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

AX7.2.4.2 Recent Studies on Effects of Lead on Primary Producers
Using literature published since the 1986 Lead AQCD (U.S. Environmental Protection
Agency, 1986a), this section examines the toxicity of Pb (individually and in metal mixtures) to
algal and aquatic plant growth, its effects on metabolic processes (e.g., nutrient uptake), and its
impact on primary productivity in natural systems.
Toxicity of Lead to Algae
The toxicity of Pb to algal growth has been investigated for a number of species including
Chlorella vulgaris, Closterium acerosum, Pediastrum simplex, Scenedesmus quadricauda,
Scenedesmu obliquus, Syneschoccus aeruginosus, and Nostoc muscorum (Jampani, 1988; Rai
and Raizada, 1989; Adam and Abdel-Basset, 1990; Fargašová, 1993; Bilgrami and Kumar,
1997). Study durations ranged from 7 to 20 days and Pb-nitrate was the most commonly used
form of Pb. Effects to algal growth (Chlorella vulgaris, Closterium acerosum, Pediastrum
simplex, Scenedesmus quadricauda), ranging from minimal to complete inhibition, have been
reported at Pb concentrations between 100 and 200,000 µg/L (Jampani, 1988; Bilgrami and
Kumar, 1997). Most studies report the percent inhibition in test groups compared to controls
rather than calculating the LOEC, NOEC, or EC50 values. Clinical signs of Pb toxicity include
the deformation and disintegration of algae cells and a shortened exponential growth phase
(Jampani, 1988; Fargašová, 1993). Other effects of Pb block the pathways that lead to pigment
synthesis, thus affecting photosynthesis, the cell cycle and division, and ultimately result in cell
death (Jampani, 1988).
From the studies reviewed, Closterium acerosum is the most sensitive alga species tested
(Bilgrami and Kumar, 1997). Exposure of these algae to 1000 and 10,000 µg/L as lead nitrate
for 6 days resulted in cell growth that was 52.6 and 17.4%, respectively, of controls (Bilgrami
and Kumar, 1997). Chlorella vulgaris, Pediastrum simplex, and Scenedesmus quadricauda were
also exposed to Pb-nitrate in this study. Compared to controls, cell growth at 1000 and
10,000 µg Pb-nitrate/L was 65.3 and 48.7%, 64.5 and 42.7%, and 77.6 and 63.2%, respectively
(Bilgrami and Kumar, 1997). Scenedesmus quadricauda exhibited a similar magnitude of effects
when exposed to lead (Pb 2+ ) for 20 days at 0, 5500, 11,000, 16,500, 22,000, 27,500, and
33,000 µg/L (Fargašová, 1993). This study reported an EC50 for growth inhibition at
13,180 µg/L (95% CI: 10,190, 14,620). Decreased cell number, but increased cell size, was
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