Microplastics are getting into mosquitoes and contaminating new food chains



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khlungcenter/Shutterstock

Amanda Callaghan, University of Reading and Rana Al-jaibachi, University of Reading

There is no doubt that plastic pollution in oceans is a growing worldwide problem. The internet is full of images of seabirds and other marine animals entangled in plastic waste, and animals starve because their guts are blocked with plastic bags.

But the problem goes much deeper than this. Much plastic pollution is in the form of microplastics, tiny fragments less than five micrometres in size and invisible to the naked eye. Our new research shows that these microplastics are even getting into tiny flying insects such as mosquitoes. And this means the plastic can eventually contaminate animals in a more unlikely environment: the air.

Microplastics can come from larger plastic items as they break down, but are also released directly into waste water in their millions in the form of tiny beads found in many cosmetic products including face wash and toothpaste (though these are now banned in many countries). Many tiny animals can’t tell the difference between their food and microplastics so end up eating them. Once inside an animal, the plastic can transfer via the food chain into fish and other creatures and eventually become a potential health problem for humans.

Mosquitoes leave the water and take microplastics with them.
Shaun Wilkinson/Shutterstock

By studying mosquitoes, we have found a previously unknown way for plastic to pollute the environment and contaminate the food chain. Our new paper, published in Biology Letters, shows for the first time that microplastics can be kept inside a water-dwelling animal as they grow from one life stage to another.

Although most microplastic research has focused on the sea, plastic pollution is also a serious problem in freshwater, including rivers and lakes. Much of the freshwater research has concentrated on animals that live in the water throughout their life. But freshwater insects such as mosquitoes start their lives (as eggs) in water and, after several stages, eventually fly away when they grow up.

Testing the mosquitoes

It occurred to us that aquatic insects might carry plastics out of the water if they were able to keep the plastics in their body through their development. We tested this possibility by feeding microplastics to mosquito larvae in a laboratory setting. We fed the aquatic young in their third larvae stage food with or without microplastic beads.

We then took samples of the animals when the larvae shed their skin to become larger fourth-stage larvae, when they transformed into a non-feeding stage called a pupa, and when they emerged from the water as a flying adult. We found the beads in all the life stages, although the numbers went down as the animals developed.

Plastics were retained as the mosquitoes went through different life stages.
Blue Ring Media/Shutterstock

We were able to locate and count the microplastic beads because they were fluorescent. We found beads in the gut and in the mosquito version of the kidney, an organ that we know survives the development process intact. This shows that not only do aquatic insects such as mosquitoes eat both sizes of microplastics, they can keep them in their gut and kidney as they develop from a feeding juvenile larva up to a flying adult.

In this way, any flying insect that spends part of its life in water can become a carrier of plastic pollution. And flying insects are eaten in their thousands by predatory insects in the air such as dragonflies as well as by birds and bats.

Our results have important implications since any aquatic insect that can eat microplastics in the water could potentially carry them in their body to their flying stage where they can move the plastics into new food chains. As a result, freshwater plastic pollution is a problem that has implications far beyond those of water quality and eventual marine pollution.

Clearly these results raise a number of questions, including what effect microplastics have on the survival and development of mosquitoes through their life stages. And we still need to examine the effect of different types and sizes of plastics on more species to see how widespread an issue this could become.The Conversation

Amanda Callaghan, Associate Professor of Zoology, University of Reading and Rana Al-jaibachi, PhD researcher, University of Reading

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

Australia’s reptiles may be spreading rat poison through the food chain



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Gould’s goanna is commonly eaten in Indigenous communities, but can contain high levels of rat poison.
Robert A. Davis, Author provided

Michael Lohr, Edith Cowan University and Robert Davis, Edith Cowan University

Introduced rats and mice have probably troubled most of us at some time in our lives. These pesky invasive rodents are found around the world. We usually target them with toxic baits to stop them spreading disease and causing environmental or commercial damage.

In some instances rat baits are useful. They can protect crops, reduce the spread of disease, keep the contents of your pantry from disappearing, or even protect endangered wildlife on islands where rats have invaded.

These baits are freely available to homeowners and are used liberally by pest controllers. However, they have potentially deadly consequences for native predatory animals that eat poisoned rats and mice.

Our new research shows that this secondary poisoning may be worsened in Australia by reptiles, which are extremely effective at spreading these poisons up the food chain – a process that may even have consequences for human health.




Read more:
Hidden housemates: rats in the ranks


While little is known about how well reptiles tolerate rodent baits, several studies have suggested that at least some reptiles are extremely resistant. In a toxicity study using one lizard species, all of the test subjects survived an incredibly high dose of the strongest poison on the market – over 4,000 times the poison per body weight needed to kill most rats.

This is probably good news for the lizards, but eating poison-supercharged reptiles may be a serious concern for their predators – and for us.

Humans eat lizards too

During a rat eradication program in the Montebello Islands, one goanna species was seen eating poisoned rats – without apparent ill effect – to the point that the green dye used in the bait was visible in their droppings. Unfortunately, this species of goanna is an important traditional food in Indigenous communities throughout Australia. To make matters worse, these poisons usually build up in commonly eaten parts of the goannas, like fat and liver tissue.

The risks associated with sublethal human exposure to rodent baits are not well known. However, recent studies in some wildlife species show that even mild chronic exposure to the longer-lasting poisons can lead to dangerous changes in the immune system.

With so many unknowns in a potentially dangerous situation, more research is urgently needed. We need to know how often and how severely the reptiles that humans eat are exposed to poison. Otherwise, some Indigenous people may have to choose between losing traditional hunting practices and risking exposure to rat poison.

Poison in the food web

In our research, we reviewed all published examples of wildlife deaths from exposure to rat bait. We found that rat poison has killed members of at least 32 native wildlife species in Australia. There are probably many more; only a few studies have looked at this problem in Australia, compared with other parts of the world.

We found that a small species of owl called the Southern Boobook is exposed to rat poison frequently, and sometimes lethally, in developed areas of Western Australia. Scavengers and prolific predators of rodents are likely to be even worse off – and these predators include a variety of threatened or endangered species such as Masked Owls, Tasmanian Devils and various species of quolls.

Most deaths will occur far from the original bait, as the poison travels through other species in the food web to reach its final destination. Without a better understanding of how baits affect Australian predators, we are unlikely to appreciate the scale of this invisible threat.




Read more:
Killing cats, rats and foxes is no silver bullet for saving wildlife


At present, powerful rat poisons are available at most supermarkets and hardware stores. The Australian Pesticides and Veterinary Medicines Authority is now reviewing how these are regulated because of concerns about human health and impacts on wildlife populations.

Other countries like the United States and Canada have already restricted the stronger poisons to licensed pest controllers. They have banned outdoor use and require lockable bait boxes to keep children and pets away from baits.

The ConversationThese steps might not be enough to overcome Australia’s unique risks, but allowing the current situation to continue is guaranteed to result in more poisonings of wildlife – and possibly unseen and unstudied effects on humans too.

Michael Lohr, PhD Student – Wildlife Ecology, Edith Cowan University and Robert Davis, Senior Lecturer in Vertebrate Biology, Edith Cowan University

This article was originally published on The Conversation. Read the original article.