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Aiming to detect possible impacts of human activities on the characteristics of the sediments of the Urias lagoon, which is a lagoonal system surrounded by the urban area of Mazatlan (NW Mexico), we determined the mean percentages of the main particle fractions, pH, CO 3 2– , organic carbon and total arsenic content in the surficial sediments of six different zones of the Urias lagoon. Sand was the dominant size fraction throughout the whole system. The highest organic matter and the lowest pH values were found in adjacent sites to industrial activities, especially to fish processing. Most arsenic concentrations were within the values of the natural local background (12.6-27.3 mg/kg), with the possible exception of sediments close to the industrial area, especially those nearby the fish processing plants, where the mean As (45.2 ± 9.3 mg/kg) exceeded the level which may have adverse effects on marine organisms (41.6 mg/kg). However, it is not excluded that such levels are results rather from the combined effect of the hydrodynamic and sediments dynamic of sediment associated to local enrichments background of the region.

The reproductive cycle in oysters has been the subject of several studies in temperate zones. However, little information is available for tropical and subtropical species. This study describes the seasonal changes in the gonadic index (GI) of two species of oysters, Crassostrea iridescens and Crassostrea corteziensis, which differ markedly in their hàbitad and time of reproduction. Both oysters were sampled at 45 days intervals in the Northwest coast of Mexico between November 1989 and October 1990. Gonadal and somatic tissue per individual were dried for three days at 90°C, weighed and recorded. The gonadic index (GI) applied in this work was calculated from: GI = Wg/ws. Were WG is the average gonadal tissue dry weight, and Ws is the average somatic tissue dry weight. Seasonal variations in the gonadal state were evident for the two species. C.iridescens exhibited only a single maximum in the year, while C. corteziensis two peaks. This situation is presumably related to the contrastable environmental conditions that prevail in the sites where each species inhabit. El ciclo reproductivo en ostras ha sido objeto de varios estudios en zonas templada. Si embargo, poca información está disponible para especies tropicales y subtropicales. Este estudio describe los cambios estacionales en el ídice gonádico (GI) de dos especies de ostras, Crassostrea iridescens y Crassostrea corteziensis, la cuaes diferen signifcativamnte en su hábitat y tiempo de reproducción. Abas ostras fueron muestradas a intervalos de 45 días cada uno en la costa noroeste de México entre noviembre de 1989 y octubre de 1990. El tejido gonádico y somático por organismo fue secado por tes días a 90·c, pesados y registrados. El índice gonádico (GI) usado en este trabao fue calculado de: Gl= Wg/ws. Donde Wg es el peso seco promedio del tejido gonáico, y Ws el peso seco promedio del tejido somáico. Las varaciones estacionaes en el estado gonádico feron evidentes para las dos especies. C iridescens presentó sólo un máximo en el año, mientra que C. corteziensis presentó dos máximos. Posiblemente esta situación es relacionada con las contrastables condicones ambíentales que prevalecen donde cada especie habita.

We determined the Hg content of blood, placenta and umbilical cord of 20 pregnant females of the viviparous Pacific sharpnose shark, Rhizoprionodon longurio and of the livers of the embryos contained in their right and left uterus, aiming to provide information on the amount of this metal offloaded during pregnancy by the mother to the embryos. Hg content varied by close or higher than one order of magnitude in all tissues and showed the decreasing trend: maternal blood > umbilical cord > placenta > embryonic livers, with placenta and embryonic livers significantly lower than maternal blood. There were highly significant correlations (P < 0.001) between the Hg content of maternal blood, cord, and placenta. Those between embryonic livers and maternal blood, cord and placenta were not significant (P > 0.05). The results suggest transplacental Hg transfer and that the liver is not the main site of Hg accumulation.

To assess if they were within the safety limits for human consumption, the Cd, Cu, Pb, and Zn contents of fish muscles, bought from separate stalls of the fish markets of nine cities of NW Mexico, were determined by atomic absorption spectrophotometry. Considering all fish and markets, the mean contents were Zn:23.23±5.83, Cu:1.72±0.63, Cd:0.27±0.07, and Pb:0.09±0.04 µg/g (dry weight). Cu, Zn, and Pb did not reach levels of concern for human consumption, but the high Cd values determined in Mazatlán (Mugil cephalus:0.48±0.15;Diapterusspp.:0.57±0.33;Lutjanusspp.:0.72±0.12; small shark:0.87±0.19 µg/g dry weight) indicate that this was the only metal of concern for human health because the daily individual consumption of fish muscle to reach the PTDI would be within 0.27 and 0.41 kg.

"Juveniles del camarón blanco Litopenaeus vannamei fueron expuestos durante 25 días a salinidades de 1, 5, y 10 ups y a la concentración de Cu2+ que se usa comúnmente en las granjas camaronícolas de México, con el propósito de observar posibles alteraciones histológicas en la glándula antenal, intestino medio, branquias y hepatopáncreas. La supervivencia fue de 100% en controles y tratamientos y no se observaron histopatologías en branquias, intestino y glándula antenal. Después de 10 días de exposición al Cu2+ a la salinidad más baja, se observaron en el hepatopáncreas desprendimiento de las células epiteliales (< 75%), infiltración de hemocitos (< 75%), y una reducción de las células R y B (100%). Las mismas alteraciones se presentaron, aunque en menor grado, a las salinidades de 5 y 10 ups. Estos efectos deberían ser considerados para establecer criterios de calidad de agua para el cultivo de camarón en agua continentales, debido a que la interacción metal-salinidad puede inducir respuestas adversas en los camarones."

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.