Concentration-time Product Research Articles

Efficacy of sodium chlorite in inactivating Vibrio parahaemolyticus attached to polyethylene terephthalate surfaces.

The inactivation of Vibrio parahaemolyticus cells attached to a polyethylene terephthalate (PET) disc in a sodium chlorite (NaClO2) solution was kinetically studied in a weakly acidic pH range of 4.0 - 6.5. The logarithmic reduction in the survival ratio depended on the concentration-time product. All inactivation curves showed a linear reduction phase, and the reduction in viable cells was greater than 4-log. No significant desorption of attached cells was observed during the inactivation treatment. The first-order inactivation rate constant (k) increased by approximately 4.5-fold for every 1.0 unit fall in pH. At all pH values, the k values calculated for the attached cells were approximately half of those for the unattached cells. These findings indicate that a weakly acidic NaClO2 solution is effective in inactivating bacteria attached to hard surfaces.

Predictive value of the product of plasma colchicine concentration and poisoning time for the prognosis of colchicine poisoning patients

Objective: To investigate the predictive value of the product of first plasmacolchicine concentration and poisoning time for the prognosis of colchicine poisoning patients, and to provide a basis for early prognosis assessment. Methods: October 2021, patients with colchicine poisoning admitted in the First Affiliated Hospitol of Wenzhou Medical University from January 2017 to September 2021 were collected, including general information such as patient gender, age, oral colchicine dose, poisoning time, the first laboratory test index andplasma colchicine concentration after admission. The patients were divided into survival group and death group according to their prognosis. The differences in clinical indicators such as admission plasma colchicine concentration, blood routine, blood biochemistry, coagulation function, and blood gas analysis were compared between the two groups, and their predictive value for the prognosis of patients were analyzed. Results: A total of 23 patients with colchicine poisoning, aged 20-85 years, were included in this study, of which 15 cases (65.22%) survived and 8 cases (34.78%) died. The first plasma colchicine concentration at admision were 0.42-53.61 ng/ml. The plasma colchicine concentration and the concentration-time product were 10.08-2147.04 h·ng/ml.Compared with the survival group, the plasma colchicine concentration and the concentration-time product in the death group were significantly increased, and the differences were statistically significant (P<0.05). Univariate logistic regression analysis showed that first plasma concentration and poisoning time>132.48 h·ng/ml, high C-reactive protein, high D-dimer, high absolute value of BE were the risk factors for the prognosis of patients with colchicine poisoning (OR=12.000, 95%CI: 1.1181-128.836; OR=1.053, 95%CI: 1.009-1.098; OR=1.219, 95%CI: 1.039-1.429; OR=1.360, 95%CI: 1.1.044-1.773; P<0.05). High prothrombin time activity was protective factor affecting the prognosis of colchicine poisoning patients (OR=0.941, 95%CI: 0.892~0.993; P<0.05). ROC curve analysis showed that the areas under the curves of first plasma concentration and poisoning time, C-reactive protein, absolute value of BE, D-dimer for predicting the prognosis of patients with colchicine poisoning were 0.918, 0.888, 0.867, 0.837, respectively, and the areas under the curves of prothrombin time activityfor predicting the prognosis of patients with colchicine poisoning was 0.788 (P<0.05) . Conclusion: The product of the first plasma colchicine concentration at admission and poisoning time is closely related to the prognosis of patients with colchicine poisoning, it can be used as a predictor for early evaluation of the prognosis of poisoned patients.

Transcriptomic Characterization of Inhalation Phosphine Toxicity in Adult Male Sprague-Dawley Rats.

Phosphine (PH3) is a highly toxic, corrosive, flammable, heavier-than-air gas that is a commonly used fumigant. When used as a fumigant, PH3 can be released from compressed gas tanks or produced from commercially available metal phosphide tablets. Although the mechanism of toxicity is unclear, PH3 is thought to be a metabolic poison. PH3 exposure induces multiorgan toxicity, and no effective antidotes or therapeutics have been identified. Current medical treatment consists largely of supportive care and maintenance of cardiovascular function. To better characterize the mechanism(s) driving PH3-induced toxicity, we have performed transcriptomic analysis on conscious adult male Sprague-Dawley rats following whole-body inhalation exposure to phosphine gas at various concentration-time products. PH3 exposure induced concentration- and time-dependent changes in gene expression across multiple tissues. These gene expression changes were mapped to pathophysiological responses using molecular pathway analysis. Toxicity pathways indicative of cardiac dysfunction, cardiac arteriopathy, and cardiac enlargement were identified. These cardiotoxic responses were linked to apelin-mediated cardiomyocyte and cardiac fibroblast signaling pathways. Evaluation of gene expression changes in blood revealed alterations in pathways associated with the uptake, transport, and utilization of iron. Altered erythropoietin signaling was also observed in the blood. Upstream regulator analysis identified several therapeutics predicted to counteract PH3-induced gene expression changes. These include antihypertensive drugs (losartan, candesartan, and prazosin) and therapeutics to reduce pathological cardiac remodeling (curcumin and TIMP3). This transcriptomics study has characterized molecular pathways involved in PH3-induced cardiotoxicity. These data will aid in elucidating a precise mechanism of toxicity for PH3 and guide the development of effective medical countermeasures for PH3-induced toxicity.

Sulfuryl fluoride as a methyl bromide alternative for fumigation of Necrobia rufipes (Coleoptera: Cleridae) and Tyrophagus putrescentiae (Sarcoptiformes: Acaridae), major pests of animal-based stored products

Sulfuryl fluoride (SF) has been registered in many countries for stored product applications as an alternative to other fumigants, especially methyl bromide (MB). Research was conducted to establish SF fumigation protocols for the mortality of pests infesting post-harvest durable commodities. The efficacy of SF against two major arthropod pests of southern dry-cured hams, the red-legged ham beetle, Necrobia rufipes, and the ham mite, Tyrophagus putrescentiae, was investigated. SF caused significant mortality in ham beetles but not for ham mites when treated for 48 h at 23 °C. Eggs of N. rufipes were more tolerant to SF than other stages fumigated. In addition, early aged (1–2 d old) eggs of N. rufipes were more susceptible to SF than late-aged (4–5 d old) eggs. Furthermore, SF fumigation led to 100% control of larvae, pupae and adults of N. rufipes by 8 g/m3 while the eggs required 20.88–24.72 g/m3 to prevent 100% hatch. However, T. putrescentiae showed high tolerance to SF as it survived concentration-time products in excess of the standard label limit 1500 g h/m3. SF studies also revealed that the eggs of T. putrescentiae were several fold more tolerant than that of the mobile stage, the nymphs and adults. SF trials under pilot-scale commercial conditions were also carried out that further supported the efficacy of SF for red-legged ham beetles but not for the ham mite. SF may not be suitable for managing ham mites based on work to date, but future work could investigate longer exposure times at higher temperatures.

Locational dynamics of concentration and efficacy of phosphine against pulse beetle, Callosobruchus maculatus (Fab)

Phosphine is considered as an effective substitute to methyl bromide (MB), an ozone depleting fumigant which was phased out honouring ‘Montreal Protocol’. Limited field studies are available on phosphine toxicity against storage insects of pulses under different climatic conditions in India. In the present study phosphine efficacy was investigated against laboratory cultured and field populations of Callosobruchus maculatus by organising field fumigation trials of 5 MT pulse stacks, each in triplicate, under varied climatic conditions. The trials were conducted at three locations, Jaipur for Cicer arietinum (chickpea), Cuttack for Vigna radiata (green gram) and Mumbai for Lathyrus aphaca (yellow pea) using conventional 56% Aluminium phosphide (AlP) tablets (2 tab/MT and 3 tab/MT) application; and gas derived from on-site phosphine generator with 77.5% granular (1.0 g and 1.5 g phosphine/m3) formulations for two exposure periods (7 and 10-days) for each dosage including untreated control. Phosphine gas concentration was monitored daily until the exposure periods using gas monitoring equipment. No emergence of adults was observed until 60 days after treatment indicating 100% insect mortality of both populations (laboratory and field) for both exposure periods using all dosages. The minimum effective phosphine gas concentration for controlling C. maculatus was observed as 300–500 ppm for 7-days exposure using 1.5 g phosphine/m3 depending on climatic conditions. A significant variation was observed in gas concentration monitored during fumigation of pulses at different locations. Average concentration-time (Ct) product for green gram was higher than that of chickpea and yellowpea. The loss of gas concentration was found to be significantly low in yellowpea treated with phosphine at moderately hot and humid climate.

Inactivation of Escherichia coli and MS2 coliphage via singlet oxygen generated by homogeneous photosensitization

The inactivation kinetics of E. coli and MS2 coliphage by singlet oxygen (1O2) were investigated in a homogeneous photosensitization system using Rose Bengal (RB) and visible light illumination (the Vis/RB system). The inactivation of E. coli and MS2 in the Vis/RB system was monitored over time with variations of several parameters such as pH, light intensity, concentration of RB, and the presence of dissolved oxygen. In addition, the concentration of 1O2 generated by the Vis/RB system was quantified using furfuryl alcohol under each microbial inactivation conditions. Based on the obtained results, the degree of microbial inactivation was quantitatively correlated with 1O2 exposure using the (delayed) Chick-Watson model. The Ct (concentration-time product) values of 1O2 required for 2 log microbial inactivation were found to be 1.3×10−4 mg·min/L for E. coli and 1.9×10−5 mg·min/L for MS2, respectively. The inactivation of E. coli exhibited an initial lag phase until 0.5×10−4 mg·min/L of Ct.

Pipe enlargement to satisfy concentration-time product for in-system disinfection in a water distribution system

C*t is used as a metric for disinfection in a water treatment plant while inside a distribution system, the concentration alone is used. For systems without a treatment plant, however, chlorine may be added in the upstream portion of the system to disinfect water. Therefore, disinfection is increased at higher chlorine concentration levels but also with enough contact time to completely disinfect the water. Therefore the use of the C*t product as a metric in the distribution system, if no upstream treatment exists, is explored here through computer modeling. The network solver EPANET was used to simulate the C*t product using water age in a method introduced here. It was found in a demonstration project that increasing the mainline pipe diameter allows the water to slow down enough to allow the C*t product to fully disinfect the water prior to reaching the first users. Specifically, for the demonstration system analyzed, an 8-inch (203 mm) mainline diameter requires 1.0 mg/L of chorine addition at the upstream end to fully disinfect the water. This shows promise for the use of pipe enlargement as a disinfection method for systems with no water treatment plant.

Survival of the Oak Wilt Fungus in Logs Fumigated with Sulfuryl Fluoride and Methyl Bromide

Abstract Methyl bromide (MB) fumigation of oak (Quercus sp.) logs destined for export is required to mitigate risks associated with movement of the oak wilt fungus, Bretziella fagacearum. Alternative fumigants with efficacy against B. fagacearum are needed because of MB's ozone-depleting properties. Fumigation with sulfuryl fluoride (SF) is considered a promising substitute. Logs (1.8 m long) were obtained from Quercus trees (18.3 to 29.2 cm diameter at breast height) that were naturally infested (NI) or artificially inoculated (AI) with B. fagacearum to compare pathogen colonization and survival following fumigation with SF and MB. The logs were fumigated with SF for 72 hours with 240, 280, and 320 g/m3 or 96 hours with 128 and 240 g/m3. MB fumigations were conducted using the current treatment schedule for oak logs destined for export (240 g/m3 for 72 h). Frequencies of successful pathogen isolation before treatment were higher for AI logs than for NI logs based on isolation rates from sapwood chips. Treatments greatly reduced frequencies of viable pathogen presence, but no treatment was successful in eradicating the pathogen. Experiments were conducted on blocks (10.2 by 10.2 by 11.4 cm3) obtained from Quercus trees to investigate simulated penetration and diffusion of SF and MB into oak logs. Slow, variable fumigant diffusion never reached concentration–time products lethal to B. fagacearum. Based on these results, reliance on SF alone as a quarantine measure may require higher concentration × time products to achieve quarantine level control of the oak wilt fungus in logs.

Developing and verifying a fumigant loss model for bulk stored grain to predict phosphine concentrations by taking into account fumigant leakage and sorption

To ensure fumigation effectiveness and address phosphine resistance concerns, fumigant concentrations and movement in a grain storage silo need to be understood. A mathematically accurate fumigation model was developed that is capable of predicting fumigant concentration and movement throughout a grain storage silo that takes into account fumigant loss from leakage and sorption, and was verified with experimental fumigation data. Equations estimating fumigant leakage and sorption were developed based on literature values and added to an existing finite element model. Fumigation data was used from a fumigation conducted on an Australian made silo filled with 45.5 tonnes of maize in Manhattan, Kansas. Two verifications were conducted based on phosphine concentration release times of 24 h and 30 h, with both verifications demonstrating accurate prediction of phosphine fumigant values and trends. The two verifications resulted in concentration-time products that were within 0.9% and 4.3% of the experimental values, respectively. The fumigation model is most accurate during the times of highest phosphine concentration. However, the model under predicted phosphine concentrations during the first 12 h of fumigation and over predicted phosphine concentrations beyond the first six days of fumigation. This fumigation model was found to be sufficiently accurate to allow for future experimentation on predicting fumigant concentrations as a function of environmental conditions and operational variable.

Efficacy of combining sulfuryl fluoride fumigation with heat to control the ham mite, Tyrophagus putrescentiae (Schrank) (Sarcoptiformes: Acaridae)

Sulfuryl fluoride (SF) could not control all life stages of Tyrophagus putrescentiae when applied at 23 °C using the highest allowable gas level. Recent work on heat treatments found 40 °C was ineffective against mites unless held for more than 48 h, a heating time that can damage ham quality. The objective of the laboratory trials reported here was to determine the lowest temperature and shortest exposure time at which SF could control mites while staying below the US EPA maximum concentration-time product (CTP) label rate of 1500 gh m−3 A 36-h fumigation with a CTP of 1400 gh m−3 killed 100% of all mite life stages at 40 °C. Mite eggs, which were determined to be the most SF-tolerant life stage, were exposed to lower CTPs of 300 or 1000 gh m−3 SF at 40 °C, control was estimated to require up to 125.71 h at 300 gh m−3 and 60.93 h at1000 gh m−3. Applying heat with SF just below the maximum allowable CTP will increase the efficacy of this fumigant, but also increases the risk of exceeding the legal limit for the gas. However, at target CTPs of either 300 or 1000 gh m−3, which would represent preferred commercial application rates of SF, good levels of mite control could not be achieved at 40 °C within a 48-h exposure.

Kinetics of the Inactivation of Vibrio parahaemolyticus in Weakly Acidic Sodium Chlorite Solution.

The kinetics of the inactivation of Vibrio parahaemolyticus in sodium chlorite (NaClO2) solution was studied in the weakly acidic pH range of 4.0 to 6.5 and at various temperatures. The logarithmic reduction of the survival ratio depended on the concentration-time product, and all the inactivation curves showed a linear reduction phase. The first-order inactivation rate constant (k) increased by approximately twice for every 0.44 unit fall in pH. During the inactivation experiments, no formation of chlorine dioxide occurred. These data indicated that undissociated HClO2 was the active species governing the inactivation of V. parahaemolyticus. It was also shown that the use of weakly acidic NaClO2 solutions containing high concentrations of ionized ClO2- gave slower kinetics of the inactivation, whereas it could achieve the significant reduction of viable cells of more than 4-log. The k value showed an Arrhenius-type temperature dependence in the temperature range of 5 to 40℃. The apparent activation energy for the inactivation of V. parahaemolyticus was estimated to be 43.5 kJ/mol. The k value increased by approximately 1.8 times for every 10℃ rise in temperature.

Effect of sulfur dioxide and modified atmosphere packaging on blueberry postharvest quality

Sulfur dioxide and modified atmospheres were evaluated to find the optimal method to control decay and prolong the quality of blueberries after harvest. To determine the most suitable MAP system for highbush blueberry (Vaccinium corymbosum, ‘Brigitta’), fruit were stored in controlled atmospheres (CO2/O2 partial pressures in kPa: 5/1; 7/15, 15/5) or an atmosphere modified by varying the amount of fruit in two modified atmosphere packaging (MAP) systems. The MAP systems employed bags with 60μm-thick low density polyethylene where the fruit were hermetically sealed in the bag: (1) without perforation (MAP 0); or (2) with two perforations of 3mm2 (MAP 2). ‘O’Neal’, ‘Duke’, ‘Legacy’, ‘Brigitta’, ‘Elliott’ and ‘Aurora’ were evaluated to reduce deterioration by the most suitable MAP system and, in a separate experiment, ‘Legacy’ fruit were fumigated with SO2 and packed in the MAP and compared with perforated bag (PB). The effectiveness of reducing blueberry deterioration was evaluated after 30–45days at 0°C. CO2 partial pressure higher than 8kPa or O2 partial pressure lower than 2kPa induces ‘Brigitta’ fruit softening. Among the evaluated cultivars, MAP 2 attained CO2 and O2 partial pressures between 4.5–6.0kPa and 13–15.0kPa, respectively. Induction of fruit softening by CO2 was dependent on the cultivar. ‘O’Neal’, ‘Duke’ and ‘Legacy’ were extremely sensitive, at CO2 concentration of 6kPa. The benefits of MAP 2 were mainly attributed to humid environment within the packages that allow reducing weight loss and symptoms of dehydration; effects that were mimicked by the perforated bag. ‘Legacy’ blueberry fruit were fumigated for 30min at 20°C with SO2 at concentration time product of 100–150 (μLL−1) h, followed by packaging in MAP 2 or in a perforated (0.3% ventilation area) low density polyethylene bag and storage for 45days at 0°C. Decay, weight loss, and the percentage of dehydrated and soft fruit were reduced effectively when the SO2-fumigated fruit were stored in either MAP 2 or the perforated bag. Decay was particularly well controlled by SO2. SO2 fumigated fruit, packed into a perforated bag was a better option than packaging the fruit into modified atmosphere bags, where the CO2 steady state partial pressure that controlled decay was extremely close to the level that injured the fruit.

Validation of hydrogen cyanide fumigation in flourmills to control the confused flour beetle

In the milling industry, the Tribolium confusum is hard to exterminate pest. We measured the concentration time product (Ct-P) achieved during the hydrogen cyanide (HCN) fumigation and examined whether the Ct-P levels in the explored Czech pilot mill were sufficient to control the field strain of T. confusum. Using an originally constructed, gastight fumigation chamber, it was estimated that the Ct-P required for the complete killing of the field strain of T. confusum was 4× higher (4.35 g/h/m3) than the levels required to kill the laboratory strain (1.25 g/h/m3). The Ct-P levels (ranging from 79 g/h/m3 to 100 g/h/m3) reached during the mill fumigations with HCN were less than half of the labelled HCN rate (240 g/h/m3). Nevertheless, the current HCN dosage is still sufficient since the Ct-P reached during the mill fumigations was at least 99× higher than that required for the exterminating to the lab strain and 18× higher than that required for the field strain extermination. These results were confirmed in mill validation testing, where 100% mortality of T. confusum adults was achieved.

P6: Hair desorption of the sulphur mustard simulants methyl salicylate and 2-chloroethyl ethyl sulfide following vapour exposure

Introduction Chemical warfare agents are compounds whose toxic properties are used to kill or incapacitate people. Their synthesis, use and stockpiling are regulated by the Organisation for the Prohibition of Chemical Weapons. Despite this narrow surveillance, exposure to chemical warfare agents may still happen. Analysis of external contamination of hair could be of high interest, especially for rescue teams. It could be particularly useful to identify chemicals to which victims were exposed, or to distinguish among a large number of potentially exposed individuals those who specifically require thorough decontamination. External contamination of hair by vapours of the sulphur mustard (SM) simulant methyl salicylate has already been demonstrated (Spiandore M., Piram A., Lacoste A., Josse D., Doumenq P., External contamination of hair as a marker of exposure to chemical warfare agents, 18 th Scientific Meeting of the Society of Hair Testing, Geneva, August 20-30, 2013). The main objective of this work is to determine desorption kinetics of SM simulants methyl salicylate (MeS) and blistering agent 2-chloroethyl ethyl sulfide (CEES) from hair following vapour exposure. Methods Locks of human hair were exposed to vaporised CEES or MeS for different times and at different concentrations in order to reach concentration-time products ( Ct ) around 900-1500 mg. min/ m 3 which corresponds to the lethal value range for SM. Desorption of MeS and CEES have been observed when transferring a contaminated lock of hair in an uncontaminated tank. Dichloromethane extracts were then analysed by GC-MS/MS operating in MRM mode. Results As previously shown for MeS, importance of external contamination of hair by CEES vapours increased with exposure duration or concentration. Depending on the vapour concentration or time of exposure, CEES content in hair represented 0.5 to 3 % of the exposure dose. MeS yielded in higher rates as its content retrieved in hair represented up to 15 % of the exposure dose. Conclusion Both SM simulants (MeS and CEES) have been quantified in hair after they have been exposed to vapours, with a simple solvent extraction. It confirms previous results that hair could be used as a marker of vapour exposure to chemical warfare agents.

Hair analysis as a useful procedure for detection of vapour exposure to chemical warfare agents: simulation of sulphur mustard with methyl salicylate.

Chemical warfare agents (CWA) are highly toxic compounds which have been produced to kill or hurt people during conflicts or terrorist attacks. Despite the fact that their use is strictly prohibited according to international convention, populations' exposure still recently occurred. Development of markers of exposure to CWA is necessary to distinguish exposed victims from unexposed ones. We present the first study of hair usage as passive sampler to assess contamination by chemicals in vapour form. This work presents more particularly the hair adsorption capacity for methyl salicylate used as a surrogate of the vesicant sulphur mustard. Chemical vapours toxicity through the respiratory route has historically been defined through Haber's law's concentration-time (Ct) product, and vapour exposure of hair to methyl salicylate was conducted with various times or doses of exposure in the range of incapacitating and lethal Ct products corresponding to sulphur mustard. Following exposure, extraction of methyl salicylate from hair was conducted by simple soaking in dichloromethane. Methyl salicylate could be detected on hair for vapour concentration corresponding to about one fifth of the sulphur mustard concentration that would kill 50% of exposed individuals (LCt50). The amount of methyl salicylate recovered from hair increased with time or dose of exposure. It showed a good correlation with the concentration-time product, suggesting that hair could be used like a passive sampler to assess vapour exposure to chemical compounds. It introduces great perspectives concerning the use of hair as a marker of exposure to CWA.

Efficacy of Fixed Bed Ozonation Treatment to Control Insects in Stored Bulk Grain

Abstract. Scale-up demonstration trials were conducted at the pilot bin facility of the Purdue University Post-Harvest Education and Research Center in June 2005, August 2006, July 2007, and October 2008 with conventional yellow maize and at a popcorn storage facility in July 2005 and 2006. The primary objective of these trials was to determine the efficacy of ozonation to control insect pests without affecting end-use quality. The setup consisted of generating ozone at a constant rate with commercially available generators, introduction in the headspace, drawdown to the plenum with a fan with a minimum air velocity through the grain of 0.03 m/s, re-circulation back into the headspace or exhausting from the plenum into another bin. Ozonation was done to attain an ozone concentration of 50 ppm in the plenum to be maintained for a period of 72 h (3,600 ppm-h). When this concentration was not achieved, an ozone concentration-time product of 3,600 ppm-h was aimed for extending the time to expose the grain mass to the same treatment effect to achieve 100% insect mortality. The trials were performed using insect bioassays with adults of maize weevil (MW) and red flour beetle (RFB). Insect mortality was essentially 100% for both MW and RFB. The concept of two phases of ozonation and the airflow rates needed to achieve the required treatment levels of 3,600 ppm-h were investigated. The trials at the popcorn facility confirmed that end-use parameters of popcorn were not affected.

Effects of peak exposure scenarios on Gammarus fossarum using field relevant pesticide mixtures

The present study investigated sublethal effects of a field relevant pesticide mixture (one herbicide, three fungicides, five insecticides) on Gammarus fossarum by considering different peak exposure scenarios, which may be generated by the inherent properties of vegetated ditches. Additional experiments aimed at the identification of germane exposure pathways (food and water). Therefore, G. fossarum were exposed in independent experiments to three scenarios, which differed besides in the peak concentration of the pesticide mixture also in the mixture's composition and exposure duration (n=20 per treatment). The exposure duration of 12 or 120min was followed by a seven-day post-exposure observation period. At a constant concentration–time product, a lower exposure duration in concert with a proportionally higher peak concentration caused a substantially elevated ecotoxicity compared to a treatment with a longer exposure duration at a lower peak concentration. Given the importance of the insecticide lambda-cyhalothrin for the mixture's ecotoxicity it may be concluded that the fast mode of action of pyrethroids mainly explains this observation. Moreover, field relevant concentrations of the pesticide mixture applied at an exposure duration of 120min resulted in reduced gammarids' feeding rate, which may be indicative for shifts in the ecosystem function of leaf litter breakdown and hence the provision of energy for local and downstream communities. Finally, the present study indicated that both pathways of exposure, namely via food or water, reduce gammarids' feeding rate synergistically. This suggests that both exposure pathways should be considered for compounds exhibiting a high Kow (e.g. pyrethroids) during the risk assessment of single substances and mixtures.

Ozone treatment effects on microbial count on maize

The ultimate goal of this research was to develop a semi-continuous flow grain treatment system and predictive model that will reduce microorganisms on grain kernel surfaces with ozone. The focus of this research was to determine the concentration-time product (CTP) of ozone required to eliminate various levels of microbial growth on grain kernels. To examine the effect of ozone on surface microbes, samples of freshly-harvested and stored maize were treated with ozone for 1 and 3 hours at average ozone concentrations of 1752 ppm, 915 ppm and 37 ppm. Microorganisms were significantly decreased by 28 to 57% after maize samples were ozonated for 1 h at 37 to 1752 ppm and 45 to 80% for 3 h at 37 to 1752 ppm. Linear regression analysis of the CTP data indicated that percent mold reduction increased at a rate of 0.0088 times the CTP. The modified Gompertz equation applied to the microbial inactivation data indicated that a 0.5 to ~1 log mold reduction on maize kernels was attained for ozone concentrations between 37 and 1752 ppm. When compared to preliminary field data from a semi-continuous flow grain treatment system, the laboratory data and the model-predicted values were reasonably close with respect to the microbial load reduction observed on maize samples taken from the system. Keywords : Ozone, Microorganisms, Treatment, Sterilization, Ozone concentration.

Continuous ozonation treatment systems as other alternative more efficient grain protection technologies

Previous static bed ozonation scale-up and demonstration trials have proven the use of ozone as an effective technology for grain protection without affecting its end-use quality. Due to the lack of current availability of high capacity ozone producing generators, grain treatment through static bed ozonation systems are limited to be used in metal silos of capacities smaller than 644-t. Also, the trials have shown that treatment time has to be of no less than 4 d during application in order to be effective for pest control. Therefore, more efficient ozonation treatment systems are needed for proper ozone usage for stored product protection. The primary objective of these research studies was to design and test a semi-continuous counter-flow ozonation and a continuous ozonation flow treatment systems in order to ozonate grain at faster rates based on the concentration-time product (CTP) of ozone required to achieve 100% insect mortality and effective mold reduction in grain. The procedure of the counter-flow semi-continuous ozonation system consisted of removing each grain layer inside a metal silo with a tapered unloading auger after each layer reached the desired ozone CTP. The treated grain is subsequently transported to a storage or shipping silo. The continuous ozonation flow system involves applying high ozone concentrations through a modified grain loading screw conveyor where ozone and grain are moving continuously in the same flow direction. The counter-flow semi-continuous ozonation system was successfully tested and proved to be a technically feasible tool for pest control and mold reduction. The continuous ozonation flow system was proved as an effective tool for treating grain during handling while achieving 100% insect mortality, and effective mold reduction. Keywords : Ozonation, Continuous treatment, Grain, Pest control, Molds.

Evaluating the Effects of Sealing Quality on Gas Leakage Rates During Structural Fumigation by Pressurization Testing and CFD Simulations

In this study, pressurization tests were conducted to quantify gas-tightness of the Hal Ross Flour Mill at Kansas State University, which was sealed at three sealing qualities, i.e., fully sealed, partially sealed, and non-sealed. A computational fluid dynamics (CFD) model of the mill was then constructed. Based on the building gas-tightness levels obtained from the pressurization tests, several sulfuryl fluoride fumigations were simulated to study sensitivities of the half-loss time (HLT) and concentration time (Ct) product of the mill as affected by sealing quality, and wind and buoyancy forces. The HLT of the fully sealed simulation case was at least two to three times greater than that of the partially and non-sealed cases, respectively. The Ct product results followed a similar trend. The results of this study emphasized the importance of the pressurization test as a useful tool for quantification of building gas-tightness and for prediction of expected HLT and Ct product of a subsequent structural fumigation.