Dialkyllead compounds

Babich and Borenfreund135 compared in vitro cytotoxicities of inorganic lead and tri- and dialkyllead compounds in fish cells (bluegill sunfish, Lepomis macrochiru). 

Concentrations of Pb(CH3)4 and other tetraalkyllead compounds in atmospheric samples, which have been measured at different locations with species specific analytical methods, are listed in Table 11. Tetraalkyllead concentrations in indoors air were found to correspond closely with those in outdoors air [24]. More data on concentrations of alkyllead compounds in ambient air have been obtained with analytical methods which measure volatile organolead compounds or total organolead [28 to 55,173]. However, these data, being based on different sampling and analytical procedures, are difficult to compare see also [56 to 64]. According to [5], the results given in [28, 29, 32, 33] are probably unreliable. In this context it has to be considered that the majority of the nonfilterable (molecular) lead seems not to be organic in nature [58, 59] recently also tri- and/or dialkyllead compounds have been determined besides Pb(CH3)4 and other tetraalkyllead compounds in both urban and rural air in the vapor phase and in atmospheric aerosols [27,174] see also [182]. For analytical procedures to determine Pb(CH3)4 in atmospheric samples, see Section 1.1.1.1.1 on p. 75. 

Chau and coworkers133 investigated the bioaccumulation of alkyllead compounds from water and from contaminated sediments by freshwater mussels, Elliptio complanata. Higher levels of trimethyllead than triethyllead species were accumulated after the same exposure period. In vivo transformation of the trialkyllead species by a series of dealkylation reactions giving dialkyllead and inorganic lead(II) species appears to take place. Rates of accumulation are higher for the more contaminated sediments133. 

The mechanism of intoxication by organolead compounds is still not understood completely, although toxic action by many individual compounds has been reported. Generalization is not allowed by the scanty literature, except for tetraethyllead, tetramethyllead, and the related tri- and dialkyllead salts 86,87,100,101,106,146,214,235,276,278,302, 303). The toxicology of these compounds has been reviewed recently... 

Y. K. Chau, P. T. S. Wong, G. A. Bengert, J. L. Dunn, Determination of dialkyllead, trialkyllead, tetraalkyllead, and lead(II) compounds in sediment and biological samples, Anal. Chem., 56 (1984), 271D274. 

Because so little is known about the products it only can be assumed that similar relations as for the analogous organotin compounds (189) hold, that is, that the dialkyllead oxides are in fact polyplumboxanes (—R2Pb— O—) , perhaps cyclic with w = 3 or 4. The alkylplumbonic acids could then have similar but cross-linked structures. A number of plumbosiloxanes are known (52,245), as well as other compounds with Pb—O—M groupings (52). 

It has not been elucidated whether Me-Bi2 can methylate inorganic lead compounds to Mc4Pb. Me-Bia and methyl pyridinatocobaloxime are unable to methylate Pb(II) salts (Lewis et al. 1973, Jarvie et al, 1975, Taylor and Hanna 1976), but inorganic Pb(IV) compounds (Taylor and Hanna 1976, Thayer 1978), dialkyllead salts (Wood 1977 a and b, Thayer 1978) and tiialkyllead salts (Thayer 1978) are able to demethylate Me-Bi2 in aqueous solutions at pH < 7. However, no evidence has been seen of successive methylation of Pb(OAc)4 in the presence of excess Me-Bi2 (Taylor and Hanna 1976, Thayer 1978). Thus, if MePb + is formed at aU, it must decompose so rapidly under experimental conditions that methylation to the more stable Me2Pb + cannot proceed to any measurable extent. The chemical pathway for the biological formation of Mc4Pb in laboratory experiments has not yet been elucidated. 

Pb(CH3)4 and other tetraalkyllead compounds are eliminated from the atmosphere via formation of tri- and dialkyllead salts [22, 23] see also [174,177]. Such alkyllead species have been speculated to cause european forest damage [86, 183] however, this proposition was rejected as entirely unproven [87] and further research was strongly recommended [172,183]. The fate of Pb(CH3)4 and other tetraalkyllead compounds in the atmosphere is reviewed in [2. 61]. 

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