Tropical mammals are living in an ever-changing chemical landscape warns a recent study, with wildlife increasingly exposed to an array of plastics, pharmaceuticals, pesticides and nanoparticles. The recent study, published in the journal Biological Conservation, warns that this underrecognized threat requires urgent action.

Colin Chapman, a biologist and professor at George Washington University, and his colleagues reviewed the body of scientific literature investigating the scope of the “chemical landscape” inhabited by tropical terrestrial mammals. A recurrent theme: a paucity of studies covering the topic offered only glimpses of the effects of pollutants.

“As a society we are intentionally poisoning tropical wildlife,” Chapman told Mongabay. “We don’t know the effects of it, but we know we’re poisoning them. We know we’re poisoning ourselves and despite this knowledge, we’re not acting.”

Living in a chemical world

Earlier this year, an international group of researchers centered around the Stockholm Resilience Centre (SRC) warned that the manufacture, use and disposal of synthetic chemicals — referred to by scientists as novel entities — has passed a crucial and dangerous environmental threshold, threatening “a safe operating space for humanity.” The novel entities pollution problem is just one of nine planetary boundaries — six of which, including climate change, have already seen their safe limits violated by human actions.

In 2019, a report by the United Nations Environment Programme (UNEP) estimated that the global chemical industry’s production capacity had reached 1.2 billion tons. In 2017, that industry was worth 5.68 trillion, a figure projected to double by 2030. In declaring the breach of the novel entities planetary boundary in January 2022, researchers emphasized that it has become impossible for science to assess the rapidly widening stream of existing and new chemicals entering the environment.

A variety of pollution routes exist in the tropics and elsewhere. Pesticides, for example, are being applied to agricultural lands at ever-greater rates. Previous estimates suggest a rate of around 2 million tons annually, though a recent study suggests 4 million tons are now used each year. Likewise, treated sewage that is spread as fertilizer can leach a harmful pharmaceutical cocktail and concentrated heavy metals into soils and groundwater. Plastics are released into the air when disposed of by burning, and also enter soils and waterways when thrown away, where they deteriorate into microplastics.

Increasing agricultural production and pharmaceutical use in tropical countries (even in remote parts of the Brazilian Amazon), combined with often lax regulations that enable the use of chemicals banned elsewhere, can heighten risk. Knowledge of the environmental impacts of all these chemical pollutants is not new, says Chapman, but research in tropical regions is lagging.

The studies and reports that do exist often focus on cases of intentional killings of wildlife using chemicals, or unintentional mass killings. Recently in India, for example, vultures died en-masse due to pesticide poisoning inadvertently spread to kill stray dogs. While such events can grab headlines and researchers’ attention, Chapman is equally concerned by systematic and prolonged chemical exposure which could cause sublethal effects.

Looking beyond the lethal

Kurunthachalam Kannan, an environmental chemist and professor in environmental medicine and pediatrics at New York University’s Langone Health, who was not involved in the study, agrees that all this chemical exposure is troubling. Currently, far more is known about sublethal effects in humans than in wildlife populations, he states: “Sublethal health effects such as reduced reproduction, suppressed immune system and altered endocrine functioning can impair survival of wildlife and can disrupt ecosystem structure and function.”

A study published last year found that consumption of fruit contaminated with deltamethrin, an agricultural insecticide, could effect reproduction in fruit-eating bats due to oxidative stress in their testes “even in low, commercially prescribed concentrations”, the authors write.

Work by Chapman and Michael Wasserman, a co-author of the recent paper, who is with the University of Indiana’s Primate Environmental Endocrinology Laboratory, indicated that chemicals, including legacy and current use pesticides and flame retardants (some recognized as endocrine disruptors), are present in the tropics. They’ve been detected in the air in and around Las Cruces and La Selva Biological Stations in Costa Rica, and at Kibale National Park in Uganda. A follow-up study found traces of these chemicals in the feces of primates such as red colobus, chimpanzees and red-tailed monkeys. Yet, no one knows the effect of these chemical exposures on these species, Wasserman adds.

“Did the animal live a little bit less? Did they get cancer? [Did exposure] cause increased mortality?” Chapman wonders, but these are questions which remain unanswered for most exposed species, including primates. It’s unlikely species are going to go extinct due to chemical pollution, he adds, but exposure could hinder conservation efforts.

Michael Bertram, an ecotoxicologist and researcher with the Swedish University of Agricultural Sciences, studies the impact of chemical pollution on animal behavior, another realm in which research is lacking, and he is also concerned. “The [paper’s] authors rightly point out that although large-scale wildlife die-offs are a clearly observable and alarming sign of the presence of chemical contaminants at toxic levels in ecosystems, it is much more common for wildlife to be exposed to an invisible mixture of multiple chemicals, [reducing their resilience as they face] other stressors such as habitat loss and climate change.”

While many of the potential pathways of chemical exposure are enumerated by the study, more exist, Bertram says. For example, research shows that fish species accumulate chemicals in high concentrations which could then be passed up the food chain.

“Tropical mammals that consume tainted fish or other aquatic prey, drink contaminated water, or come into contact with contaminated sediment, will therefore be exposed to potentially harmful contaminants,” Bertram reports. “The fact that Chapman and colleagues provide such a comprehensive list of pathways by which tropical animals can be exposed to contaminants, but still many more pathways exist, is indicative of the scale of the problem with which we are confronted.”

An additional concern is the synergistic impact of chemical pollution when combined with other stressors.  Wholesale conversion of forest to agriculture, or the eating away at forest edges by fields, pastures and roads, can ramp up chemical exposure, says Wasserman: “The more you fragment a landscape, the more edge there is where you have contact between human dominated landscapes in the forest, and therefore more places for all those novel entities to enter the ecosystem.”

Climate change can also interact with chemical pollution in multiple ways, exacerbating or altering the effects of some contaminants. Chapman’s study cites the example of global warming-triggered forest fires leading to deaths due to smoke inhalation among elk populations.

“This is just one of many examples where one form of environmental change, in this case climate change which increases the likelihood and severity of fires, drives an increase in another form of environmental change, the contamination of air (and water) with particulate matter,” says Bertram. But once again, the impacts of potentially toxic forest fire smoke on tropical mammals has not been well documented.

Monitoring health, researching effects

Clearly, tropical mammals face an ever-escalating chemical crisis, yet how serious this problem may be, remains unclear. Chapman and Wasserman urge further research and long-term monitoring to better understand the issue, but until more studies are done, they say, the precautionary principle should be implemented regarding chemical use.

“I think studying this in wild primates has a lot of potential,” notes Wasserman. “They are the ideal biosentinel for understanding exposure to novel entities, but also for human health concerns.”

Long-term monitoring of wildlife population health would not only aid in understanding and quantifying the scale and impact of chemical pollution, but also provide an early warning system for detecting emerging diseases, adds Chapman — a particularly relevant sensing system in the wake of the Covid-19 pandemic.

NYU’s Kannan agrees that chemical impacts on tropical wildlife require far more study. “We need to grow and support a future generation of researchers in the area of wildlife ecotoxicology,” he states. “Furthermore, interdisciplinary research on the topic is needed which requires collaborations with wildlife biologists, veterinarians, toxicologists, chemists, and more importantly, community engagement and support.”

International bodies such as UNEP and the International Panel on Chemical Pollution have made similar calls for interdisciplinary research, and are working towards the development of a Global Science-Policy Panel to address the issue.

Meanwhile, Chapman and his colleagues are actively investigating levels of plastics and pesticides in the feces of primates at over 20 sites in Central and South America, Africa, and Asia. This far flung effort, Chapman adds, is an example of the kind of research and monitoring needed in the long-term to truly understand the chemical landscape in which tropical mammals are now living.

“In order to act in an informed way, we need to have the infrastructure, the research capacity [and] more information about sublethal effects,” he concludes. “We have to revamp how that information is being collected and scale up that information.”

Banner image: Mountain gorillas thrive on rainforest foliage, but if that foliage happens to be tea leaves sprayed with pesticides on national park-adjacent plantations, they can be poisoned. Image by Ludovic Hirlimann via Flickr (CC BY 2.0)

Citations:

Bertram, M. G., Martin, J. M., McCallum, E. S., Alton, L. A., Brand, J. A., Brooks, B. W., … Brodin, T. (2022). Frontiers in quantifying wildlife behavioural responses to chemical pollution. Biological Reviews. doi:10.1111/brv.12844

Chapman, C. A., Steiniche, T., Benavidez, K. M., Sarkar, D., Amato, K., Serio-Silva, J. C., … Wasserman, M. D. (2022). The chemical landscape of tropical mammals in the Anthropocene. Biological Conservation, 269, 109522. doi:10.1016/j.biocon.2022.109522

Oliveira, J. M., Lima, G. D., Destro, A. L., Condessa, S., Zuanon, J. A., Freitas, M. B., & Oliveira, L. L. (2021). Short-term intake of deltamethrin-contaminated fruit, even at low concentrations, induces testicular damage in fruit-eating bats (Artibeus lituratus). Chemosphere, 278, 130423. doi:10.1016/j.chemosphere.2021.130423

Wang, S., Steiniche, T., Romanak, K. A., Johnson, E., Quirós, R., Mutegeki, R., … Venier, M. (2019). Atmospheric occurrence of legacy pesticides, current use pesticides, and flame retardants in and around protected areas in Costa Rica and Uganda. Environmental Science & Technology, 53(11), 6171-6181. doi:10.1021/acs.est.9b00649

Wang, S., Steiniche, T., Rothman, J. M., Wrangham, R. W., Chapman, C. A., Mutegeki, R., … Venier, M. (2020). Feces are effective biological samples for measuring pesticides and flame retardants in primates. Environmental Science & Technology, 54(19), 12013-12023. doi:10.1021/acs.est.0c02500

Wu, D., Li, Q., Shang, X., Liang, Y., Ding, X., Sun, H., … Chen, J. (2021). Commodity plastic burning as a source of inhaled toxic aerosols. Journal of Hazardous Materials, 416, 125820. doi:10.1016/j.jhazmat.2021.125820

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Researchers hope the enzymes could create a truly circular system for the PET plastics that are still manufactured.

[Source Photos: rawpicel and rawpixel]

Jill Fransen considers herself a serious recycler, the kind of person who knows the difference between various plastics, takes care to sort them, and drives five miles from her home in Portland, Oregon’s, North Tabor neighborhood to drop off refuse at a recycling center.

Over nearly a dozen years, Fransen’s routine was pretty well established. Then in late 2020, she heard about Ridwell, a subscription-based recycling service that had just been introduced in Portland. For about $12 per month, Ridwell would pick up items — stuff that many recycling programs won’t accept, like certain plastics and spent lightbulbs — right from one’s front porch, and take everything to its local plant to sort and redistribute for recycling or re-use.

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 the 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.

Investigating how plastics and pathogens interact

We focused on three parasites that are common contaminants in marine water and seafood: 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 diseases 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 to 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 gel-like 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.

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 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.

A-One Health problem

One Health is an approach to research, policy, and veterinary and human medicine that emphasizes the close connection between 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 a better understanding of 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.

This article was originally published on The Conversation by Emma Zhang and Karen Shapiro at University of California, Davis. Read the original article here.

Though its effects are not always visible to the naked eye, plastic is choking life on Earth. Birds are dying from plastic accumulating their intestines. Animals are full of microplastics, and humans are unintentionally eating a credit card’s worth of plastic every week, which is seeping into our bloodstream. And the ocean is becoming an open plastic dump to the extent that microplastic particles may outnumber zooplankton. 

These harrowing scenes could come to define our planet’s future. The process for manufacturing plastic exacerbates climate change, and the prevalence of plastic in the environment has led to heartbreaking sights like sea turtles with straws stuck up their noses. Yet because plastic is designed to be durable and lasting, scientists who dream of permanently removing it from our environment have often despaired of solutions. 

One oft-floated pipe dream as to how to alleviate plastic pollution: can we breed something that will consume it?

RELATED: How plastic pollution threatens our health, food systems, and civilization itself

A new study suggests that an enzyme which targets polyethylene terephthalate (PET) — a widely-used polymer found in a majority of consumer packaging products that comprises 12 percent of all global waste — could make that scientific dream, which is also planetary necessity, into a reality.

The key ingredient was a natural enzyme known as PETase, according to the paper published in the scientific journal Nature. Using a machine learning model, scientists at the University of Texas at Austin’s Cockrell School of Engineering and College of Natural Sciences figured out what mutations would cause the enzyme to be able to quickly break down the targeted types of plastic waste.

“Collectively, our results demonstrate a viable route for enzymatic plastic recycling at the industrial scale,” the researchers conclude in their paper.

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“Enzyme scale-up has been a well-explored problem in many industries,” Hal Alper, professor in the McKetta Department of Chemical Engineering at UT Austin, told Salon by email when asked how long it would take for this enzyme to be available on a wide scale. “Therefore, we feel that this part of the problem is easily achievable in a short period of time. The more challenging aspect will be implementing enzyme degradation on a large scale with mixed stream plastics.” (Mixed stream plastics are all non-bottle plastics collected from the waste stream, or the entire life cycle of the garbage produced in a community.)

Alper added, when asked about how the new team’s research built on previous efforts to address plastic pollution, “We utilized the enzymes that have been found in bacteria evolved to use PET. By starting with this enzyme as a scaffold, we applied machine learning techniques to substantially improve upon function.”

As Alper’s reply indicates, this was not the first effort to find biological means of solving the plastic pollution problem. It all began, as much of scientific history does, with a random crucial discovery. In March 2016, Japanese researchers found a bacteria known as Ideonella sakaiensis that, they marveled, would “eat” the plastic outside of an Osaka bottle factory until it turned into sludge. “The new species, Ideonella sakaiensis, breaks down the plastic by using two enzymes to hydrolyze PET and a primary reaction intermediate, eventually yielding basic building blocks for growth,” the scientists wrote.

Plastic-eating bacteria was later discovered in Oregon and Germany by subsequent researchers, demonstrating to scientists that there could be a biological solution to the plastic problem. By 2020, scientists at the University of Portsmouth had managed to alter the PETase enzyme to create a supposed “cocktail” that could digest plastic up to six times faster than normal. In the abstract of their paper, the researchers singled out the discovery of the Ideonella sakaiensis as vital to their research, as well as addressing an international catastrophe.

“Plastics pollution represents a global environmental crisis,” the authors wrote. “In response, microbes are evolving the capacity to utilize synthetic polymers as carbon and energy sources.”

Last year, scientists at the University of Edinburgh announced that E. coli, a common bacteria, could be used to convert PET into vanillin, the primary component of extracted vanilla beans. They even suggested that the vanillin might be able to be safely consumed by humans, although they emphasized that further experiments would be required.

Joanna Sadler, a biotechnology professor at the University of Edinburgh who was not involved in the most recent study but was involved in the E. coli study, seemed hopeful about the developments in the latest paper. Sadler characterized the new enzyme as the “fastest enzyme reported to date” in terms of the speed at which it can “depolymerise” different plastic substrates. 

“This makes it a very promising technological development in the field, and demonstrates the ‘evolvability’ of this enzyme,” Sadler said.

Alper, not surprisingly, echoed Sadler’s hopeful tone.

“Our enzyme is up to 30x more efficient than reported enzymes and operates at lower temperatures and thus saves on energy input and improves the ease of downstream processing,” Alper wrote to Salon.

For more Salon articles on plastic pollution: