Resumen de Fate and effects of waterborne contaminants of emerging concern in the soil-plant system. Impact of biochar soil amendment to mitigate their plant uptake
Water scarcity is an issue of global concern due to the increase of the population and the climate change, which both increase the water demand. Many arid and semiarid countries are facing high water stress and the use of reclaimed water becomes a valuable resource. Many countries' economy is based on the agro-food sector, with amounts ca. the 70% of water demand. For this reason, reclaimed water represents an important component of wise water management.
Wastewater treatment plants (WWTP) are designed to remove efficiently some biodegradable compounds, however, they are not able to remove a number of recalcitrant organic coñtamina0nts known as chemical oxygen demand (COD). There are many sources of water pollution, and contaminants of emerging concern (CECs) including many compounds that they are not legislated and recently some effects to the environment have been observed. For example, pharmaceuticals, personal care products, flame retardants, microplastics, etc.
Consequently, plants are exposed to a huge number of chemical contaminants that are present not only in water, but also in air or soil. For this reason, it is important to understand the dynamics involved in the plant uptake of these CECs and more specifically in crops.
In this Thesis, the uptake of some CECs, chosen by their occurrence in the environment and their physical-chemical properties, has been assessed. To elucidate the factors that are involved in the uptake of these contaminants, three different experiments were performed in a greenhouse.
Therefore, this Thesis is divided in the three experiments. In the first one, the plant uptake of some CECs with a perlite:sand mixture and its modelling were assessed. Moreover, a mass balance was performed to evaluate the persistence of the CECs in the substrate. Then, by inverse modelling, the half-lives of CECs in the soil-plant system were estimated.
In the second experiment, most of the CECs that were added in the irrigation water were taken up by lettuce. Hence, in this experiment, biochar, which is a soil improver, was assessed as a soil amendment to mitigate the uptake of these CECs in lettuce. To confirm this hypothesis, different biochar amendments were performed (O, 2.5 and 5% w/w biochar) to an agricultural soil from the Llobregat's Delta. Finally, it could be observed that the addition of biochar, reduced the concentration of CECs in lettuces.
Since these two experiments demonstrated that CECs can be uptaken by crops and translocated to edible parts, and it well known that plants can metabolize xenobiotics through transformation, conjugation and sequestration steps, in the third experiment, an enzymatic digestion was performed to determine the conjugated CECs fraction. Interestingly, the conjugated fraction accounted up to more than 80%, which should be taken into account in risk assessment studies.
Finally, in the same experiment, some effects of CECs to lettuce were elucidated. Visual differences between non-exposed and exposed lettuce were observed. For this reason, a metabolomic approach was applied to correlate the presence of CECs with the changes in the metabolome and the changes in chlorophyll content and plant morphology.
