Lead species, ionic

A mixture of Me3210PbCl and 210Pb(NO3)2 was used to study the rate of ionic trimethyl-lead uptake by exposed plant surfaces. More specifically, the mean cumulative activity of the lead toxicants transferred across tomato cuticle was measured daily over a six-day period. Reversed-phase HPLC was used to separate and identify the lead species crossing the plant cuticle. It was found that appreciably more trimethyllead(I) (75% of the theoretical) than inorganic lead(II) (39%) was transferred. The apparent rate constants derived from the first-order plot of time in days versus the difference in observed activity were 0.0788 and 0.0346 day-1 for transfer of the trimethyllead(I) and inorganic lead(II), respectively. 

There is very little information about the stabilities of lead species in aqueous solution containing less than lOngdm-3 lead. No changes in concentrations of ionic organolead species in water occurred over a period of 3 months when samples were stored at 4°C in the dark (Van Cleuvenbergen et al., 1992). Freezing is probably the best means of preserving soils and sediments. 

The electrodeposition of lead, Pb, has been investigated in an acidic EMICl-AICI3 ionic liquid [27]. A divalent lead species, Pb(II), can be introduced by dissolving lead dichloride, PbCl2, or the anodic dissolution of metallic Pb. Metallic Pb is obtained by the reduction of Pb(II) ... 

Decay in organisms relates to toxicity, and half-lives and excretion rates are dealt with elsewhere in this chapter. Toxicity arises because of easy absorption in mammals, leading to the loss of one alkyl group to form the trialkyl species. It is these trialkyl species which can most easily deliver lead and so cause toxicity. Decay does therefore take place by sequential loss of alkyl groups (similar to organotin species. Section 12.13.9), and so a series of alkyl, ionic, and inorganic lead species are excreted by mammals. 

Lead within soils is distributed between solid and liquid phases, with the latter of major importance to the issue of lead bioavailability, for example, to plant roots where uptake can occur. Studies of lead species in this liquid mobile phase indicate that they exist as both complexed and ionic forms although the latter as simple ions are present in very low concentrations. The extent to which lead can move through soils, in turn, is the extent to which lead binds to insoluble organic and mineralogical inorganic species. The former are typically humic and fulvic acid derivatives, and the latter are surfaces of clays and metal oxides (U.S. EPA, 1986). The factors most important for lead movement within soils are pH, cation exchange capacity of... 

Birnie, S. E., Hodges, D. J., Determination of Ionic Alkyl Lead Species in Marine Fauna, Environ. Technol. Letters 2 [1981] 433/42. 

Ionic lead species were stable in water stored in the dark at 4°C for up to 3 months, while tetraalkylated lead was less stable. ... 

We have collected much, often redundant, data, and are now able to examine them systematically to determine which measures are the most useful in predicting a child s mental development. We really do not know how or when low levels of lead contamination disturb brain development. Thus, without imposing any prior restrictions, we should evaluate many measures of lead burden. In the absence of an assay for the bioactive species (ionic ) of lead at the target organ (brain) at the critical time(s), blood lead measurements (which are mostly erythrocyte bound lead, and which represent a very small fraction of the body s total lead level) were used to assess the child s body burden. 

A precipitation reaction occurs when two or more soluble species combine to form an insoluble product that we call a precipitate. The most common precipitation reaction is a metathesis reaction, in which two soluble ionic compounds exchange parts. When a solution of lead nitrate is added to a solution of potassium chloride, for example, a precipitate of lead chloride forms. We usually write the balanced reaction as a net ionic equation, in which only the precipitate and those ions involved in the reaction are included. Thus, the precipitation of PbCl2 is written as... 

Receptor models are powerful tools for source apportionment of particulates because a vast amount of particulate species characterization data have been collected at many sampling sites worldwide, and because many aerosol species are primary pollutants. Most of the information available is for elemental concentrations, eg, lead, nickel, and alurninum, although more recent measurements have provided data on concentrations of ionic species and carbonaceous compounds. At a sampling (or receptor) site, the aerosol mass concentration of each species i is... 

It is evident from Fig. 22.2 that only in very dilute solutions are monomeric vanadium ions found and any increase in concentrations, particularly if the solution is acidic, leads to polymerization. nmr work indicates that, starting from the alkaline side, the various ionic species are all based on 4-coordinate vanadium(V) in the form of linked VO4 tetrahedra until the decavana-dates appear. These evidently involve a higher coordination number, but whether or not it is the same in solution as in the solids which can be separated is uncertain. However, it is interesting to note that similarities between the vanadate and chromate systems cease with the appearance of the decavanadates which have no counterpart in chromate chemistry. The smaller chromium(VI) is apparently limited to tetrahedral coordination with oxygen, whereas vanadium(V) is not. 

The ionic species 5, as well as 6, represent the so-called activated dimethyl sulfoxide. Variants using reagents other than oxalyl chloride for the activation of DMSO are known. In the reaction with an alcohol 1, species 5, as well as 6, leads to the formation of a sulfonium salt 7 ... 

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