Reducing sediment and phosphorus in tributary waters with alum and polyacrylamide.

The Salton Sea is the largest inland water body in California, covering an area of 980 km(2). Inflow to the Salton Sea (1.6 km(3) yr(-1)) is predominately nutrient-rich agricultural wastewater, which has led to eutrophication. Because internal phosphorus release from the bottom sediments is comparatively low and external phosphorus loading to the Salton Sea is high, reduction of tributary phosphorus is expected to reduce algal blooms, increase dissolved oxygen, and reduce odors. Removing both dissolved phosphorus and phosphorus-laden sediment from agricultural drainage water (ADW) should decrease eutrophication. Both alum and polyacrylamide (PAM) are commonly used in wastewater treatment to remove phosphorus and sediment and were tested for use in tributary waters. Laboratory jar tests determined PAM effectiveness (2 mg L(-1)) for turbidity reduction as cationic > anionic = nonionic. Although cationic PAM was the most effective at reducing turbidity at higher speeds, there was no observed difference between the neutral and anionic PAMs at velocity gradients of 18 to 45 s(-1). Alum (4 mg L(-1) Al) reduced turbidity in low energy systems (velocity gradients < 10 s(-1)) by 95% and was necessary to reduce soluble phosphorus, which comprises 47 to 100% of the total P concentration in the tributaries. When PAM was added with alum, the anionic PAM became ineffective in aiding flocculation. The nonionic PAM (2 mg L(-1)) + alum (4 mg L(-1) Al) is recommended to reduce suspended solids in higher energy systems and reduce soluble P by 93%.

Toxicity and repellency of borate-sucrose water baits to Argentine ants (Hymenoptera: Formicidae).

The oral toxicity of boron compounds to the Argentine ant, Linepithema humile (Mayr), was evaluated in laboratory tests. The ants were provided 25% sucrose water containing 0.5 and 1% boric acid, disodium octaborate tetrahydrate, and borax. Lethal times of these solutions were a function of the concentration of boron. In field tests, the ants showed no discrimination between disodium octaborate tetrahydrate and boric acid. There was a significant reduction in consumption of sucrose water with > 1% boric acid.

Environmental biochemistry of chromium.

Chromium is a d-block transitional element with many industrial uses. It occurs naturally in various crustal materials and is discharged to the environment as industrial waste. Although it can occur in a number of oxidation states, only 3+ and 6+ are found in environmental systems. The environmental behavior of Cr is largely a function of its oxidation state. Hexavalent Cr compounds (mainly chromates and dichromates) are considered toxic to a variety of terrestrial and aquatic organisms and are mobile in soil/water systems, much more so than trivalent Cr compounds. This is largely because of differing chemical properties: Hexavalent Cr compounds are strong oxidizers and highly soluble, while trivalent Cr compounds tend to form relatively inert precipitates at near-neutral pH. The trivalent state is generally considered to be the stable form in equilibrium with most soil/water systems. A diagram of the Cr cycle in soils and water is given in Fig. 6 (Bartlett 1991). This illustration provides a summary of environmentally relevant reactions. Beginning with hexavalent Cr that is released into the environment as industrial waste, there are a number of possible fates, including pollution of soil and surface water and leaching into groundwater, where it may remain stable and, in turn, can be taken up by plants or animals, and adsorption/precipitation, involving soil colloids and/or organic matter. Herein lies much of the environmental concern associated with the hexavalent form. A portion of the Cr(VI) will be reduced to the trivalent form by inorganic electron donors, such as Fe2+ and S2-, or by bioprocesses involving organic matter. Following this conversion, Cr3+ can be expected to precipitate as oxides and hydroxides or to form complexes with numerous ligands. This fraction includes a vast majority of global Cr reserves. Soluble Cr3+ complexes, such as those formed with citrate, can undergo oxidation when they come in contact with manganese dioxide, thus reforming hexavalent Cr. In trace amounts, Cr is an essential component of animal nutrition, functioning mainly in glucose metabolism, and possibly in fat metabolism. While shown to be nonessential for plants, it is required by some microbes, possibly as a cofactor for specific enzyme systems. Bacteria with plasmid-conferred resistance to Cr(VI) have been isolated from water, soil, and sediments, and the resistance mechanisms have been somewhat characterized. One of the chief mechanisms is bioreduction of toxic Cr(VI) to the relatively nontoxic Cr(III). This has been shown to occur directly, by enzymatic processes at the cell membrane, and indirectly, with microbially produced H2S acting as the reductant.(ABSTRACT TRUNCATED AT 400 WORDS)

Mineral Precipitation and Trace Oxyanion Behavior during Evaporation of Saline Waters.

Evaporation basins used for the disposal of agricultural drainage waters in central California contain elevated trace element levels that pose hazards to groundwater quality and wildlife visiting the ponds. A study was conducted to evaluate the solution dynamics of mineral-forming elements and trace oxyanions (U, Mo, and V) during evaporation of saline waters whose chemical compositions evolve according to two distinct chemical divides, and to characterize the evaporite minerals formed from the complete evaporation of these waters. The alkali and alkaline earth metals exhibited nonconservative behavior, forming evaporite minerals such as bloedite, calcite, aragonite, gypsum, halite, thenardite, and trona. Molybdenum behaved nonconservatively, while V exhibited conservative behavior that did not differ whether V was initially added as V(IV) or V(V). Uranium displayed conservative behavior under conditions of low U concentrations and high alkalinities. Nonconservative behavior was observed for U, however, under higher U concentrations and low alkalinities. We conclude that V and U in waters with alkalinities >10 mmolc L-1 will not accumulate in evaporation pond minerals. In ponds with low alkalinity, U will partition to a solid mineral phase.

Inhibition of cyclic AMP formation in N1E-115 neuroblastoma cells is mediated by a non-cardiac M2 muscarinic receptor subtype.

The cardioselective muscarinic antagonist, AF-DX 116 [11[2-[(diethyl-amino)-methyl]-O-1-piperidinyl]-5,11-dihydro-6H-pyrido- [2,3-b][1,4]-benzodiazepine-6-one), was weak at blocking the M2 muscarinic receptor-mediated inhibition of cyclic adenosine monophosphate (cAMP) formation in mouse neuroblastoma cells (clone N1E-115). In contrast, the glandular-selective antagonists, hexahydro-sila-difenidol (HHSiD) and 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP), were quite potent at inhibiting this response, being 14- and 318-fold more potent than AF-DX 116 in this regard, respectively. According to the rank order of potency of these two classes of antagonists, these data provide the first pharmacological evidence that inhibition of cAMP formation in a neuronal tissue is mediated by a non-cardiac M2 muscarinic receptor subtype.

Poisson regression models of Canadian census division migration flows.

"This paper examines the amount, spatial pattern, and correlates of migration in Canada at the census division scale. The effects of distance, economic prosperity, social and cultural conditions, community size, and the housing market are investigated.... Poisson regression techniques were used to avoid the estimation problems frequently encountered in log-normal regression."

Pseudo-noncompetitive antagonism of muscarinic receptor-mediated cyclic GMP formation and phosphoinositide hydrolysis by pirenzepine.

Pirenzepine selectively antagonized muscarinic receptor-mediated cyclic GMP formation in a noncompetitive fashion in mouse neuroblastoma cells (clone N1E-115). These effects of pirenzepine were time- and concentration-dependent and they were also reversible. Interestingly, whereas atropine elicited competitive antagonism of the cyclic GMP response at low concentrations, it also behaved like a noncompetitive antagonist at higher concentrations and its effects were partially reversible. Using additional approaches to study the mechanisms underlying this anomalous antagonistic profile of pirenzepine, we investigated whether this deviation from competition could be due to the short time of exposure to muscarinic agonists (30 sec) used in cyclic GMP measurements. Our data indicated that the mode of pirenzepine-induced antagonism of ligand binding to muscarinic receptors was different when assessed using nonequilibrium (30 sec) or equilibrium (1 hr) incubations. Thus, pirenzepine appeared to be noncompetitive and competitive under these two conditions, respectively. Furthermore, although pirenzepine blocked receptor-mediated phosphoinositide hydrolysis competitively when the response was measured at 20 min, it was clearly noncompetitive using 5-min incubations. Therefore, the noncompetitive antagonism by pirenzepine detected in cyclic GMP measurements might be only apparent and might be attributed, at least in part, to a lack of an equilibrium state under the specific conditions of these assays.

Interregional labor migration and information flows.

A model of interregional labor migration is developed that incorporates a complex system of information concerning migration and employment opportunities, as well as a heterogeneous population in which groups of workers differ in their assumed levels of skill, attitudes toward risk, and willingness to move. "Three channels are examined: interpersonal communication, general source information, and specific source information targeted at unemployed workers. In this process, trajectories of welfare levels (composed of wage plus nonwage benefits), information flows, vacancy and unemployment levels are generated for different worker and job types, regional aggregates, and the system as a whole. The behavior of the model is examined by means of numerical simulations and sensitivity analyses."

An elementary simulation model of the job matching process within an interregional setting.

PIP: Using a dynamic multiregional model, this paper discusses the job search and migration process and how they are affected by welfare levels, regional wage scales, and stress. This model relaxes the homogeneity assumptions; therefore, different skills and skill requirements exist. Despite the obvious importance of wages to both the worker and employer, the model assigns workers to jobs without regard to the wage paid; the objective function maximizes society's benefits rather than that of either the worker or the employer in isolation. 2 extreme salary distributions are used: 1) salaries are depressed to the point where the marginal worker receives a salary approaching zero; and 2) the employees control the gaming process and thus accept only high salaries. The interregional model assumes 2 types of people exist--movers and stayers. Migration occurs in response to a difference between a person's current level of utility and that level thought to be obtainable in another region. Proximal regions with lower stress values will reduce flows to more attractive, distant regions. An optimal interregional matching requires workers to engage in an interregional search for better opportunities; welfare levels and regional wage scales are determined. Welfare differentials perceived by the workers give rise to stress, and migration occurs if the experienced level of stress is greater than the perceived risk. Despite some limitations, the basic model formulated here produces reasonable results and further study is warranted. The introduction of the game theoretic formulation of the labor market into the geography literature provides a new and potentially important way to study labor migration.^ieng