Environmental Risk Assessment of Glyphosate and Aminomethylphosphonic Acid (AMPA) in Portuguese Groundwater Ecosystems

The aim of the present study was to assess the risk related to the exposure of groundwater ecosystems to herbicide glyphosate and its non-relevant metabolite aminomethylphosphonic acid (AMPA) based on the quotient between measured concentrations gathered from the Water Resources Information System of Portugal, and groundwater quality standards set in legislation and estimated from environmental quality standards in surface waters. Glyphosate was analyzed in 103 groundwater samples collected from 80 wells located in 21 aquifer systems from the four hydrogeological units of mainland Portugal, between 2019 and 2021. It was detected in 14% of the total samples; however, only 10% presented concentration levels above 0.1 µg/L, the groundwater quality standard, and none of these values exceeded the value of 8.67 μg/L estimated from the annual average environmental quality standard proposed for glyphosate in surface waters. In comparison, AMPA was detected in only 5% of 63 groundwater samples, in four dug wells. In both compounds, the maximum concentration level was quantified in a dug well located in the O25-Torres Vedras aquifer system, from the Western unit, with 4.69 and 4.24 μg/L for glyphosate and AMPA, respectively. The results of this study demonstrate that it is extremely important to raise awareness and offer training to farmers on the sustainable use of plant protection products and good agricultural practices, in order to prevent groundwater contamination and improve its quality. There is also an urgent need to carry out ecotoxicological tests with further groundwater species from different functional groups in order to obtain a quality standard that accurately represents the groundwater communities.