Cyanobacteria and agriculture: the link behind toxic flowers

The massive increase in cyanobacteria is a growing threat worldwide. A study by Udelar and FAUBA in the Uruguay River basin revealed that one of the main drivers of the phenomenon is the intensive use of phosphate fertilizers in soy cultivation.

Cyanobacterial blooms have negative effects on human and animal health, and have become increasingly frequent in recent decades. Because it is a phenomenon with multiple causes, it is difficult to treat it effectively and on a scientific basis. In this context, a study by the University of the Republic of Uruguay (Udelar) and the Faculty of Agronomy of the UBA (FAUBA) pointed out that flowering increased in the Uruguay River basin hand in hand with agricultural production based on the intensive use of pesticides, especially fertilizers phosphates. What productive alternatives are there?

Cyanobacteria are photosynthetic microorganisms that have inhabited Earth’s waters for millions of years and contribute to the functioning of ecosystems. However, when aquatic environments change, some multiply exponentially and can produce cyanotoxins that cause negative health effects.”, said Carla Kruk, professor at the Institute of Ecology and Environmental Sciences at the Faculty of Sciences and at the MEDIA department at the Centro Universitário Regional Leste, both at Udelar.

Health consequences of exposure to cyanobacteria

If we come into contact with large concentrations of these toxins directly in the water we drink or bathe in, or indirectly when we eat animals or vegetables that have come into contact with cyanobacteria, we can suffer liver allergies or neurological damage. . On the other hand, continuous exposure to low concentrations can lead to tumors.Kruck added.

Gervasio Piñeiro, professor of Ecology at FAUBA and co-author, along with Kruk et al. and other researchers from work published in the scientific journal Biology of Global Change, indicated that the proliferation of cyanobacteria is a phenomenon that can have numerous causes and that it is essential to identify them in order to take measures based on scientific studies. In this context, they compared how different mechanisms could explain the blooms from the 1960s to the present in the Uruguay River basin, an area that encompasses Argentina, Uruguay and Brazil.

Carla and Gervasio analyzed changes in rainfall, temperatures, land use, river flows and also in the water quality of the entire basin. “We observed that in the last 20 years, cyanobacterial blooms have become more and more frequent and that the main cause was agricultural production that intensively uses agrochemicals.”, highlighted Pineiro.

Drastic increase in recent decades of cyanobacteria

Cyanobacteria, phosphorus pollution, water, agriculture, fertilizers, soy, liver, allergies
The Uruguay River is 1,900 km long and its basin has an area of ​​36,500,000 hectares.

Beginning in the 2000s, the number of cyanobacteria in water and the species producing cyanotoxins increased dramatically. Between 1963 and 2005, no alert levels of cyanobacteria were detected, and between 2010 and 2020, 200 cases were reported. “We found that they were strongly correlated with the increase in agricultural area and new forms of production. In particular, the area dedicated to soy grew from 0% to 40% and, thus, the use of inputs used to produce it grewKruck stressed.

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In this sense, Carla explained that, when it rains, pesticides —and occasionally phosphate fertilizers— pass from the soil into the water and the cyanobacteria use these nutrients and exponentially increase their biomass. Gervasio added that there is currently a large area of ​​soybeans that is fertilized with phosphorus, or even overfertilized, and that the nutrients also reach the water through soil erosion. “From the agronomic side, it’s a yellowish light turning red. We have to change the ways of producing”.

expand alternatives

In this context, Piñeiro, CONICET researcher at the IFEVA Institute (UBA-CONICET), listed a wide range of good agronomic practices that can be implemented: “for example, improving fertilization practices, using service crops that protect the soil and prevent it from eroding, or using trap crops near streams to capture nutrients and prevent them from running into water”.

He also proposed redesigning landscapes so that they have multiple functions and benefits. “Not only to produce soybeans or corn, but also to provide clean water. There are technologies and knowledge, but it takes a lot of awareness for them to be used more widely. It is a very complex problem that requires multiple approaches.”.

Cyanobacteria, phosphorus pollution, water, agriculture, fertilizers, soy, liver, allergies
Kruk stated that in the Uruguay River basin, the arrival of soybeans meant a drastic change in the area planted with different crops and in the way of production.

An absent view of health and the environment

In turn, Kruk warned that there is a lack of publicity about the health risks involved in exposure to cyanobacteria. “There are cases of intoxication by nautical sports in waters with cyanobacteria bloom. A few years ago, an almost 2-year-old girl had to receive a liver transplant after bathing with her family in water laced with cyanotoxins.”.

On the other hand, flowers make it difficult to make water drinkable. The researcher said that four purification plants that were located on the Uruguay River, on the Uruguayan bank, had to be closed and several coastal towns lost this source of drinking water.

It is one of the great problems of the Uruguay River, but it also occurs in Argentine lagoons, as demonstrated by a recent work published in the journal Ecología Austral. Until some time ago, blooms that were intermittent occurred mainly in summer, but have become permanent in many water bodies.”, commented Pineiro. Finally, Carla and Gervasio agreed that measures need to be taken in areas such as health, production and law to deal with this recurring problem.

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