To test the hypothesis that sediment would have a synergistic effect on the toxicity of lead to cladocerans, we performed life table demography experiments with two pelagic (Diaphanosoma birgei and Moina micrura) and one littoral (Alona rectangula) cladoceran species. Life table demography experiments were conducted at three levels of turbidity (0, 17 and 170 NTU) and six concentrations of lead (as PbCl2) from 0 to 0.71 mg l−1. Median lethal concentrations (LC50) for A. rectangula, D. birgei and M. micrura were 7.06 ± 0.39, 3.16 ± 0.25 and 3.24 ± 0.69 mg l−1 of Pb. Life table study showed that in general, the presence of sediments in test jars allowed an overall increase of 20–75% in both survivorship and reproduction of the cladoceran species exposed to different concentrations of Pb. At 0.04 mg l−1 of Pb, the population growth rates were 0.127 for A. rectangula, 0.037 for D. birgei and 0.471 d−1 for M. micrura in the absence of sediments but were elevated in their presence (0.309, 0.141 and 0.722 d−1, respectively). The data have been discussed in relation to their importance in shallow, turbid Mexican waterbodies.
