Geochemical patterns in the soils of Zeeland : natural variability versus anthropogenic impact

Abstract

Soils can both be a sink and a source for many components influencing our environment. These components may either be beneficial or damaging and for assessing the current environmental condition knowledge about the extent these components are present in the soils is necessary.

For the Netherlands the government demanded a nation wide inventory of soil contamination by drafting so called soil pollution risk maps. These maps pertain to levels of priority chemicals relative to their legal thresholds in soil. However, I argue that using methods as used in establishing geochemical baselines and deriving models to estimate the anthropogenic enrichment based on these baselines provide much more insight in the extent of the contamination, or enrichment, of the soils.

Therefore a large geochemical survey, using a consequent sampling design and analytical methods, was done in Zeeland, south-west of the Netherlands. The young Holocene marine clayey sediments in the agricultural area were sampled at two depths in the profile, using the deeper layer as a reference. A specific survey was used to estimate the extent of spatial variability. The results indicated a distinct human influence can be discerned and that elements like Cd, Cu, Sn, Sb, Pb, Zn, As are enriched. These elements have also more variability, both in spatial as in attribute space, than the non-anthropogenic influenced elements. The result indicated also that the used legal threshold levels (streefwaarden) are a overestimation of the natural soil background composition.

To assess the soil concentrations of DDT and its derivatives and metabolites (sum DDT), the most troublesome organic components due to exceedance of legal limits, likewise statistical methods as for the inorganic assessment were used. The data was taken from local surveys demanded by the authorities using national standards for sampling design and analytical procedures. This research indicated that the sum DDT values were highly variable, in general determined by small scale variability, resulting in limited value of the data.