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Humic substances have proved to be very important fractions in soils, playing a key role especially in agricultural soil and influencing chemical and physical soil properties. Spectroscopic methods are widely used to identify the quality of soil humic substances. In this study, 16 soil samples were selected from the Soil Bank of the Soil Science Laboratory at Szent István University, Gödöllő. The samples were extracted using the Hot Water Percolation (HWP) method and the amount of dissolved organic carbon (DOC) in each fraction was measured. The kinetics of the DOC extraction process with the HWP method was estimated. The Ultraviolet Visible (UV-VIS) technique was used to characterize the properties of HWP-dissolved organic carbon (HWP-DOC), measuring absorbance at 200–700 nm. Among the humification parameters, the absorbance ratios at 254 and 365 nm (E2/E3) and 465 and 665 nm (E4/E6), the specific UV absorbance (SUVA) and the UV absorbance ratio index (URI) were estimated. The K factor (humus stability coefficient) and E2/E3 and E4/E6 in NaOH and NaF extracts were also measured. The properties of HWP-DOC were similar in most of the soil samples. There was a good correlation between the content of HWP-DOC and the absorbance at 254 nm. URI, SUVA, E2/E3 and E4/E6 indicated that most of the HWP-DOC in the samples consisted of fulvic acid components with greater activity, simpler structure and low molecular weight.

Ochratoxin A is a mycotoxin produced by Aspergillus and Penicillium species. This mycotoxin is a common contaminant of various foods including cereal products, spices, dried fruits, coffee, beer and wine. Besides species assigned to Aspergillus section Circumdati, black Aspergilli including A. niger, A. carbonarius and A. sclerotioniger are also able to produce this mycotoxin. Black Aspergilli have been found to be the predominant fungi contaminating pistachio nuts worldwide. We examined the species distribution of black Aspergilli on Iranian pistachio nuts. Sequence-based identifications have been carried out using partial calmodulin sequence data. Our data indicate that instead of the potential ochratoxin and fumonisin producing A. niger species, A. tubingensis dominates on Iranian pistachio nuts. This species is unable to produce either of these mycotoxins, consequently do not contribute to mycotoxin contamination of pistachio nuts in Iran. Further studies are in progress to clarify the role of other Aspergilli in ochratoxin contamination of pistachio in Iran.