Correlation between surface and underground aquatic environment pH and pKa in pesticide ionization and contribution to water contamination

Abstract

The behavior of a pesticide in the environment depends on the physical and chemical properties of the environment. The migration of these substances between the environmental matrices depends on the physicochemical properties of these compounds, including pH and the acid or base ionization equilibrium constant (pKa), which define the time these substances remain in the environment, considering that pH more acid is more conducive to a longer permeation time in the environment. The research aimed to correlate the pH values, measured in the water samples collected in the superficial aquatic environment, irrigation channel of the Perimeter Irrigated Board of Russas (PITR), and underground in the municipality of Russas - Ceará. The properties were analyzed in four collection cycles for pesticides: Acephate, Aldicarb, Ametrine, Dimethoate, Imidacloprid, Permethrin and Tebuconazole. The pKa values of the pesticides were obtained from the International Union of Pure and Applied Chemistry (IUPAC), the pH measurements were carried out in situ. The study showed that the results show an acid tendency in the samples collected in the rainy season, which favors the leaching of substances and a longer period of permanence in the environment. It is also observed that the waters of the PITR showed a basic trend, and this is possibly due to the presence of organic matter along the channel. In this study, it was observed that the substances Acephate, Tebuconazole, are weak acids of moderate intensity, which can remain longer in the environment, and Aldicarb and Ametrine, are very weak acids with moderate intensity.