Wednesday, May 25

Pesticides: The poison that remains for decades on the skin of the earth | Science

A man pours pesticide on a crop in Mexico last August.
A man pours pesticide on a crop in Mexico last August.SEMARNAT

The impact of human activity on the planet alters even the most resistant systems. Among the criteria that scientists consider to baptize the new geological era as Antopocene, the period characterized by the imprint of human action, is, among others, the widespread use of pesticides for more than 70 years. Two different studies have found traces of these chemical compounds in soils that have not been applied for between three and 20 years.

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One of the investigations, led by Violette Geissen, from the Soil Physics and Land Management group at the University of Wageningen (Holland), with Spanish and Portuguese collaboration, has analyzed 340 agricultural lands (dedicated to growing oranges, grapes, potatoes and other horticultural products) from the participating countries over a triennium and has found residues of between 16 and five pesticides in 70% of the samples, including those from those lands that had abandoned the use of chemical compounds three years before the study.

Fernando Madrid Díaz, researcher at Agrochemistry, Environmental Microbiology and Soil Conservation of the Institute of Natural Resources and Agrobiology of Seville (IRNAS-CSIC) and alien to the study, although it considers these findings of residues due to the widespread use of pesticides “normal”, it agrees with the study in the need to take them into account. “Pesticides are toxic compounds, they are designed to be,” he says. However, he explains that they are necessary to maintain production capacity at the levels demanded by demand. And he adds: “They are toxic and not ideal, but there are no immediate alternatives. It is investigated with biopesticides, of natural origin and more biodegradable, and creating ecosystems that are favorable to the control of pests, but their short-term effects are not the same ”.

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In this sense, Geissen details in his study, published this month in Enviromental Pollution, that the “dependence on pesticides in Europe’s agricultural systems [zona objeto del estudio] to ensure yields in plant production and livestock, they involve the use of an average of 340,000 to 370,000 tons of active substances annually ”, according to statistics from the FAO. “Of the 487 active substances approved for sale in the EU”, according to the research, “almost half are bioaccumulative [pueden acumularse en los organismos de seres vivos], 25% are persistent in the soil for more than 100 days and 30% have a high aquatic toxicity ”.

The problem of the use of pesticides comes when, due to its concentration, it ends up being toxic

Fernando Madrid Diaz, researcher in Agrochemistry, Environmental Microbiology and Soil Conservation at IRNAS

For Madrid Díaz, this last aspect is one of the most dangerous: “When it reaches the water, that pollution is more difficult to contain.” He also considers the study of persistence important. In this sense, he clarifies: “Any pesticide includes a biodegradability study, which is established based on the time necessary to cause the desired effect, but this is not exact: it depends on the type of soil (if it is sandy, for example) or the weather”. “The problem,” he concludes, “comes when, due to its concentration, it ends up being toxic.”

In this sense, the study led by Geissen assures: “Most pesticides are applied during the growing season of the crops, which results in a peak of residues in the soils during this period. However, they can persist long after application and accumulate in the soil over the years ”.

This persistence is an explanation for the fact that, although the highest number of residues per sample (16) were found in 70% of the soils with conventional farms, up to a maximum of five pesticide residues were detected in organic farming lands.

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of the decades

The findings coincide with another study published by the American Chemical Society and with Judith Riedo, from the University of Zurich, as lead author. In this study, the researchers measured the surface characteristics of the soil and the concentrations of 46 regularly used pesticides and their decomposition products in samples taken from 100 fields that were managed with conventional or organic practices. The researchers also found pesticide residues at all locations, including farms converted to organic more than 20 years prior to the study. According to the result of the investigation, “multiple herbicides and a fungicide remained in the surface soil after conversion to organic farms, although the total number of synthetic chemicals and their concentrations decreased significantly the longer the fields were under this type of management” .

Some of the pesticides could have contaminated organic fields by traveling through air, water, or soil from nearby conventional fields.

Riedo provides an explanation in his study: “Some of the pesticides could have contaminated organic fields by traveling through air, water or soil from nearby conventional fields.” This presence of chemical compounds also affects, according to the research, the beneficial microbial presence. “The presence of these substances can decrease the health of the soil,” conclude the researchers.

The persistence of persistent organic pollutants (POPs) beyond the ground remains a matter of study. The latter, released by the Karolinska Institute of Sweden, a group of researchers has found a fortnight of these compounds in the adipose tissue of 20 fetuses that died in the third trimester of gestation between 2015 and 2016. These substances included HCB, a pesticide used to protect food crops from fungi; DDE, an insecticide used in the mid-20th century, and variants of PCBs, chemicals that were used for electrical products. The study only investigated the presence and concentration of the chemicals, but not their relationship to potential health risks.

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Matter of numbers

Jesús Arias Salgado, owner of several farms in the Guadalquivir valley, assures that the limitations imposed by the EU regarding the use of chemical components for the management of crops are already exhaustive. “We are almost ecological. But I have studied the possibility of transforming the farms into organic ones, in whole or in part, and I don’t get the numbers, “he says. This farmer sells to three of the main European distribution chains.

A study published in the journal One Earth this month he considers, on the contrary, that it is possible. According to this work, “an ecological, sustainable and biodiversity-friendly agri-food system could be applied in Europe.” To do this, according to the publication, it would be necessary: ​​changes in diet, with a lower consumption of animal products from intensive livestock; a crop rotation system that incorporates nitrogen-fixing legumes, which would make it possible to avoid synthetic nitrogen fertilizers and pesticides; and combine crops and livestock for optimal manure recycling. “It would be possible to reinforce the autonomy of Europe, feed the population planned for 2050, continue to export cereals to countries that need them for human consumption and, above all, substantially reduce water pollution and greenhouse gas emissions from the agriculture ”, say the researchers.

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