This document describes a method to compare the quality of soils by determining the fatty acid composition of the leaves of plant species grown in these soils. This method does not make it possible to determine an optimal value of the Omega-3 index and, therefore, cannot be used to determine the intrinsic quality of a soil from a specific area (regarded as homogeneous). The method can only be used to compare the quality of soils between various areas. This method is applicable to: soils from contaminated sites; amended soils; soils after remediation; soil with waste products (e.g. slurry, manure, sludge or composts). Alternatively, the quality of soils can be assessed by determining the Omega-3 index of Lactuca sativa seedlings grown in these soils under controlled conditions (i.e. phytotronic chamber) and by comparing these values to those obtained from control soils (see Annex B).