Questo sito utilizza cookie di terze parti per inviarti pubblicità in linea con le tue preferenze. Se vuoi saperne di più clicca QUI 
Chiudendo questo banner, scorrendo questa pagina, cliccando su un link o proseguendo la navigazione in altra maniera, acconsenti all'uso dei cookie. OK

Qualifying and quantifying linuron degradation capacity with colorimetric reaction? Test case on a linuron treated agricultural soil

The phenylurea herbicides (PUH), such as diuron, isoproturon (IPU) and linuron, are one of the main categories of crop protection products and they kill weeds and other plants that grow where they are not wanted. In recent years researchers are paying greater attention to this family of herbicides because of their high biotoxicity and possible carcinogenic properties and because they require several weeks to months for their removal from the environment. Biodegradation is recognized as the primary force in transformation and mineralization of phenylurea herbicides. Degradation products of phenylureas such as 3,4-dichloroaniline (3,4-DCA) may be even more persistent and bind strongly to soil constituents. The 3,4-DCA (possible metabolite from linuron or diuron) displayed a much higher toxicity than their mother compounds. Several tests can be used to see if there is degradation capacity for herbicides present in soil. The most important techniques are mineralization and degradation experiments. In this study, a facile and sensitive method (diazotization-coupling colorimetric test) was tested to see if it is capable to detect and / or quantify the metabolites of isoproturon, linuron and diuron. If this is possible the researchers can replace the time consuming and costly experiments (like mineralization experiments and detection of metabolites in degradation experiments by HPLC) by a colorimetric test to detect aniline compound metabolites of PUH. This was tested on aniline compounds by testing the colorimetric reaction introduced by Pease et al (1962) on this metabolite. In the first part of this study we wanted to test the possibility to create the metabolite by chemical hydrolysis of the herbicide or to create it by means of microbial degradation , so we tried to detect and quantify the aniline compound with color reaction and to compare the results with those obtained by HPLC.
Then in the second part a case study on a linuron treated agricultural soil was performed. Nine soil microcosms were set up in glass columns and subjected to different irrigation treatments during 4 weeks: (1) a discontinuous irrigation with sterile tap water (this treatment is designated as H2O), (2) a discontinuous irrigation with sterile tap water containing linuron (50 mgL-1) (this treatment is designated as ? x LIN), (3) a single addition of 1mL of 50 mgL-1 linuron in sterile tap water at the start of different treatments, followed by discontinuous irrigation with sterile tap water (this treatment is designated as 1x LIN). Each treatment was performed in triplicate. Just before the start of the different irrigation treatments and after 4 weeks of incubation small amounts of soil were taken from the surface of the soil column and mineralization and degradation experiments (evaluated with both HPLC and the colorimetric test) were started. After four weeks of different linuron treatments soil samples were taken for DNA-extraction to perform a molecular analysis of the Variovorax population and the linuron degradation genes under different exposures. The results obtained shows an effect of the exposure to linuron on the soil microbial community. Although we could not detect a significant increase in the suspected linuron degrading genus (Variovorax), we could observe a shift in the Variovorax community. Under the influence of the discontinuous linuron supply a Variovorax population (S) not part of the dominant Variovorax populations in soils without linuron supply, seems to have become more dominant. This implies that this strain plays an important role in situ linuron degradation and thus supports the hypothesis of Breugelmans et al. (2007) that the genus Variovorax plays a dominant role in in situ linuron degradation. Based on the results obtained in this study, significant differences in the qualification of linuron degradation and the quantification of 3,4-DCA as main metabolite of linuron between HPLC and the diazotization-coupling reaction was observed. We can therefore conclude that the colorimetric reaction is not trustworthy for the quantification of 3,4-DCA and thus for the detection of linuron degradation.

Mostra/Nascondi contenuto.
1 1. INTRODUCTION 1.1. Crop protection products Agriculture and industry increasingly need to use a wide variety of synthetically produced chemicals such as insecticides, fungicides, herbicides, and other crop protection products (Don et al., 1981).The use of crop protection products is necessary to meet the world‟s demand on foodstuff and so far there are no alternatives that can compete with them (Gonçalves et al., 2005). The Food and Agriculture Organization of the United Nations (FAO) defines a crop protection product as any substance or mixture of substances intended for preventing, destroying or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals causing harm during or otherwise interfering with the production, processing, storage or marketing of food, agricultural commodities, wood and wood products or animal feedstuff or which may be administered to animals for the control of insects, arachnids or other pests in or on their bodies. The term includes substances intended for use as a plant-growth regulator, defoliant, desiccant or fruit-thinning agent or agent for preventing the premature fall of fruit and substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport. It is evident that crop protection products, so defined, are used for the variety of benefits it provides to mankind, but unfortunately it also has some side effects (Jeyaratnam 1990). Slow degradation of crop protection products in the environment and extensive or inappropriate usage by farmers can lead to environmental contamination of the water, soil, air, several types of crops and indirectly to humans (Gonçalves et al., 2005). Crop protection products may enter the soil either by direct applications (e.g. agricultural practices) or indirect applications (e.g. accidental spillage, leaks at pesticide dump sites, discharge of wastes from production facilities, or urban pollution) (Sannino et al., 2001). Herbicides are one of the main categories of crop protection products and they kill weeds and other plants that grow where they are not wanted (U.S.EPA ,1995). Among these substances there are the phenylurea herbicides that are a group of herbicides used mainly in either pre- or post emergence treatment of cotton, fruit, cereal, or other agricultural crops ( Sørensen et al., 2008). Some of the phenylurea herbicides such as diuron are also applied as total herbicides on non-crop areas such as roads and railway lines (Giacomazzi et al., 2004). This group of herbicides was introduced shortly after Second World War and became one of the most important classes of crop protection products (Sørensen et al., 2003). In recent years researchers are paying greater attention to this family of herbicides because of their high biotoxicity and possible carcinogenic properties and they require several weeks to months for their removal from the environment (Benitez et al., 2009). Due to their extensive use, the phenylurea herbicides are detected in surface water and

Laurea liv.II (specialistica)

Facoltà: Ingegneria

Autore: Giuseppe Castagna Contatta »

Composta da 69 pagine.

 

Questa tesi ha raggiunto 106 click dal 19/04/2011.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.