Spatial and Temporal Distribution of Trace Metals in Shallow Marine Sediments of the Yucatan Shelf, Gulf of Mexico.

We investigated the spatial and temporal distribution of V and Cd in surface sediments of the Yucatan Shelf to establish current average values for the area. V and Cd concentrations are similar to those reported internationally for limestone rocks and surface marine sediments. The observed variability of V concentrations between cruises may be the result of changes in ocean current direction in summer (SW-S) and strong prevailing winds in autumn (N-NE). In addition to the hydrodynamics described above, Cd variations may also be associated with inputs of particulate material by upwelling events and subsequent transport and distribution to the shelf by the Yucatan Channel current (autumn). Considering that both metals showed significant spatial and temporal differences, a range of values for V (0.4-1.5 µg g-1) and Cd (0.05-0.2 µg g-1) are proposed as baseline reference for sediments of the Yucatan Shelf.

Vanadium and Cadmium in Shallow Marine Sediments: Spatial and Temporal Behavior in the Tamaulipas Continental Platform, Gulf of Mexico, Mexico.

This study analyzed 27 surface sediment samples from the Tamaulipas Continental shelf to determine the spatial-temporal distribution of V and Cd (spring-summer 2016; summer 2017). Average V concentrations (99 ± 18 mg g-1) were similar to that previously reported values for the area, while average Cd concentrations reflect uncontaminated sediments at surface level of the shelf. Inputs of V and Cd may be related to hydrocarbon and anthropogenic contributions from South and North of the Gulf of Mexico. The variability shown by both elements results from the hydrodynamics and hydrology of the area produced by local currents, eddies of the Loop Current, resuspension of fine sediments and contribution of terrigenous material. Considering that both metals showed significant differences (Shapiro-Wilk, p = 0), baseline concentrations could not be established, instead a reference interval of 79-122 µg g-1 for V and 0.121-0.258 µg g-1 for Cd in sediments from the Tamaulipas platform is suggested.

Sand as a relevant fraction in geochemical studies in intertidal environments.

Soil and sediment samples from several intertidal environment exposed to different types of contamination were studied to investigate the importance of grain size in relation to the capacity of the substrates to retain trace metals. The unfractionated samples (referred to as bulk samples) were separated into the following grain/size fractions: fine-coarse sand (2-0.100 mm), very fine sand (0.100-0.050 mm), silt (0.050-0.002 mm), and clay (0.002 mm). The sample into its fractions was carried out was in a glove box under high-purity N2 atmosphere in order to minimize any alterations to the samples. The bulk samples were characterized in terms of physicochemical properties such as pH, redox potential, and grain size. The total organic carbon (TOC), total sulfur (S), iron (Fe) pyrite, Fe, and manganese (Mn), and trace metals lead (Pb), mercury (Hg), chromium (Cr), and nickel (Ni) were analyzed in the bulk samples and in each fraction. The sand fractions were also examined by scanning electron microscopy (SEM). Comparisons of the above parameters were made between fractions and between each fraction and the corresponding bulk sample. The fine-coarse sand fraction contained high levels of the primary elements of the geochemical processes that occur in marine sedimentary environments such as TOC, total Fe, Mn, and S. The net concentrations of these four elements were higher in the fine-coarse sand fraction than in the very fine sand fraction and were similar to the net concentrations in the silt and clay fractions. Detailed SEM analysis of the sand coarse fraction revealed the presence of Fe and aluminum oxyhydroxide coatings in the oxic layers, whereas the framboidal pyrites and coatings observed in the anoxic layers were Fe sulfides. The presence of the various coatings explains why the trace metal concentrations in the sand fine-coarse fraction were similar to those in the clay fraction and higher than those in the very fine sand fraction. The present results highlight the importance of the sand fraction, which is generally disregarded in geochemical and environmental studies of sedimentary layers.

Trace metals in sediments and Zostera marina of San Ignacio and Ojo de Liebre lagoons in the central pacific coast of Baja California, Mexico.

San Ignacio and Ojo de Liebre lagoons in central Baja California, Mexico are nursery and grazing grounds for whales and turtles. Ojo de Liebre Lagoon also supports a salt mine operation. By concentrating trace metals via evaporation, this activity might harm biota. Consequently, salt mining might be incompatible with the lagoon's ecological role. Eelgrass can incorporate these elements and reroute them to other organisms. Trace metals in sediments (Cd, Co, Cu, Mn, Ni, Pb, Zn, and Fe) were measured at both lagoons. Some (Cu, Mn, Pb, and Zn) were also measured in Zostera marina patches at both lagoons. The results did not show elevated metal concentration at any lagoon, either for sediments or eelgrass. No statistically significant differences between lagoons were found. However, eelgrass at both lagoons showed larger concentration ranges than in sediments. Also, a correlation exists between sediment metal concentration and its concentration in eelgrass. Surprisingly, several sediment metal concentrations are higher than those considered as elevated for the Southern California Bight.

Cadmium and phosphate variability during algal blooms of the dinoflagellate Lingulodinium polyedrum in Todos Santos Bay, Baja California, Mexico.

Dinoflagellate algal blooms (DABs), with Lingulodinium polyedrum as the dominant species, have increased over the past few years in coastal areas off Baja California, Mexico. Vertical and temporal variability of particulate cadmium (Cdp), dissolved Cd (Cdd), PO4(3-) and Cdd/PO4(3-) were investigated during two intense DABs of L. polyedrum that occurred during the fall of 2011 and 2012 in Todos Santos Bay. Results were then, compared with data gathered in the absence of algal blooms during the autumn of 2013. In both algal blooms, L. polyedrum tended to be concentrated near the surface throughout the duration; however, during DAB 2011 the number of cells was twice as abundant ([10.0 ± 8.0] × 10(5) cells L(-1)) as in DAB 2012 ([5.0 ± 4.4] × 10(5) cells L(-1)). During DAB 2011, Cdp increased significantly (up to 1.02 ± 0.99 nmol kg(-1)) and was positively correlated with the cell abundance of L. polyedrum, suggesting that this dinoflagellate is able to assimilate and concentrate Cdd. Likewise, Cdd (up to 0.71 ± 0.17 nM) increased in the days of highest cell abundance, which could be attributed to uptake and subsequent regeneration of Cdd resulting from the remineralization of organic particulate matter produced during the bloom, as well as with the presence of organic ligands secreted by L. polyedrum that could keep Cdd in solution. During DAB 2011, dissolved Cdd/PO4(3-) ratios exhibited high vertical and temporal variability in the upper 5 m of the water column, but remained virtually constant near the bottom, suggesting a depth-dependent decoupling between these two dissolved components during the bloom development. Given the observed differences in the vertical and temporal variability of Cdd, Cdp, and PO4(3-) between these two intense DABs, we propose the existence of an abundance threshold of approximately 10(6) cells L(-1) of L. polyedrum above which Cd and PO4(3-) significantly increased due to remineralization in coastal waters during the bloom development.

Cd concentration in the soft tissue vs. the nacreous layer of Mytilus californianus.

The soft tissue of Mytilus californianus has the capacity to decrease its Cd concentration in the order of days. However, for medium-term (months) pollution surveys it is necessary to find alternative structures capable of integrating Cd concentrations during longer periods of time. The recently deposited nacreous layer of the shell of M. californianus is proposed as such a structure. Daily variability of Cd concentration in the soft tissue and in the recently deposited nacreous layer of a natural population of mussels was compared during a period of 26 days in organisms collected from an upwelling zone of British Columbia. Statistical analysis of the Cd concentrations indicated that the nacreous layer presented less significant differences between days than the associated soft tissue. Only one shell sample showed significant differences in Cd concentrations, probably related to environmental conditions and stress arising from mussel population density. Experimental results carried out in the laboratory confirmed that the recently deposited nacreous layer of M. californianus is a better medium-term indicator of Cd in seawater, especially at low concentration exposures of this element, those similar to the ones encountered in natural environments.

Heavy metal geochemistry of saltmarsh soils from the Ría of Ortigueira (mafic and ultramafic areas, NW Iberian Peninsula).

Concentrations of Fe, Mn, Ni, Cu, Cr and Zn in their total, silicate, organic, reactive and pyrite fractions were determined in soils collected from the Ortigueira saltmarshes (Esteiro, Ladrido and Mera, NW Iberian Peninsula), from sediments of the Landoi and Esteiro Rivers, and from sludge generated by a nearby dunite mine. The Esteiro saltmarsh presented clear enrichments of the four metals studied (first 10 cm), especially of Ni and Cr, whose concentrations were among the highest. It is proposed that the elevated Cr and Ni levels found in the Esteiro saltmarsh were derived from recent contributions of the mine, which are partially discharged into the Landoi River. Total Cu and Zn concentrations were lower than the corresponding ones for Cr and Ni. Under suboxic conditions, Ni, Cr, Cu and Zn were mainly associated with the reactive fraction. Under anoxic conditions, Cu and Ni were associated mainly with the pyrite phase. Pyritic Zn and Cr concentrations were relatively low and similar in all three saltmarshes; however, where anoxic-sulfidic conditions prevailed these two metals were mainly associated with the reactive and organic fractions.

Elemental concentrations in different species of seaweeds from Loreto Bay, Baja California Sur, Mexico: implications for the geochemical control of metals in algal tissue.

Concentration levels of 21 elements were analyzed by instrumental neutron activation analysis (Rb, Cs, Ca, Sr, Ba, Sc, Cr, Fe, Co, Ni, Zn, Se, As, Sb, Th, U, Br, Hf, Ta, Zr, and Ag) in seven different seaweed species (Codium cuneatum, Sargassum sinicola, Padina durvillaei, Laurencia johnstonii, L. papillosa, Gracilaria pachidermatica and Hypnea pannosa), collected in a shallow coastal zone from Bahia de Loreto, Baja California Sur, Mexico. Measured concentrations in algal tissue spanned almost eight orders of magnitude (from 2.0 x 10(-3) microg g(-1) for Hf to 1.2 x 10(5) microg g(-1) for Ca). Ca was consistently the most abundant element in all analyzed seaweeds, followed by Fe and Sr. Brown algae showed a tendency to incorporate higher concentrations of elements than red and green algae. Additionally, there were significant linear correlations (P < 0.05 to P < 0.001) between a total of 76 different pairs of elements, some of them (e.g. Rb-Ni, Rb-Ag, Sc Cr, Sc-Fe, Sc Ni, Sc Hf, Cr Fe, Fe Ni, Fe-Hf and Ni-Th) highly correlated (r2 > 0.900). A significant correlation (r2 = 0.701, n = 18, P < 0.001) exists between our measurements in the tissue of algae and their corresponding average elemental concentrations in oceanic water from the North Pacific Ocean. Hence, overall elemental abundance in algal tissue apparently is controlled by the elemental abundance in oceanic water, whereas metabolic processes as well as environmental factors relevant to each region modify the final concentration of a given element in the body of a macroalgae.

Mercury and cadmium concentrations in farmed bluefin tuna (Thunnus orientalis) and the suitability of using the caudal peduncle muscle tissue as a monitoring tool.

Three regions (cephalic, central, and caudal) of the dorsal and ventral muscle tissue (R1 through R6) and the caudal peduncle muscle tissue (CPMT) of 20 farmed bluefin tuna (Thunnus orientalis) were analyzed for mercury (Hg) and cadmium (Cd) concentrations. Region 1 (cephalic-ventral) had significantly lower concentrations of Hg but significantly higher concentrations of Cd than did the other regions. However, average metal concentrations of all regions (R1 through R6) were only 6% lower for Hg and were not significantly different for Cd from those in the CPMT. Therefore, the CPMT was used to monitor the concentrations of these two metals in more than 100 farmed tuna collected from July 2004 to January 2009 under the assumption that the Cd concentrations in the CPMT would be representative of the Cd concentration in the whole body and that the Hg concentrations would be, in the worst case, overestimated by approximately 6%. The Hg and Cd concentrations in these tuna were inversely related to the condition index, i.e., the tuna in better condition had the lowest concentrations of these metals. The mean concentrations in the CPMT of all fish analyzed were 0.31 ± 0.17 µg/g wet weight for Hg and 0.007 ± 0.006 µg/g wet weight for Cd. These concentrations were below the limits established by Mexican regulations for seafood (1.0 and 0.5 µg/g for Hg and Cd, respectively) and Japan (0.4 µg/g for Hg).

Millimeter-scale resolution of trace metal distributions in microbial mats from a hypersaline environment in Baja California, Mexico.

Microbial mats from two ponds with different salinities from the saltern of Guerrero Negro (Mexico) points toward millimeter-scale coherent variations in trace metal (Me) concentrations (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn). Total, HCl-leachable and pyrite-associated Me showed a trend of increasing concentrations with increasing depth suggesting gradual addition of reactive Me probably as a result of metal sulfide precipitation at depth. The trends in Me profiles can be ascribed to the establishment and maintenance of microzones that promote geochemical processes, bacterial population distributions, and differential mass transport within the mats. Degrees of trace metal pyritization (1 ± 1% for Zn to 24 ± 7% for Cd) as well as metals associated with the pyrite fraction (<1.4-36 ± 18 nmol g(-1) for Zn and Mn, respectively) were low, as expected from a reactive Fe-limited system like Guerrero Negro. Calculated enrichment factors showed that Ni (2.6 ± 2.1), Co (5.5 ± 4.0), Pb (9.4 ± 7.4), and Cd (57 ± 39) were, on average, enriched in the microbial mats of Guerrero Negro. Natural enrichments of Cd, Pb, and Co in sediments along the coast of Baja California and metabolical requirements of Co and Ni by the predominant cyanobacteria in the Guerrero Negro mats may explain these enrichments. Metal characteristics in microbial mats could be advantageously used as biosignatures to identify their presence in the geological record or in other planetary systems.