Determination of low molecular weight organic acids (LMWOAs) in environmental samples

Abstract

This paper presents a quick method to identify and quantify ten low molecular weight organic acids in environmental samples (e.g., soil, cultivation substrate). The procedure involves extraction of the acids from the sample with a dilute acid of a pH of 2, followed by the separation and quantification of ten acids, i.e., oxalic, formic, acetic, malic, maleic, lactic, malonic, succinic, fumaric, and citric, by reversed-phase liquid chromatography (RPLC). The detection limit was in the range from 8.6 × 10-4 nM to 0.014 microM, with recovery in the range from 60 to 100%. A proven method was applied for the determination of exudate components in the king oyster mushroom (Pleurotus eryngii) post-cultivation straw substrate spiked individually with Cu2+, Co2+, Cd2+, Zn2+ and Ni2+ at 10 mM. The generation/exudation of LMWOAs was metal dependent and was strongly induced by Ni and Cd, less induced by Co and Cu, and suppressed by Zn ions. At 10 mM of Ni, the total concentration of the acids was about 6 times as high as that of the control. We can assume that particular metals alter the mycelium growth and mushroom physiology mainly through the competitive inhibition of nutrients such as Fe and Ca, and also by the inactivation of metalloenzymes, responsible for the substrate mineralization and antioxidant potential. Moreover, organic ligands do not only enhance the solubility of the trace metals, but also they reduce their toxicity to the mushroom, increasing uptake/accumulation abilities during bioremediation of soil/medium contaminated with heavy metals