Influence of temperature on physical properties of non-aqueous pesticide formulations and spray diluents: Relevance to u.l.v. applications

The viscosity, surface tension and volatility of a range of ultra-low-volume (ULV) spray diluents and pesticide formulations were measured at 5°C and 20°C. For u.l.v. application of 1.0 to 1.5 litre ha^?1 through conventional boom and nozzle systems or rotary (Micronair) atomisers, it is concluded that the spray medium should have a viscosity of ?30 mPa s at 20°C. The surface tension values covered only a narrow range and showed little temperature dependence. There was no clear optimum and all surface tensions within the range measured would appear to be acceptable for ULV applications. The volatility factor, 1/(A.T_1/2), where A represents the percentage of non-volatile material in the spray mixture and T_1/2, the half-life (minutes) of evaporation, should be <40 times; 10^?5.     

Partitioning of etofenprox under simulated California rice‐growing conditions

BACKGROUND: The pyrethroid insecticide etofenprox is of current interest to rice farmers in the Sacramento Valley owing to its effectiveness against the rice water weevil, Lissorhoptrus oryzophilus Kuschel. This study aimed to describe the partitioning of etofenprox under simulated rice field conditions by determining its Henry's law constant (H) (an estimate of volatilization) and organic carbon‐normalized soil–water distribution coefficient (K_oc) at representative field temperatures. A comparison of etofenprox and λ‐cyhalothrin is presented using a level‐1 fugacity model. RESULTS: Experimental determination of H revealed that etofenprox partitioned onto the apparatus walls and did not significantly volatilize; the maximum value of H was estimated to be 6.81 × 10^?1 Pa m³ mol^?1 at 25 °C, based on its air and water method detection limits. Calculated values for H ranged from 5.6 × 10^?3 Pa m³ mol^?1 at 5 °C to 2.9 × 10^?1 Pa m³ mol^?1 at 40 °C, based on estimated solubility and vapor pressure values at various temperatures. Log K_oc values (at 25 °C) were experimentally determined to be 6.0 and 6.4 for Princeton and Richvale rice field soils, respectively, and were very similar to the values for other pyrethroids. Finally, temperature appears to have little influence on etofenprox sorption, as the log K_oc for the Princeton soil at 35 °C was 6.1. CONCLUSION: High sorption coefficients and relatively insignificant desorption and volatilization of etofenprox suggest that its insolubility drives it to partition from water by sorbing to soils with high affinity. Offsite movement is unlikely unless transported in a bound state on suspended sediments. Copyright © 2009 Society of Chemical Industry     

Breakdown rates of dimethoate in fruit and vegetable dips

In order to determine the effect of pH and temperature on post-harvest dip solutions of dimethoate (500 mg litre^?1), the half-lives and pseudo first-order rate constants were calculated from measurements at pH 4, 6, 8, 10, 11.5, and at two temperatures 25 and 52°C. The half-lives ranged from 206 days to 39.3 min at 25°C, and from 5.6 days to 205s at 52°C; the rate constants ranged from 3.9 × 10^?8 s^?1 to 2.9 × 10^?4 s^?1 at 25°C, and from 1.4 × 10^?6 s^?1 to 3.4 × 10^?3 s^?1 at 52°C. The results show that the water used in dips should have a pH≤7. The addition of benomyl to the dip solutions at two concentrations (0.5 and 1.0 g litre^?1) had no effect on the half-lives and rate constants. The use of hard and salted waters in dips also showed no major effect. A formula was developed that gives the half-life of the dimethoate as a function of the pH and temperature.     

Neurophysiological studies of the effects of permethrin upon pyrethroid resistant (kdr) and susceptible strains of dipteran larvae

Permethrin at concentrations as high as 10^?6 had no detectable effect upon neuromuscular transmission at 20-21°C in the body-wall muscles of susceptible larvae of Lucilia sericata and susceptible and resistant (kdr) strains of larvae of Musca domestica. At the higher concentrations of 5 × 10^?6M, muscle cells in all strains and species of larva were slowly depolarised, resulting in failure of neuromuscular transmission when the level of depolarisation corresponded with the peak height of the postsynaptic potentials. Multiple postsynaptic potentials were sometimes obtained in response to a single electrical stimulus to the motor axon. Neither of these effects is considered to result from interference with release of the neurotransmitter or its binding to the postsynaptic receptors. Spontaneous activity in sensory nerve fibres from susceptible larvae was increased followed by intermittent bursting and block at concentrations of permethrin as low as 10^?9M at 20-21°C and 10^?10 at 26°C. Resistant larvae of M. domestica were 1000 times less sensitive, needing concentrations of permethrin as high as 10^?6M at 20-21°C and 10^?7M at 26°C to affect sensory discharge. The results are discussed in relationship to the cause of knockdown by pyrethroid insecticides and to possible changes in the nervous system which may be brought about by the kdr resistance factor.     

Degradation and adsorption of 14C-MCPA in soil—influence of concentration, temperature and moisture content on degradation

MCPA was weakly absorbed in soils with 2.4, 3.0 and 2.9% humus. K_d-values were 0.7, 0.9 and 1.0, respectively. In soil, not previously treated with MCPA, the degradation of 0.05 mg kg^?114C-MCPA followed first-order reaction kinetics whereas degradation of 5 mg kg^?1 was only first-order for 2 weeks; exponentially increasing degradation rates followed indicating enrichment of the soil with MCPA decomposers. Degradation was monitored by evolution of ¹⁴CO₂. The influence of temperature on degradation of MCPA (4 mg kg^?1) could initially be described by Q₁₀ values or by the Arrhenius equation. After 1 day of incubation in two field soils Q₁₀ values were 3.3 and 2.9, respectively, between 0°C and 29°C; the activation energies were 87 and 76 kj mol^?1. Exponentially increasing degradation rates followed with doubling times of about 4.0, 1.8, 1.2 and 0.6 days at 6,10, 15 and 21°C, respectively. After 51 days of incubation, at temperatures between 6°C and 29°C, about 60%¹⁴C was evolved in CO₂ and only traces of MCPA were left in the soil. At 0°C and at 40°C only 1% and 10%¹⁴C, respectively, were evolved as CO₂ after 51 days. ¹⁴C-MCPA (4 mg kg^?1) was incubated at moisture contents from that in air-dried soil to 2.3 times field capacity. Optimum for degradation was from 0.6 to 1.2. field capacity. Degradation was very slow where water contents were below the level of wilting point and was nil in air-dried soil. In wet soil degradation was delayed, but even in water-logged soil (2.3 times field capacity) MCPA was decomposed after 4 to 5 weeks at 10°C.     

Hydrolysis of 1, 3-dichloropropene in dilute aqueous solution

Hydrolysis of [¹⁴C]-radiolabeled 1, 3-dichloropropene (1, 3-D) was studied at pH 5, 7 and 9 at 10, 20 and 30°C in sterile buffered water. The rate of hydrolysis was independent of pH at each temperature, with measured half-lives of 3-1 (±0.l), 11.3 (±0.5) and 51 (±2.3) days at 30, 20 and 10°C, respectively. The activation energy for the hydrolysis reaction was determined to be 23.9 kcal mol^?1 deg^?1. One hydrolysis product was formed during the course of the study and was identified by co-chrornatography with analytical standards, using h.p.l.c., to be 3-chloroallyl alcohol. The alcohol appeared to be stable to further hydrolytic conversion and was formed in the same cis: trans ratio as in the initial 1, 3-D starting material, indicating essentially identical rates of hydrolysis for the cis and trans isomers of 1, 3-D.     

Relation between volatility rating and composition of phenoxy herbicide ester formulations

A CIPAC/AOAC test with tomato plants is used to specify the volatility ratings of herbicide ester formulations. This work compares the tomato plant test with an alternative chemical one. The concentrations of esters and the effective molecular weight and density of each formulation were used with the ester vapour pressures to calculate its herbicide vapour pressure as complete, and evaporated formulations. The range was from 28.8 mPa (at 257deg;C) for a mixture of 2,4–D esters to 0–07 mPa (at 25°C) for a 2,4,5–T-(iso-octyl) formulation, as complete formulations, and 35-5 and 0–16 mPa (at 25°C) as evaporated ones. A value of 0–6 mPa (at 25°C) was selected on the basis of the tomato plant test as the cut-off area for low-volatile esters and is recommended to be included in specifications for herbicide esters. Formulations with a herbicide vapour pressure above 3.3 mPa (at 25°C) are high-volatile ones according to the tomato plant test, while between 0–6–3.3 mPa (at 25°C) is a borderline region where the test gives mixed results. Levels of 2,4–D-ethyl and methyl were added to pure 2–ethylhexyl esters of 2,4–D and a 2,4,5–T-(iso-octyl) formulation to find what level of contamination would change the rating of these esters from low to high volatile. Formulations of 2,4–D-(iso-octyl) should not contain more than 11 g litre^?1 2,4–D as methyl ester or 2.0 g litre^?1 2,4–D as ethyl ester. Formulations of 2,4,5–T-(iso-octyl) should not contain more than 26 g litre^?1 2,4–D as methyl ester or 4.7g litre^?1 2,4–D as ethyl ester.     

Minimum concentration levels of methyl bromide required for full efficacy against seven species of stored-product beetle at two temperatures

The dosages of methyl bromide required to control insect pests can be expressed as concentration, time (Ct) products for concentrations down to a certain minimal level, here defined as the efficacy threshold, below which Habers Ct rule (C×t=k,a constant for mortality) no longer applies. Twelve strains of seven species of stored-product beetle were tested to identify efficacy threshold concentrations at 15°C and 25°C. For each strain the efficacy threshold was higher at 25°C than at 15°C. Different species differed widely in the threshold levels identified. Strains with a higher than usual tolerance to methyl bromide than their standard stock counterparts had slightly higher efficacy thresholds at 25°C but not at 15°C. The order of tolerance of the standard stocks to methyl bromide at 15°C was Tribolium confusum> T. castaneum> Oryzaephilus surinamensis> Rhyzopertha dominica> Sitophilus granarius> S. zeamais> S. oryzae, and at 25°C Tribolium castaneum > T. confusum> R. dominica> O. surinamensis> S. granarius> S. zeamais> S. oryzae. The order of efficacy thresholds largely reflected the order of susceptibility, S. oryzae and S. zeamais having the lowest efficacy thresholds of about 0.6 mg litre^?1 at 15°C and 1.3-2.0 mg litre^?1 at 25°C, while Tribolium spp. had the highest, 1.3-2.0 mg litre^?1 at 15°C and 2.5-4.0 mg litre^?1 at 25°C.     

The physical and chemical properties of the herbicide cinmethylin (SD 95481)

Cinmethylin (SD 95481), is a novel herbicide developed for the selective pre-emergence control of many annual grass weeds in a wide range of temperate and tropical crops. Representing new herbicide chemistry, cinmethylin is in the cineole family. Cinmethylin is a mobile colourless liquid with a boiling point of 313°C under an inert atmosphere at atmospheric pressure. It has a density of 1015 kg m^?3 and a viscosity of 70–90 mPa s, both at 20°C. It is miscible in all proportions with most organic solvents but has a low solubility, 63 mg litre^?1, in water. It has a vapour pressure of 10.2 mPa (20°C) and the vapour pressure/temperature relationship is given by log_e P(Pa)=28.9–9816/T (K). The n-octanol/water partition coefficient is 6850 and soil organic matter/water sorption coefficient (K_om) ranges between 165 and 235 over the three types of soil used in these studies. Cinmethylin is stable in water over the pH range 3–11. Solutions of cinmethylin in water or solvents are reasonably stable to sunlight, though thin films on a quartz surface photooxidise mainly to an ester within 24 h. This rate can be reduced by the addition of photostabilisers or by sorption onto soil surfaces. In an inert atmosphere cinmethylin is stable to high temperatures, though, in air, oxidation occurs at temperatures above 100°C to give the same product as by photodecay.     

N-Nitrosodimethylamine content of aqueous dimet hylamine and phenoxy herbicide/dimethylamine formulations during storage

N-Nitrosodimethylamine (NDMA) levels in samples of 600 g litre^?1 aqueous dimethylamine (DMA) solution stored at 4, 25 and 40°C, in formulations of the DMA salt of 2, 4-dichlorophenoxyacetic acid (2, 4-D) and of the DMA salt of 4-chloro-2-methylphenoxyacetic acid (MCPA) at 40°C were monitored using a gas-liquid chromatograph coupled with a thermal energy analyser (g.l.c./t.e.a.). The NDMA content of aqueous DMA at 4°C increased from 0.32μgg^?1 to 8.6μgg^?1 in 156 days. At 25°C it increased from 0.20μgg^?1 to 10.5 μgg^?1 in 156 days and at 40°C from 0.76μgg^?1 to 7.12μgg^?1 in 54 h. At 40°C, the NDMA in the 2, 4-D/DMAsalt increased from 0–53μgg^?1 to 2.79μgg^?1 in 96 days and in the MCPA/DMA salt from 0.48μgg^?1 to 5.51 μgg^?1 in 21 days.     

Alkylation of guanine in mice in vivo by organophosphorus insecticides. I. Trichlorphone and butonate

Following intraperitoneal administration to male mice of trichlorphone, 4 mg/animal = 160 mg/kg and butonate, 5 and 10 mg/animal = 200 and 400 mg/kg, labeled by ¹⁴C in the OCH₃-groups, nucleic acids taken from different organs and urine were analyzed for [7-¹⁴C]methylguanine. The limit of detection was 2 × 10^?8, calculated as ¹⁴C relative to the total dose. The maximum of ¹⁴C in 7-methylguanine was 2 × 10^?7 in lung, kidney, and testicles and 3 × 10^?6 in liver. The excretion rate of 7-MeG from nucleic acids is very rapid, a halflife of 2.0 hr was measured in liver from butonate and of < 24 hr was calculated in the whole body from trichlorphone, contrary to the excretion rate of 3.0–3.5 days following administration of strongly genotoxic agents. The relative amounts of [7-¹⁴C]methylguanine excreted in the urine were determined and compared with data for dichlorvos, dimethyl sulfate, and methyl methanesulfonate from the literature. Following intraperiotoneal administration, the methylating capability towards N-7 of guanine in nucleic acids is given by the ratio of about 100:10:25 for dichlorvos, butonate, and trichlorphone, respectively.     

The biochemical mechanism of action of the dinitroaniline herbicide oryzalin

Dinitroaniline herbicides such as oryzalin (3,5-dinitro-N⁴,N⁴-dipropylsulfanilamide) disrupt mitosis in the meristematic cells of seedling plants by inhibiting the formation of microtubules. For further understanding of the biochemical mechanism of action of oryzalin, laboratory analyses with isolated plant tubulin must be employed. Plant tubulin from flagella of the alga Chlamydomonas was isolated and purified. This tubulin was incubated with [¹⁴C]oryzalin, and free oryzalin was separated from oryzalin bound to plant tubulin by miniature DEAE-cellulose chromatography. Scatchard analysis predicts a molar ratio of oryzalin bound to plant tubulin of 1.0 ± 0.1 when oryzalin is incubated with plant tubulin for 30 min at pH 6.9 and 25°C. The association constant for the oryzalin-tubulin complex is 2.08 ± 0.08 × 10⁵M^?1 at 25°C. The thermodynamic values for the formation of the oryzalin-tubulin complex at 25°C are ΔG^o = ?7.25 ± 0.02 kcal mol^?1, ΔH^o = 6.5 ± 0.2 kcal mol^?1, and ΔS^o = 46 ± 2 cal mol^?1 deg^?1 (mean ± standard error). Oryzalin has little or no affinity for intact microtubules, previously denatured plant tubulin, actin, bovine serum albumin, calmodulin, ferredoxin, trypsin, or urease, indicating oryzalin is specific for the biologically active conformation of plant tubulin. Oryzalin binds to plant tubulin to form a complex that may be incapable of polymerizing into microtubules.     

Biodegradation of the Organophosphate Insecticide Coumaphos in Highly Contaminated Soils and in Liquid Wastes

Approximately 400000 litres of cattle dip wastes containing approximately 1500 mg litre⁻¹ of the organophosphate insecticide coumaphos are generated yearly along the Mexican border from a USDA program designed to control disease-carrying cattle ticks. Use of unlined evaporation pits for the disposal of these wastes has resulted in highly contaminated soils underlying these sites. Previous work has shown that microbial consortia present in selected dip wastes can be induced to mineralize coumaphos. Our results demonstrate that similar microbial consortia are present in coumaphos-contaminated soils from eight waste sites and that these organisms are capable of mineralizing cou-maphos in these soils using soil slurries to less than 1 mg litre⁻¹ in 7–10 days at 28°C. In addition, our results show that these consortia are able to colonize pea gravel in trickling gravel filters and can be used in these filters to metabolize coumaphos from dip wastes to less than 0·1 mg litre⁻¹ in 7–10 days at 28°C. These simple systems offer potential low cost means to detoxify coumaphos-containing wastes and to bioremediate soils contaminated with this organophosphate compound.     

Effect of temperature on the toxicity of low concentrations of methyl bromide to diapausing larvae of the warehouse moth Ephestia elutella (Hübner)

The performance of low concentrations of methyl bromide against diapausing larvae of Ephestia elutella at 15 and 25°C was assessed in extended exposure periods. At concentrations of 1.9 mg litre^?1 and below, test batches required higher concentration-time (ct) products for 100% kill at 25°C than at 15°C. The minimum concentration at which the concentration: time relationship still applied was between 1.3 and 1.9 mg litre^?1 at 15°C, whereas at 25°C it was between 2.7 and 4.0 mg litre^?1. For many individuals within each population sample, however, lower concentrations at moderate dosage levels remained lethal. At 25°C, a ct product of about 90 mg litre^?1 h gave between 53 and 77% kill at 6.1, 4.0, 2.7 and 1.9 mg litre^?1. The trends observed suggest that the most tolerant members of the population have an enhanced ability to detoxify methyl bromide at the higher temperature. The implications of the results for the build-up of resistance and for practical control measures are discussed.     

Hydrolysis of the pyrethroid insecticide fenpropathrin in aqueous media

The hydrolysis of [¹⁴C] fenpropathrin ( I ) [(RS)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate] was studied in buffer solutions at pH 1.9–10.4, and in natural river and sea water at 25, 40, 55 and 65°C under laboratory conditions. The hydrolysis of I proceeded predominantly through neutral (pH independent) and base-catalysed processes in the regions below pH 3.9 and above pH 7.0, respectively, whereas both reactions occurred between pH 3.9 and 7.0. The rates of hydrolysis of I in buffer solutions were similar to those in one sample of river and one sample of sea water. If this obtains generally, it may be expected that the half-life of I in natural waters, normally within the range pH 5–9, will range from 1.54 to 1080 days at 40°C, 11.3 to 8520 days at 25°C and, by extrapolation of the data obtained in buffer solutions, 106 to 83 000 days at 10°C. The rate constants for hydrolysis of I in aqueous media can be expressed by: Where log k_N = 9.60–(5.56 × 10³ T^?1) and log k_B = 7.32–(2.56 × 10³ T^?1). The calculated rate constants were in good accord with the observed values in buffer solutions. Cleavage of the ester linkage was more rapid than hydration of the cyano group at any pH and temperature tested.     

Comparison between the penetration characteristics of methyl bromide and ethanedinitrile through the bark of pine (Pinus radiata D.Don) logs

BACKGROUND

Ethanedinitrile (EDN) is a fumigant being commercialized worldwide as an alternative phytosanitary treatment to methyl bromide (MB) for forest products. The penetration characteristics of MB and EDN were measured through the bark of wooden blocks (100 × 100 × 50 mm) cut from the upper (average bark thickness 5 ± 2 mm) and lower (average bark thickness 25 ± 5 mm) trunk of recently felled pine (Pinus radiata D.Don) trees. Doses of 48 g m⁻³ MB and 50 g m⁻³ EDN were applied to chambers at 10 and 20°C for 10 h.

RESULTS

Penetration of MB was influenced by the interaction between fumigation time and temperature, with concentrations increasing at a higher rate at 20°C compared with at 10°C. After 10 h, an average concentration of 8.05 ± 0.89 g m⁻³ had penetrated the bark of log sections at 20°C, whereas 5.20 ± 0.89 g m⁻³ was measured at 10°C. By contrast, the factors examined in this study did not significantly impact the penetration of EDN. Concentration × time (CT) values for MB under the bark were 35.20 ± 2.30 g h m⁻³ at 10°C and 55.85 ± 9.58 g h m⁻³ at 20°C; whereas for EDN, CT values were 19.50 ± 6.80 g h m⁻³ at 10°C and 19.08 ± 4.10 g h m⁻³ at 20°C.

CONCLUSION

MB can achieve a higher concentration under the bark of log sections during simulated fumigations, but all of the factors examined affected the ability of MB to penetrate the bark of wooden blocks. By comparison, the penetration of EDN through the bark is more consistent than MB under laboratory conditions. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Depression of the minimum concentration of methyl bromide effective against diapausing warehouse moth larvae at 15°c by prior exposure at a moderate concentration

Warehouse moth (Ephestia elutella) larvae in diapause were exposed at 15°C to methyl bromide at 8 mg litre^?1 for 14.5 h and then immediately exposed at a lower concentration. The exposure at 8 mg litre^?1 killed 44–69% of the larvae treated. Subsequent concentrations down to 1.1 mg litre^?1 obeyed Haber's rule (concentration × time= k, a constant for mortality), but a higher concentration-time product (ct) was required for over 90% kill at 0.8 mg litre^?1. Only concentrations down to 1.9 mg litre^?1 obey Haber's rule if there is no prior exposure at a higher concentration. Although minimum effective concentrations are lower at 15°C than at 25°C, exposure at a higher concentration depresses the subsequent level to a similar extent at each temperature. The contribution to the efficacy of a treatment, of low concentrations persisting at the end of fumigation, is thus likely to be even greater at moderate to low temperatures than at 25°C. The implications for the development of resistance to methyl bromide are discussed.     

Vapor pressure and volatility of β-asarone,the main ingredient of an indigenous stored-product insecticide,Acorus calamus oil

The effect ofAcorus calamus products on insects is reviewed briefly. A sudden, dramatic drop occurs in the insecticidal, gaseous phase activity of calamus oil on stored-product pests, when the exposure temperature is lowered from 30° to 25°C. In an attempt to explain this finding, the vapor pressure of the main constituent of IndianAcorus calamus essential oil, β-asarone, was determined by three methods: (i) extrapolation with a gas-chromatographic method according to Jensen and Schall; (ii) calculation from boiling points with the Clausius-Clapeyron equation; and (iii) direct measurement with the Knudsen cell. The values of vapor pressure of β-asarone at 30°C according to these three methods were 3.3 x 10^-3, 3.7 x 10^-3 and 9.8 x 10^-4 Torr, respectively. The volatility of β-asarone under the conditions of the fumigant experiments mentioned above was assayed by determining the weight loss from 50 mg asarone allowed to evaporate at 30°C from a filter paper disk into a 400 ml hermetically closed glass vessel. The weight loss was approximately 0.75 mg/400 ml receptacle space (≈1.9 mg/l) for every 10 days from day 0 to day 40.     

Gas-liquid chromatographic determination of hydrazine in maleic hydrazide formulations and in samples stored at an elevated temperature

A method is described for the analysis of small amounts of hydrazine in maleic hydrazide formulations. Following derivative formation with pentafluorobenz-aldehyde, the pentafluorobenzaldehyde azine was extracted with hexane and determined by gas-liquid chromatography with electron-capture detection. Recoveries of 72-80% were obtained from samples fortified with 1 and 10 μg of hydrazine. The limit of detection was 0.05 mg kg^?1. Fourteen commercial formulations with maleic hydrazide concentrations ranging from 180-360 g litre^?1 were investigated. The hydrazine content of the maleic hydrazide used in these formulations ranged from less than 0.05 to 53 mg kg^?1. During the storage of two samples at 50°C for 10 weeks, the hydrazine contents increased from 2.2 to 124 and 0.4 to 54 mg litre^?1, respectively.