78446 - Pollutants in the soil-water-plant system

Learning outcomes

At the end of the teaching, students will aquire the expertize to evaluate, to analyze and, from a theoretical point of view, to predict the main depuration processes acted by the soil-plant system against organic and inorganic pollutants by retention and degradation mechanisms. Specifically, students will be able: (i) to correlate the behaviour of pollutants in the soil-water-plant system with their physical and chemical properties and those of the soil and water considered;  (ii) to produce a report on topics related to the behaviour of pollutants in the soil-water-plant system; (iii) to understand scientific reports on the evaluation and prevision of the main phenomena of pollution of soil, water and plants.

Course contents

1. Classroom teaching (36 hours)

1.1. Adsorption of pollutants by soil components (10 hours)

1.1.1. Soils characteristics and pollutants adsorption. Introduction to the program. Definitions of pollutant. Partition equilibria among the environmental compartments. Soil texture: structure of expandable and non-expandable phyllosilicates and adsorption. Siloxane cavity as nucleophilic reactor. Effect of isomorphic substitutions and hydration rate of clays on the adsorption of organic and inorganic pollutants. Soil organic matter and adsorption. Adsorption on soil oxides and hydroxides. State diagram of hematite and gibbsite. Adsorption as a function of soil pH.

1.1.2. Pollutant characteristics and soil adsorption. Physical and chemical characteristics: solubility, vapor pressure, Henry constant, Partition coefficient n-octanol/water (Kow), soil-water partition coefficient (Kd), acid and base dissociation constants (Ka and Kb), pollutant charge effect on soil adsorption.

1.1.3. Macroscopic effects of pollutant adsorption by soil. Adsorption and desorption isotherms: batch and column techniques. Reversible and irreversible adsorption mechanisms. Thermodynamics of adsorption.

1.1.4. Soil adsorption and retention at molecular scale. Adsorption mechanisms: Van der Waals interactions, hydrophobic interaction. Adsorption as a cooperative process. Hydrogen bonding. Protonation and adsorption. Cation exchange. Water bridging and cation bridging. Anion exchange. Ligand exchange.

1.2. Transformation of pollutants in soil and water (8 hours)

1.2.1. Abiotic degradation. Potential energy of adsorption (reversible and irreversible adsorption). Adsorption and abiotic degradation. Soil characteristics and degradation. Inner sphere and outer sphere complexes. Effect of isomorphic substitutions on pollutant degradation. pH-Dependent homogeneous and heterogeneous hydrolysis. Photolytic transformations: Direct photolysis and Jablonsky diagramme. Indirect photolysis. Water potabilization by titania.

1.2.2. Biotic degradation. Definition and characteristics. Physical and chemical characteristics of the soil-root interface. Rhizosphere gradients: pH, nutrients, redox potential, exudates, microbial and enzymatic activities. Effect of rhizosphere activities on the soil mineral structure. Soil characteristics and biotic degradation. Direct and indirect microbial degradation. Oxidation, hydrolysis and reduction transformations. Biological beds.

1.3. Heavy metals and potentially toxic elements (8 hours)

1.3.1. Metals in the soil-water-plant system. Metals and heavy metals. Metal speciation in soil and in the soil water (ions, ionic pairs, organometal complexes). Metal availability as a function of soil/water pH. Dissolved organic matter and metal transfer to water bodies. Metal speciation and redox potential. Phytoextraction of metals in the form of chelates. Heavy metal toxicity: cupper, cadmium, arsenic, nickel, and lead.

1.3.2. Acid rain. Formation, evolution, and effects on the soil-plant system. Buffering of soil components against acidification (carbonates, organic matter, base metals). Aluminum mobilization: formation of free species, effect on root cell wall.

1.4. Pollution of soil-water system and plant contamination (10 hours)

1.4.1. Soil pollution. Groundwater Ubiquity Score (GUS) Index. Mitigation of soil and water pollution. Current Directives on soil and water pollution. Sustainable decontamination strategies: Chemical and physical approaches, cation exchange, composting, phytoremediation.

1.4.2. Plant uptake. Phytostabilization: Root concentration factor as a function of pollutant Kow. Phytodegradation: Transpiration Stream Concentration Factor as a function of pollutant Kow. Plant translocation of acid pollutants: ionic trap theory. Enzymatic phytotransformation: phase I (oxidation, hydrolysis, reduction), phase II (conjugation with biomolecules with low molecular weight), Phase III (conjugation with biomolecules with high molecular weight). Phytovolatilization.

1.4.3. Plastics in the soil-water-plant system. Production, environmental fate, effect on soil characteristics (humidity, organic matter content, microorganisms etc). Interactions between micro- and nano-plastics and other pollutants in soils and water bodies. Mechanism of entrance of plastics into plants.

2. Case studies (24 hours)

2.1. Animal manure as fertilizers. Strategies to contain antibiotics, antimicrobial resistance, nitrates, and gas emissions.

2.2. Constructed wetlands. Humid areas designed to remove plant nutrients and pollutants from wastewater, stormwater, or agricultural runoff, by the means of spontaneous processes such as filtration, adsorption, precipitation, and biological degradation: modeling the dissipation rate.

2.3. Micro- and nano-plastics in agricultural soils. Characteristics, measurements, and quantification. Effects on soil health and food safety.

Each case study is introduced by a technical seminar. Two groups of students will be asked to read different scientific reports/reviews and to report the group’s discussion and possible solutions. Laboratory activities of extraction of pollutants from soil and quantification will be performed. Lab activities are held at the Laboratory of Chemistry, Biochemistry and Food technologies (Lab CBA).

Readings/Bibliography

Periodic table of the elements.

All the handouts will be available. If needed, handouts in english are available for foreign students.
The following books/chapters are suggested:
Agrofarmaci - Conoscenze per un uso sostenibile, Gruppo Perdisa Editore, II Parte (pg. 151-377). The book will be made available by the teacher.
Marschner H., Mineral Nutrition of Higher Plants. Academic Press, London, 1995. Chapter 15: The soil/root interface.

Teaching methods

During the classroom teaching, the students will acquire the knowledge of the main pollution/depuration mechanisms of the soil-water-plant system, the main techniques to preserve the quality of soil and water bodies and the strategies available to mitigate some pollutions case studies. The knowledge acquisition and the comprehension of students will be monitored along the entire teaching period through a continuous interactions between the teacher and students through a problem solving approach. The teacher-student interaction is also finalized to improve the development of the evaluation skills and to increase the communication ability ofthe students.

During the laboratory activities, the students will learn: (i) to define the rationale of the laboratory trials; (ii) the knowledge of the techniques adopted to conduct the trials, (iii) handling the samples and evaluate the treatment of the soil/water/plant samples; (iv) the collection and elaboration of collected results; (v) the interpretation of results into the light of the knowledge acquired during the teaching activities in the classroom. At lab scale, some pollution scenarios will be presented and the students, in small groups or alone, will select a possible strategy to follow. At the end, a report will be produced and will be defended at the oral exam.

Assessment methods

The knowledge of the main topics will be evaluated by considering the quality of the laboratory report and the strategy adopted to solve the case study. At the same time, specific questions will be asked to verify the comprehension of the main topics considered during the teaching activities. The final quotation has to be at least equal to 18/30. The final quotation of the Course "Chemical and Biochemical Quality of Soil" will be the mean of this quotation and that obtained for the Course of "Indexes of Soil Quality" (27562). You can, on request, sustain the final exam in English. Teaching tools

Teaching tools

Blackboard, Projector, Handouts, slides, Periodic Table of the Elements

Office hours

See the website of Ilaria Braschi