Modelling the accumulation of organic contaminants in soil from the agricultural use of sewage sludge and the significance for human health and the environment

Abstract

La principal forma de gestionar los lodos generados en las plantas de tratamiento de aguas residuales es el reciclaje en tierras de cultivo. Sin embargo, esta práctica también puede introducir elementos potencialmente tóxicos (EPT), contaminantes orgánicos persistentes (COP) y compuestos orgánicos “emergentes“ al suelo. Por ello, esta se ha regulado para los EPT; sin embargo, no para los contaminantes orgánicos (CO). Esta investigación evalúa la significancia potencial para la salud humana y el medio ambiente de la acumulación de CO en el suelo debido al uso a largo plazo de lodos en la agricultura, a través de un modelo. Las concentraciones contemporáneas de CO en los lodos muestran la presencia de COP y CO “emergentes“. Se ejecutó el modelo usando estas concentraciones y la acumulación a largo plazo resultó en un incremento de las concentraciones en el suelo mezclado con lodos respecto a sus niveles de fondo. Comparando los resultados obtenidos con el modelo con valores de análisis del suelo (en inglés, soil screening values o SSV), se concluye que los esfuerzos de regulación de CO deben priorizarse para a los Perfluoro-n-octane (PFO) debido a su significancia potencial para la salud humana y el medio ambiente.

The recycling of sewage sludge (SS) to farmlands is the main way to manage it, because of its benefits. However, it can also introduce PTE, POPs and “emerging” organic pollutants to the soil. To prevent risks to human health and environment, current regulatory framework applies to PTEs in agricultural soils that have been amended with SS. However, organic contaminants (OCs) have not been regulated in the United Kingdom. To assess their potential significance human health and environment, a model of the accumulation of OCs in soil due to long-term use of sewage sludge in agriculture has been performed. This model has a limit of 100 years of annual SS amendments, since Zn is the limiting element within the current regulatory framework for PTEs; and considers a quantity of SS applied annually to agricultural soil that is based on nitrogen best practices. Contemporary concentrations of OCs in UK sludges show the presence of POPs and “emerging” OC, which are not necessarily decreasing in reference to past years. The model was run with these concentrations and the long-term accumulation resulted in an increment in the mixed soil concentrations with respect to the background soil concentrations. The model was run with the limit values for OCs in sewage sludge that was suggested in the Working document on sludge - Third Draft; the results showed that within the current regulatory framework of PTEs, the regulation of the OCs is irrelevant. Comparing the results obtained in the long-term accumulation model with reported soil screening values (SSVs), it is shown that efforts must be redirected to PFOs because of their potential significance to human health and the environment.