Biodegration of α and β-endosulfan in soil by a fungal isolate

• Main Author: Mercado, Jericho Victor L.
• Format: text
• Language: English
• Published: Animo Repository 2010
• Subjects: Endosulfan—Biodegradation; Endosulfan—Environmental aspects; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/6128; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/13173/viewcontent/CDTG004821_P.pdf
• Institution: De La Salle University

Endosulfan is a cyclodiene organochlorine pesticide used worldwide for the last three decades before it was banned or regulated due to its toxicity and persistence. In 1993, endosulfan was banned for use in the Philippines. However, exemptions were made for pineapple plantations in 1995. But then, due to the recent capsizing of the ferry MV Princess of the Stars near the shores of Romblon, a temporary ban was imposed by the Philippine Fertilizer and Pesticide Authority (FPA) in March 2009 for all uses of endosulfan in the country. Biodegradation is a process wherein microorganisms are utilized to degrade hazardous organic compounds into harmless or less harmful substances. This study investigated the biodegradation of endosulfan in soil using a local fungal isolate. The first phase of the study involves the enrichment, isolation and screening of fungi from soil with history of endosulfan application. The indigenous microorganisms in the soil sample with history of endosulfan application were enriched by suspension in potato dextrose broth amended with technical-grade endosulfan and chloramphenicol as antibacterial agent. The microorganisms were subjected to a five-stage enrichment process in which the concentration of technical-grade endosulfan was increased gradually from 10 to 100 mg/l for 210 h. The enriched cultures were inoculated on potato dextrose agar with 50 mg/l endosulfan. Four (4) fungal isolates, labeled as P701, P702, P601 and P801, were obtained by successive plating. The fungal isolates were screened based on endosulfan degradation utilizing a 2 x 4 full factorial design. Each isolate was grown in light-shielded shake-flasks oscillating at 160 rpm at a temperature of 27.0 + 0.5°C for 14 days. Two (2) nutrient media containing 50 mg/l technicalgrade endosulfan were tested on each isolate: one with endosulfan as the sole-carbon source (NM-SCS) and the other with endosulfan as the solesulfur source (NM-SSS). Screening results showed that isolate P601 exhibited the highest total endosulfan degradation at 84.56% along with the NM-SSS at 73.40%. The combination of isolate P601 and NM-SSS yielded 91.35% total endosulfan degradation (93.85% for alpha-endosulfan and 90.29% for beta-endosulfan). Isolate P601 with NM-SSS was then used for the soil biodegradation runs. The second phase of the study involved the use of isolate P601 in the soil biodegradation runs utilizing a 23 full factorial design with 3 center points. The effects of inoculum size, soil moisture content and initial concentration of endosulfan on the biodegradation of endosulfan in soil were determined. Parallel to the soil biodegradation runs were the chemical hydrolysis runs which involved the test for endosulfan degradation at alkaline conditions. Results of the soil biodegradation runs showed that inoculum size and soil moisture content set at the designated low level, and initial concentration of endosulfan set at high level yielded the highest specific endosulfan degradation rate at 775.38 ug endosulfan per day per mg dry weight biomass. This setting corresponds to inoculum size equal to 3.19 mg dry weight/Kg dry soil, soil moisture content equal to 50% of the water holding capacity, and initial endosulfan concentration equal to 50 mg/Kg dry soil. The most significant factor was identified to be the inoculum size. On the other hand, the chemical hydrolysis tests showed significant total endosulfan degradation in alkaline soil conditions at 41.52% total endosulfan (39.34% for the alpha-isomer and 42.32% for the beta isomer). The third phase of the study involved the determination of endosulfan biodegradation products and kinetic model fitting. The biodegradation products from the run which exhibited the highest percentage of total endosulfan degradation (Run R8) were identified using Gas Chromatography/Mass Spectroscopy (GC/MS). Alpha-endosulfan was seen to confound other endosulfan-related compounds, endosulfan ether and chlorendic anhydride, in the same peak. Endosulfan sulfate was not detected in the GC/MS analysis but it was detected during endosulfan quantification using a Gas Chromatograph equipped with Electron Capture Detector (GC-ECD). Formation of metabolites was observed when the pre-treatment and post-treatment GC-ECD chromatograms were compared. Moreover, the kinetic parameters were determined to be 37.15 day-1 for the specific growth rate (umax), 25.75 mg endosulfan/Kg dry soil for the half-saturation coefficient (Ks) and 284.64 mg dry weight of mycelia per mg endosulfan for the yield coefficient (YX/S).