Toxic species molybdenum

Sodium molybdate and other molybdenum compounds in toxic baits have potential for termite control (Brill et al. 1987). Baits containing 1000 mg Mo/kg were fatal to 99% of the termite Reticu-litermes flavipes in 48 days. After 8 to 10 days, termites became steel-gray in color, but appeared otherwise normal. Mortality began only after day 16. Termites did not avoid the poisoned bait, even at concentrations of 5000 mg Mo/kg. Yoshimura et al. (1987) reported similar results with another species of termite sodium molybdate killed 100% of the workers in a colony of Copotermes formo-sanus within 24 h after eating filter paper treated with a 5% solution. Some other species of insects — including fire ants (Solenopsis sp.) and various species of beetles and cockroaches — were not affected when exposed to baits containing 5000 mg Mo/kg for 48 days (Brill et al. 1987). 

Another oxyanion of interest to soil chemists is that of tungsten, which is in itself important but is also important because it forms polymers and reacts with both molybdenum and phosphorus oxyanions to form mixed polymers. Because tungsten species are toxic, its oxyanionic species, including polymers, are of interest [28],... 

The assessment of plant-available soil contents can frequently be achieved and validated by field experiments for nutritionally essential elements, and, for a few potentially toxic elements such as chromium, nickel and molybdenum, at the moderately elevated concentrations that can occur in agricultural situations. The validation of extraction methods, devised for agricultural and nutritional purposes, is much less easy to achieve when they are applied to heavy metals and other potentially toxic elements, especially at the higher concentrations obtained in industrially contaminated land. This is not surprising in view of the fact that for some heavy metals, for example lead, there is an effective root barrier, in many food crop plants, to their uptake and much of the metal enters plants not from the root but by deposition from the atmosphere on to leaves. In these circumstances little direct correlation would be expected between soil extractable contents and plant contents. For heavy metals and other potentially toxic elements, therefore, extraction methods are mainly of value for the assessment of the mobile and potentially mobile species rather than plant-available species. This assessment of mobile species contents may well, however, indicate the risk of plant availability in changing environmental conditions or changes in land use. 

Not only arsenic, cadmium, lead, mercury, nickel, aluminum, molybdenum, and bromine, but also zinc, copper and selenium are uniformly toxic to the immune system, although the ultimate effect depends on the species of animals studied and the route and mode of administration. An important feature of inorganic toxicity is the observation that in animals, some metals affect the immune system at doses that are unaccompanied by other clinical manifestations of toxicity. A similar effect also occurs in man (Chowdhury and Chandra 1991)... 

The availability of soil Mo to plants varies with soil characteristics as well as with crop species. The ideal Mo concentration in soil solution should range between 10" and lO- M, the threshold value being 10 M, below which crop plants show Mo deficiency. Molybdenum concentrations in soil solution of about IQ- M are toxic to plants (Kubota, Lemon, and Allaway, 1963). 

Nayyar, V. K., Randhawa, N. S., and Pasricha, N. S. (1977b). Molybdenum accumulation in forage crops. III. Screening of forage species for their capacity to accumulate molybdenum as Mo-toxic soils. J. Res. Punjab Agric. Univ. 14 406-10. 

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