Resumen de Novel developments in the diffusive gradient in thin films (dgt) technique for the determination of bioavailable mercury and other trace metals in aquatic and terrestrial environments
Mercury (Hg) is a natural and abundant element in the earth‘s crust, but its presence in the environment has increased, mostly, due to the anthropogenic sources which have been done in the past and also in the present. It is a heavy metal with a high toxicity, especially the bioavailable species of Hg because they can be bioaccumulated and biomagnified in the food chains, reaching high Hg concentrations in the last step of the chain. Nevertheless, the contamination from other metals is a global concern because of their presence (in the case of lead or cadmium) or their excess (such as nickel, zinc or copper) in the environment. Focusing on the soil, the incorporation of the bioavailable fraction of these elements in the agricultural soils turns the crops to intermediate reservoirs, arriving to the animals and human beings through the intake. This leads to an essential claim for the determination of the metal bioavailable fraction in the environment for the control of the different pollution sources as well as the possible remediation of the impacted ecosystems.
For this reason, a passive sampling called ―Diffusive Gradient in Thin film‖ (DGT) technique was used in this PhD. This passive sampler is able to measure the labile concentration of the species concerned in the environment, in a specific deployment time. Through its diffusive mechanism, DGT technique is able to mimic the biologic membranes and, therefore, it can be considered as a good tool to evaluate the bioavailability of the metals in the environment.
Due to the ability of this technique to be used in different matrixes, this thesis could be separated in two different parts. In chapters 3, 4 and 5 can be found the experiments in the aquatic systems, whereas the chapters 6, 7 and 8 contain the studies in the terrestrial environments.
The studies from the chapters 3 and 4 were performed in the low part of the Ebro River basin due to the environmental interest which causes the historical Hg pollution from the chlor-alkali Flix factor. In the Chapter 3, different preliminary probes in the laboratory were determined for the application of polymeric inclusive membranes (PIM) in the DGT design for the study of Hg in the Ebro River. Subsequently, the most optimal PIM-DGT design was applied in the field together with the DGT devices to be compared. In the Chapter 4, a correlation between the amount of phytochelatins from two different macrophytes found in the Ebro River and the bioavailable Hg concentration from DGT devices was studied in two different seasons of the year. Finally, the experiment from Chapter 5 was carried out in the Tully River, on the north-east of Queensland (Australia). The aim was to study the impact from one fungicide with a Hg base used in the past massively in the cultivations around this river to control a pineapple disease of sugarcane.
Afterwards, in the chapters 6, 7 and 8 were included the studies in the terrestrial systems. Concretely, the first two experiments were based on the application of two different DGT devices with different pore size in two soils with different characteristics. The first one was focused on the difference between these two selected soils and the second one was oriented towards one type of soil and, applying two different organic amendments (biochar and compost), their effectiveness for the immobilization of Hg in soil was determined. Finally, the Chapter 8 was explained a similar study as in the Chapter 7 but in this case 6 different trace metals were measured: cadmium, chromium, copper, nickel, lead and zinc. By means of a sequential extraction and, together with the lettuces analysis, the effectiveness of the different organic amendments to immobilize metals in soil as well as the application of DGT technique to predict the metal uptake by lettuces were determined.
