Chlorpyrifos In Soil Research Articles

Stability of [14C]Lindane, [14C]Chlorpyrifos, and Coumaphos in Model Cattle Dip

Stabilities of lindane, chlorpyrifos, and coumaphos were studied in simulated cattle dipping vat. The half-life (DT50) of lindane was found to be only 4 days. By 9 weeks' time, 99% of the lindane had dissipated from model vat. Chlorpyrifos was insoluble in water. The first-phase half-life of chlorpyrifos was found to be 22 days. Bound chlorpyrifos in soil was found at less than 5%. Stability of coumaphos was found to be related with the pH of water. The first-phase half-life (DT50) of coumaphos in the control vat was 99 days, which increased to 114 days in the vat containing superphosphate fertilizer used as buffer but remained 98 days with sodium citrate. Chlorferon, potasan, and an unidentified compound were found to be present with coumaphos. Keywords: Acaricides; lindane; chlorpyrifos; coumaphos; cattle dip

Persistence of Chlorpyrifos in Soils under Different Moisture Regimes

Chlorpyrifos is an organophosphorus insecticide used to control insect pests in soil. The fate of chlorpyrifos in soils under different moisture regimes is of interest because application directions specify soil-surface treatments for a number of agricultural and urban pests. Chlorpyrifos was degraded rapidly in all air-dry soils and slightly more slowly in soils at field capacity and/or under submerged conditions. Degradation rates were influenced by clay-catalysed hydrolysis under air-dry conditions and neutral or alkaline hydrolysis under submerged conditions. Degradation was faster in Bellary soil (chromic haplustert) and slower in Chettalli soil (ustic palehumult) under all three moisture regimes. The calculated half-lives ranged from 1·6 to 10·0, 5·2 to 22·0 and 8·7 to 25·1 days under air-dry, field capacity and submergence respectively at an application rate of 10 mg kg-1. © 1997 SCI.

Factors Affecting the Hydrolytic Degradation of Chlorpyrifos in Soil

The abiotic hydrolysis of the organophosphorus insecticide chlorpyrifos was examined in 37 different soils, which were chosen to represent a wide variety of physicochemical characteristics (e.g., pH 3.8−8.5). Samples of soil were sterilized via γ-irradiation, treated with [14C]chlorpyrifos at 10 μg/g, and incubated under standardized conditions (25 °C, field moisture capacity, darkness) for up to 4 months. Chlorpyrifos hydrolysis proceeded at a slow rate (<0.008 day-1) in acidic soils (pH ≤ 7). In alkaline soils, however, hydrolytic rate constants varied greatly (0.004−0.063 day-1). Corresponding hydrolytic half-lives for acidic and alkaline soils ranged from 92 to 341 and 11 to 200 days, respectively. Correlation analyses indicated that soil pH was the independent variable displaying the strongest association with hydrolytic rate constant (r = 0.55), but multiple regression models based on combinations of this parameter with other soil properties, including phosphatase enzyme activities, did not offer strongly predictive models for explaining the variability in kinetics observed (best fit r2 = 0.59). Incubation of chlorpyrifos with both sterile and nonsterile soils revealed that although both microbial and hydrolytic mechanisms contributed to chlorpyrifos degradation in all soils, there were clearly soils in which hydrolysis constituted the major route of degradation. Chlorpyrifos hydrolysis was greatly accelerated under low moisture conditions, both in acidic and alkaline soils. Additional experiments in several soils that displayed rapid chlorpyrifos hydrolysis at 10 μg/g provided evidence that the hydrolytic reaction was inhibited at higher concentration (1000 μg/g). Results highlight the importance but also the complex nature of the hydrolytic breakdown of chlorpyrifos in soil. Under certain conditions (e.g., some alkaline soils, air-dry soils) hydrolysis may be the driving factor modulating chlorpyrifos persistence. Keywords: Chlorpyrifos; soil; hydrolysis; degradation

Chlorpyrifos degradation in soil at termiticidal application rates

AbstractChlorpyrifos [O,O‐diethyl O‐(3,5,6‐trichloro‐2‐pyridyl) phosphorothioate] is an organophosphorus insecticide applied to soil to control pests both in agricultural and in urban developments. Typical agricultural soil applications (0.56 to 5.6 kg ha−1) result in initial soil surface residues of 0.3 to 32 μg g−1. In contrast, termiticidal soil barrier treatments, a common urban use pattern, often result in initial soil residues of 1000 μg g−1 or greater. The purpose of the present investigation was to understand better the degradation of chlorpyrifos in soil at termiticidal application rates and factors affecting its behaviour. Therefore, studies with [14C]chlorpyrifos were conducted under a variety of conditions in the laboratory. Initially, the degradation of chlorpyrifos at 1000 μg g−1 initial concentration was examined in five different soils from termite‐infested regions (Arizona, Florida, Hawaii, Texas) under standard conditions (25°C, field moisture capacity, darkness). Degradation half‐lives in these soils ranged from 175 to 1576 days. The major metabolite formed in chlorpyrifos‐treated soils was 3,5,6‐trichloro‐2‐pyrid‐inol, which represented up to 61% of applied radiocarbon after 13 months of incubation. Minor quantities of [14C]carbon dioxide (&lt; 5%) and soil‐bound residues (⩽ 12%) were also present at that time. Subsequently, a factorial experiment examining chlorpyrifos degradation as affected by initial concentration (10, 100, 1000 μg g−1), soil moisture (field moisture capacity, 1.5 MPa, air dry), and temperature 15, 25, 35°C) was conducted in the two soils which had displayed the most (Texas) and least (Florida) rapid rates of degradation. Chlorpyrifos degradation was significantly retarded at the 1000 μg g−1 rate as compared to the 10 μg g−1 rate. Temperature also had a dramatic effect on degradation rate, which approximately doubled with each 10°C increase in temperature. Results suggest that the extended (3–24 + years) termiticidal efficacy of chlorpyrifos observed in the field may be due both to the high initial concentrations employed (termite LC 50 = 0.2– 2 μg g−1) and the extended persistence which results from employment of these rates. The study also highlights the importance of investigating the behaviour of a pesticide under the diversity of agricultural and urban use scenarios in which it is employed.

Dispersion of chlorpyrifos in soil beneath concrete slabs.

Dispersion of chlorpyrifos in soil beneath concrete slabs.

Efficacy of Chlorpyrifos in Soil in ‘Florunner’ Peanut Fields to Lesser Cornstalk Borer (Lepidoptera: Pyralidae)

Survival of lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), larvae in soil from conventionally tilled and planted ‘Florunner’ peanut, Arachis hypogaea L., fields treated with chlorpyrifos in Alabama and Florida was evaluated by testing first instars every 2 wk after application. Treatments were an untreated control and granular chlorpyrifos applied at planting, planting plus pegging, pegging, or flowering. Larval survival in soil from treated plots varied with time of application, location, and year. Application of chlorpyrifos at planting was effective in 1986 and 1987 (42 and 102 d in Alabama; 102 and 72 d in Florida). The fewer days of effectiveness in Alabama in 1986 was probably caused by accelerated chlorpyrifos degradation from hot, dry weather during the growing season. Effectiveness of the application at flowering time was at least as great as effectiveness of the application at pegging. This study indicates that application of chlorpyrifos at flowering or pegging would be more effective for lesser cornstalk borer management than an application at planting, and that these applications would provide adequate control of the lessercornstalk borer during pod-fill.

Factors Influencing the Persistence and Effectiveness of Chlorpyrifos in Soil

Chemical dissipation rates and insecticidal effectiveness against the cabbage maggot, Delia radicum (L.), were determined for row-band applications of chlorpyrifos at planting with two formulations, two methods of application, and three dilutions of water-based spray drenches in field tests on Sultan silt loam. Zero-day residues ranged from 85 to 97% of the amount applied. Time for 50% loss of insecticide ranged from 3 to 56 days. Insecticide applied in granular formulation dissipated slower than insecticide formulated as water-based spray emulsions, and soil-incorporated treatments always dissipated slower than unincorporated soil-surface treatments. Chlorpyrifos residues of water-based sprays that weathered under high mean temperatures disappeared considerably faster than residues that weathered under lower mean temperatures. Incorporated chlorpyrifos gave better cabbage maggot control than surface deposits. There was little difference in the degree of maggot damage between spring and summer tests even though residues of summer applications declined faster than those of spring applications. Increasing the water volume for soil-surface spray drenches from 3.5 to 33.2 liters of finished spray per 300 m of row increased chemical persistence and effectiveness, but only slightly.

Degradation of Chlorpyrifos in Soil: Influence of Autoclaving, Soil Moisture, and Temperature1

The decomposition of 14C-ring-labeled chlorpyrifos was followed in 2 soils for a 32-week period under laboratory conditions at 25°C. Time required for 50% loss of parent compound in Chehalis clay loam and Sultan silt loam was 4 and 12 weeks, respectively. Faster breakdown of the insecticide in the clay loam was due to microbial degradation since initial halflives of 24 weeks were observed in both autoclaved soils. Radioactivity from degraded chlorpyrifos was recovered as 3,5,6-trichloro-2-pyridinol, as expired CO2, and as a nonextractable soil-bound residue component. After 32 weeks, 47% of the radioactivity from degraded insecticide were recovered as CO2 in the clay loam as compared to only 8% in the silt loam. Temperature had a pronounced effect on the decay rate of chlorpyrifos in Sultan silt loam during a 24-week incubation period at 15°, 25°, and 35°C; initial half-lives were 25, 13, and 6 weeks, respectively. Soil moisture contents ranging from 3–20% did not affect insecticide degradation rates in the Sultan silt loam.