Disease-causing parasites can hitch a ride on plastics and potentially spread through the sea, new research suggests

The sticky biofilms that form on microplastics can harbor disease-causing pathogens and help them spread. Tunatura/iStock via Getty Images Plus

by Karen Shapiro, University of California, Davis and Emma Zhang, University of California, Davis

Typically when people hear about plastic pollution, they might envision seabirds with bellies full of trash or sea turtles with plastic straws in their noses. However, plastic pollution poses another threat that’s invisible to the eye and has important consequences for both human and animal health.

Microplastics, tiny plastic particles present in many cosmetics, can form when larger materials, such as clothing or fishing nets, break down in water. Microplastics are now widespread in the ocean and have been found in fish and shellfish, including those that people eat.

As researchers studying how waterborne pathogens spread, we wanted to better understand what happens when microplastics and disease-causing pathogens end up in the same body of water. In our recent study published in the journal Scientific Reports, we found that pathogens from land can hitch a ride to the beach on microscopic pieces of plastic, providing a new way for germs to concentrate along coastlines and travel to the deep sea.

Aerial shot of boat floating through plastic pollution on water
Microplastic pollution has negative consequences for human, animal and environmental health. Yunaidi Joepoet/Moment via Getty Images

Investigating how plastics and pathogens interact

We focused on three parasites that are common contaminants in marine water and seafoods: the single-celled protozoans Toxoplasma gondii (Toxo), Cryptosporidium (Crypto) and Giardia. These parasites end up in waterways when feces from infected animals, and sometimes people, contaminate the environment.

Crypto and Giardia cause gastrointestinal disease that can be deadly in young children and immunocompromised individuals. Toxo can cause lifelong infections in people, and can prove fatal for those with weak immune systems. Infection in pregnant women can also cause miscarriage or blindness and neurological disease in the baby. Toxo also infects a wide range of marine wildlife and kills endangered species, including southern sea otters, Hector’s dolphins and Hawaiian monk seals.

To test whether these parasites can stick onto plastic surfaces, we first placed microplastic beads and fibers in beakers of seawater in our lab for two weeks. This step was important to induce the formation of a biofilm – a sticky layer of bacteria and gellike substances that coats plastics when they enter fresh or marine waters. Researchers also call this sticky layer an eco-corona. We then added the parasites to the test bottles and counted how many became stuck on the microplastics or remained freely floating in the seawater over a seven-day period.

Biofilms are vast communities of microbes that can form on almost any surface, including your teeth.

We found that significant numbers of parasites were clinging to the microplastic, and these numbers were increasing over time. So many parasites were binding to the sticky biofilms that, gram for gram, plastic had two to three times more parasites than did seawater.

Surprisingly, we found that microfibers (commonly from clothes and fishing nets) harbored a greater number of parasites than did microbeads (commonly found in cosmetics). This result is important, because microfibers are the most common type of microplastic found in marine waters, on coastal beaches and even in seafood.

Plastics could change ocean disease transmission

Unlike other pathogens that are commonly found in seawater, the pathogens we focused on are derived from terrestrial animal and human hosts. Their presence in marine environments is entirely due to fecal waste contamination that ends up in the sea. Our study shows that microplastics could also serve as transport systems for these parasites.

These pathogens cannot replicate in the sea. Hitching a ride on plastics into marine environments, however, could fundamentally alter how these pathogens move around in marine waters. We believe that microplastics that float along the surface could potentially travel long distances, spreading pathogens far from their original sources on land and bringing them to regions they would not otherwise be able to reach.

On the other hand, plastics that sink will concentrate pathogens on the sea bottom, where filter-feeding animals like clams, mussels, oysters, abalone and other shellfish live. A sticky biofilm layer can camouflage synthetic plastics in seawater, and animals that typically eat dead organic material may unintentionally ingest them. Future experiments will test whether live oysters placed in tanks with and without plastics end up ingesting more pathogens.

Diagram illustrating how pathogens can associate with biofilms on microplastics and spread through the sea.
The biofilms that form on microplastics can help pathogens spread through the sea. Emma Zhang, CC BY-NC-ND

A One Health problem

One Health is an approach to research, policy and veterinary and human medicine that emphasizes the close connection of animal, human and environmental health. While it may seem that plastic pollution affects only animals in the ocean, it can ultimately have consequences on human health.

Our project was conducted by a multidisciplinary team of experts, ranging from microplastics researchers and parasitologists to shellfish biologists and epidemiologists. This study highlights the importance of collaboration across human, animal and environmental disciplines to address a challenging problem affecting our shared marine environment.

Our hope is that better understanding how microplastics can move disease-causing pathogens in new ways will encourage others to think twice before reaching for that plastic straw or polyester T-shirt.

Karen Shapiro, Associate Professor of Pathology, Microbiology and Immunology, University of California, Davis and Emma Zhang, Veterinary researcher, University of California, Davis

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Microplastics and pollution combine to become much more toxic: Study

Read the full story in Environmental Health News.

Microplastics can pick up pollution in their travels and pose an even greater threat to human health, according to a new study.

In the ocean, for example, toxic compounds can hitch a ride on plastic and make the material 10 times more toxic than it would normally be, according to the research published earlier this year in Chemosphere.

Although the dangers of both microplastics and harmful compounds have been studied individually, few researchers have look at their combined effect. This study is also unique in that the researchers tested these polluted plastic particles on human cells—most previous research has focused on the impacts on marine life.

New scoring scale tracks the harmful effects of salt pollution in freshwater streams and rivers

Read the full story from the University of Maryland.

A new study sheds light on how salinization from winter road salt combined with other pollutants creates ‘chemical cocktails’ that can jeopardize the ecological balance of waterways, including those in the Washington, D.C. area. The researchers developed a new five-stage scale (Stage 0-IV) to track the progression of this damage, a tool that could inform public policy in the future. Parts of the Potomac, the Anacostia and Rock Creek waterways are in Stage III on the scale for at least part of the year.

Birds of prey populations across Europe suppressed by lead poisoning from gun ammunition

Read the full story from the University of Cambridge.

Poisoning caused by preying on or scavenging animals shot by hunters using lead ammunition has left the populations of many raptors – or birds of prey – far smaller than they should be, according to the first study to calculate these impacts across Europe.

Aging of microplastics increases their adsorption affinity towards organic contaminants

microplastics

Kartik Bhagat, Ana C. Barrios, Kimya Rajwade, Abhishek Kumar, Jay Oswald, Onur Apul, François Perreault (2022). “Aging of microplastics increases their adsorption affinity towards organic contaminants.” Chemosphere 298, 134238. DOI: 10.1016/j.chemosphere.2022.134238

Abstract: When released in the environment, microplastics undergo surface weathering due to mechanical abrasion and ultraviolet exposure. In this study, the adsorption of two model contaminants, phenanthrene and methylene blue, by weathered high density polyethylene (HDPE) and polypropylene (PPE) was evaluated to understand how the microplastics’ aging influences contaminant adsorption. Microplastics were aged through an accelerated weathering process using ultraviolet exposure with or without hydrogen peroxide. Adsorption isotherms were conducted for both contaminants on pristine and aged microplastics. The adsorption of organic contaminants was higher on aged microplastics than on pristine ones, with methylene blue having the highest affinity increase with aging at 4.7-fold and phenanthrene having a 1.9-fold increase compared to the pristine particles. To understand the mechanisms involved with higher adsorption of contaminants by aged microplastics, changes in the specific surface area and surface chemistry of aged microplastics were characterized by Fourier Transform Infrared Spectroscopy, X-ray Photoelectron Spectroscopy, zeta potential, X-ray tomography, and Brunauer–Emmett–Teller krypton adsorption analyses. The results of this study show that oxidation of microplastics can enhance the adsorption of organic contaminants, which may increase their role as vectors of contaminants in the aquatic food chain.

Microplastics increase the toxicity of organic pollutants in the environment by a factor of 10, study finds

Read the full story from Tel-Aviv University.

A new study found that in a marine environment, microplastics absorb and concentrate toxic organic substances and thus increase their toxicity by a factor of 10, which may lead to a severe impact on human health.

Tiny tire particles inhibit growth of organisms in freshwater, coastal estuaries, studies find

Read the full story from Oregon State University.

Small particles from tires inhibited the growth and caused adverse behavioral changes in organisms found in freshwater and coastal estuary ecosystems, two new research papers found.

How poisonous mercury gets from coal-fired power plants into the fish you eat

Coal-fired power plants are a source of mercury that people can ingest by eating fish. Mark Wilson/Getty Images

by Gabriel Filippelli, IUPUI

People fishing along the banks of the White River as it winds through Indianapolis sometimes pass by ominous signs warning about eating the fish they catch.

One of the risks they have faced is mercury poisoning.

Mercury is a neurotoxic metal that can cause irreparable harm to human health – especially the brain development of young children. It is tied to lower IQ and results in decreased earning potential, as well as higher health costs. Lost productivity from mercury alone was calculated in 2005 to reach almost $9 billion per year.

One way mercury gets into river fish is with the gases that rise up the smokestacks of coal-burning power plants.

The Environmental Protection Agency has had a rule since 2012 limiting mercury emissions from coal-fired power plants. But the Trump administration stopped enforcing it, arguing that the costs to industry outweighed the health benefit. Now, the Biden administration is moving to reassert it.

I study mercury and its sources as a biogeochemist at Indiana University-Purdue University Indianapolis. Before the EPA’s original mercury rule went into effect, my students and I launched a project to track how Indianapolis-area power plants were increasing mercury in the rivers and soil.

Mercury bioaccumulates in the food chain

The risks from eating a fish from a river downwind from a coal-burning power plant depends on both the type of fish caught and the age and condition of the person consuming it.

Mercury is a bioaccumulative toxin, meaning that it increasingly concentrates in the flesh of organisms as it makes its way up the food chain.

A person's hands old a smallmouth bass, with the fish's mouth open
Mercury accumulates as it moves up the food chain. doug4537 via Getty Images

The mercury emitted from coal-burning power plants falls onto soils and washes into waterways. There, the moderately benign mercury is transformed by bacteria into a toxic organic form called methylmercury.

Each bacterium might contain only one unit of toxic methylmercury, but a worm chewing through sediment and eating 1,000 of those bacteria now contains 1,000 doses of mercury. The catfish that eats the worm then get more doses, and so on up the food chain to humans.

In this way, top-level predator fishes, such as smallmouth bass, walleye, largemouth bass, lake trout and Northern pike, typically contain the highest amounts of mercury in aquatic ecosystems. On average, one of these fish contains enough to make eating only one serving of them per month dangerous for the developing fetuses of pregnant women and for children.

How coal plant mercury rains down

In our study, we wanted to answer a simple question: Did the local coal-burning power plants, known to be major emitters of toxic mercury, have an impact on the local environment?

The obvious answer seems to be yes, they do. But in fact, quite a bit of research – and coal industry advertising – noted that mercury is a “global pollutant” and could not necessarily be traced to a local source. A recurring argument is that mercury deposited on the landscape came from coal-burning power plants in China, so why regulate local emissions if others were still burning coal?

That justification was based on the unique chemistry of this element. It is the only metal that is liquid at room temperature, and when heated just to a moderate level, will evaporate into mercury vapor. Thus, when coal is burned in a power plant, the mercury that is present in it is released through the smokestacks as a gas and dilutes as it travels. Low levels of mercury also occur naturally.

Although this argument was technically true, we found it obscured the bigger picture.

A view of the river with a bridge and the city in the background.
People sometimes fish along the White River where it flows through Indianapolis. alexeys via Getty Images

We found the overwhelming source of mercury was within sight of the White River fishermen – a large coal-burning power plant on the edge of the city.

This power plant emitted vaporous mercury at the time, though it has since switched to natural gas. We found that much of the plant’s mercury rapidly reacted with other atmospheric constituents and water vapor to “wash out” over the city. It was raining down mercury on the landscape.

Traveling by air and water, miles from the source

Mercury emitted from the smokestacks of coal-fired power plants can fall from the atmosphere with rain, mist or chemical reactions. Several studies have shown elevated levels of mercury in soils and plants near power plants, with much of the mercury falling within about 9 miles (15 kilometers) of the smokestack.

When we surveyed hundreds of surface soils ranging from about 1 to 31 miles (2 to 50 km) from the coal-fired power plant, then the single largest emitter of mercury in central Indiana, we were shocked. We found a clear “plume” of elevated mercury in Indianapolis, with much higher values near the power plant tailing off to almost background values 31 miles downwind.

The White River flows from the northeast to the southwest through Indianapolis, opposite the wind patterns. When we sampled sediments from most of its course through central Indiana, we found that mercury levels started low well upstream of Indianapolis, but increased substantially as the river flowed through downtown, apparently accumulating deposited mercury along its flow path.

We also found high levels well downstream of the city. Thus a fisherman out in the countryside, far away from the city, was still at significant risk of catching, and eating, high-mercury fish.

The region’s fish advisories still recommend sharply limiting the amount of fish eaten from the White River. In Indianapolis, for example, pregnant women are advised to avoid eating some fish from the river altogether.

Reviving the MATS rule

The EPA announced the Mercury and Air Toxic Standards rule in 2011 to deal with the exact health risk Indianapolis was facing.

The rule stipulated that mercury sources had to be sharply reduced. For coal-fired power plants, this meant either installing costly mercury-capturing filters in the smokestacks or converting to another energy source. Many converted to natural gas, which reduces the mercury risk but still contributes to health problems and global warming.

The MATS rule helped tilt the national energy playing field away from coal, until the Trump Administration attempted to weaken the rule in 2020 to try to bolster the declining U.S. coal industry. The administration rescinded a “supplemental finding” that determined it is “appropriate and necessary” to regulate mercury from power plants.

On Jan. 31, 2022, the Biden Administration moved to reaffirm that supplemental finding and effectively restore the standards.

More than a quarter of U.S. coal-fired power plants currently operating were scheduled as of 2021 to be retired by 2035. EIA

Some economists have calculated the net cost of the MATS rule to the U.S. electricity sector to be about $9.6 billion per year. This is roughly equal to the earlier estimates of productivity loss from the harm mercury emissions cause.

To a public health expert, this math problem is a no-brainer, and I am pleased to see the rule back in place, protecting the health of generations of future Americans.

Gabriel Filippelli, Chancellor’s Professor of Earth Sciences and Executive Director, Indiana University Environmental Resilience Institute, IUPUI

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Interactions between bee gut microbiotas and pesticides

Read the full story from the University of Ottawa.

A major review has provided the first field-wide summary of how pesticide exposure affects social bee gut microbiotas and what pesticide-induced disturbances mean for bee hosts.

Connecting the Dots: Plastic Pollution and the Planetary Emergency

Download the document.

This report sounds the alarm on pollution caused by plastic throughout its lifecycle by exposing how it drives pollution, biodiversity loss and climate change, compromises human health and poses a direct threat to planetary boundaries. Based on this, it provides recommendations on how to ensure multidimensional, long-term and collaborative policy that considers plastic pollution as a planetary boundary threat and takes into account its knock-on impacts on other environmental crises.