Recent dioxin levels in zone A of Seveso: northern part of the "Bosco delle Querce" and the soil covering the landfills "Collina di Meda" and "Collina di Seveso"

In order to avoid any risk associated with the reopening of the Bosco delle Querce to the public, the Fondazione Lombardia per I'Ambiente decided to i nvestigate the present PCDD/F concentrations in the soil and the biota of t his area. In 1995, soil sampling sites were selected according to the peak concentrations measured before the remediation of the area and the subdivis ion into two depths, 0-15 and 15-30 cm. Additionally, samples of conifer ne edles, leaves, grass, mushrooms, moss and earth worms were taken in 1994 an d 1995. The samples were extracted in Soxhlet apparatus. The extraction was followed by a liquid chromatographic cleanup using an automated instrument from Fluid Management Systems. The measurements were made using a high res olution gaschromatograph (HP-5980) coupled with a double focusing high reso lution sector held mass spectrometer (VG AUTOSPEC Ultima). All 2,3,7,8-subs tituted PCDD/Fs, including 2,3,7,8-TCDD, were analyzed and the toxicity equ ivalents (Int-TE) were calculated. Most of the soil measurements showed no great differences between topsoil and underlying soil. Generally the Int-TE levels in 32 soil samples were within the range of industrial regions not exceeding the concentration of 16 pg/g dry soil, and more than 70% of the s amples were below 5 pg/g. For comparison, 20 pg Int-TE/g soil can be consid ered as a typical urban background burden. However, in all samples-especial ly in the higher concentrated ones-2,3,7,8-TCCD made a significant contribu tion to the Int-TE which is unusual in urban environments. This is obviousl y due to the accident history of the investigated site since mainly 2,3,7,8 -TCDD was released in 1976. Interestingly, the highest concentrations were measured, not at the sites of maximal concentration in 1976, but in the nor thwest of the area where lower concentrations were found after the accident . It is not yet clear if this is due to insufficient remediation or other r easons. This should be clarified by additional measurements on samples from these sites. Also, the concentration of PCDD/Fs in biota generally lay wit hin the typical range of urban and industrial regions, but a partial effect of the accident could again be seen. Concentrations of all samples which c ould be considered as monitors for the emission in this area, such as leave s, conifer needles and grass, were below 5 pg/g Int-TE with mostly only min or contributions of 2,3,7,8-TCDD. This indicated that the major input origi nated from the polluted air in the industrial region of Milan and not from the accident. Concentrations in biological monitors which were more closely related to soil contamination, such as mosses and earth worms, were in the range of 5-25 pg/g Int-TE with a major contribution of 2,3,7,8-TCDD, and t hus mirrored the situation of the soil which still showed a significant imp act of the TCDD emissions during the accident.