Mercury and selenium in the filter-feeding whale shark (Rhincodon typus) from two areas of the Gulf of California, Mexico

Mercury and selenium were measured for first time in the endangered species whale shark (Rhyncodon typus) from two areas of the Gulf of California, Bahía Los Angeles (BLA) and Bahía La Paz (LAP) using dermal biopsies of seventy specimens. Additionally, nineteen zooplankton samples from LAP were analysed. Concentrations (ng/g, wet weight (ww)) in biopsies of BLA ranged from 1 to 40 for Hg and 100 to 680 for Se; while in LAP varied from 1 to 9 for Hg and 11 to 850 for Se. A positive correlation was found for Hg in BLA males biopsies with length. Hg and Se concentrations in the zooplankton from LAP were 1.6 ± 1.8 and 770 ± 930 ng/g, respectively. Hg biomagnification factor ranged from 0.8 to 5.3 in sharks. A molar excess of Se over Hg was found in the biopsies and the zooplankton.

Trace metals accumulation patterns in a mangrove lagoon ecosystem, Mazatlan Harbor, southeast Gulf of California

Water, surface sediments, the mussel Mytella strigata, the mangrove oyster Crassostrea corteziensis, and the green macroalgae Caulerpa sertularioides from four locations in Mazatlan Harbor on the southeast coast of the Gulf of California, were analyzed to determine concentrations and distribution patterns of cadmium, copper, mercury, lead, and zinc. Total metal concentrations in water in the present study exceed the background levels in open sea and coastal waters. Total metal concentrations in sediments were ordered as follows: Zn > Pb > Cu > Cd > Hg, but for the bioavailable fraction were ordered as Zn > Cu > Pb > Cd > Hg. The concentrations in bioavailable levels fall between the Threshold Effects Level (TEL), and Probable Effects Level (PEL), criteria for sediment quality. Distribution patterns for metals in organisms were ordered Zn > Cu > Pb > Cd > Hg with seasonal variations for Pb and Zn. Correlations between Cd, Cu, Pb and Zn were indicative of similar assimilation and storage mechanisms and common sources of contamination. These correlations also indicated that bioavailability was not simultaneous for Cd and Pb. Bioconcentration factors (BCF) show different patterns in different organisms. For the oyster the metals were ordered Zn >> Cu > Cd approximately Hg > Pb, for the mussel Hg > Cu approximately Zn approximately Cd > Pb and for the macroalgae Zn >> Cu > Pb > Cd > Hg. Based on BCF results in the lagoon system, the oyster C cortezienzes can be used as a biomonitor of Zn and Cu exposure, the mussel M. strigata of Hg exposure and the green macroalgae C. serticularioides of exposure to all five metals studied.

Chronicling a century of lead pollution in Mexico: stable lead isotopic composition analyses of dated sediment cores

Analyses of lead isotopic compositions (204Pb, 206Pb, 207Pb, and 208Pb) of dated sediment cores from two coastal estuaries and two inland lakes chronicle the predominance of industrial lead emissions in Mexico over the past century. These isotopic ratios exhibit a shift in composition from the turn of the previous century (1900) that corresponds with measurable increases (from 2- to 10-fold) in lead concentrations in the cores above their baseline values (3-22 microg/g)--both changes are consistent with the development of Mexican lead production for export and the manufacture of tetraethyl lead additives for Mexican gasolines. While subsequent changes in lead concentrations in the cores correspond with calculated emissions from the combustion of leaded gasoline in Mexico, isotopic compositions of the cores remain relatively constant throughout most of the 1900s (e.g., 206Pb/207Pb = 1.200 +/- 0.003; 208Pb/207Pb = 2.463 +/- 0.004). That isotopic constancy is attributed to the widespread pollution from lead production in Mexico and the dispersion of some of that lead used as an additive in Mexican gasolines.

Nutrient cycling at the sediment-water interface and in sediments at Chiricahueto marsh: a subtropical ecosystem associated with agricultural land uses

A study was conducted to examine the potential role to accumulate and transform nitrogen and phosphorus of a common wetland type marsh; the site is located in a subtropical environment that receives agricultural pollutants. Chiricahueto marsh effectively removes N and P from surface waters. It is clear that the diagenetic processes are mainly controlled by the exponential decomposition of organic matter that takes place at the sediment-water interface and in the sedimentary column, under oxic and suboxic-anoxic conditions, respectively. Mass balances indicated a net sedimentation of 11.3 g Nm(-2)x yr (-1) and 3.9 g Pm(-2) x yr (-1), which results in an annual regeneration of 1.7 g Nm(-2) and 0.8 g Pm(-2) at the sediment-water interface under oxic conditions. A major remineralization rate was estimated in 6.4 g Nm(-2) x yr (-1) and 1.1g Pm(-2) x yr (-1) into the sedimentary column where suboxic to anoxic conditions occur by the utilization of nitrate, Fe and Mn as electron acceptors. The estimated burial fluxes in the deeper sediments (>50 cm) were 1.5 g Nm(-2) x yr (-1) and 0.4 g Pm(-2) x yr (-1).