A nonlinear, dynamic, simulation model for transport, and whole plant allocation of systemic xenobiotics following foliar application. IV: Physicochemical properties requirements for optimum absorption and translocation

The relationship between the physicochemical properties (molar volume, partition coefficient, and dissociation constant) of slow-acting systemic postemergence xenobiotics and their uptake and translocation to the sites of action was investigated using the nonlinear, dynamic simulation model ERMESSE. When the pK_a was held constant at 4.0, the model enables the prediction of the uptake of a systemic xenobiotic as a function of its partition coefficient and molar volume. The model also considered the effects of the physicochemical properties of a systemic xenobiotic on its long-distance translocation within the vascular tissues. For instance, when the log K_ow and pK_a were held constant at 1.5 and 6.0, respectively, the model predicted a higher translocation rate (55%) for molecules with a small (e.g., MV = 100 cm³ mol⁻¹) as opposed to a large (e.g., MV = 300 cm³ mol⁻¹, 33%) molar volume. In addition, the theoretical predictions from the ERMESSE model showed that any xenobiotic with a molar volume not exceeding 300 cm³ mol⁻¹ could provide an uptake ?50% and a translocation rate ?25% when its log K_ow is between −0.5 and 2.5 and its pK_a is between 0.0 and 8.0.     

A Derived Climatology of Water Temperatures for the Mississippi Catfish Industry

A 36 year (1951–1986) record of water temperatures in Mississippi catfish ponds is synthesized from relationships with existing air temperature records. Multiple regression analysis is used to produce the following predictor equations for morning and afternoon pond temperatures: morning pond temperatures = 2.218 + 0.062(max air temp, day before) + 0.285(min air temp, same day) + 0.561 (afternoon pond temp, day before) (1) afternoon pond temperatures
= 2.071 - 0.068(min air temp, same day) + 0.651 (morning pond temp, same day) + 0.373(max air temp, same day) (2)
The derived pond temperature record is analyzed to produce annual average regimes; daily average, maximum, and minimum temperatures with standard deviations; and probabilities at 10 levels of Occurrence through the year and for each individual month. Applications for the aquaculture industry are presented and evaluated.     

Effects of high concentrations of dietary vitamin E and ethoxyquin on the performance of laying hens

1. Three experiments were carried out with light strain laying hens to evaluate the effects of relatively high doses of dietary vitamin E (125 mg/kg food) or ethoxyquin (EQ) (250 mg/kg food) on their laying performance. The control diet contained 5 and 125 mg/kg vitamin E and EQ, respectively. The experimental diets were fed either from one or 32 weeks until 88 or 89 weeks of age. 2. The two antioxidants did not affect the growth of the pullets, age at first egg, final body weight, average egg weight or relative abdominal fat pad size and liver weight at the termination of the experiments. In two out of three experiments, vitamin E and EQ did not affect egg production, food efficiency or mortality; in the third experiment vitamin E significantly (P less than 0.05) improved egg production and food efficiency after an outbreak of Newcastle disease which occurred at 34 weeks of age. EQ significantly reduced mortality during the course of this experiment, but did affect the variables of performance. In two experiments vitamin E consistently improved shell density, although a significant effect was observed in only one of the eight determinations carried out. EQ did not affect this variable. 3. The uterine muscle was more susceptible to oxidation than the drumstick meat, as evaluated by TBA values. In both tissues, vitamin E significantly and consistently decreased TBA values and restricted their increase during incubation, while EQ was less effective, particularly in the drumstick meat. 4. It is concluded that increasing vitamin E and EQ concentrations in diets of laying hens have no effect on the decrease in egg production due to aging. However, vitamin E may minimize the decline in egg production and food efficiency following the outbreaks of some diseases and slightly improve--under certain yet undefined conditions--shell density.     

Response of multiple seeded cocklebur and other cocklebur types to herbicide treatment

Multiple seeded cocklebur has been found in the last decade in Texas, and described as a biotype of Xanthium strumarium L with up to 25 seeds per bur instead of the usual two. The multiple seeded bur typically produces up to nine seedlings, causing concern that it may be harder to control than normal seeded common cocklebur. The efficacies of a series of fungal and conventional commercial herbicides have been compared in the greenhouse on seedlings of multiple seeded cocklebur from Texas (MSC-TX) and normal common cockleburs from Texas (NCC-TX), Arkansas (NCC-AR), Illinois (NCC-ILL) and two from Mississippi (NCC-MS#1, NCC-MS#2). Three measures of herbicidal activity (reductions in plant height and dry weight, and mortality) were used. The fungal herbicide Alternaria helianthi (Hansf) Tubaki & Nishihara at 1 x 10(5) conidia ml(-1) + 2 g liter(-1) Silwet L-77 with an 8-h dew period was an effective herbicide with all biotypes, as were the commercial chemical herbicides chlorimuron (14.8 g ha(-1)), imazaquin (29.6 g ha(-1)), sodium hydrogen methylarsonate (MSMA; 279.1 g ha(-1)) and imazethapyr (39.5 g ha(-1)). The membrane-disrupting organic arsenical MSMA was effective with all biotypes, whereas commercial chemical herbicides which act by inhibiting branched-chain amino acid synthesis (chlorimuron, imazaquin and imazethapyr) were less effective against normal seeded common cocklebur biotypes with short stature. These studies showed that multiple seeded cocklebur was at least as susceptible to the biological agent A helianthi and to the conventional commercial herbicides studied as were normal seeded cockleburs, suggesting that existing methods should be adequate to control this novel biotype.     

Effects of moisture,temperature, and biological activity on the degradation of isoxaflutole in soil

The effects of several environmental factors on the dissipation, transformation, and mineralization of isoxaflutole were investigated in laboratory incubations. In the soil, isoxaflutole hydrolyzed to a diketonitrile derivative, which is the active form of the herbicide. The diketonitrile was then metabolized to an inactive benzoic acid derivative and later into two unknown products, which were found only in small quantities. Degradation of isoxaflutole was faster in soil maintained at -100 or -1500 kPa compared to that in air-dry soil. At 25 degrees C, the half-lives for isoxaflutole were 9.6, 2.4, and 1.5 days in air-dry, -1500 kPa, and -100 kPa moisture regimes, respectively. A simple Arrhenius expression described the response of isoxaflutole transformation (mineralization and transformation) to temperature in the range of 5 to 35 degrees C. An activation energy value (E(a)) of 67 kJ/mol for isoxaflutole suggested the transformation of the herbicide to the diketonitrile derivative was primarily a chemical reaction. Moreover, biological activity had little effect on the hydrolysis of isoxaflutole, with half-lives of 1.8 and 1.4 days in sterile and nonsterile soil, respectively. However, the transformation of diketonitrile to benzoic acid and the production of the unknown products were greatly reduced in the sterile soil, suggesting one or more biologically mediated processes.     

Attempts to achieve low‐weight broiler breeder hens by severe growth depression during various periods up to 6 weeks of age and food allocation below the recommendations thereafter

1. Three experiments were carried out with White Rock (Anak) female chicks to evaluate the possibility of obtaining low‐weight breeder hens and to assess their reproduction potential. Such hens were obtained by early growth depression induced by either severe food restriction (SFR) from 1 or 2 to 3 or 4 weeks of age, or a low‐protein diet (LPD) fed from 0 to 6 weeks of age, or the use of diets containing 0·7 or 0·8% zinc as ZnO from 1 to 3 weeks of age, followed by food allocation below recommendation up to 22 or 67 weeks of age.

2. Body weights (BW) of the birds whose growth had been depressed were consistently and at time significantly lower than those of the control birds throughout the experiments. Age at first egg was delayed in hens previously fed the LPD and the diet containing the higher concentration of ZnO, and in those exposed to SFR from 2 to 4 weeks of age. BW at that time tended to be lower in birds whose growth had been depressed, although a significant effect was observed in only one experiment.

3. Egg production and egg size were not significantly affected by the various treatments, except for the lower production in hens fed the LPD at an early age.

4. Negative regressions (on an individual basis) were consistently observed between BW at 22 weeks of age and age at first egg, and between age at first egg and number of eggs laid. Positive regressions were observed between age at first egg and BW at that time. The regressions between BW at 22 weeks of age and number of eggs laid were positive but not always significant.

5. Severe growth depression at an early age (produced by food restriction or ZnO supplemented diet, but not LPD) followed by decreased allocation of food afterwards, could provide a means for reducing BW of broiler breeder hens without adversely affecting egg production. This procedure may save 2·5 to 6·6% of the food consumed during the life span of the birds.     

Dissipation of the herbicide [14C]dimethenamid under anaerobic conditions in flooded soil microcosms

The objective of this research was to investigate the dissipation of the herbicide dimethenamid under anaerobic redox conditions that may develop in the soil environment. Soil-water biometers were prepared with a saturated soil and made anaerobic by either glucose pretreatment (according to the Environmental Protection Agency registration study for anaerobic fate) or N2 sparging. Treatments included glucose pretreatment, NO3- + SO42- amendment, unamended, and autoclaved. Volatile, aqueous, extractable, and bound (unextractable) 14C-residues were quantified and characterized. The redox potential decreased over time, and evidence of denitrifying, iron-reducing, sulfate-reducing, and methanogenic conditions was observed, depending on the amendments. Anaerobic degradation of 14C-dimethenamid occurred in all treatments, and the time observed for 50% disappearance (DT50) was 13-14 days for nonautoclaved treatments. 14C-metabolites accumulated to up to 20% of applied 14C. At least two major metabolites were observed in nonautoclaved treatments, whereas only one was observed in autoclaved microcosms. More than 50% of the applied 14C was eventually incorporated into soil-bound residue.     

Disruption of the CFTR gene produces a model of cystic fibrosis in newborn pigs

Almost two decades after CFTR was identified as the gene responsible for cystic fibrosis (CF), we still lack answers to many questions about the pathogenesis of the disease, and it remains incurable. Mice with a disrupted CFTR gene have greatly facilitated CF studies, but the mutant mice do not develop the characteristic manifestations of human CF, including abnormalities of the pancreas, lung, intestine, liver, and other organs. Because pigs share many anatomical and physiological features with humans, we generated pigs with a targeted disruption of both CFTR alleles. Newborn pigs lacking CFTR exhibited defective chloride transport and developed meconium ileus, exocrine pancreatic destruction, and focal biliary cirrhosis, replicating abnormalities seen in newborn humans with CF. The pig model may provide opportunities to address persistent questions about CF pathogenesis and accelerate discovery of strategies for prevention and treatment.     

A climatological basis for conserving groundwater and reducing overflow in aquaculture ponds in the Southeast United States

Drop-fill water management schemes for aquacultural ponds reduce both groundwater use and effluent release. A drop-fill scheme assumes that pond water level will be allowed to decrease to the “drop” depth before makeup water is used to return it to the “fill” depth, which is typically some fraction (e.g., 1/2) of the drop depth. This paper compares predicted performance of drop-fill schemes at five sites in the Southeast U.S. (Thompsons, TX, Stuttgart, AR, Stoneville, MS, Clemson, SC, and Fairhope, AL). The locations were chosen to assess the effect of the east–west precipitation gradient and the south–north change from maritime to continental characteristics on the drop-fill approach in this region.

Performance of the drop-fill schemes was based on calculated daily water balances for ponds using 40-year (1961–2000) precipitation (P) and evaporation (E) records at the sites. Pond evaporation is assumed to be 0.8 × pan evaporation. Since performance differences based on regional P minus E (P−E) records was the subject of this work, ponds were assumed identical in other respects (i.e., all ponds were assumed to be levee-type and to have zero infiltration).

Simulated drop-fill schemes tested included (in cm): 0/0, 5/2.5, 10/5, 15/7.5, 20/10, 25/12.5, 30/15, 45/22.5, 60/30, 90/45, and 120/60. Each scheme was simulated using daily time steps for 40 years at each site. Results suggested that rigorous adherence to even a modest drop-fill scheme results in substantial reductions in both groundwater use and effluent release. It also appears that P−E conditions at all sites allow implementation of more aggressive drop-fill schemes in properly designed ponds that will require no supplemental groundwater for most years. This was also true with respect to effluent release at three of five sites. At two sites, precipitation was sufficiently large that zero effluent years were either not predicted (Fairhope) or relatively uncommon (Clemson) for any drop-fill scheme.