Title: Effects of synthetic surfactants on the fate of pesticides and trace metals in soil
Authors: Hernandez Soriano, Maria del Carmen; S0186890
Issue Date: 30-Jun-2009
Abstract: Surfactants are solubilising agents that are commonly used in householdand industrial applications. A large fraction of surfactants used is emitted to wastewater they can reach the soil through wastewater irrigation or applications of sewage sludge and pesticides. Surfactants are relatively harmless in the soil ecosystem since they are readily degradable and have low toxicity. However, surfactants can facilitate the mobility of different contaminants in soil, and this indirect risk of surfactants on groundwater contamination prompted this study. The aim of this soil chemical study is to evaluate the effects of different types of surfactant on mobility of four organophosphorous pesticides and of the trace metals Cu, Cd, Pb and Zn. Surfactants assayed through this thesis were selected as representative of compounds used in agriculture, i.e. their presence in pesticide formulations or their presence in sludge and wastewater.Sorption and desorption of organophosphorous pesticides were measured in the presence of different surfactants (cationic, anionic and non-ionic) through batch assays in 9 different Mediterranean soils. The presence of a cationic surfactant increased pesticide retention in soils more than 100 times for the most hydrophobic compound, and this increase was most pronounced in soils with high CEC values, suggesting that sorption of the cationic surfactant promotes pesticide binding at the hydrophobic moiety of the surfactant. Addition of non-ionic and anionic surfactants increased or decreased the pesticide retention in soil, depending on soil characteristics and type of pesticide, with a factor of 2 at most.A degradation experiment of the same organophosphorous pesticides in a Mediterranean soil in the presence of three different surfactants (cationic, anionic and non-ionic) or wastewater showed that the non-ionic surfactant enhanced degradation rates for all the pesticides except the mosthydrophobic and at high cationic surfactant concentration, pesticide half lives were increased 3–10 times, and in the case of the most hydrophobic compound (diazinon), circa 55% of the added concentration was still recovered in the soil after 4 months of incubation. These results indicate that increased pesticide sorption in presence of cationic surfactantsdiminishes the availability of pesticides to microorganisms, thus decreasing biological degradation.The effect of surfactants on trace metal solubility was studied in short-term (24 h) batch experiments or in a long-term (1 70 days) incubationexperiment with a collection of 8 soils and different surfactants. Submicellar concentrations of cationic surfactants decreased trace metal solubility about 5 20%, while submicellar concentrations of anionic surfactants increased metal solubility by 30% at most. Cationic surfactants decreased the concentrations of dissolved soil organic matter, likely by promoting sorption of the hydrophobic matter. In contrast, anionic surfactant increased the soil organic matter solubility by reducing soluble Ca2+ that acts as a coagulant for organic matter. The changes in soluble soil organic matter statistically explained surfactant effects and this was confirmed by speciation calculations. Above the critical micelle concentration, the increase in metal solubility was up to 100-fold and was largely related to the relative increase in soil organic matter solubilitythat was pronounced at these high surfactant concentrations due to micellar solubilization.Effects of irrigation with A22 on metal leaching were assessed in column experiments at two flow rates and at different surfactant concentrations. Leaching with A22 increased copper (Cu) concentration in the leachates up to three times compared to the control treatment and Cu was not mobilised by complexation with the surfactant, but indirectly through solubilisation of soil organic matter. The solubilisation of soil organic matter is likely related to the precipitation of A22 with Ca2+ ions.The solution Ca concentration at the highest A22 dose was only half of that in the control, which likely resulted in solubilization of humic substances, thereby facilitating leaching of soil DOC and associated Cu ions.Overall, the most significant effects are, in general, the enhancement of hydrophobic pesticides retention by cationic surfactants and the increased solubilisation of organic matter and resulting mobility of trace metals by anionic surfactants.
Table of Contents: Summary vii
Samenvatting xi
Resumen xv
Chapter 1 General introduction and objectives 1
1.1 Surfactants 1
1.1.1 Definition and classification 1
1.1.2 Surfactants properties 3
1.1.3 Production and use 4
1.2 Surfactants in soil 5
1.2.1 Sources of surfactants in soil 5
1.2.2 Soil remediation techniques 6
1.3 Effect of surfactants on the fate of pesticides and trace metals in soil 7
1.3.1 Pesticides 7
1.3.2 Trace metals 10
1.4 Objectives, hypotheses and outline of this work 14
Chapter 2 Response surface methodology for the microwave assisted extraction of insecticides from soil samples. 19
Abstract 19
2.1 Introduction 19
2.2 Materials and methods 21
2.2.1 Materials 21
2.2.2 Chemicals 22
2.2.3 Instrumentation 23
2.2.4 Calibration curves and recovery experiments 23
2.2.5 Extraction and analysis 24
2.2.6 Experimental design 24
Screening design 25
Box-Behnken design (BBD) 26
Application of the method to spiked samples 29
2.3 Results and discussion 29
2.3.1 Analytical method performance 29
2.3.2 Screening design 30
2.3.3 Response surface design 32
2.3.4 Optimization 36
2.3.5 Validation of the method 37
2.3.6 Applicability to spiked soil samples with different characteristics 38
2.4 Conclusions 39
Chapter 3 Interaction of pesticides with a surfactant modified soil interface: Effect of soil properties. 41
Abstract 41
3.1 Introduction 41
3.2 Materials and methods 42
3.2.1 Materials 42
3.2.2 Chemicals 43
3.2.3 Pesticide sorption 43
3.2.4 Extraction and analysis 44
3.2.5 Statistical analysis 44
3.3 Results and discussion 45
3.3.1 Pesticide sorption by soils in aqueous solution 47
3.3.2 Pesticide sorption by soils in TW80 and A22 solutions 49
3.3.3 Pesticide sorption by soils in HDTMA solutions 50
3.3.4 Competitive effect on dimethoate sorption 52
3.4 Conclusions 53
Chapter 4 Retention of organophosphorous insecticides on a calcareous soil modified by organic amendments and a surfactant. 55
Abstract 55
4.1 Introduction 55
4.2 Materials and methods 56
4.2.1 Soil and organic amendments 56
4.2.2 Insecticides 56
4.2.3 Adsorption and desorption isotherms 57
4.2.4 Extraction and analysis 57
4.3 Results and discussion 58
4.3.1 Adsorption isotherms 58
4.3.2 Desorption isotherms 61
4.4 Conclusions 63
Chapter 5 Degradation of insecticides in a Mediterranean soil in the presence of wastewater and surfactant solutions. A kinetic model approach. 65
Abstract 65
5.1 Introduction 65
5.2 Material and methods 67
5.2.1 Soil 67
5.2.2 Chemicals 67
5.2.3 Pesticide degradation 68
5.2.4 Extraction and analysis 69
5.2.5 Dehydrogenase activity 69
5.2.6 Mathematical treatment of the data 70
5.3 Results and discussion 71
5.3.1 Pesticide degradation in soil treated with Milli Q water 71
5.3.2 Pesticide degradation in soil treated with surfactant solutions 75
5.3.3 Pesticide degradation in soil treated with Granada wastewater 78
5.3.4 Individual pesticide degradation 79
5.3.5 Dehydrogenase activity 80
5.3.6 Model fitting 81
5.4 Conclusions 83
Chapter 6 Short and long-term effects of surfactants on the solubility of trace metals and soil organic matter 85
Abstract 85
6.1 Introduction 86
6.2 Material and methods 87
6.2.1 Soils 87
6.2.2 Incubation experiment 88
6.2.3 Batch assays 88
6.2.4 Estimation of proportion of soil- and surfactant-derived DOC 89
6.2.5 Precipitation of anionic surfactants with calcium 90
6.2.6 Metal complexation 90
6.3 Results 91
6.3.1 Precipitation of anionic surfactants 91
6.3.2 Complexation of anionic surfactants with metals 92
6.3.3 Incubation experiment 93
6.3.4 Batch experiments 96
6.4 Discussion 106
Chapter 7 Effect of time and soil-solution ratio on the release of metals from contaminated soil during extraction with Aerosol 22 109
Abstract 109
7.1 Introduction 109
7.2 Materials and Methods 111
7.2.1 Soil 111
7.2.2 Chemicals and analytical conditions 111
7.2.3 Desorption tests 111
7.2.4 Kinetic modelling 112
7.2.5 Modelling the effect of solution/soil ratio 113
7.3 Results 113
7.3.1 Assessment of equilibrium conditions 113
7.3.2 Effect of solution/soil ratio 115
7.4 Conclusions 117
Chapter 8 Copper leaching from soil as affected by the anionic surfactant Aerosol 22. 119
Abstract 119
8.1 Introduction 120
8.2 Materials and methods 121
8.2.1 Column experiment 121
8.2.2 Chemical analyses 122
8.3 Results 123
8.4 Discussion 130
Chapter 9 General conclusions 133
Background. 133
Conclusions 133
Overall conclusion and outlook 138
References 139
List of publications 151
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division Soil and Water Management

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