Reddy and Vaidyanath (1978) investigated the mutagenic activity of metallic salts, including lead chloride, on chlorophyll mutations in rice. Rice seeds were exposed to a 10-4 M aqueous solution of lead chloride for 24 hours. The pooled results of three
replicates indicated mutant frequencies of 0.65% in the M1 and 0.04% in M2 generations. These values represent relatively weak mutagenic acticity compared with that reported for other metallic salts, including barium (6.36% in the M1 and 0.68% in the M2) and cadmium (5.23% in the M1 and 0.46% in the M2).
Sandhu et al. (1989) evaluated the clastogenicity of lead tetraacetate in the Tradescantia micronucleus assay, using Tradescantia paludosa clone 4430, as described by Ma et al. (1983). Plant cuttings were exposed for 30 hours by hypotonic uptake through stems, with no time for recovery. Results were expressed as micronuclei per 100 tetrads. Of the compounds tested (aldrin, arsenic trioxide, 1,2-benz[a,h]anthracene, dieldrin, heptachlor, lead tetraacetate, and tetrachloroethylene), lead tetraacetate was the most clastogenic, inducing 17.79 ± 8.56, 18.93 ± 2.90, and 13.07 ± 5.50 micronuclei/100 tetrads at concentrations of 0.44, 2.55, and 11.75 ppm, respectively. Micronucleus formation was significantly greater (P < 0.05) than in the solvent control (2.90 ± 2.0).
Table 5-1. Genotoxicity of lead compounds in prokaryotic systems
Resultsa
Species (test system) End point
With metabolic activation
Without metabolic
activation Compound Concentrationb Reference
lead acetate NA Bruce and Heddle 1979c, Dunkel et al. 1984c lead nitrate 22–180 µM Kharab and Singh 1985c lead chromate 0.2 mg Nestmann et al. 1979c
S. typhimurium E. coli Bacillus subtilis mutation or DNA modification – –
lead chloride and acetate 25 mM Nishioka 1975c S. typhimurium (TA 1535) S. typhimurium (TA 1537) E. coli (KMBL 1851) S. marcescens mutation ND + – + +
lead bromide 0.5–68 µg/plate 0.5–68 µg/plate 1.91–3.27 mM 1.91–4.63 mM
Maslat and Haas 1989
lead chloride NA Fukunaga et al. 1982c lead nitrate 22–180 µM Kharab and Singh 1985c lead chromate 25 mM Nestmann et al. 1979c
S. cerevisiae gene conversion
or mitotic recombination
– –
lead acetate 5% (v/v) Simmon 1979a, 1979bc Source: ATSDR 1999. a ND = not determined. b NA = not available. c
Ma et al. (1992) determined the synergistic effects of mixtures of lead tetraacetate, arsenic trioxide, dieldrin, and tetrachloroethylene on genotoxicity in the Tradescantia micronucleus assay. Lead tetraacetate (0.44 ppm) alone increased the frequency of micronucleus formation in plants exposed for 30 hours over that in the solvent controls. Gill and Sandhu (1992) determined the genotoxic effects of arsenic trioxide, dieldrin, and lead tetraacetate alone and in combination in the Tradescantia micronucleus assay. The chemicals or their mixtures were either (1) mixed into soil, and exposure to the target cells was through the roots of intact plants grown in the soil, or (2) prepared as an aqueous solution, and exposure was by absorption through the stems of plant cuttings. Lead tetraacetate was tested at concentrations of 4 µg/mL in the aqueous test system and and 4 mg/kg in the soil test system. Soil-grown plants exposed to lead tetraacetate had significantly more (P < 0.05) micronuclei than did the controls (11.2 ± 2.3 vs. 5.1 ± 0.6 micronuclei per 100 tetrads, respectively). No difference was observed between the lead- exposed and control plants grown in aqueous media (2.9 ± 0.5 vs. 2.3 ± 0.1 micronuclei per 100 tetrads, respectively). The clastogenicity of lead tetraacetate was altered by the ratio of individual chemicals in the aqueous or soil media.
Lerda (1992) determined the effect of lead nitrate (at concentrations of 0.1, 1.0, 10, 50, 100, or 200 ppm) on root growth, cell proliferation, and chromosomal aberrations in
Allium cepa. The effect of lead nitrate on root growth was determined by measuring the
length of 10 to 20 roots per onion bulb at 24-hour intervals for 96 hours. Lead nitrate at a concentration of 100 or 200 ppm completely inhibited root growth. At lower
concentrations, the rate of growth was reduced in a dose-dependent manner. Likewise, cell proliferation, which was determined at the root tip 12, 24, and 48 hours after
exposure, was progressively reduced at high concentrations. However, this inhibition was transient; proliferation had recovered by 48 hours after exposure. No difference from controls was observed in cell proliferation at concentrations up to 10 ppm. At each exposure level, 5,000 cells were examined for chromosomal aberrations. The frequency of chromosomal aberrations in cells from onions exposed to lead nitrate at 0.1 or 1.0 ppm did not differ from that of the non-exposed controls. However, significantly (P < 0.05) more cells contained chromosomal aberrations in plants exposed at 10 ppm than in non- exposed controls (0.18 vs. 0 per 5,000 cells). The author stated that these results
supported those of his previous studies demonstrating that lead compounds induced chromosomal aberrations in persons occupationally exposed to lead (Lerda 1992). Minissi et al. (1998) examined the genotoxicity of sediments from the Tiber River and its tributaries in the urban area of Rome, using a micronucleus assay in Vicia faba root tips. All samples were collected in July 1992. Sediments were assayed for content of the 13 most important chemicals of the polycyclic aromatic hydrocarbon (PAH) group and for some heavy-metal ions (cadmium, chromium, copper, nickel, lead, and zinc). The lead concentration in the sediments ranged from 12.4 to 43.5 ppm. The frequency of
micronuclei was significantly (P < 0.01) higher in plants exposed to sediment collected from 8 of the 10 sites than in the controls. These sites also contained significant amounts of PAHs and other metal ions (see Table 5-2).
Table 5-2. Genotoxicity of lead compounds in plants in vivo
Species End point Results Compound Concentration Reference
Tradescantia clone 4430 micronucleus formation + lead tetraacetate 0.44 to 11.75 ppm in water; 4 µg/kg in soil Sandhu et al. 1989, Ma
et al. 1992, Gill and
Sandhu 1992 inhibition of root growth + lead nitrate 0.1, 1, 10, 50, 100, 200 ppm Lerda 1992 cell proliferation + lead nitrate 0.1, 1, 10, 50, 100, 200
ppm Lerda 1992 Allium cepa chromosomal aberrations + lead nitrate 0.1, 1, 10, 50, 100, 200 ppm Lerda 1992
Vicia faba micronucleus formation
+ lead with other metals