Glyphosate and aminomethyphosphonic (AMPA) contents in Brazilian field crops soils

Abstract

Because of a lack of direct measurements, the presence and persistence of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in agricultural soils of Brazil remains unknown. This paper aims at reporting glyphosate and AMPA contents in Brazilian field crop soils at the country scale from southern states to eastern Amazon. Brazilian field crop farmers are among the highest users of glyphosate-based herbicides (GBH) in the world. Soybean and corn field crop soils from 17 sites were collected at two depths (i.e. 0-20 cm and 20-40 cm) in 2016 and 2018. The study area encompasses three regions of Brazil: southern Brazil, central-west Brazil and eastern Amazon, all having in common intensive, conventional, large-scale grain farming. ßGlyphosate and AMPA contents were measured using a GC-ECD following soil extraction. Both chemicals were ubiquitously detected in soils cultivated under various agricultural practices ranging from ploughing to no-till ones. Average measured glyphosate and AMPA contents were 0.08 ± 0.09 µg/g and 0.17 ± 0.16 µg/g respectively with maximum values of 0.57 µg/g and 0.98 µg/g. Glyphosate plus AMPA contents in the top 40 cm of soils presented cumulated amounts exceeding the annual glyphosate inputs via GBH. This is interpreted as a multiannual persistence of these chemicals in Brazilian agricultural soils. Downward migration of glyphosate and AMPA is also suspected with regard to the vertical distribution of these chemicals along with deeper soil horizons. This study highlights the backlash of conservation agriculture as far as glyphosate and AMPA presence in agricultural soils are concerned. These compounds persistence in Brazilian soils appear to be longer than what is usually reported in the literature, especially so for tropical environments. The worldwide concern about the ubiquitous presence of glyphosate and AMPA in the environment needs a broader screening in Brazilian field crop soils since the majority of the available data comes from Argentina, Europe and to a lesser extent North America.