Pesticides physico-chemical characteristic

Surfactants are often used in agrochemical formulations as adjuvants, e.g. as wetting agents to improve the physico-chemical characteristics of the solution and to increase the uptake of active ingredients (e.g. pesticides) [6-8]. The surfactants can be included in pesticide products and/or added to the tank mix prior to use however, they rarely exceed 1% of the total applied spray. Examples of typical surfactants used in agrochemical formulations are shown in Table 2.8.3 [9]. 

Pesticides are usually applied directly onto plants or into the soil. Some of them penetrate into all the parts of the plant, independently of the method of their application. The residual amount is also affected by the dosage and number of applications, physico-chemical characteristics of the substance, the form of the preparation, type of plant and soil, and atmospheric conditions as well as the length of the period between the treatment and harvesting. 

Chlordecone is a pesticide very resistant to degradation, that is, with a long lifetime [8] it was used mainly for the protection of banana plantations. Now, chlordecone is becoming a new source of contaminatiOTi for cultivated roots as it is still polluting agricultural soils. In the literature [9], it is shown that allophanic soils retain and trap more pesticides than other kinds of soils. Therefore, allophanic soils could be highly polluted but less contaminated for crops and water, and the clay microstructure should be an important physico-chemical characteristic governing the fate of the pesticide in the environment. 

Recently, numerous approaches have been studied for the development of cheaper and most effective adsorbents containing biopolymers. The most widespread biopolymers are polysaccharides [190], chitin [167, 139, 7] and cyclodextrin [157, 26, 32]. These biopolymers reach the increasing demand for treatment of industrial wastewater before their use or disposal. Because the pollutants creates environmental and health diffieulties, associated with heavy metals and pesticides and their deposit through the food chain [39]. Traditional methods for the elimination of heavy metals from industrial wastewater may be inefficient or costly, particularly when metals are present at low concentrations [30, 184]. Chitin, chitosan and oligosaccharides represent interesting and attractive alternative adsorbents because of their particular structure, physico-chemical characteristics, chemical stability, high reactivity and excellent selectivity towards metals. Moreover, Ihey are abundant, renewable and biodegradable resources and have a capacity to associate by physical and chemical interactions with a wide variety of molecules [22, 131]. 

To seek compounds with optimal characteristics for external and internal transfer on a rational basis requires an understanding of pesticide availance and how this is influenced by physico-chemical and biophysical properties to predict the most effective compounds then requires a knowledge of the relationship between these properties and molecular structure. This paper briefly reviews the considerable progress which has been made in these directions and the prospects for future advance. 

---