Minimum Residual Level Research Articles

Attractiveness of Different Coloured Sticky Traps to the South African Citrus Thrips (Scirtothrips aurantii Faure) in Avocado, KwaZulu-Natal, South Africa

The South African citrus thrips, Scirtothrips aurantii, is a recently confirmed economic pest in South African avocado. Scarring damage by thrips results in corky tissue development, making the fruit unsuitable for export and potentially costing the country in lost export revenue. Thrips management is complicated by the multiple and protracted flowering patterns of susceptible cultivars. In addition, widespread pesticide resistance of thrips and the negative environmental effects along with minimum residue levels for export fruit limit the application of pesticides for thrips control. Monitoring an insect pest's presence and abundance is the first step in thrips management. This study aimed to investigate S. aurantii's colour preferences, establish the distribution of thrips in the orchard and population dynamics from flowering to fruit establishment. Attractiveness followed the order yellow > blue, white, clear > red, black, purple and orange. Thrips were evenly distributed throughout the orchard, with the highest populations occurring during flowering (August), declining sharply and picking up in the summer months starting December. Yellow sticky cards are recommended as a monitoring tool.

Storm surges in the water level variation in the New Port (gulf of Ob)

The processing of 6-hourly intervals level measurements at the New Port polar station was previously difficult due to poor data quality and the lack of methodology for assessing them and bringing observations into uniform rows. Therefore, since the second half of the 20th century, no research of wind-induced water has been carried out. In 2015, for the first time, the authors formed a base of residual levels (observations minus forecasting) for 1977–2012 on 6-hourly intervals observations of water level at the New Port station using the method of tide calibration. In the present work, a period of observations with relatively reliable data for 1977–1991 was selected for the research of the storm surges in the water level fluctuations. Surges are considered in comparison with the 5 % probability, and ranges with 95 % probability. The annual distribution of the number of surges and ranges showed an average of 12.4 surges and 11.2 ranges per year. The maximum number of surges and ranges was observed in 1981 and was 21 surges and 27 ranges. In the time course of fluctuations of residual levels during the above period, the maximum with the value of 634 cm was noted in 1987 and occurred during the autumn period (ice composition). The length of the surges varied between 0.25 days and 13.5 days. Most of the surges occurred in the period June-October (78.8 %) with the largest number in September (22,8 %). In the period January-May the number of surges decreases to 7.6 % and is zero in April. The lowest ranges residual level was observed in 1986 (343 cm above zero fasting). The total fluctuation of the residual level in New Port during the period of 6-hourly intervals level observations in 1977–1991 was 291 cm. This is 23 cm more than was recorded at the Cape Kamenny station. The length of the ranges varied from 1 day to 8 days. The majority of the intra-annual distribution of the number of ranges over a multi-year period was observed in July–October (83.7 %) with the maximum number in September (28.1 %). A small number of ranges were observed in January and March, and their total absence in April and May. The duration of surges and ranges is inversely dependent on their growth rate. Thus, the highest growth rate of the residual level at the deposit of 5.1 cm/hour corresponds to the duration of the deposit of 0.25 days. The greatest duration of growth of the surge level (9.25 days) corresponds to a speed of 0.14 cm/h. The drop in the level during the range occurred at the highest speed of 11.6 cm/h, the rise from the minimum residual level – at the speed of 6.97 cm/h. Corresponding to these rates, the duration of the decline and rise of the range level was 0.15 cm/h. The highest rise time of the residual range level was 5.25 days at an intensity of 0.44 cm/h.The authors declare that they have no competing interests.

Constraints faced by the banana growers in adoption of risk management practices in drip irrigated banana cultivation

The study to know constraints faced by the banana growers in adoption of risk management practices in drip irrigated banana cultivation was conducted on a random sample of 220 drip irrigated banana growers in Anand district of Gujarat state. The data were collected by personal contacts.Major economic problems faced by the banana growers in management of risk in drip irrigated banana cultivation were heavy cost of installation of drip irrigation system, high cost of fuel to use engines for irrigation and high cost of spare parts of drip irrigation system. As far as technological constraints faced by the banana growers were lack of sufficient electricity, problem of salty ground water and difficulty in interculturing operations. Non-availability of quality material of DIS with reasonable rates, lack of technical guidance from company agent in time and delay in sanction of loan and subsidy were the major administrative constraints faced by the banana growers. Whereas, in case of marketing related constraints faced by the banana growers were absences of support price during glut in the market, high cost of transportation and lack of timely information regarding demand and supply of the produce. Personal and socio-psychological constraints faced by the farmers in management of risk during drip irrigated banana cultivation were lack of knowledge about schedule of water soluble fertilizers application, lack of knowledge about use of fertilizers, liquid fertilizers, GR etc. and lack of knowledge about plant protection of banana crop. While, lack of knowledge about export procedure, lengthy procedures and formalities for export of produce and lack of knowledge about minimum residual level of chemical were the major export related constraints faced by the banana growers in drip irrigated banana cultivation.

Minimum free chlorine residual level required for the inactivation of Escherichia coli O157:H7 and trihalomethane generation during dynamic washing of fresh-cut spinach

Abstract Even though chlorination of wash water in the fresh-cut industry is a common practice, little is known about the minimum free chlorine residual level required to keep water free from foodborne pathogens and its concomitant generation of disinfection by-products. This work aimed to provide insight to these issues. Two kinds of tests were performed to simulate a fresh-cut industry washing tank of spinach. In the first, a washing tank containing clean water was continuously filled with concentrated process wash water with high organic matter obtained from spinach and inoculated with an Escherichia coli O157:H7 cocktail (5 log CFU/ml). A peristaltic pump dosed a chlorinated solution to the washing tank during the test in order to adjust free chlorine (FC) concentration to 1 and 3 mg/l. In the second test, the washing tank already contained process wash water from the beginning of the experiments and the FC concentration was adjusted to 3 and 5 mg/l. Results showed that the maintenance of a FC concentration of ca. 5 mg/l (until a maximum of 7 mg/l) during washing of fresh-cut spinach kept the wash water free from the pathogen during one hour although trihalomethane levels > 1000 μg/l were generated. Results indicate that a minimum residual level of ca. 7 mg/l FC is an effective treatment to inactivate E. coli O157:H7 under industrial conditions. Validation of sanitizer efficacy by using a dynamic system might facilitate the implementation of selected treatments in the food industry.

Multiresidue Analysis of Phenylurea Herbicides in Environmental and Drinking Water by Capillary Electrophoresis

The present paper describes the application of capillary electrophoresis in the micellar mode to the separation and quantitative determination of five phenylurea herbicides, viz. monuron, linuron, diuron, isoproturon, and monolinuron, in water samples. Using uncoated fused silica capillary and phosphate-borate buffer (pH 7.0) containing SDS, the five pesticides are resolved in less than 15 min and quantitatively determined by an ultraviolet detector at 244 nm. Method optimization and validation parameters are presented. Good linearity and repeatability were observed for all the compounds studied (correlation coefficients 0.999). The feasibility of the method developed was tested by simultaneous determination of these herbicides in environmental and drinking water samples at the minimum residue levels (MRLs) (0.1 μg/L) after solid-phase extraction (SPE) preconcentration procedure.

Determination and Degradation of Methomyl in Tomatoes and Green Beans Grown in Greenhouses

A liquid chromatographic (LC) method using UV detection at 233 nm was used to study the degradation of methomyl in tomatoes and green beans grown in greenhouses. A liquid-liquid extraction with CH2Cl2-methanol (90 + 10, v/v) and a cleanup step with Florisil were combined with LC to isolate, recover, and quantitate the pesticide. Average recoveries obtained at spike levels of 0.03 and 0.40 mg/kg were 83.2-84.7% for tomatoes and 83.3-87.5% for green beans. Determination limits were 0.03 mg/kg for tomatoes and 0.01 mg/kg for green beans. Levels of methomyl residues were studied in tomatoes and green beans grown in an experimental greenhouse to establish the effect of the kind of greenhouse, application dose, species grown, and climatic conditions on the degradation of this pesticide. Analysis of variance showed that doses did not affect the response. The half-life, however, is greater in a flat-roof greenhouse than in an asymmetric-roof greenhouse and is significantly longer for green beans than for tomatoes and longer in winter than in spring. A preharvest time of about 5 days may be suitable for green beans sprayed with methomyl. Tomatoes show residue levels at the time of application lower than Spanish minimum residue levels.

Toxicity and Repellency of Potting Soil Treated with Bifenthrin and Tefluthrin to Red Imported Fire Ants (Hymenoptera: Formicidae)

The Lc 50 and LC 90 of bifenthrin in potting soil for female alates of the red imported fire ant, Solenopsis invicta Buren, were 1.1 and 5.2 ppm, respectively. For tefluthrin, the Lc 50 and LC 90 were 8.5 and 19.0 ppm, respectively. These results may provide a basis for setting minimum residue levels for the enforcement of quarantine regulations. Pots filled with soil treated with either bifenthrin or tefluthrin at the label rate of 25 ppm were exposed to small colonies of S. invicta without alternative nesting sites. After 48 h, 6% of the bifenthrin-treated pots and 24% of the tefluthrin-treated pots were considered infested under quarantine standards. When exposure was lengthened to 2 wk, all pots were uninfested. Implications for the imported fire ant quarantine program are discussed.

Expression of gonadotropin-releasing hormone (GnRH) receptor gene is altered by GnRH agonist desensitization in a manner similar to that of gonadotropin beta-subunit genes in normal and castrated rat pituitary.

It was previously established that the administration of a potent GnRH agonist such as triptorelin (D-Trp6-GnRH) induced desensitization of pituitary gonadotropic cells, resulting in decreased expression of gonadotropin beta-subunit genes and the suppression of LH and FSH synthesis and release. Binding of GnRH to the pituitary is also affected by agonist treatment. To examine the desensitizing effects of GnRH agonist on the expression of the pituitary GnRH receptor (GnRH-R) gene, male rats were given triptorelin (long-acting formulation, 300 micrograms/kg), and levels of GnRH-R messenger RNA (mRNA) were determined by Northern and dot blot hybridization to a 32P-labeled rat complementary DNA probe. Abundances of gonadotropin alpha-subunit, LH beta, and FSH beta mRNAs were examined in parallel, using appropriate probes. A rapid time-dependent decrease in the level of GnRH-R mRNA was observed in rats after triptorelin administration. A minimum residual level of mRNA, in the range of 20-25% of the initial value, was attained as early as 5 h after treatment. Levels further stabilized to 25-30% after a small transient increase to 45% on day 5. A single injection was effective for at least 30 days, after which GnRH-R mRNA levels slowly returned to normal, suggesting a progressive abolition of agonist effects. A concomitant acute depletion of mRNA levels was observed for LH beta and FSH beta (50% decrease in about 48 and 3 h, respectively), whereas the alpha-subunit message increased (rapidly reaching a level 1.8-fold that in control rats after 1-2 days). Castration induced a 3.8-fold elevation in the amounts of GnRH-R mRNA after 3 weeks, whereas alpha, LH beta, and FSH beta mRNAs increased by 6.2-, 7.9-, and 4.2-fold, respectively, compared to corresponding values in intact animals. Administration of the GnRH agonist readily prevented, for as long as 3 weeks, the stimulatory effects of castration on the GnRH-R mRNA and mRNAs for the beta-subunit of gonadotropins, but not for the alpha mRNA, which remained at a high level. When triptorelin was administered 3 weeks postoperatively, the castration-induced increase in LH beta and FSH beta was totally abolished, and no significant effect was noted on alpha-subunit mRNA. In conclusion, these data demonstrate that expression of the GnRH-R gene is subject to regulation and depends on GnRH stimulation, in a manner that indicates susceptibility to desensitizing action by the long-acting GnRH analog, triptorelin.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzyme catalyzed polymerization and precipitation of aromatic compounds from aqueous solution

Horseradish peroxidase enzyme (HRP), once activated by hydrogen peroxide, initiates the oxidation of a wide variety of aromatic compounds. Reaction products undergo a non-enzymatic polymerization to form water insoluble aggregates which are readily separated from solution. HRP was selected for application in wastewater treatment systems due to its stability and retention of its catalytic ability over wide ranges of pH and temperature. HRP activity was optimal between pH 5.7 and 8.5 with peak activity occurring at neutral pH. Activity increased with temperature up to 50 °C and declined at higher temperatures due to thermal inactivation. HRP was inactivated rapidly by hydrogen peroxide in the absence of an aromatic substrate. The efficiency of removal that was achieved was dependent on the nature of the aromatic undergoing treatment and the amount of enzyme provided due to the finite lifetime of the catalyst. Optimization of pH significantly improved catalytic efficiency with a corresponding savings in treatment costs. Optimal catalytic lifetime of HRP was achieved in the pH range of 7 to 9 for the eight phenolic compounds treated. The minimum residual level to which aromatic substrates were removed from solution was independent of the starting concentration of the aromatic substrate. Enhanced removal of hard-to-remove compounds was noted when mixtures of aromatic substrates were treated. Key words: horseradish peroxidase enzyme, polymerization, wastewater, phenols, aromatics amines.