An alternative approach for the use of water solubility of nonionic pesticides in the modeling of the soil sorption coefficients

Abstract

The collection of data to study the damage caused by pesticides to the environment and its ecosystems is slowly acquired and costly. Large incentives have been established to encourage research projects aimed at building mathematical models for predicting physical, chemical or biological properties of environmental interest. The organic carbon normalized soil sorption coefficient (Koc) is an important physicochemical property used in environmental risk assessments for compounds released into the environment. Many models for predicting logKoc that have used the parameters logP or logS as descriptors have been published in recent decades. The strong correlation between these properties (logP and logS) prevents them from being used together in multiple linear regressions. Because the sorption of a chemical compound in soil depends on both its water solubility and its water/organic matter partitioning, we assume that models capable of combining these two properties can generate more realistic results. Therefore, the objective of this study was to propose an alternative approach for modeling logKoc, using a simple descriptor of solubility, here designated as the logarithm of solubility corrected by octanol/water partitioning (logSP). Thus, different models were built with this descriptor and with the conventional descriptors logP and logS, alone or associated with other explanatory variables representing easy-to-interpret physicochemical properties. The obtained models were validated according to current recommendations in the literature, and they were compared with other previously published models. The results showed that the use of logSp instead of conventional descriptors led to simple models with greater statistical quality and predictive power than other more complex models found in the literature. Therefore, logSP can be a good alternative to consider for the modeling of logKoc and other properties that relate to both solubility and water/organic matter partitioning.