Question

Salinity-dependent toxicities of zinc oxide nanoparticles to the marine diatom thalassiosira pseudonana

Answer 1

An approach is presented for determining the influence of two key variables, pH and salinity (S), on the toxicity of four common heavy metals bound to sediments in estuaries. Two samples of environmental sediment taken from two estuaries in southern Spain (the Huelva estuary and the Guadalquivir River estuary), together with a dilution of toxic mud from the Aznalcóllar (Spain) mining spill (April 1998) were used to determine their toxicity at different values of pH (6.5, 7.5, and 8.5) and salinity (10, 20, and 30) on the estuarine clam Ruditapes philippinarum. Two different endpoints, sublethal, indicated by clam reburial (median effective burial time [ET50]), and relative mortality (median lethal concentration [LC50]), were used to quantify the toxicity associated with the heavy metals. Neither salinity nor pH was found to influence the toxic responses measured by the behavioral endpoint (ET50). However, a strong effect on the LC50 related to pH and salinity was detected, with the toxicity of the heavy metals being increased at low values of both variables (pH= 6.5 and S= 10). The mechanism of heavy metals uptake through water may explain this influence of pH and salinity on the lethal toxicity detected. The results show differences in the toxicity of these heavy metals bound to sediments depending on whether the origin of metal contamination is chronic or ac

Influence of salinity on fertilization and larval development toxicity tests with two species of sea urchin



Sea urchin embryo-larval development (ELD) and fertilization tests have been widely used in ecotoxicity studies and are included in regulatory frameworks. Biological processes occur naturally within a range of salinity that depends on the species considered. In an attempt to determine the optimum range of salinity, ELD and fertilization bioassays were performed at different salinities (15–40.5‰) with two species of Atlantic sea urchin: Arbacia lixula and Paracentrotus lividus. In the ELD assay, the optimum range





The formation of toxic surface blooms of the motile raphidophyte Heterosigma akashiwo often occurs too quickly to be attributed to cell reproduction. Rapid appearance of surface blooms is more consistent with the hypothesis that a dispersed cell population aggregates at the surface due to a combination of physical factors and swimming behavior. Because of the frequent association of Heterosigma bloom formation with a decrease in surface salinity, we hypothesize that a layer of low-salinity water over a high-salinity layer will suppress nearsurface vertical mixing and this halocline will enable up-swimming cells to rapidly aggregate at the surface. For this hypothesis to be viable, Heterosigma cells must be able to swim across salinity jumps of a sufficient magnitude to temporarily suppress vertical mixing. We tested whether this requirement is satisfied by using computerized video analysis to quantify swimming behavior and vertical distribution of Heterosigma within a vertical salinity structure. Swimming behavior is affected by the presence of a salinity jump and depends on the strength of the jump: cells stopped swimming upwards and aggregated below a fresh water interface; cells reduced upward swimming speed with a salinity jump from 28 to 8‰, and upward swimming speed was unchanged in cells encountering a salinity jump from 28 to 16‰. We used observed swimming behaviors to parameterize a model of a 2-layer stratified water column in which vertical mixing is suppressed at the halocline and modeled by eddy diffusivity within each layer. The model predicts rapid aggregation of cells to the surface layer