Suitability of the OCDE tests to estimate contamination with 2,4-dichlorophenol of soils from Galicia (NW Spain)

The objective of the present study was to verify whether the generic reference levels (GRL) for soils contaminated with 2,4-dichlorophenol (2,4 DCP), established by Spanish legislation and published in the Real Decreto 9/2005, are accurate for Galician soils. For this, the surface horizons of seven soils under different types of land use were experimentally contaminated with different doses (between 0 and 10,000 times the GRL) of 2,4 DCP, and were then were subject to OECD toxicity test numbers 208 (root emergence and elongation) and 216 (soil nitrogen mineralization). The results obtained for the nitrogen mineralization test were difficult to interpret because they varied among soils, whereas the results of the root germination and elongation test were more coherent — the values decreased with increasing doses of contaminant added to the soil. The results suggest that the root elongation test reflects the effect of this contaminant more clearly than the soil nitrogen mineralization test. Nevertheless, considering that in the lowest quality soils (i.e. agricultural soils containing a very low level of organic matter) contaminant doses of up to 1000 times the GRL did not affect root germination and elongation, it is clear that the GRL indicated in the relevant legislation are very low for the soils under study and that the threshold should be established taking into account the soil characteristics.