Effect of pH, Dissolved Organic Carbon, and Sodium Dodecyl Sulfate to Degradation of Fenobucarb Insecticide in Paddy Soil-Water System

ABSTRACT

In paddy rice farming systems, the degradation of insecticides from the soil reduces their occurrence as well as their levels in surface and groundwater. Degradation of insecticide fenobucarb in the paddy soil-water system was carried out by surface soil collected from paddy rice in the Hue province of Vietnam. Experiments were conducted using a batch technique, the fenobucarb-spiked paddy soils were shaken end-over-end with solutions of pH 7, pH 9, 25 mg L⁻¹ DOC, and 1 critical micelle (cmc) sodium dodecyl sulfate (SDS). After each period (24, 48, 72, … 144 hours), the soil solutions were separated into the aliquot and the solid phase to analyze fenobucarb and intermediate metabolic products 2-sec-butyl phenol. The decrease of fenobucarb and the appearance of (2-sec-butyl-phenol) were the result of hydrolysis and biodegradation by fenobucarb-acclimatized microorganisms that were capable of degrading fenobucarb in the paddy soil. The degradation of fenobucarb in both the soil and water phases in the paddy soil-water system was enhanced in the experiment with pH 7, followed by those with pH 9, 25 mg L⁻¹ DOC, and 1 cmc SDS. With pH 9, in addition to decomposition by bacteria present in the soil, fenobucarb was hydrolyzed under basic conditions. The presence of 25 mg L⁻¹ DOC and 1 cmc SDS in the aqueous solution increased desorption and microbial activity in the soil and increased the biodegradation efficiency of fenobucarb in the paddy soil-water system. However, the degradation of fenobucarb in the 1 cmc SDS solution was inhibited because SDS solution may be preferentially utilized by microorganisms, and fenobucarb would have a competitive effect with SDS. Irrigation water for paddy fields often receives untreated domestic and industrial wastewater that may contain multiple compounds such as DOC and SDS. Therefore, it contributes to the elimination of fenobucarb insecticide in the paddy soil-water system.

KEYWORDS:

• Degradation
• insecticide
• fenobucarb
• dissolved organic carbon
• paddy soil

Acknowledgments

We are grateful to all colleagues who helped us during sampling. This research was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) [104.04-2017.319].

Disclosure statement

No potential conflict of interest was reported by the authors.

Credit authorship contribution statement

Ha Thu Trinh: sample preparation, writing manuscript, supervision, and review. Giang Truong Le, Yen Hai Dao, Hanh Thi Duong, Mai Thi Dang, Bjarne W. Strobel: sample preparation, data treatment, reviewing and editing.

Additional information

Funding

This research was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) [104.04-2017.319].