Mineralization of pesticides

Hapeman-Somich, CJ. Mineralization of pesticide degradation products in Pesticide Transformation Products, Fate and Significance in the Environment, ACS Symposium Series 459, Somasundaram, L. and Coats. J.R., Eds. (Washington. DC American Chemical Society, 1991), pp. 133-147. 

A large number of studies reports the use of photocatalytic reactions for the mineralization of pesticides [33], herbicides [34], toxic organic compounds [18, 35, 36], dyes [22, 37, 38], pharmaceuticals [39, 40]. 

Surface-active substances (SAS) are the most widespread contaminants of sewage and natural waters. They translate in small dispertion condition liquid and firm polluting substances - chlororganic, mineral oils, pesticides. Therefore, the SAS contents determination in water solutions is now one of actual tasks of analytical chemistry. 

In many cases, there is difficulty in preserving residues in samples after collection and prior to pesticide analysis which coincides with a rapid further degradation and mineralization of the pesticide residues under most environmental conditions. Storage stability studies and studies on the reactivity of sample collection equipment in addition to field quality assurance procedures can help address some of these questions. Concerns are accentuated for compounds that have short half-lives in the environment but still have high acute toxicity. 

KoC is an important parameter which describes the potential for movement or mobility of pesticides in soil, sediment and groundwater. Because of the structural complexity of these agrochemical molecules, the above simple relationship which considers only the chemical s hydrophobicity may fail for polar and ionic compounds. The effects of pH, soil properties, mineral surfaces and other factors influencing sorption become important. Other quantities, KD (sorption partition coefficient to the whole soil on a dry weight basis) and KqM (organic matter-water partition coefficient) are also commonly used to describe the extent of sorption. K0M is often estimated as 0.56 KoC, implying that organic matter is 56% carbon. 

In the adsorption with Tenax alone satisfactory results were obtained, while in the presence of mineral oil a considerable proportion of the organophos-phorus pesticides (particularly Malathion and Parathion-methyl) was not adsorbed and was recovered in the filtered water. This drawback can be overcome by adding a layer of Celite 545 which, in order to prevent blocking of the column, is mixed with silanised glass wool plugs. A number of analyses of surface and estuarine sea waters were carried out by this modified Tenax column and simultaneously by the liquid-liquid extraction technique. To some of the samples taken, standard mixtures of pesticides were also added, each at the level of 1 xg/l (i.e., in concentration from 13 to 500 times higher than that usually found in the waters analysed). One recovery trial also specifically concerned polychlorobiphenyls. The results obtained in these tests show that the two extraction methods, when applied to surface waters that were not filtered before extraction, yielded very similar results for many insecticides, with the exception of compounds of the DDT series, for which discordant results were frequently obtained. 

Introduction and setting The purpose of this study was to identify and quantify the sources of heavy metals, especially lead, in soils and plants of the Lower Guadiana River basin and thereby model the potential mobility of lead. Other than direct pollution from mining, the main sources of heavy metal pollution in the environment are by diffuse pollution (Callender, 2004). In agricultural areas this can include lead from the use of pesticides, fertilizers and municipal sludge (Alloway, 1985). Metals can be attached or associated with different mineral phases in the soil, this along with environmental parameters determinesthe availability to plants. 

The assessment of the sustainability of the cultivation of energy crops includes the input and recycling of nutrients, the application of pesticides, the water-use efficiency, the consumption of fossil fuels and the balance of soil carbon. The aim is to recycle the nutrients, which is simple in the case of anaerobic digestion by applying the digestate to the field. If crops are combusted many of the minerals can be returned via the ash. In the case of liquid biofuels, exported nutrients are lost and have to be replaced. The application of pesticides, mainly herbicides, can often be reduced in comparison to food production, but the energy yield per hectare might be reduced if the share of weeds exceeds certain thresholds. Water use efficiency,... 

The European Climate Change Program insisting of the C sequestration, the reduced production/application of pesticides and mineral fertilizers, the improved water retention, and workability. 

Hydrolysis reactions occur by nucleophilic attack at a carbon single bond, involving either the water molecule directly or the hydronium or hydroxyl ion. The most favorable conditions for hydrolysis, e.g. acidic or alkaline solutions, depend on the nature of the bond which is to be cleaved. Mineral surfaces that have Bronsted acidity have been shown to catalyze hydrolysis reactions. Examples of hydrolysis reactions which may be catalyzed by the surfaces of minerals in soils include peptide bond formation by amino acids which are adsorbed on clay mineral surfaces and the degradation of pesticides (see Chapter 22). 

The interest in mineral-promoted organic reactions stems from the need to understand the fate of pesticides in soils and pollutants in sedimentary environments (8), petrogenesis (20-27), humification (19, 28, 29), the origin and evolution of life (1, 30), the use of clays as catalysts in industrial processes (31-37), in pharmaceutical applications (3), and as pigments and fillers in paper, plastic, and rubber (37). 

Nutritional factors may influence the toxicity of pesticides. Research in this area has primarily focused on the role of dietary proteins, particularly sulfur-containing amino acids, trace minerals, and vitamins A, C, D, and E. Studies in rats show that inadequate dietary protein enhances the toxicity of most pesticides but decreases, or fails to affect, the toxicity of a few. The results of these studies have shown that at one-seventh or less normal dietary protein, the hepatic toxicity of heptachlor is diminished as evidenced by fewer enzyme changes (Boyd 1969 Shakman 1974). The lower-protein diets may decrease metabolism of heptachlor to heptachlor epoxide. 

Fig. 8.48 Summary data of pesticide residues in the soil environment, sho wing the distribution between mineralization and extractabihty (A) atrazine, (B) dicamba, (C) isoproturon, (D) hndane, (E) paraquat and (F) tiifluralin. Reprinted from Mordaunt CJ, Gevao B, Jones KC, Semple KT (2005) Formation of non-extractable pesticide residues observations on compound differences, measurement and regulatory issues. Entiron Pollution 133 25-34. Copyright 2005 with permission of Elsevier...

Surface-catalyzed degradation of pesticides has been examined in the context of research on contaminant-clay interactions. Such interactions were observed initially when clay minerals were used as carriers and diluents in the crop protection industry (Fowker et al. 1960). Later specific studies on the persistence of potential organic contaminants in the subsurface defined the mechanism of clay-induced transformation of organophosphate insecticides (Saltzman et al. 1974 Mingelgrin and Saltzman 1977) and s-triazine herbicides (Brown and White 1969). In both cases, contaminant degradation was attributed to the surface acidity of clay minerals, controlled by the hydration status of the system. 

Sorption. Kqp values have been looked upon as constant for neutral organic chemicals. Independent of soil type (73). The parameter Is valid for comparison of leaching potential of pesticides with widely varying water solubility however. It Is difficult to make quantitative comparisons among polar organics. For example, note the wide range In Kq, for oxamyl described In Table IV. This may be due In part to Interactions with soil mineral fractions which become Important when the soil organic matter content Is low (56,112). Also, use of water solubility... 

Bernstein, D. N., T. T. Drew, and M. Kuschner (1980). The translocation and fate of sized man-made mineral fibers following exposure by intratracheal instillation in rats, pp. 343-390. In Levin, A., ed. Proceedings of the National Workshop on Substitutes for Asbestos. EPA Doc. No. 560/3-80-001. Office of Pesticides and Toxic Substances, Washington, DC. 

EINECS is a closed list containing 100,106 entries and counts for about 99% of the chemicals volume on the market. EINECS include chemical substances produced from natural products by chemical modifications or purification, such as metals, minerals, cement, refined oil, and gas substances produced from animals and plants active substances of pesticides, medicaments, fertilizers, and cosmetic products food additives a few natural polymers and some waste and by-products. They can be mixtures of different chemicals occurring namrally or as an unintentional result of the production process. 

Gratzel et al. demonstrated a wide variety of organophosphorus pesticides, including paraoxon, parathion, and malathion, which possess aromatic side chains and/or sulfur atoms can be totally decomposed into carbon dioxide and the corresponding mineral acids by irradiation in a solar simulator in the presence of anatase TiO2 suspensions [41]. The balanced equation based on carbon dioxide evolution for the mineralization of parathion is represented by Eq. (6) ... 

Nitrophenols are persistent pollutants and commonly found in industrial wastewaters. Degradation of nitrophenols to less dangerous materials or mineralization is difficult by natural process involving biodegradation or oxidation. Nitrophenols are commonly found in degradation of pesticides such as parathion and nitrofen. Kiwi et al. (1994) showed efficient photo-and dark oxidation via Fenton-like reactions on 2 and 4-nitrophenols. Photolysis of acidic solutions of H2Oz give OH radicals as primary photoproducts (Baxendale and Wilson, 1957) as follows ... 

---