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

1997). The most sensitive primary producers reported in the literature for effects to growth were
Closterium acersoum and Azolla pinnata (Gaur et al., 1994; Bilgrami and Kumar, 1997). The
least sensitive primary producers reported in the literature for effects to growth were
Synechococcus aeruginosus and Lemna gibba (Jampani, 1988; Miranda and Ilangovan, 1996).
Exposure to Pb in combination with other metals is generally less toxic to growth than exposure
to lead alone. Studies have shown that lead adversely affects the metabolic processes of nitrate
uptake, nitrogen fixation, ammonium uptake, and carbon fixation (Rai and Raizada, 1989). Lead
in combination with nickel or chromium produced synergistic effects for nitrate uptake,
nitrogenase activities, ammonium uptake, and carbon fixation (Rai and Raizada, 1989).
Leads Effects on Primary Productivity
Lead nitrate and Pb-acetate have been shown to have adverse effects on the primary
productivity of aquatic plants in two water bodies in India (Jayaraj et al., 1992). One of the two
water bodies was a freshwater tank that receives wastewater and supports a rich population of
hyacinths, and the other was a wastewater stabilization pond. Water quality characteristics in the
freshwater tank were pH = 7.5, dissolved oxygen = 6 mg/L, and water hardness (CaCO3) =
100 mg/L. Water quality characteristics in the wastewater pond were pH = 8.1, dissolved
oxygen = 6.2 mg/L, and water hardness (CaCO3) = 160 mg/L (Jayaraj et al., 1992). Lead nitrate
concentrations of 500, 5000, 10,000, 25,000, and 50,000 µg/L were combined with appropriate
water samples in light and dark bottles and suspended in each of the water bodies for 4 h. The
concentrations of Pb-acetate (5000, 10,000, 25,000, 50,000, and 100,000 µg/L) were applied in
the same manner. The EC50 values were determined based on the concentration required to
inhibit gross productivity (GP) and net productivity (NP) by 50% (Jayaraj et al., 1992). The
results demonstrated that Pb-nitrate was more toxic to primary production than Pb-acetate.
In the freshwater tank, Pb-nitrate EC50 values for GP and NP were 25,100 and 6310 µg/L,
respectively, compared to Pb-acetate EC50 values of 50,100 and 28,200 µg/L for GP and NP,
respectively (Jayaraj et al., 1992). In the stabilization pond, Pb-nitrate EC50 values for GP and
NP were 31,600 and 28,200 µg/L, respectively, compared to Pb-acetate EC50 values of 79,400
and 316 µg/L for GP and NP, respectively (Jayaraj et al., 1992). The higher toxicity reported in
the freshwater tank was attributed to differences in species composition and diversity. The
freshwater tank was dominated by water hyacinths that decreased the photic zone available for
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