Dissipation of pendimethalin in the soil of field pea (Pisum sativum L.) and detection of terminal residues in plants

Dissipation of Pendimethalin in Soil Under Direct Seeded and Transplanted Rice Field

The dissipation of pendimethalin applied in direct seeded rice (DSR) and transplanted rice (TPR) field at 1.0 and 2.0 kg a.i. ha^-1 followed biphasic first order kinetics (R² > 0.91) and was comparatively faster under flooded TPR than DSR. The half-life (DT₅₀) of pendimethalin in the soil ranged from 2.22 to 2.80 days in the initial phase and 23.51 to 24.66 days in the final phase in TPR for both application rates. However in DSR, DT₅₀ varied from 3.67 to 4.35 days in the initial phase and 34.19 to 34.99 days in the final phase. Residues of pendimethalin in soil samples analyzed by HPLC and GC-MS/MS were below the detection limit (< 0.003 µg g^-1) for both the application rates in DSR and TPR whereas 0.003-0.009 µg g^-1 and 0.003-0.008 µg g^-1 residues of pendimethalin were found in rice grain and straw samples, respectively.

Effect of repeated application of pendimethalin on its persistence and dissipation kinetics in soil under field and laboratory conditions

The repeated application of herbicide can alter its persistence in the environment. In India, wheat fields are exposed to herbicide application at least once in the cropping season. The present study investigated the dissipation behavior of pendimethalin applied annually to a wheat field over four cropping seasons from 2012 to 2016. The dissipation studies were also conducted under laboratory conditions during 2015-2016. Pendimethalin from soil and wheat grain samples was extracted using matrix solid-phase dispersion and quantified using high-performance liquid chromatography and gas chromatography-tandem mass spectrometry. The average recoveries of pendimethalin from soil and crop produce ranged from 81.3% to 103.1%. The half-life of pendimethalin ranged from 20.9 to 31.3 days and 9.4 to 60.2 days under field and laboratory conditions, respectively. Dissipation of pendimethalin varied significantly over the years under field conditions and was comparatively faster than under laboratory conditions. On the other hand, non-significant variation in the dissipation of pendimethalin in soils under laboratory conditions was observed. The residues of pendimethalin in crop produce at harvest were below the maximum residue limit set by EPA.

Effect of a non-woven fabric covering on the residual activity of pendimethalin in lettuce and soil

BACKGROUND

Lettuce (Lactuca sativa L.) is a crop that is very sensitive to herbicide contamination owing to its short growing season. The use of long-residual herbicides and non-woven fabric coverings could therefore influence pendimethalin concentrations in soil and lettuce.

RESULTS

The pendimethalin half-life in soil ranged between 18 and 85 days and was mainly affected by season (i.e. weather), and especially by soil moisture. Pendimethalin degradation in soil was slowest under dry conditions. A longer pendimethalin half-life was observed under the non-woven fabric treatment, but the effect of varying application rate was not significant. Pendimethalin residue concentrations in lettuce heads were significantly influenced by pendimethalin application rate and by non-woven fabric cover, especially at the lettuce's early growth stages. The highest pendimethalin concentration at final harvest was determined in lettuce grown on uncovered plots treated with pendimethalin at an application rate of 1200 g ha-1 (7-38 µg kg-1 ). Depending on growing season duration and weather conditions, pendimethalin concentrations in lettuce grown under non-woven fabric ranged from 0 to 21 µg kg-1 .

CONCLUSION

Use of transparent non-woven fabric cover with lettuce can help to reduce application rates of soil herbicides and diminish the risk of herbicide contamination in the harvested vegetables. © 2016 Society of Chemical Industry.

Effect of Soil Fumigation on Degradation of Pendimethalin and Oxyfluorfen in Laboratory and Ginger Field Studies

Herbicides are usually applied to agricultural fields following soil fumigation to provide effective weed control in high-value cash crops. However, phytotoxicity has been observed in ginger seedlings following the application of herbicides in fumigated fields. This study tested a mixture of herbicides (pendimethalin and oxyfluorfen) and several fumigant treatments in laboratory and field studies to determine their effect on the growth of ginger. The results showed that soil fumigation significantly (P < 0.05) extended the degradation period of these herbicides in the field and in laboratory studies. The half-life of pendimethalin was extended by an average of approximately 1.29 times in the field and 1.74 times in the laboratory. The half-life of oxyfluorfen was extended by an average of about 1.19 times in the field and 1.32 times in the laboratory. Moreover, the extended period of herbicide degradation in the fumigant and nonfumigant treatments significantly reduced ginger plant height, leaf number, stem diameter, and the chlorophyll content. The study concluded that applying a dose below the recommended rate of these herbicides in chloropicrin (CP) or CP + 1,3-dichloropropene fumigated ginger fields is appropriate, as application of the recommended herbicide dose in fumigated soil may be phytotoxic to ginger.

Persistence of Pendimethalin in/on Wheat, Straw, Soil and Water

Pendimethalin, a dinitroaniline group of organic herbicide compounds used as pre emergence weed control in wheat, onion and soyabean crops in India. The experiments were designed to study the harvest time residues of pendimethalin in wheat grain and straw its dissipation behaviour in soil and water. At harvest time, the residues of pendimethalin in wheat grain and straw were found to be below determination limit of 0.001 mg kg(-1) following single application of the herbicide at the rate of 1 (T1/single dose) and 2 (T2/double dose) kg a.i. ha(-1). Soil samples from the field were collected periodically and analysed by GC-ECD system. In soil, initial deposits of 4.069 and 10.473 mg kg(-1) of pendimethalin persisted up to 90 days and dissipation followed first order kinetics with half life period of 12.03 days in T1 and 13.00 days in T2. Residues of pendimethalin studied in water under laboratory conditions at 0.5 (T1) and 1.0 (T2) mg L(-1) levels persisted up to 90 days. Dissipation kinetics followed first order kinetics with half-life values of 12.70 and 13.78 days at single and double dose, respectively. Limit of determination in grain, straw and soil were 0.001 mg kg(-1) and in water was 0.001 mg L(-1). Application of the herbicide is considered quite safe from consumer and environmental point of view.