Alkaline extractions from humic material are used to risk assessment in soils. However, there are questions about the type of extraction most suitable for this evaluation. Thus, this work evaluated different soil extractions in search of realistic environmental conditions (simulated rain). The parameters obtained revealed significant differences between the levels and structural characteristics of organic matter, depending on the extractant used, reinforcing the importance of developing methodologies and analytical procedures that minimize structural changes and may be more representative of the molecular structures of organic matter found in soils. The results showed that the material extracted by simulated rain is similar to the fulvic acids of the soil organic matter extracted by alkaline extraction showing the importance of this type of extraction for risk assessment studies in soils.

O objetivo do presente trabalho foi otimizar o procedimento para extração de substâncias húmicas de turfa, utilizando fluxo contínuo, com diferentes extratores (NaOH, KOH e Na4P2O7). A influência do extrator na capacidade de complexação das substâncias húmicas por macro e micronutrientes também foi investigada. Os resultados mostraram que a extração por fluxo contínuo é eficaz, reduzindo o tempo necessário para o passo de extração e, além disso, indicando que as substâncias húmicas apresentaram elevada afinidade para os nutrientes essenciais Ca2+ e Mg2+. Além disso, as maiores capacidades de complexação foram obtidas quando utilizou o extrator Na4P2O7, mostrando não só a eficiência desse composto como agente de extração, mas também a sua aplicação promissora no processo, uma vez que a sua elevada capacidade de complexação permite disponibilizar os nutrientes complexados, bem como diminuir a quantidade de estes nutrientes que podem ser lixiviados, contribuindo, assim, para evitar contaminação do meio ambiente.

The aim of the present work was to optimize a procedure for extraction of humic substances (HS) from peat, using continuous flow with different extractants (NaOH, KOH and Na4P2O7). The influence of extractant on the complexing capacity of humic substances for macro and micronutrients was also investigated. Our results showed that the extraction by flow is efficient, reducing the time required in the extraction step and, furthermore, indicating that the extracted HS have a high affinity for the essential nutrients Ca and Mg. Moreover, an enhanced complexation was achieved by using Na4P2O7, demonstrating not only the efficiency of this compound as extractant, but also its promising application in the process, since its high complexing capacity allows to make available the complexed nutrients as well as diminishing the amount of these nutrients that could be lixiviated, thus contributing to prevent environmental contaminations.