel up the food chain, accumulating in the fatty tissue of predatory animals, including people. Some of these pollutants are linked with developmental and reproductive impacts on wildlife, and may have similar effects on humans. The consequences may be serious for Native people in the North, because traditional food sources are being contaminated.

Environment Canada scientists measure and monitor concentrations of these toxic chemicals to learn more about how they are exchanged among air, land and water. Similar studies being carried out in Russia – both by Canadian scientists and by Russian colleagues using analytical equipment Canada donated several years ago – are yielding useful data for global comparisons, and providing additional insight into the impact on shared resources such as the Arctic Ocean.

An important breakthrough has been the recent development of a technique for identifying the age and source of some of these chemicals. Certain persistent organic pollutants (POPs) have right- and left-handed molecules that are mirror images of one another. While new formulations tend to have equal amounts of both, differences in the way these molecules are metabolized by microbes and enzymes in the biological system change this ratio as the chemical ages. The tracers show the grasshopper effect quite clearly. By separating them, it should be possible to determine how long they have been travelling, and whether they have spent time on land or in water. By matching them with weather records, scientists should also be able to find out where the chemicals are from.

In the figure below, approximately 10% of the highest cases of p,p’-DDT (a component of DDT) arriving at two Integrated Atmospheric Deposition Network stations on the Great Lakes are tracked back to potential sources in the south using weather records.

Information obtained through these and other Canadian studies is the foundation of international negotiations for global bans on certain of these toxics. Canada is playing a leadership role in these efforts. They include the recent negotiation of protocols for POPs and heavy metals under the United Nations Economic Commission for Europe – to be signed this June – and other initiatives are now being launched with other parts of the world through the United Nations Environment Programme. Canada’s work in the Great Lakes and Arctic provides powerful evidence that persistent toxic pollutants are travelling long distances, and the efforts have raised global awareness of an important issue.

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Grasshopper effect serves pollutants onto plates of Arctic peoples

“I spent the first 10 years of my life travelling in dogsled, fishing for food,” says Sheila Watt-Cloutier, an Inuk from Kuujjuaq, Nunavik, in Northern Quebec, Canada.

In a matter of a few decades, that livelihood has dramatically changed. Environmental challenges such as the presence of persistent organic pollutants the fish and animals the Inuk eat, and melting snow and ice threaten the health and food security of the roughly four million who call the Arctic home.

“Knowing that the Arctic is the air conditioner of our planet, and that it is breaking down at an unprecedented speed, it seems to me that it would be the business of the world to keep us alive,” says Watt-Cloutier.

Persistent organic pollutants include pesticides, industrial chemicals and hazardous by-products of combustion. Specific health effects of these pollutants consist of cancer, allergies and hypersensitivity, damage to the central and peripheral nervous systems, reproductive disorders, and disruption of the immune system.

“Persistent organic pollutants can be transported over large distances through air and water—this is clearly evidenced by what we see happening in the Arctic, a region which many people consider as a pristine wilderness,” says Jan Dusik, Principal Adviser for Strategic Engagement for the Arctic and Antarctic at UN Environment.

In addition, these pollutants can move across vast distances from the southern hemisphere to the northern hemisphere by what is called the “ grasshopper effect ”. This means that they evaporate with warm air and return to earth with rain and snow in the colder areas of the globe.

Therefore, persistent organic pollutants released in one part of the world can, through a repeated (and often seasonal) process of evaporation and deposit, be transported through the atmosphere to regions far away from the original source . Over the course of several years, they approach the Arctic in a series of seasonal jumps.

As global warming increases, chemicals volatilize more readily into the atmosphere, increasing their presence in the air and other matrices.

Traditional butchering. Photo by Reuters

Persistent organic pollutants are present in animals through a process of bioaccumulation and biomagnification , and levels are particularly high in animals at the top of the food chain, as predators eat the contaminated tissue of other species. Concern has therefore been raised about the potential health effects on human diets which rely on traditional marine food resources such as whale, seal, walrus and fish.

The link between chlorinated persistent organic pollutants and fatty acids in humans is well known. Adverse effects of persistent organic pollutants include disruption of the immune system , and cardiovascular diseases that are frequent in Greenland Inuit. The pollutants are also known to accumulate in breast milk.

Given the cultural importance and health benefits of these traditional foods to the diets of Indigenous Peoples like the Inuit, dealing with the issue of contamination requires a risk-benefit approach to balance the benefits with the risks of exposure. The Arctic Council’s Arctic Monitoring and Assessment Programme recommends this analysis be carried out at the local level in close consultation with affected communities.

Moreover, new harmful links between these pollutants and the lives of indigenous Arctic people are being unearthed.

“A slew of new compounds including stain repellents, flame retardants and pharmaceuticals are showing up in the Arctic . There are, so far, about 150 such compounds,” says Robert J. Letcher , one of the authors of a new study on pollutants in the Arctic .

Bear in Greenland

The Stockholm Convention

The Stockholm Convention , which entered into force in 2004, sets out a range of control measures to reduce and, where feasible, eliminate persistent organic pollutants releases, including unintentional emissions. The Convention, which was negotiated under the auspices of UN Environment, also aims to ensure the sound management of stockpiles and waste consisting of or containing these pollutants.

The Stockholm Convention acknowledges that, “Arctic ecosystems and indigenous communities are particularly at risk because of the biomagnification of persistent organic pollutants and that contamination of their traditional foods is a public health issue”.

The Stockholm Convention, which now includes 182 countries as of November 2018, attempts to limit the spread of persistent organic pollutants, but they are still around.

“While much has been done to limit introduction of persistent organic pollutants into the environment globally, the fight to totally eliminate such pollutants, which disproportionately affect the health of people and fauna living in the Arctic, must go on,” says Jan Dusik.

People living in the Arctic also have to face a range of other challenges including climate change, which melts ice and snow and further affects the entire food chain. Plastic pollution, including by microplastics, is building up in the region. Carbon dioxide is also acidifying the Arctic Ocean.

Although people who live in the Arctic continue to feel the impact of persistent organic pollutants, because these persistent substances are still harming people as well as the environment, Sheila Watt-Cloutier sees the Stockholm Convention as a tremendous victory-and one to build upon.

“We [Inuit] are able to move mountains,” she says. “We should lead the world on the climate change battle.”

For further information please contact Jan Dusik .

www.unenvironment.org

What Is the Global Distillation Effect?

may be, their bodies have been shown to have one of the highest levels of toxic pollutants of any creature, even though they live in remote locations away from major manufacturing and urban centres [1] . More than 200 different chemical compounds can be found in any polar bear impacting their immune system and even cognitive skills [2] .

But how did those chemicals end up there in the first place?

Polar bears may live in the Arctic, far away from most sources of pollution, but due to the global distillation effect, pollutants find their way even to the most remote regions of the world such as the Arctic, and enter local ecosystems in different ways. This does not only affect polar bear populations but also other species living in the Arctic including local indigenous populations.

How does the global distillation effect happen?

The global distillation effect is the process by which certain substances are transported from warmer to colder regions. This happens when chemicals and other pollutants that are released into the environment evaporate and in the form of vapour are then transported in colder areas where the vapour condenses and the pollutants are deposited as toxic rain or snow.

Global distillation explains why relatively high concentrations of pollutants have been found in the Arctic and in the bodies of animals and people who live there, even though most of the chemicals have not been used in the region.

The process does not always involve a direct flow of pollutants from warmer regions to colder ones; pollutants may condense and then become vapour again in different places depending on climate conditions. This is why the phenomenon is also called the “grasshopper effect”.

It is also important to keep in mind that the global distillation effect is not a one-way process: atmospheric currents can carry chemicals in both directions, towards both colder and warmer regions of the planet.

But there is a net transfer of chemicals to colder regions such as the Arctic and mountain tops, because colder climates favour the deposition of pollutants in the environment. In addition, pollutants are more likely to degrade and be eliminated from our environment in warmer regions [3] .

Persistant organic pollutants are to blame

Whether a substance can undergo this process primarily depends on its unique physical and chemical characteristics. Research has shown that pollutants most likely to behave in this way fall into the category of chemicals called persistent organic pollutants.

Persistent organic pollutants, or POPs, are chemicals that can stay in the environment for long periods of time, can interact with soil, water and air, can accumulate in living organisms including humans and are toxic to both humans and wildlife [4] . POPs are regulated under the UN Stockholm Convention which has regulated pesticides such as DDT and chemicals such as PCBs.

The health impacts of persistent organic pollutants

The global distillation effect is therefore particularly concerning as the properties of the chemicals that are transported through this process can cause severe health problems to the ecosystem, from smaller organisms like benthic organisms to top predators like polar bears and humans.

POPs can cause a variety of diseases ranging from cancer and damage to the central and peripheral nervous systems to reproductive disorders and disruption of the immune system that can have a transgenerational effect, affecting both parent and offspring [4] .

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Geophysical Research Letters

The significance of the grasshopper effect on the atmospheric distribution of persistent organic substances

Meteorological Institute, University of Hamburg, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

Max Planck Institute for Meteorology, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

Meteorological Institute, University of Hamburg, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

Max Planck Institute for Meteorology, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

[1] Slowly degradable, semivolatile organic compounds (SOCs) may undergo more than one volatilization‐transport‐deposition cycle through the atmosphere (multi‐hopping). The significance of this process for the potential for long‐range transport (LRT) is addressed for the first time. We use a multicompartment model which in turn is based on a general circulation model. The results suggest that both transport by single‐hopping and multi‐hopping contribute significantly to LRT of DDT and γ‐HCH (lindane) and to accumulation in high latitudes. A larger fraction of the molecules transported by multi‐hopping than of the molecules transported by single‐hopping is deposited to the world’s oceans. Multi‐hopping prevails in the boundary layer far from the source regions. However, single‐hopping contributes an almost equal amount to the deposition of DDT and γ‐HCH in the Arctic.

Citing Literature

Supporting Information

Filename Description
grl19476-sup-0001-t01.txtplain text document, 671 B Tab‐delimited Table 1.
grl19476-sup-0002-t02.txtplain text document, 852 B Tab‐delimited Table 2.

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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Geophysical Research Letters

The significance of the grasshopper effect on the atmospheric distribution of persistent organic substances

Meteorological Institute, University of Hamburg, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

Max Planck Institute for Meteorology, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

Meteorological Institute, University of Hamburg, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

Max Planck Institute for Meteorology, Centre for Marine and Atmospheric Sciences (ZMAW), Hamburg, Germany

[1] Slowly degradable, semivolatile organic compounds (SOCs) may undergo more than one volatilization‐transport‐deposition cycle through the atmosphere (multi‐hopping). The significance of this process for the potential for long‐range transport (LRT) is addressed for the first time. We use a multicompartment model which in turn is based on a general circulation model. The results suggest that both transport by single‐hopping and multi‐hopping contribute significantly to LRT of DDT and γ‐HCH (lindane) and to accumulation in high latitudes. A larger fraction of the molecules transported by multi‐hopping than of the molecules transported by single‐hopping is deposited to the world’s oceans. Multi‐hopping prevails in the boundary layer far from the source regions. However, single‐hopping contributes an almost equal amount to the deposition of DDT and γ‐HCH in the Arctic.

1. Introduction

[2] Semivolatile organic compounds (SOCs) may undergo more than one cycle through the atmosphere (multi‐hopping or ‘grasshopper effect’), because their vapor pressure is such that ambient temperatures allow for atmospheric condensed as well as gaseous states and low degradability prevents them from rapid breakdown at the ground (land or ocean) upon atmospheric deposition. The potential for several volatilisation‐transport‐deposition cycles makes the global environmental exposure particularly difficult to assess. Unlike in the case of single‐hopping pollutants, such as the classical air pollutants (e.g., sulfur dioxide), it is not only the spatial and temporal emission patterns, the atmospheric oxidants distribution and the actual weather which determine the distribution and fate, but, additionally, the ground conditions and their spatial and temporal variabilities i.e., the retaining capacity influenced by temperature, water availability and organic matter content come into play. Furthermore, also the spatial substance usage patterns may contribute to the horizontal and vertical gradients of the substances’ dispersion. The role of these various influences on distribution and fate remains to be elucidated.

[3] It has been hypothesized that accumulation in cold environments (‘cold condensation’) and large‐scale fractionation of similar substances are controlled by the substance’s vapor pressure [ Wania and Mackay, 1993 ]. It is well established that large‐scale atmospheric transport to high latitudes is quite efficient. E.g., in high latitudes of the northern hemisphere the ‘Arctic haze’ phenomenon is caused by rapid transport (within a few days in late winter and early spring) of polluted air from mid latitudes into the European Arctic [ Shaw and Khalil, 1989 ].

[4] Global distribution of chemicals was studied by multimedia (multicompartment) models which account for the volatilisation tendencies of SOCs and for the retaining capacities of ground compartments under simplifying scenarios, such as temporally invariant and/or zonally averaged temperatures, depositions and transport efficiencies [ Scheringer and Wania, 2003 , and references therein]. The meridional gradients predicted are consistent with the cold condensation hypothesis. As the statistics and geographic distribution of transport patterns are not captured by these models, the grasshopper effect can better be addressed by a multicompartment model which encompasses an atmospheric transport model.

2. Methodology

2.1. Model Description and Substance Properties

[5] We used for the first time a multicompartment model which comprises an atmosphere general circulation model (AGCM), to study the large‐scale transport and distributions of SOCs. The processes in the model have been described previously [ Lammel et al., 2001 ; Semeena and Lammel, 2003 ]. Ground compartments (soil top layer and vegetation surfaces) and the ocean surface mixed layer are coupled as single‐layer compartments to the AGCM. Inter‐ and intra‐compartmental mass exchange processes of SOCs comprise volatilization, transport, atmospheric wet and dry deposition, transfer to the deep sea, dissolution in cloudwater, and partitioning to aerosol particles (adsorption only, following Junge). Air‐sea exchange is parameterized following the two‐film model. The depth of the ocean mixed layer is spatially resolved and seasonally varying. SOC transfer to the deep sea is represented as consequence of the seasonal variation of the mixed layer depth: The substances dissolved in the lower part of the mixed layer are considered to be lost to the deep sea when the mixing depth decreases in spring [cf. Lammel et al., 2001 ]. Suspended particulate matter in ocean is neglected. For the here reported simulations the model was used with the AGCM ECHAM, version 5 [ Roeckner et al., 2003 ] and with modifications regarding dry deposition of gaseous molecules (now resistance scheme) and the aerosol module (now dynamic sources, microphysics and size‐dependent sinks using a preliminary version of the aerosol sub‐model HAM) [cf. Stier et al., 2004 ].

[6] Two SOCs with very different properties are studied, p,p′‐DDT (1,1,1‐trichloro‐2,2‐di‐(p‐chlorophenyl)‐ethane) and γ‐HCH (γ‐hexachlorocyclohexane or lindane). Because of environmental and human health risks these insecticides were banned from agricultural usage in most countries between 1972 and 1992 (DDT) or many countries since 1990 (γ‐HCH). Due to their persistence and LRT potential, these substances are ubiquitous in the global environment, with downward trends in air and other compartments in recent years.

[7] The physico‐chemical properties and environmental degradation rates for DDT and γ‐HCH for this study (Table 1) are taken from the literature [cf. Rippen, 2000 ; Klöpffer and Schmidt, 2001 ]. DDT has a higher affinity to soils and a lower vapor pressure and water solubility than γ‐HCH. As some substance properties are not known, assumptions had to be made on the temperature dependencies (degradation in ocean, soils and on vegetation assumed to double per 10 K temperature increase) and degradation rate coefficients for DDT (0 in ocean, kOH (2) = 1 × 10 −13 cm 3 /molec/s). No degradation of the aerosol particle‐bound molecules and of those dissolved in cloudwater was assumed. The degradation rates in soils were also adopted for the vegetation compartment.

γ‐HCH DDT
Water solubility (298 K) [mg l −1 ] 7.4 3.4 × 10 −3
Enthalpy of solution ΔHsol [kJ mol −1 ] 27 27
Saturation vapor pressure p [Pa] (298 K) 2.9 × 10 −3 3.4 × 10 −5
Enthalpy of vaporization ΔHvap [kJ mol −1 ] 115 115
Octanol‐water partitioning coefficient Kow [−] 3.98 × 10 3 1.55 × 10 6
OH reaction rate constant kOH [cm 3 molec −1 s −1 ] 1.9 × 10 −13 1.0 × 10 −13
ΔE/R of OH reaction [K −1 ] −1710 −1300
Degradation rate in ocean water kocean [s −1 ] (298 K) 2.3 × 10 −8 0
Degradation rate in soil ksoil [s −1 ] (298 K) 2.0 × 10 −8 4.1 × 10 −9
  • a Data sources are available through the authors.

2.2. Model Experiments and Substance Entry

[8] Ten year simulations of a test run and a control run were performed. In the test run, the SOC is precluded from re‐volatilisation upon atmospheric deposition to land surfaces or the ocean by setting the re‐volatilization rate to zero (single‐hopping transport mode). The mass balance is still closed. In the control experiment, the SOC is allowed to undergo re‐volatilisation (multi‐hopping transport mode) according to substance properties and local conditions (or degradation in the ground compartment). The fraction transported by multi‐hopping (FMH) of the SOC is accessible by subtraction of the test run output fields from the control run output fields. The temporal, vertical and horizontal resolutions of the runs were 30 min, 19 levels (within 1000–10 hPa) and ca. 2.8° × 2.8° (i.e., T42), respectively. The scenarios describe 1980 usage of the chemicals. The geographic distributions of the application of the two insecticides in the world’s agriculture are based on country‐level FAO data scaled with the crop density distribution (1° × 1°) [ Semeena and Lammel, 2003 ]. In 1980, γ‐HCH and DDT were applied in all major agricultural economies, except for several European countries, Australia, Brazil, Canada and the US which had phased out DDT by that time. The latitudinal center of gravity (COG, as derived from a zonal distribution) [ Leip and Lammel, 2004 ] of DDT application was at 25°N. The global usage patterns of γ‐HCH in 1980 can be considered as representative of most globally used pesticides and will not deviate tremendously from the emission pattern of industrial chemicals (latitudinal COG at 39°N). Without a geographic differentiation, we assume application to take place continuously, Jan–Dec over ten years, day and night. The applied amounts are assumed to be distributed 20% to soil and 80% to vegetation surfaces. The SOCs enter the air by later volatilization from vegetation surfaces and soils.

[9] The spatial pattern of volatilization of the substance transported by single‐hopping is determined by the usage pattern only, while the spatial pattern of volatilization in the control run reflects the superposition of usage, deposition and degradation patterns. The model experiment is artificial as it neglects some temporary SOC reservoirs (land and sea ice, vegetation, except its surfaces) and does not represent any historic situation. Model‐predicted air concentrations were compared to observations at remote sites in the 1980s and discrepancies mostly within a factor of three and up to one order of magnitude were found.

[10] Due to the fast turnover in the atmosphere and vegetation surfaces compartments, quasi‐steady‐state is reached in these compartments within 3–6 years, while the soil and ocean compartments are still filling, because of the large capacities and relatively slow turnover. In the 10th year of the control run, 3, 53, and 43% of the global burden of DDT and 7, 40, and 53% of γ‐HCH are stored in air, on terrestrial surfaces (vegetation plus soils) and in the ocean surface layer, respectively. The vertical distributions in the atmosphere stabilize after 5 years from the initialization of the simulation (Figure 1). The burden of γ‐HCH residing in the stratosphere reaches quasi‐steady‐state 1–2 years later than in the atmosphere as a whole (Figure 1b). This is in accordance with the understanding that the age of air is 1–5 years at 100–10 hPa and mostly Manzini and Feichter, 1999 ]: 15% of each γ‐HCH and DDT are found in heights corresponding to

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