Membrane lipid peroxidation in lichens determined by the TBARS assay as a suitable biomarker for the prediction of elevated level of potentially toxic trace elements in soil

Abstract

The use of biomarkers defined as measurable biological parameters at the sub-organism level in which structural or functional changes indicate the presence of pollutants is a promising approach to identify affected sites. The aim of the study was to test the suitability of the level of membrane lipid peroxidation in the widespread epigeic lichen Cladonia rei for the assessment of soil pollution and to develop an effective method to recognise elevated concentrations of potentially toxic trace elements in soil. We collected lichen and soil substrate samples from variously polluted sites and determined the level of membrane lipid peroxidation in the thalli using the thiobarbituric acid-reactive substances (TBARS) assay. Based on the concentrations of Zn, Pb, Cd and As in the soil samples, we calculated the Pollution Load Index (PLI) for particular sampling sites to consider the combined effect of several toxic elements. The model of relationships between TBARS concentrations and PLI revealed that membrane lipid peroxidation does not increase linearly with PLI value, which suggests that above a certain threshold, oxidative stress induced activation of defence aimed at counteracting deleterious effects. We observed that if PLI exceeded the value of 100, the concentrations of TBARS were markedly increased and did not drop below 30 nmol g−1 DW. On the other hand, in lichen samples collected at sites with PLI < 10, TBARS concentrations were lower and as a rule did not exceed 25 nmol g−1 DW. Therefore, we concluded that the effect of soil pollution on membrane lipid peroxidation in the thalli of C. rei can be used in passive soil quality biomonitoring, according to the principle that an increased level of membrane lipid peroxidation is predictive for increased concentrations of elements in the host substrate. Given that this species has not been analysed in detail for the use of biomarkers, this study establishes a baseline and supports practicable use of TBARS concentrations in lichens as biomarkers.