SummaryThe purpose of the present investigation has been to find the general level and the background level for pollution of soil with dioxins in Denmark, to investigate whether geographical or regional differences exist, to find is such differences are caused by pollution from industrial sources or urban centres. Further to study the influence of culturing and fertilising as well as the variation with depth.
The analytical method used comprised air-drying, soxhlet extraction in toluene, classic clean up on silica and alumina, and high resolution GC/MS. The method was checked on existing soil samples.
The fall 2001 samples of topsoil were collected from ploughed fields, grass fields, gardens or parks without any known contamination with chemicals, sludge or ash. The collection was nation-wide and ranged from Skagen in N to Gedser in S, and from Esbjerg in W to Bornholm in E. In the predominantly westerly wind, the contamination from presumed sources were investigated by sampling exposed zones 1-3 km east of the sources. These comprised larger industrial centres and urban regions, MSW and HSW incinerators, power plants and a steel mill. For comparison, reference samples from rural or remote locations were included. In addition, soils of low and high sludge amendment and a depth profile from a preserved area were analysed.
The results showed that in the depth profile from the preserved soil, far the most dioxin is found in the topsoil depth 0-10 cm, while deeper only minute amounts are found.
The dioxin content in the topsoil of the preserved area (0.9 ng/kg I-TEQ) is about three times higher than that of the low sludge amended soil, whereas that of the high sludge amended soil is about 100 times higher (about 30 ng/kg I-TEQ). That soil, however, has been dressed with amounts of sludge so high that it amounts to a sludge deposit. For comparison, the average in Danish sludge is 10 ng/kg I-TEQ.
In the study of the geographical distribution, the highest dioxin contents 15 ng/kg-I-TEQ were found in soils from parks and gardens in Copenhagen, and 2,2 ng/kg-I-TEQ in a football field in Nyborg near the HSW incinerator. This indicates that the soil in Copenhagen and perhaps also in other cities are considerably contaminated with dioxin.
The dioxin contents in all remaining samples, originating from rural areas, were below 1 ng/kg I-TEQ.
A remarkable result of the investigation is that the exposed zones East of the sources did not display higher dioxin content than the reference zones. Hence, the contamination from source on the surrounding land could not be demonstrated. This is the case for all exposed zones investigated near Ålborg, Århus, Esbjerg, Fredericia, Odense, Roskilde, Kyndby, Frederiksværk and Rødovre.
The total mean of the exposed zones and the reference zones were 0.74 and 0.67 ng/kg I-TEQ, respectively. The difference is neither of practical importance nor statistically significant. Hence, not either in the overall data elevated dioxin level in the exposed zones could be established.
For the reference samples, a geographical North-South gradient and a West-East gradient seem to be present.