Pesticides in water, sediments and biota of semi-closed coastal lagoons: sources, pathways and impact on aquatic organisms

Abstract

Pesticides are vast class of compounds formulated to control pest. They are applied all over the world and their presence in the environment, especially in coastal lagoons has been inevitable. The knowledge gap concerning pesticides fate in coastal lagoons and their impact on the aquatic organisms as well as the lack of sensible analytical methods for their measurement was the driving force of this work. Focus was made on the pesticides classified as priority substances within the Water Framework Directive (WFD). Óbidos Lagoon (Leiria, Portugal) is of economic importance and as any coastal lagoon, is exposed to anthropogenic activities being for those reason the selected area for all the studies. To fulfill the analytical gaps concerning the priority pesticides (PPs), sensible analytical methodologies were developed for the determination of those pesticides in sediments and macroalgae Ulva sp. of Óbidos Lagoon. The application of such methodologies allowed an in-depth knowledge of pesticides historical application, sources and pathways inside the lagoon. Interestingly, results in the analysis of Ulva sp. show a tendency to accumulate some of the PPs only under adverse weather conditions which points the importance of the climate global changes in the uptake and partition of the PPs in coastal lagoons. Rural activities in the watershed were found to be the main source of the PPs in Óbidos Lagoon. Soil runoff and discharges through small tributaries are the main vehicles of entrance into the lagoon. PPs sediments monitoring reveals that past and present applications of those compounds have been carried out. The low hydrodynamism of the lagoon branches (Barrosa) favors the retention of the pesticides in this part of the lagoon. Among the list of the studied PPs, lindane, p,p’-DDT and the metabolite heptachlor epoxide show to be at levels above the ‘’probable level effect’’ with possible adverse impacts in aquatic organisms. Dissipation studies with chlorpyrifos revealed the importance of salinity, water turbulence and addition of dissolved organic matter (DOM) in its environmental fate. DOM is a very complex mixture of thousands of organic compounds with different sizes, charges and polarity. The development of a new gradient elution extraction methodology that uses a mixture of eluents with different polarities allowed the fractionation of DOM based in its hydrophobicity. Improving knowledge of DOM molecular-level composition is crucial for a better understanding of its reactivity and consequently its impact on pesticides environmental fate.