The toxic effects of four powder detergents: two laundry detergents (A and B), one household detergent (C), one dishwashing detergent (D), and the surfactant alkylbenzene sulfonate (LAS) were analyzed in this study on organisms from different trophic levels (microalgae, cladocerans, ostracods, amphipods, macrophytes, and fish). LC and EC values obtained in the toxicity bioassays varied between 0.019 and 116.9 mg L. The sensitivity of the organisms to the detergents was (from most sensitive to least sensitive) Ostracods > microalgae > amphipods > cladocerans > fishes > macrophytes. The toxicity of the commercial products (from most toxic to least toxic) was LAS > D (dishwashing detergent) > A (laundry detergent) > B (laundry detergent) > C (household detergent). When comparing the sensitivity of organisms that inhabit temperate zones (T = 18 °C) to those that are found in tropical zones (T > 25 °C), it was clear that the species that inhabit the tropics are more sensitive to detergents.

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We conducted an evaluation of alterations produced in the valve closing speed of juvenile Argopecten ventricosus (Catarina scallop) exposed to the metals cadmium, chromium and lead, because of the connection of this response to the state of health of the mollusk. Bioassays were conducted with 50 juveniles (length 3 +/- 0.5 cm) exposed to 0.02, 0.1, 0.2 mg Cd l(-1); 0.1, 0.5, 1.0 mg Cr l(-1); 0.04, 0.2, 0.4 mg Pb l(-1) and 0.8 and 1.6 mg Cd + Cr + Pb l(-1) for 480 h. The average valve closing speed at the end of the experiment was under 1 s in the control group, from 2 to 3.6 s in the bioassays with cadmium, from 1.4 to 3.4 s with chromium, from 3 to 12 s with lead, and from 12 to 15 s with the metal mixtures. It was found that there are significant differences between the values recorded in assays with metals and the control (P < 0.05). The retardation of valve closing in the organisms exposed to toxic substances is probably caused by damage to the sensory cilia located on the edge of the mantle.

The effects of Cd, Cr, Pb and their mixtures on the growth and sensitivity of the scallop Argopecten ventricosus were analyzed in this study. Cadmium showed to be more toxic metal to juveniles (96 hour median lethal concentration (LC(50)) = 0.396 mg Cd/L), followed by lead (LC(50) = 0.830 mg Pb/L) and chromium (LC(50) = 3.430 mg Cr/L). Cadmium toxicity was 8 times higher than chromium and 2 times than lead. The most toxic combination was Cd + Cr + Pb. (LC(50) = 0.302 mg/L). Based on toxic units analyses (T.U.), a synergistic effect was observed for Cr + Pb and Cd + Cr + Pb. (T.U. = 0.374; T.U. = 0.403), and antagonic effects for Cd + Cr and Cd + Pb (T.U. = 1.26; T.U. = 1.43) respectively. The level of effect (from high to low) on the growth of A. ventricosus juveniles was: Cd > Cd + Cr + Pb > Cr > Pb. The EC(50) (metal concentration where a reduction of 50% growing rate is observed) obtained were: Cd = 0.018 mg/L, Cd + Cr + Pb = 0.104 mg/L, Cr = 0.51 mg/L and Pb = 4.21 mg/L. These results suggest that A. ventricosus juveniles are more sensitive to these metals in comparison to other juveniles from other bivalve species (e.g., A. irradians, Mytillus edulis, Crassostrea virginica).

To understand the population growth potential of different species of rotifers in nature, field collections through seasons are essential. We sampled zooplankton (and measured selected physicochemical variables) from the Madín reservoir, a high altitude eutrophic urban waterbody from Mexico, every month for a year. Qualitative analysis of zooplankton revealed 28 rotifer species and four cladoceran crustaceans plus one unidentified copepod. Cephalodella catellina (1400 ind L -1 ), Horaella thomassoni (550 ind L -1 ), Conochilus dossuarius (380 ind L -1 ) and Filinia longiseta (25 ind L -1 ) had higher peak density than other rotifers. Based on the concentrations of nitrates and phosphates, chlorophyll a levels or different diversity indices (e.g., Carlson, Shannon-Wiener, Pantle and Buck, Ejsmont-Karabin's TSI Rot ), the waterbody is eutrophic to hypertrophic, depending on the season. In this waterbody we observed high densities of Aphanothece sp. which is a toxic picocyanobacterium. During the blooms of Aphanothece, we also recorded higher densities of H. thomassoni and C. catellina. Based on the gut contents we found that both these rotifer species feed on Aphanothece in this waterbody. This study thus suggests the potential growth of Horaella, Cephalodella, Conochilus and Filinia in this eutrophic reservoir containing blooms of Aphanothece.