tag:theconversation.com,2011:/us/topics/polychlorinated-biphenyls-60237/articlesPolychlorinated biphenyls – The Conversation2022-10-17T17:38:56Ztag:theconversation.com,2011:article/1916512022-10-17T17:38:56Z2022-10-17T17:38:56ZSnow can spread and worsen the effects of pollutants in the environment<figure><img src="https://images.theconversation.com/files/488312/original/file-20221005-25-3ul0kh.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5068%2C3368&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Snow's physical properties mean that it can accumulate chemicals from the environment, including nanoparticles from car exhaust.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/snow-can-spread-and-worsen-the-effects-of-pollutants-in-the-environment" width="100%" height="400"></iframe>
<p>By October, autumn’s arrival brings with it the promise of winter — and snow. </p>
<p>And with it comes a quieter world, thanks to snow’s ability to absorb noise. This is because the spaces between snow crystals limit sound waves from bouncing around, creating a soundproofing effect. </p>
<p>Snow also adsorbs other matters it comes into contact with. Adsorption is when substances adhere on surfaces of materials (usually liquids or solids). The adsorptive properties of snow are the reason for some of its unique features, including its loosely bound crystalline porous structure with finely divided individually shaped flakes with large surface areas. </p>
<p>Its dynamic changes between ice and liquid states facilitate the absorption and release of pollutants, depending on prevailing surface and atmospheric conditions. </p>
<p>As an analytical material chemist with a research background in adsorption, I am interested in understanding how various materials — like snow — adsorb certain substances, like persistent organic and vehicular exhaust pollutants.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a pile of dirty snow at a street corner" src="https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">During winter, piles of snow like this one become a regular sight.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
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</figure>
<h2>Snow and pollution</h2>
<p>In the winter, snow becomes a superabsorbent for a wide range of <a href="https://doi.org/10.1016/j.scitotenv.2020.144136">pollutants</a>, including vehicular exhaust particulate matters, <a href="https://doi.org/10.1016/j.microc.2014.10.010">persistent organic pollutants</a> (POPs), trace metals and <a href="https://doi.org/10.1016/j.watres.2021.117493">chlorides from road salts</a>. </p>
<p>As snow subsequently moves around or melts, most of these pollutants find their way into underground pipes and aquifers. </p>
<p>POPs are some of the most dangerous pollutants because they remain active, lasting for several years within their environments before <a href="https://doi.org/10.1016/j.rsma.2022.102688">finally degrading into other chemical forms</a>. POPs, such as polychlorinated biphenyls, organochlorine pesticides and perflouroalkylated substances, have <a href="https://www.epa.gov/international-cooperation/persistent-organic-pollutants-global-issue-global-response">severe environmental impacts</a>. </p>
<p>They are classified under the <a href="https://www.canada.ca/en/environment-climate-change/services/canadian-environmental-protection-act-registry/historical/plans-policies/statement-pops-negotiations/backgrounder-persistent-organic-pollutants.html">Toxic Substances Management Policy as Track 1 substances in Canada, and are usually targeted for environmental removal</a>. </p>
<p>Just like POPs, very little is also known about how chemical pollutants from the exhausts of gasoline-powered vehicles interact with snow. </p>
<p>In Canadian cities, snow is moved around through various means, including snow melts, during plowing, on tires of vehicles or even soles of pedestrian shoes. During transportation, changes in ground surface pressure and ambient temperature can also affect the adsorption rates of chemical pollutants on snow. </p>
<p>Research conducted in Québec has shown that snow adsorbs significant amounts of organic pollutants and aerosol particles from exhaust pipes <a href="https://doi.org/10.1016/j.envpol.2017.01.082">within 30 minutes of exposure</a>. These researchers also observed the adsorption of aerosol particles with larger particulate sizes (approximately 50-400 nm) relative to smaller nanoparticles (less than 50 nm).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cars follow behind three snowplows on a highway" src="https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Snow carrying pollutants from road salts and vehicle exhausts can make its way into water systems.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Health effects</h2>
<p>POPs are introduced into the environment through agricultural and industrial practices. Most of them may have come from other anthropogenic sources but are unintentionally released from simple events like <a href="https://nepis.epa.gov/Exe/ZyPDF.cgi/70000AZL.PDF?Dockey=70000AZL.PDF">burning household waste</a>. </p>
<p>Burning industrial, municipal or medical wastes can also release dioxins and furans. <a href="https://www.atsdr.cdc.gov/ToxProfiles/tp94-c6.pdf">Toxaphene</a> and <a href="https://www.atsdr.cdc.gov/ToxProfiles/tp90-c6.pdf">hexachlorobenzene</a> could originate from uncontrolled insecticide and pesticide waste disposal. Upon exposure during winter, these chemical pollutants find their way into the snow, then into surface water and up the food chain. They can adversely affect aquatic life when subsequently introduced into the aquatic ecosystems. </p>
<p>POPs and exhaust particulate matters can <a href="https://www.epa.gov/international-cooperation/persistent-organic-pollutants-global-issue-global-response">affect human health</a>. They can cause allergies, hypersensitivity, birth defects and neurological disorders. Most POPs are carcinogens. Some of them may alter the nervous systems, leading to chronic health conditions. POPs can also affect reproductive health and disrupt the immune system. Some particulate matters cause lung inflammation and increase the risk of blood clotting. </p>
<p>These severe impacts on human health and environment sustainability are why POPs are <a href="https://www.canada.ca/en/environment-climate-change/corporate/international-affairs/partnerships-organizations/persistent-organic-pollutants-stockholm-convention.html">currently regulated under the Stockholm Convention, as adopted by Canada in 2001</a>. </p>
<p>Between applicable industries and environmental monitoring agencies, federal and provincial governments and us, everyone has a part to play. All hands must be on deck in providing sustainable regulations for these pollutants. And as we approach winter, measures should be developed to reduce the amount of pollutants that can accumulate and persist in snow.</p><img src="https://counter.theconversation.com/content/191651/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eduok, U. does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From persistent chemicals to exhaust particulate matter, snow accumulates highly toxic pollutants. Regulations are needed to address the impacts on water supplies and the food chain.Eduok, U., Senior Research Associate, Chemistry, Western UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1123462019-04-02T10:41:42Z2019-04-02T10:41:42ZKids exposed to flame retardant PBDE are at risk for lifelong liver or cardiovascular problems<figure><img src="https://images.theconversation.com/files/266586/original/file-20190329-70986-1q75yi3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Most baby clothes, toys, bedding and furniture are treated with flame-retardant chemicals.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/baby-clothes-newborn-pastel-colors-326694860">vkuslandia/SHutterstock.com</a></span></figcaption></figure><p>What factors determine if you will experience healthy and cheerful aging or if it will turn into an endless chain of suffering from numerous health conditions? </p>
<p>Many factors shape our health, including genetics, diet, physical activity, smoking and stress. Some other factors may be as powerful but may not yet be recognized. </p>
<p>I am an environmental toxicologist studying how man-made chemicals affect our health. I was always interested in understanding how our current health is shaped by chemical exposures during the embryonic and early postnatal period – life stages that are particularly sensitive to environmental stressors. </p>
<p>To address these questions, I focused on the analysis of long-term health effects induced by a family of chemicals used as flame retardants called <a href="https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_perchlorate_january2014_final_0.pdf">polybrominated diphenyl ethers (PBDEs)</a>. The first patent for PBDE use as a flame retardant was issued in 1960, and manufacturing of commercial products containing PBDEs, such as building materials, electronics, furnishings, motor vehicles, plastics, polyurethane foams, baby pajamas and others, <a href="https://doi.org/10.1016/j.scitotenv.2008.05.003">began in 1965</a>. PBDEs were first detected by scientists in <a href="https://doi.org/10.1016/0045-6535(87)90291-8">animal tissues in the 1980s</a>. </p>
<p>Later studies showed that concentrations of these chemicals in human blood, milk and tissues were <a href="http://doi.org/10.1021/es035082g">increasing exponentially over the past 30 years, doubling every five years</a>, while their health effects were poorly understood.</p>
<h2>Early exposures trigger lifelong changes in blood lipids</h2>
<p>In one of my experiments, I fed mice one of the PBDEs most often found in human blood and milk – BDE-47. The <a href="http://doi.org/10.1210/js.2016-1011">female mice received it</a> from day 8 of their pregnancy until the end of nursing (postpartum day 21). </p>
<p>We exposed mice to 0.2 milligrams of this chemical per kilogram of body weight. This caused BDE-47 concentrations in the fat of experimental animals to reach similar levels to concentrations found in humans living in big American cities. This comparison is used in toxicology to ensure that laboratory experiments use doses relevant for human exposures. </p>
<p>We were surprised to find that triglyceride levels were significantly altered in the offspring of exposed mothers, even though exposure to BDE-47 ceased three months earlier. Triglycerides are main constituents of body fat and cell membranes in humans and other animals.</p>
<p>To understand how BDE-47 changes blood triglycerides and other lipids, <a href="http://doi.org/10.3389/fendo.2018.00548">my laboratory conducted another experiment</a> with mice. Lipids are insoluble molecules that are used to store energy and as structural components of cell membranes. </p>
<p>We hypothesized that changes in blood lipids result from changes in liver function. It is well-known that the liver regulates composition of lipids in blood. The liver can synthesize new lipids, destroy them, secrete lipids to blood and absorb them from blood. </p>
<p>To test our hypothesis, we exposed female mice to BDE-47 daily during pregnancy or during the period of lactation and analyzed health outcomes in offspring when they reached one year old – roughly equivalent to 50 years in humans. </p>
<p>This experiment again demonstrated that short-term exposure to BDE-47 during early steps of development results in long-lasting effects on blood lipids in mice. These effects were very similar in animals that were exposed during the embryonic period or during nursing. </p>
<h2>Reprogramming the balance of lipid in blood and liver</h2>
<p>In exposed animals, levels of blood triglycerides fell by half, and <a href="http://doi.org/10.3389/fendo.2018.00548">livers accumulated 20 percent to 40 percent more lipids than in mice that were never exposed to the chemical</a>. Activity of many liver genes encoding enzymes important for lipid metabolism was altered in exposed mice. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266845/original/file-20190401-177196-xgnkmm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stages of liver damage. In severe cases, high levels of fat in the liver can lead to liver cancer.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/stages-liver-damage-disease-healthy-fatty-1071451652">wowow/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Among key proteins involved in lipid metabolism, one was particularly high. This protein – CD36 – is responsible for pumping lipids from blood to the liver. Increased amount of CD36 in exposed animals is likely responsible for lowering lipids in blood and raising them in the liver, resulting in increased accumulation of these fats in the liver. </p>
<p>We observed that lower-exposure dose (0.2 mg/kg) and higher-exposure dose (1.0 mg/kg) regulated CD36 in opposite directions. Lower dose resulted in decreased CD36 and elevated blood triglycerides, while higher dose raised CD36 and decreased blood triglycerides. We think it is important to note that both tested doses were in the range of human exposures. </p>
<h2>Do changes in CD36 pose health risks?</h2>
<p>Our findings demonstrate that exposure to BDE-47 during early development can alter the levels of CD36 in either direction in mice and that both increase and decrease in CD36 may be deleterious. </p>
<p>When we exposed mice to high doses of BDE-47, this increased levels of the CD36 protein, which causes excessive accumulation of fat in liver cells. This condition is called nonalcoholic fatty liver disease. It is the <a href="http://doi.org/10.1002/hep.20701">most common form of chronic</a> <a href="http://doi.org/10.1097/01.mpg.0000239995.58388.56">liver disease among adults and children</a>. </p>
<p>Around <a href="https://doi.org/10.1002/hep.20466">one-third of the American population has</a> nonalcoholic fatty liver disease, and it is a risk factor for <a href="https://doi.org/10.1038/nrgastro.2013.41">Type 2 diabetes, hypertension, cardiovascular and kidney disease</a>, <a href="https://doi.org/10.1016/j.jhep.2011.10.027">liver cirrhosis and liver cancer</a>.</p>
<p>On the other hand, decreased activity of CD36 will lead to higher lipid levels in the blood and result in <a href="https://medlineplus.gov/atherosclerosis.html">atherosclerosis</a> – a disease in which plaques of lipids build on the walls of vessels. Atherosclerosis is the primary risk factors for <a href="https://healthmetrics.heart.org/wp-content/uploads/2017/06/Heart-Disease-and-Stroke-Statistics-2017-ucm_491265.pdf">heart attack, which causes around 800,000 deaths annually</a> in the U.S. alone. Thus, early life exposure to this environmental chemical may completely reprogram lifelong health trajectory.</p>
<p>Studies published by other laboratories confirm that <a href="https://doi.org/10.1007/s00204-018-2292-y">PBDEs disrupt lipid metabolism in rats</a> and <a href="https://doi.org/10.1007/s00204-018-2177-0">increase risk of nonalcoholic fatty liver disease</a> in mice exposed during early steps of development.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=280&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=280&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=280&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=352&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=352&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266843/original/file-20190401-177163-1eavddz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=352&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">High levels of blood triglycerides can cause the buildup of fatty plaques that eventually block blood flow.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/closeup-atherosclerosis-3d-rendering-1036109620">Crevis/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>Still at risk?</h2>
<p><a href="https://doi.org/10.1021/es303879n">PBDEs were banned in Europe by 2008</a> and <a href="https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_perchlorate_january2014_final_0.pdf">voluntarily withdrawn by industry in North America by 2013</a>. It is likely that PBDEs’ production ceased all over the world, although data are missing for many regions. However these chemicals are still present in products used in U.S. households and cars. PBDEs are very stable compounds. Once released into the environment, they accumulate in sediments and in fatty tissues of wildlife and humans and stay there for many years. For example, the <a href="https://doi.org/10.1021/es1035046">half-life of different PBDEs</a> in the human body is between one and seven years. In the environment they found their way to fatty tissues of animals, many of which represent important sources of food for us.</p>
<p>Although production of PBDEs has ceased in developed countries, some studies report that concentrations of PBDEs in human tissues in the U.S. <a href="http://doi.org/10.1021/acs.est.7b00565">continue to grow</a>. </p>
<p>People born in the U.S. and Canada during the last 15 to 20 years were exposed during their early life to environmental concentrations of PBDE, comparable to those that reprogrammed lipid metabolism in our experiments with mice. Thus, we believe that about 20 percent of the North American population may be at risk of conditions associated with altered lipid concentrations in blood and liver. </p>
<p>Will these people develop aging-related conditions more readily than previous generations? The answer is yet to come. It is likely that PBDEs are not the only culprit. Many other ubiquitous pollutants, such as <a href="https://doi.org/10.1016/j.tox.2012.07.007">polychlorinated biphenyls (PCBs)</a>, <a href="https://www.toxicology.org/pubs/docs/Tox/2018Tox.pdf">dioxin (TCDD) and perfluorinated compounds (PFOS, PFNA)</a>, are known today to affect CD36 in mice. </p>
<p>It is not yet clear if effects of these other chemicals are as long-lasting as effects of PBDE. It is also not yet clear if effects of chemical exposures observed in mice are the same in humans. Mice are the most widely used animal model for testing the toxicity of pharmaceuticals and industrial chemicals, and animal toxicology studies generally are applicable to humans, <a href="https://www.ncbi.nlm.nih.gov/books/NBK215893/">although responses of laboratory animals</a> and humans to chemicals may differ in type and severity.</p><img src="https://counter.theconversation.com/content/112346/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexander Suvorov receives funding from:
1. University of Massachusetts - Amherst (startup funding), expired
2. Institute of general Genetics of the Russian Academy of Sciences (research contract), expired
3. USA Department of State (research grant), expired
4. USA National Institutes of Health (research grant), current</span></em></p>Brief exposure to a family of chemicals used as flame retardants early in life can permanently alter fat levels in the blood and liver, raising the risk of liver cancer and heart disease.Alexander Suvorov, Assistant Professor, UMass AmherstLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1040202018-09-27T20:58:36Z2018-09-27T20:58:36ZKiller whales: why more than half world’s orcas are threatened by leftover industrial chemicals<figure><img src="https://images.theconversation.com/files/238343/original/file-20180927-72336-1sk1r1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Tory Kallman / shutterstock</span></span></figcaption></figure><p>More than half of the world’s killer whales are threatened by a group of toxic industrial chemicals that accumulate in their blubber and can be passed on from mother to calf. That’s according to a new study led by scientists in Denmark and published in the journal <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aat1953">Science</a>. Killer whale populations found in the most polluted seas around Japan, Brazil, the UK or in the northeast Pacific, the authors report, are “tending toward complete collapse”.</p>
<p>Polychlorinated biphenyls (PCBs) are a ghost from the past. These chemicals were produced in immense quantities from the 1930s onwards and were broadly phased out in the 1970s/1980s as environmental concerns grew. </p>
<p>As they were very stable and were unable to conduct an electrical current (and therefore excellent insulators), they were mainly used in the electrical supply industry. These same properties also saw them being used in a whole array of miscellaneous applications including as sealants and additives <a href="https://pubs.acs.org/doi/10.1021/acs.est.8b00966">in construction</a>.</p>
<p>It is this chemical stability that means PCBs stubbornly refuse to degrade in the environment and I have spent the past 25 years studying how these and other contaminants end up <a href="http://www.lancaster.ac.uk/lec/about-us/people/crispin-halsall">accumulating in the Arctic</a>, for instance. However, there are two other properties that make these particular chemicals uniquely problematic, unlike, say, common air pollutants or most heavy metals. </p>
<p>The first is that PCBs are semi-volatile, which means that over time they can evaporate into the atmosphere but then later deposit on surfaces when encountering cooler temperatures or with rainfall or attached to particles. Over decades this continued evaporation and deposition (termed “cycling”) has ensured that they’re smeared around the entire planet. PCBs are just as likely to be found <a href="https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JC010651">deep in the ocean</a> or in <a href="https://pubs.acs.org/doi/abs/10.1021/es040076l">Arctic snow</a> as they are in neighbourhood soils, although the concentrations in soil close to “primary sources” such as cities may be <a href="https://research-portal.uws.ac.uk/en/publications/the-variability-of-polychlorinated-biphenyls-levels-in-urban-soil">orders of magnitude higher</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=416&fit=crop&dpr=1 600w, https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=416&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=416&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=522&fit=crop&dpr=1 754w, https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=522&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/238351/original/file-20180927-72336-18wr2dj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=522&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The PCB cycle leads to ‘biomagnification’ in killer whales.</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/cgi/doi/10.1126/science.aat1953">Desforges et al / Science</a></span>
</figcaption>
</figure>
<p>The second problem is that PCBs tend to work their way up the food web, accumulating in ever higher concentrations as tiny animals (and their unwanted chemicals) are eaten by small animals, who are eaten by larger animals (who take on those same chemicals), and so on. This process of “biomagnification” is most evident in marine food webs where fatty tissue like blubber (a home for PCBs) is an important feature of animals at the top of the food web such as killer whales.</p>
<h2>New diets mean new exposure</h2>
<p>So, if the chemicals were largely phased out in the early 1980s, why are they continuing to cause a problem? It’s true that background concentrations have declined over the past 20 years or so, based on measurements of PCBs <a href="https://pubs.acs.org/doi/abs/10.1021/es102134d">in the air</a> in <a href="https://www.ncbi.nlm.nih.gov/pubmed/19686961">animals such as seabirds</a> and even in <a href="https://www.researchgate.net/publication/303090756_A_validated_method_for_rapid_determination_of_dibenzo-p-dioxinsfurans_PCDDFs_polybrominated_diphenyl_ethers_PBDEs_and_polychlorinated_biphenyls_PCBs_in_human_milk_focus_on_utility_of_tandem_solid_phas">human breastmilk</a>. But the trend varies from place to place and between different species, and there is evidence that <a href="https://www.sciencedirect.com/science/article/pii/S0921818115301909">climate change is disturbing the “cycling” of these chemicals</a>, potentially slowing the rate of environmental decline.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=397&fit=crop&dpr=1 754w, https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=397&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/238353/original/file-20180927-48659-1jq0uek.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=397&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Largest circles (eg near Brazil, California, the UK and Gibraltar) represent the highest concentrations of PCBs in killer whale blubber. Land map shows PCB usage 1930-2000.</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/cgi/doi/10.1126/science.aat1953">Desforges et al / Science</a></span>
</figcaption>
</figure>
<p>Furthermore, complex foodwebs in northern oceans, particularly around Europe and North America (where most PCBs were produced and used) are undergoing subtle alterations. Predators like sharks, large fish or killer whales are changing their diets and exploiting new prey, which in turn <a href="https://www.nature.com/articles/s41598-017-13496-9">alters their exposure</a> to PCBs and other contaminants.</p>
<h2>PCBs are here for some time to come</h2>
<p>What can be done? Unfortunately, the horse has bolted as such and it would implausible to remove “background levels” of PCBs from the world’s oceans.</p>
<p>The key objective now is to maintain surveillance of these chemicals, whether they be in air, water, soil or animals. In most developed countries, end-of-life action ensures that old industrial materials with PCBs are subject to high temperature incineration (an effective way of ensuring complete destruction). Similarly, grossly contaminated industrial sites or dumps are subject to expensive clean-up and incineration activities. </p>
<p>But, while this is effective and safe at a local level, such measures will account for only a very small fraction of the total PCB inventory, most of which is out in the wild. International efforts by organisations like the <a href="https://www.unenvironment.org/explore-topics/chemicals-waste/what-we-do/persistent-organic-pollutants/pcb-elimination-network">UN Environment Programme</a> (UNEP) are ensuring that member states are undertaking “stocktaking” activities, containing old storage or dump sites, and undertaking monitoring programmes. This is particularly important across parts of Asia and <a href="https://www.researchgate.net/publication/229553423_The_legacy_of_persistent_organic_pollutants_in_Azerbaijan_An_assessment_of_past_use_and_current_contamination">key states of the former Soviet Union</a>, where PCB production and use was also high.</p>
<p>The legacy of PCBs will continue to haunt us for some while to come. Scientists estimate that the final resting place or “sink” for PCBs is likely to be <a href="https://pubs.acs.org/doi/10.1021/es801703k">organic rich soils</a> across the Northern Hemisphere or even <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2006GL025953">ocean sediments</a>. However, in the meantime, PCBs continue to cycle around the environment and are still present in mother’s milk. Maternal transfer from adult female to calf is the key exposure route for most marine mammals and this chemical stress (supplemented by an array of chemical pollutants other than PCBs), alongside climate change induced stress, is a major concern.</p><img src="https://counter.theconversation.com/content/104020/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Crispin Halsall receives funding from NERC.</span></em></p>PCBs were phased out three decades ago. But they’re still lingering in the ocean.Crispin Halsall, Reader in Environmental Chemistry, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.