Soundness of in situ lipid biomarker analysis: Early effect of heavy metals on leaf fatty acid composition of Lactuca serriola

In previous studies we proposed the plant leaf fatty acid composition, and more precisely the ratio C18:3/(C18:0 + C18:1 + C18:2) as a tool to diagnose soil contamination ex situ. These studies led us to normalize this parameter as a biomarker of soil quality using Lactuca sativa growing under controlled conditions as the plant model species. The evaluation of the toxic effects of pollutants is more difficult to grasp in a real and more complex environment. Hence we developed a study to test the hypothesis that plant leaf fatty acid composition could be used also as a reliable tool to diagnose soil contamination in situ. We tested whether Lactuca serriola (prickly lettuce) could be used as a plant model species for such studies, primarily because it is widely distributed in various European countries and recorded at different habitats, and regarded as an ancestor of the cultivated lettuce L. sativa that was used for ex situ experiments. The results show that the lipid biomarker values were significantly lower in leaves of L. serriola grown on a metallurgic landfill soil than in leaves of plants harvested on surrounding countryside areas. To determine whether the value of the lipid biomarker in L. serriola leaves could be correlated to the soil metal content, we also measured the metal content of the soil corresponding to the rhyzospheric areas from where the prickly lettuce leaves were harvested. The results of the Principal Component Analysis (PCA) show that the lipid biomarker is negatively correlated with both Ni and Cr content. Moreover, these results show that the lipid biomarker values measured in situ were repeatable from year to year, confirm that this biomarker measured in situ would provide an early indication of a plant's exposure to metal, and could be therefore used to facilitate or strengthen the diagnosis of soil