The present study determined the average mercury bioaccumulation in the muscle tissue of four shark species (Carcharhinus falciformis, Prionace glauca, Sphyrna zygaena and Isurus oxyrinchus) captured in the Baja California Peninsula. We also evaluated biomagnification of some prey consumed by sharks. All sharks' species had mercury levels over the limit specified by the Mexican government for human consumption. Blue shark (P. glauca) presented highest mercury values (1.96 ± 1.48 μg/g Hg d.w.) and it was the unique specie that showed a negative correlation with mercury content (Rs = -0.035, p = 0.91). Scomber japonicus was the prey with high content of mercury (0.57 ± 0.02 μg/g).

Tuna, like most large pelagic fish, are highly exploited by man, and it is, therefore, important to determine mercury (Hg) levels in these species in order to establish allowable limits for their consumption and/or contamination levels in the environment. In this study, we evaluated Hg accumulation in yellowfin tuna (Thunnus albacares) muscle in two different geographic sites of the eastern Pacific Ocean. There was a positive association between Hg content and tuna size in the equatorial zone (EQZ). Using adjusted sizes, the site of origin was a determinant factor in Hg accumulation. Sex, by contrast, did not affect Hg levels, suggesting that males and females have similar feeding habits. No Hg concentration was over the Hg content thresholds for large marine predators adopted by Mexican norms and by North American authorities (1 μg g(-1) w.w.). Hg input due to yellowfin tuna consumption represented from 9.84% to 35.87% in Baja California Sur and from 14.78% to 53.87% in EQZ of the provisional tolerable weekly intake adopted by the World Health Organization. The target hazard quotient for Hg was <1 in each group of the population studied, which indicates that consumption of yellowfin tuna is not a threat to human health.

The aim of this study was to determine the biomagnification of mercury through the principal prey of the blue shark, Prionace glauca, off the western coast of Baja California Sur, Mexico, as well as the relationship between mercury and selenium in blue sharks. High levels of mercury were found in shark muscle tissues (1.39 ± 1.58 μg/g wet weight); these values are above the allowed 1.0 μg/g for human consumption. The mercury to selenium molar ratio was 1:0.2. We found a low correlation between mercury bioaccumulation and shark size. Juveniles have lower concentrations of mercury than adults. Regarding the analyzed prey, the main prey of the blue shark, pelagic red crab, Pleuroncodes planipes, bioaccumulated 0.04 ± 0.01 μg/g Hg wet weight, but the prey with higher bioaccumulation was the bullet fish Auxis spp. (0.20 ± 0.02 μg/g wet weight). In terms of volume, the red crab P. planipes can be the prey that provides high levels of mercury to the blue shark.

Concentrations of seven metals (As, Cd, Cr, Cu, Pb, Ni, and Zn) were analyzed in 33 bone tissue samples of Antillean manatees (Trichechus manatus manatus) found dead in lagoons and rivers of Tabasco and Campeche in the Gulf of Mexico and Chetumal Bay in the Caribbean region. The concentrations of Cr, Cu, Pb, and Zn were significantly different between regions, with greater levels found in the Gulf of Mexico group than in the Mexican Caribbean group (p < 0.05). Pb concentrations differed significantly between adults and calves. No differences were observed between sexes. Metal concentrations detected in the manatee bones were higher than most of those reported for bones in other marine mammals around the world. Future studies are necessary to establish whether the metal concentrations represent a risk to the health of the species.

We analyzed total mercury and selenium bioaccumulation in muscle tissue and cartilage fibers (fins) from smooth hammerhead shark, Sphyrna zygaena, caught off Baja California Sur, Mexico. In muscle tissue, the mercury concentration ranged from 0.005 to 1.93 microg g(-1) ww (wet weight), which falls within the safety limits for food set by international agencies (Hg > 1.0 microg g(-1) ww). Only one specimen showed a mercury value that exceeded this limit. In fins, the mercury bioaccumulation was lower (<0.05). Selenium in muscle ranged from 0.11 to 1.63 microg g(-1) ww, while in fins it ranged from 0.13 to 0.56 microg g(-1) ww.

Caudal scutes were collected from 92 Morelet's crocodiles (Crocodylus moreletii) between May and August 2012, in three Wildlife Management and Use Units (UMAs, from its name in Spanish) and three wild sites in Campeche, Mexico. The UMAs are intensive, with an ex situ approach to manage crocodiles in captivity. The concentrations of arsenic, mercury, lead, nickel, cadmium and chromium were analyzed in each sample. As and Pb were detected in all samples, Hg in 86 and Ni in 74. The metal concentrations estimated were higher than most of the concentrations reported for skin, tail tip and caudal scutes in other crocodilians around the world. The concentration of As, Pb and Ni was significantly greater in the free-ranging groups than in the captive groups in UMAs (p < 0.05). Negative linear relationship was estimated between the snout-vent length and the concentration of Pb (in five groups) and Ni (in three groups). In this region C. moreletii is exposed to metals contamination and more studies are necessary to establish if represents a risk to their populations.

The objective of the present study was to evaluate two markers: chromium oxide (Cr 2 O 3 ) and titanium dioxide (TiO 2 ). We evaluate the interaction between Cr 2 O 3 and TiO 2 , and the techniques used to determine it, using atomic absorption spectrophotometry (AAS) and photometry simple (PS). We used six growing sheep distributed in a replicated Latin square 3 × 3 design, with adjustment for the residual error effect. The TiO 2 and Cr 2 O 3 -TiO 2 produced values similar to those obtained by total faecal collection (TFC) or the use of Cr 2 O 3 alone, determined by AAS and PS. Digestibility of the marker/TFC ratio was similar (p > .05) between markers and technique. The use of TiO 2 alone or in combination with Cr 2 O 3 seems to be a suitable alternative to TFC and Cr 2 O 3 to calculate apparent digestibility of the total digestive tract determined in sheep by PS and AAS.ARTICLE HISTORY

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