Two types of experiments are performed to determine (i) the leaching potential of the test substance, and (ii) the leaching potential of transformation products in soils under controlled laboratory conditions.

At least duplicate leaching columns are packed with untreated, air-dried and sieved soil (< 2 mm) up to a height of approximately 30 cm. Afterwards they are saturated and equilibrated with an “artificial rain” solution and allowed to drain. Then the surface of each soil column is treated with the test substance (non-volatile in water and soil) and/or with aged residues of the test substance. Artificial rain is applied to the soil columns and the leachate is collected. After the leaching process the soil is removed from the columns and is sectioned into an appropriate number of segments depending on the information required from the study. A reference substance (atrazine or monuron) should be used in the leaching experiments. For each soil segment and leachate fraction, the amounts of test substance, transformation products, non-extractables and, if included, of the reference substance should be given in % of applied initial dose.

OECD (2004), Test No. 312: Leaching in Soil Columns, OECD Guidelines for the Testing of Chemicals, Section 3, OECD Publishing, Paris, https://doi.org/10.1787/9789264070561-en.