Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

carbon sources (including glucose), all had protective effects, and reduced Pb toxicity at 300 and
400 mg Pb/L. Both studies proposed similar hypotheses regarding nutrient-Pb mechanisms that
led to reduced toxicity. One hypothesis was that the nutrients were able to reverse toxic effects.
The second hypothesis was that the nutrients interacted directly with Pb, in some way
sequestering the metal so as to inhibit its metabolic interaction with the organism (Rao and
Reddy, 1985; Jampani, 1988).
Rai and Raizada (1989) investigated the effects of Pb on nitrate and ammonium uptake as
well as carbon dioxide and nitrogen fixation in Nostoc muscorum over a 96-h period. Test
specimens were exposed to 10, 20, and 30 mg Pb/L. At 20 mg Pb/L, nitrate uptake was inhibited
by 64% after 24 h and by 39% after 96 h. Ammonium uptake was inhibited, and similarly,
inhibition decreased from 72% inhibition after 24 h to 26% inhibition after 96 h of exposure.
Carbon dioxide fixation and nitrogenase activity followed similar patterns, and results indicated
that Pb exposure can affect the uptake of some nutrients in N. muscorum.
Adam and Abdel-Basset (1990) studied the effect of Pb on metabolic processes of
Scenedesmus obliquus. They found that nitrogenase activity was inhibited by Pb nitrate, but
enhanced by Pb-acetate. As photosynthetic products and respiratory substrates, carbohydrate
and lipid levels were altered by Pb. Above 30 mg/L of Pb-nitrate, both macronutrients were
reduced. However, Pb-acetate was found to increase carbohydrate levels. Results suggest that
Pb can have an effect on macronutrients in S. obliquus and that effects may vary depending on
the chemical species.
Simòes Gonçalves et al. (1991) studied the impact of light, nutrients, air flux, and Pb, in
various combinations, on growth inhibition in the green algae Selenastrum capricornutum.
Results indicated that at lower Pb concentrations (