Distribution and accumulation of Cd, Cu, Hg, Pb and Zn in the surface sediments of El Tobari Lagoon, central-East Gulf of California: An ecosystem associated with agriculture and aquaculture activities.

The purpose of this research is to provide a comprehensive assessment of the concentration levels and spatial variability of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb) and zinc (Zn) in El Tobari Lagoon in surface sediments during two seasons for several geochemical variables that could explain the observed heavy metal variability. Seventy-two surface sediments samples were collected in 12 different sites of the El Tobari Lagoon. Sediment samples were dried and subjected to acid extraction using a microwave system and five metals (Cd, Cu, Hg, Pb and Zn) were measured using atomic adsorption spectrometry. A certificate sediment material and blanks were used as quality control purposes. The enrichment factor (EF) and the index of geoaccumulation (Igeo) were calculated as index of metals contamination for the sediments, using aluminum as the conservative element. The five metals examined in sediments from El Tobari Lagoon exhibited a linear correlation with Al as result of the large specific surface areas of these sediment components and the chemical affinities between them. The metals contents in sites of the El Tobari Lagoon were variable, and Cd, Cu and Hg presented a seasonal behavior. The enrichment factor and index of geoaccumulation analysis indicated that Cd and Hg exhibited a certain extent (EF for Cd ranged from 4.10 to 10.29; EF for Hg ranged from 2.77 to 12.89) of anthropogenic pollution, while Cu showed sporadic (EF ranged from 0.43 to 2.54) anthropogenic contamination. The highest concentrations of Cd, Cu and Hg were found in the sites that regularly received discharge effluents from agriculture and aquaculture.

Comparative bioaccumulation of trace metals using six filter feeder organisms in a coastal lagoon ecosystem (of the central-east Gulf of California).

The Tobari Lagoon, located in the central-east coast of the Gulf of California, receives effluents from the Yaqui Valley, one of the most extensive agricultural areas of México. The Tobari Lagoon also receives effluents from nearby shrimp farms and untreated municipal sewage. Surface sediment samples and six different species of filter feeders (Crassostrea corteziensis, Crassostrea gigas, Chione gnidia, Anadara tuberculosa, Chione fluctifraga, and Fistulobalanus dentivarians) were collected during the dry and the rainy seasons and analyzed to determine concentrations of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn). Seasonal variations in metal concentrations in sediment were evident, especially for Cd, Cu, Hg, and Zn. The total and bioavailable concentrations of the five metals are not elevated in comparison to other areas around the world. The percentages of bioavailable respect to total concentrations of the metals varied from 0.6 % in Hg to 50.2 % for Cu. In the organisms, Hg showed the lowest concentrations (ranged from 0.22 to 0.65 µg/g) while Zn showed the highest (ranged from 36.6 to 1,702 µg/g). Linear correlations between the levels of Cu, Pb, and Zn in the soft tissues of C. fluctifraga and C. gnidia, and A. tuberculosa and C. gnidia were found. Seasonal and interspecies variations in the metal levels in filter feeders were found; F. dentivarians, C. corteziensis, and C. gigas exhibited the highest levels, could be used as biomonitors of metals contamination in this area.

A ten-year monitoring of essential and non-essential elements in the dolphinfish Coryphaena hippurus from the southern Gulf of California.

The concentrations of As, Cd, Cu, Pb and Zn were measured in muscle tissue of Coryphaena hippurus captured in the southern Gulf of California to determine inter-annual variations and their relation with environmental parameters for the period 2006-2015; additionally, health risk to consumers was assessed according to levels of studied elements and rate of fish consumption in northwest Mexico. During 2014 and 2015 the levels of As, Cd, Cu, and Zn were significantly lower than the rest of the years; in the case of As, it was also significantly lower in 2010. Oceanic Niño Index was negatively correlated with Zn concentrations in fish, while sea surface temperature was negatively correlated with Zn, Pb and Cd concentrations in dolphinfish. The simultaneous occurrence of the analyzed elements in muscle of dolphinfish indicated that health effects on consumers are not likely to occur; nevertheless, fishermen with elevated fish consumption might be at risk.

Seasonal variations in the concentrations of metals in Crassostrea corteziensis from Sonora, México.

This study examines seasonal variations in the concentrations of Cd, Cu, Pb, and Hg in experimentally cultured Crassostrea corteziensis, an oyster species known to have high resistance to physical and chemical stressors. The highest levels of Cd (4.92 mg/kg), Cu (3.45 mg/kg), and Pb (0.67 mg/kg) were detected in oyster samples collected during the summer, while Hg concentrations were similar (0.03 to 0.04 mg/kg) throughout all seasons. Results indicate that except for Cd, Crassostrea corteziensis accumulates metals to levels below those recommended by the US. FDA and the Mexican government. For Cd, its concentration correlates more strongly with the temperature of the oyster's environment rather than to the oyster growth cycle.

Determination of total metals in cultivated oysters (Crassostrea gigas) from the northwest coast of Mexico by microwave digestion and atomic absorption spectrometry.

Bivalves such as oysters often accumulate heavy metals, and therefore can be used to monitor changes of pollutant concentrations in the environment. Cultivated oysters from the northwest coast of Mexico are widely used for human consumption and thus have an important commercial value. Information was gathered on the concentration of these elements in oysters (Crassostrea gigas) cultivated on the coast of Sonora. Oysters were randomly collected from April to October 1997, from 6 different locations (65 individuals per site) in 4 different months. Metals were determined by microwave digestion followed by atomic absorption spectroscopy. The mean values (microg/g fresh weight) for each metal were: Cd, 0.76; Cu, 3.64; Zn, 17.71; Pb, 0.50; As, 0.05; Hg, 0.03; and Se, 0.21. The results show that, except for Cd, concentrations of regulated metals were under the maximum permitted values specified by regulatory agencies of Mexico and were comparable to those reported from other areas.

Use of microwave digestion and atomic absorption spectrophotometry to determine chromic oxide as a digestibility marker in feed, feces, and ileal content.

Most conventional digestion procedures, such as dry ashing and wet ashing, are tedious and labor intensive. Microwave digestion is a good alternative, because microwave dissolution is faster, safer, and simpler, and provides more controlled reproducible conditions than conventional methods. The purpose of this study was to develop a microwave digestion method for mineralizing meat and bone meal diets, feces, and ileal contents. Each sample was heated on a hot plate for 10 min, dry ashed at 65 degrees C for 4 h, and transferred into microwave vessels. Then, 10 mL 70% HNO3 was added. Samples were digested for 7, 10, and 20 min at 95, 90, and 85% power, respectively. After the heating cycle, 6 mL 30% H2O2 was added, and samples were returned to the microwave for a second heating cycle of 1 and 7 min at 95% and 90% power, respectively. Finally, chromium concentration was determined by flame atomic absorption spectrophotometry. The digestion method was validated by using a standard reference material, SRM domestic sludge 2781, with a certified chromium value of 195 +/- 9 micrograms/g. The value obtained in this study was 178 +/- 11 micrograms/g, for a difference of 17 micrograms/g. Spike recovery experiments resulted in 103.16 and 100.35% recoveries of chromium from diet and feces samples, respectively. Coefficients of variation were 10.8 and 7.8%, respectively.