Extraction agrochemical from soil

The extraction of polyaromatic hydrocarbons from soil and urban particulates by superheated water was reported in 1994 [17]. Extraction of compounds up to ben-zo[a]pyrene was virtually complete in 15 min at 250°C, with a flow rate of 1 ml mim and a sample of 0.5 g. Good but less complete results were obtained when extracting urban air particulates. The pressure did not influence the extraction behavior, provided it was sufficient to maintain water as a Hquid. The extraction of polychlorinated biphenyls from soil and a river sediment was also found to be complete in 15 min at 250°C [18]. Work with a wider range of compounds showed that extraction was class selective [6, 19], with phenols and Hghter aromatics being extracted at 50 to 150°C, polyaromatic hydrocarbons and lighter ahphatics at 250 to 300°C, but the heavier ahphatics only removed by steam at 250 to 300°C. This selectivity has been compared to other extraction methods [20]. The extraction of agrochemicals from soil has also been studied [6]. 

Analysis of agrochemical samples from soils after extraction by Soxhlet methods are now replaced by analysis following supercritical extractions (Clement et al., 1997). 

The last two forms include up to 2% of the total metal content but they are considered as most important for plant nutrition. Until recently in agrochemical, nutrient and ecological investigations attention has been paid mostly to these two forms and analysis has been performed after extraction with water, buffer solutions or other weak extraction media. However the anthropogenic activity leads among other things to increase in soil pH. The result is slow transition from the silicate to the aluminium buffer region where heavy and toxic metals are released from the minerals. Therefore it is very useful to know more about the content of soils than the usual available quantities. 

---