Isidro Osuna-López

Histological effects of a combination of heavy metals on Pacific white shrimp Litopenaeus vannamei juveniles

Exposure to different levels of a mixture in equitoxic concentrations of Cd, Cu, Fe, Hg, Mn, Pb and Zn, equivalent to between 5 and 0.5% the individual respective 96-h median lethal concentrations (0.05-0.005AF: application factors) caused dose- and time-dependent damages to the hepatopancreas, gills, epipodites and midgut tissues of Litopenaeus vannamei juveniles. After between 1 and 3-4 weeks, there was between 50 and 100% loss of the hepatopancreas R cells and of the tubules regular structure. Gill alterations were observed between 2 and 3 weeks with 0.05-0.025 and 0.005AF, respectively. Epipodites showed time- and dose-dependent increasing degrees of melanization, and hemocytic enteritis was observed with 0.025 and 0.01AF. Exposure to 0.05 and 0.025AF caused also 50 and 12% mortalities after 2 and 3 weeks respectively, showing that even at these low levels the mixture of these metals may have a mid-term lethal effect. For this reason, the assessment of risk and of safe levels of toxic substances added to any natural environment through human or natural sources, should not neglect the effects on biological systems caused by the interaction of minute amounts of toxicants, which would be harmless unless present in combination.

Toxicity of metal mixtures to the Pacific white shrimp Litopenaeus vannamei postlarvae

According to the literature, the safe level of a toxic substance for any given organism may be calculated from its median lethal concentration multiplied by a suitable application factor (AF: usually 0.1 and 0.01). The medial lethal concentrations for Litopenaeus vannamei postlarvae exposed to the mixtures in equitoxic proportions of Cd-Hg, Hg-Zn and Hg-Pb were close to one order of magnitude lower than the values calculated from individual toxicity tests, indicating a synergistic effect, while the mixture Cd-Zn showed an antagonistic effect. Exposure to the mixture of Cu, Fe, Mn, Zn, Cd, Hg and Pb caused 63.3% and 100% mortality after 21 and 13 days for 0.05 and 0.1 AF, showing that environmental safe concentrations of toxicants should not be calculated from individual toxicity tests.

The Effect of Initial Cell and Nutrient Concentrations on the Growth and Biomass Production of Outdoor Cultures of Dunaliella sp.

The final concentrations of non-axenic outdoor mass cultures of Dunaliella sp. grown for two or three days in f/2 and 2f media were found to be dependent on the initial cell concentration, since the cultures started with 80 × 103 cells ml-1 gave better yields than those started with 40 × 103 cells ml-1. There was a correlation between nutrient availability and cell yields: the two and three days-old cultures started with 40 × 103 cells ml-1 and grown in medium f/2 had lower concentrations than those grown in 2f medium, whereas in cultures with 80 × 103 cells ml-1 inoculum the yield was significantly higher only after three days. The lowest dry biomass yields after two and three days were with the inoculum of 40 × 103 cells ml-1 and medium f/2.

The contents of Cd, Cu, Pb and Zn of the white shrimp Litopenaeus vannamei (Boone, 1931) of six coastal lagoons of Sinaloa, NW Mexico

Litopenaeus vannamei is the most important shrimp species in the traditional fishery of the coastal lagoons of the State of Sinaloa (NW Mexico), and most of the landings are consumed locally. Since these lagoons receive important volumes of agricultural, industrial and urban effluents, consumption of this shrimp could pose risks to human health. The mean content of Cd, Cu, Pb and Zn determined in the hepatopancreas of shrimp from commercial landings from six lagoons of Sinaloa were higher than those of the muscle. There was a weak correlation between the Zn content of the two tissues (P.0.05) and the correlations were not significant for Cd, Cu and Pb (P>0.1). The concentrations found in the shrimp muscle were comparable or lower than those determined in commercial landings of different crustaceans from other geographic areas. According to our results the consumption of local shrimp poses no risks to human health.