Potential degradation efficiency of Chlorella vulgaris towards methamidophos and diazinon

Abstract

Pesticides are chemical substances that have become essential for global food production. However, their extensive use has resulted in significant environmental and health costs. Among the most widely used are diazinon and methamidophos, an insecticide and acaricide, respectively. These chemicals are classified as highly hazardous with high toxicity upon contact, ingestion, and inhalation. They are known to cause mutagenic effects, cancer, damage to the endocrine and nervous systems of humans, and their high solubility makes them likely to be found in soil, water, air, and certain foods. In this research, we evaluated the use of the microalga Chlorella vulgaris for phycoremediation of these two pesticides. The first step was to establish and optimize the growth parameters of C. vulgaris to maintain the microalgae in a state of reproduction. Favorable results were obtained at pH 7.0, a dilution ratio of 1:2 for the culture medium, and a photoperiod of 12 h of light and 12 h of darkness. Subsequently, the Minimum Inhibitory Concentration (MIC) and the Half-Maximal Effective Concentration (EC50) of the pesticides diazinon and methamidophos were evaluated. The microalga exhibited a high tolerance rate, with concentrations exceeding those naturally found in the environment. Based on these results, the conditions for assessing the biodegradation of both pesticides by the microalga were established. The outcome showed degradation percentages of 96 % for diazinon (25 mg L−1) and 100 % for methamidophos (500 mg L−1). In addition, the analysis of intermediate metabolites during the biodegradation process of both pesticides revealed the formation of less toxic compounds compared to the precursors and possibly complete mineralization as well; this given the positive response in terms of inorganic phosphate generation during the degradation. Finally, we propose biodegradation pathways for methamidophos and diazinon based on the detected metabolites and available information on biodegradation by certain bacteria.