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publicado em 22/04/2013 às 18h30:00
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Study shows how herbicide used on soybeans is carcinogenic to rats

According to researcher, diuron causes necrosis of the lining of the bladder, which predisposes to the development of tumors

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Research identifies mode of action of diuron, a herbicide widely used in soybean and sugar cane, which caused bladder cancer in rats. We show that when excreted in urine, diuron or its metabolites cause multiple foci of necrosis in the urothelium, bladder coating. In response, the lining proliferates to replace the injured areas. A continuous cell proliferation, if maintained for a long time, eventually leads to errors in successive copies of DNA, some predisposing to the development of tumors, said Dr. John Lauro Viana de Camargo, Professor of Pathology, Faculty of Medicine of Botucatu, State University Paulista (UNESP) and coordinator of the study.

The study confirmed the carcinogenic potential of diuron for mice and showed that this condition can occur even at doses five times lower than those previously considered harmful. According to the researcher, this mode of action diuron shows that operates in a non-genotoxic, ie, does not cause, at the beginning or directly damage DNA. Such damage tends to occur at later times, if exposure is maintained for long time. The carcinogenic potential of this herbicide for the human species had already been warned by the United States Environmental Protection Agency (EPA), the Environmental Protection Agency of the United States government.

The changes induced rat bladder diuron occur according to a dose-response relationship, i.e. the higher the dose, the more molecular changes, histological and ultrastructural happen, Camargo explained. In this line, we identify the call threshold dose - an amount below which the herbicide is not carcinogenic, even if the animal is exposed to it for a long time.

According to the researcher, its toxicity is manifested very early on the first day of exposure to high doses. Evaluated its gene expression response of urothelium is apparently adaptive, suggesting that, if exposure is stopped, the bladder back to normal. The problem exists if the doses are high and exposure maintained for a long time, he said.

When given in relatively high doses to mice, diuron causes blood toxicity. In this case the target is the predominant spleen, an organ related to immunity and blood supply, which consistently showed increased volume due to excessive accumulation of blood and cellular debris, said Camargo. This change was also observed in male offspring of pregnant rats that had received diuron at high doses.

The study of diuron was part of a thematic project called Agricultural Pesticides as a risk factor. Besides diuron researchers also investigated the effects in rats and mice, five pesticides whose residues were found by the National Agency for Sanitary Surveillance (ANVISA) in tomatoes available to the population.

Male rats fed for eight weeks with diets containing that mixture of pesticides at relatively low doses, the system showed hepatic biotransformation of chemicals potentially more active, said Camargo.

This finding suggests that the bodies of the animals would be making an extra effort to get rid of foreign substances to which they were being exposed. But the mixture is not promoted the development of liver cancer in rats that had been artificially made predisposed to such disease.

Another worrisome effect was found. Male rats fed the diet containing pesticides had reduced mobility of sperm. This finding may indicate impairment of fertility in animals, said Camargo.

His care to say may indicate, and does not, is because they have not been verified changes in other parameters related to the male reproductive system, as levels of sex hormones, sperm morphology, sperm production daily, the speed of transit through the epididymis - the duct that collects the sperm produced in the testes - and the histological structure of the testis and epididymis.

Based on the same criteria of prudence, Camargo avoids extrapolating to humans the findings in rats. "Extrapolation of the results should be made wisely and relevance of the results taken with caution, said.

For the extrapolation rigorous, no need to compare the metabolic and biological processes by which substances are studied in each species and cause, "mused the professor.

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diuron herbicide cancer    bladder cancer    Faculty of Medicine of Botucatu    Universidade Estadual Paulista (UNESP)    United States Environmental Protection Agency   
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