Trace elements in the silky shark Carcharhinus falciformis in the Central Pacific Mexican Shelf.

Mercury (Hg), cadmium (Cd) and copper (Cu) concentrations were determined in muscle, liver and fin of the silky shark (Carcharhinus falciformis) caught in the Central Pacific Mexican Shelf. Liver tissue presented the highest concentrations of Cd (2.83 µg g-1 wet weight (ww)) and Cu (2.34 µg g-1 ww). For muscle and fin, Cu presented the highest concentrations (0.97 and 1.80 µg g-1 ww, respectively). Liver concentrations were influenced by the maturation stages for the three elements. Immature organisms exhibited lower trace element concentrations than adults. No significant differences were found between sexes, except for Cu concentrations in muscle, where adult females present higher levels than adult males. One muscle sample (2.3 %) exceeded the Mexican Legislation for Hg (1.0 µg g-1 ww) and five muscles samples (11.6 %) exceeded the Mexican limit for Cd (0.5 µg g-1 ww). Meat consumption of this species can be a risk to human health if it is ingested regularly.

Mercury maternal transfer in two placental sharks and a yolk-sac ray from Baja California Sur, Mexico.

Total mercury (THg) concentrations were measured in muscle and liver of two placental viviparous sharks, the Pacific sharpnose shark (Rhizoprionodon longurio) and the brown smooth-hound (Mustelus henlei); as well as in the muscle, liver, and yolk of the yolk-sac viviparous speckled guitarfish (Pseudobatos glaucostigmus) in Baja California Sur. The aim was to determine which factors could be involved in maternal transfer and resultant maternal and embryonic THg concentration. Higher THg concentrations were found in pregnant females compared to embryos paired tissues. THg concentrations of embryo tissues decreased with total length (TL), except for the muscle of the Pacific sharpnose shark. THg concentrations of embryo muscle was positively related to THg concentration in the muscle of pregnant females. Embryos TL, muscle THg concentration of pregnant females, percentage of THg concentration in embryos, along with the reproductive strategy are relevant factors required to improve our understanding of THg concentration in embryo tissues.

Contamination knows no borders: Toxic organic compounds pollute plastics in the biodiversity hotspot of Revillagigedo Archipelago National Park, Mexico.

Plastic pollution is ubiquitous and not even remote protected islands are safe from it. Floating debris can adsorb toxic compounds that concentrate on their surface, being available to the animals that ingest them. For this reason, a baseline study of plastic pollution was conducted in the remote Revillagigedo Archipelago, in the Mexican Pacific Ocean. In 47 manta net samples an average of 4.8 plastics/1000m2 was found, 73% of the pieces being <5 mm. Polyethylene and polypropylene were the most common polymers found. The chemical analysis of organic pollutants revealed that organochlorine pesticides, polycyclic aromatic hydrocarbons and polychlorinated biphenyls are adsorbed on the plastics collected in the area. Filter feeding megafauna such as humpback whales, manta rays and whale sharks could ingest contaminated micro and macroplastics. Plastics were found also on the beach, where they are available to the ingestion by terrestrial animals, including endemic species endangered to extinction.

Isotopic (δ15 N) relationship of pregnant females and their embryos: Comparing placental and yolk-sac viviparous elasmobranchs.

Nitrogen stable isotopes ratios (δ15 N) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark (Rhizoprionodon longurio), and a yolk-sac viviparous species, the speckled guitarfish (Pseudobatos glaucostigmus). The R. longurio embryo tissues were 15 N enriched compared to the same tissues in the pregnant female, using the difference in δ15 N (Δδ15 N) between embryo and adult. Mean Δδ15 N was 2.17‰ in muscle, 4.39‰ in liver and 0.80‰ in blood. For P. glaucostigmus, embryo liver tissue was significantly 15 N enriched in comparison with liver of the pregnant female (Δδ15 N mean = 1.22‰), whereas embryo muscle was 15 N depleted relative to the muscle of the pregnant female (Δδ15 N mean = -1.22‰). Both species presented a significant positive linear relationship between Δδ15 N and embryo total length (LT ). The results indicated that embryos have different Δδ15 N depending on their reproductive strategy, tissue type analysed and embryo LT .

Seasonal variation in the abundance of marine plastic debris in Banderas Bay, Mexico.

A floating plastic monitoring program was conducted for two years on a weekly basis in Banderas Bay, Mexico. A total of 94 samples were collected from May 2016 to April 2018 in the southern part of the bay. Half (57%) of them contained plastic debris; 79% of it being <5 mm in length. Polypropylene and Polyethylene were the most abundant polymers, accounting for 45% and 43% of the plastic pieces (pp), respectively. The highest abundance of plastic pieces was found in July 2016, with a maximum of 0.3 pp/m3 found in one sample. The amount of floating plastics was significantly higher in the hurricane season compared to the dry season (p < 0.001). This suggests that rainfall may play a significant role in the offload of plastics from land-based sources into the bay.

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 ±â€¯1.8 and 770 ±â€¯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.

Trophic Structure and Biomagnification of Total Mercury in Ray Species Within a Benthic Food Web.

Stable isotopes of C (δ13C) and N (δ15N) were used to explore the trophic structure and evaluate mercury (Hg) biomagnification in the food web of muscle of three commercially important ray species from the Pacific coast of Baja California Sur (PCBCS): the shovelnose guitarfish (Pseudobatos productus), banded guitarfish (Zapteryx exasperata), and bat ray (Myliobatis californica). The food web of these ray species predominately consisted of zooplankton, three species of fish, and five species of invertebrates. Mean δ15N values in all species ranged from 10.54 ± 0.18‰ in zooplankton to 17.84 ± 0.81‰ in the shovelnose guitarfish. Mean δ13C values ranged from - 22.05 ± 0.75‰ in the red crab to - 15.93 ± 0.78‰ in the bat ray. Mean total Hg concentration ([THg]) in all species ranged from 0.0009 ± 0.0002 mg kg-1 ww in zooplankton to 0.24 ± 0.19 mg kg-1 ww in the banded guitarfish. The food web magnification factor was 6.38 and significantly greater than 1.0. The present study describes [THg] biomagnification in the benthic food web of three ray species of the PCBCS. This provides an important baseline knowledge of the biomagnification dynamics and pathways of Hg in this environment for these multiple interacting species.

Mercury concentrations in three ray species from the Pacific coast of Baja California Sur, Mexico: Variations by tissue type, sex and length.

Total mercury concentrations ([THg]) were determined in muscle and liver of the bat ray (Myliobatis californica), shovelnose guitarfish (Pseudobatos productus) and banded guitarfish (Zapteryx exasperata). Generalized linear models (GLM) were used to determine the effects of size and sex in [THg] and showed that both are determinants of [THg] in these species. The [THg] in both tissues significantly increased with length especially in sexually mature organisms with a steeper slope for mature male than mature female. This may relate to elasmobranchs sexual dimorphism driven variation in growth rates. Median muscle [THg] was significantly greater than liver in each ray species but there were some individuals with higher liver [THg] than muscle. There were individuals with muscle [THg] higher than the advisory thresholds of 0.2 and 0.5mgkg-1ww (2.4 and 11% of the bat ray; 2.1 and 10% of the shovelnose guitarfish; 12.6 and 45% of the banded guitarfish, respectively).

Lead in shrimp Litopenaeus vannamei Boone in sublethal concentrations.

Determination of the accumulation and elimination of sublethal lead (Pb) in different shrimp tissues may be useful as an indicator of uptake and elimination characteristics of this metal. Aquaculture ponds are particularly influenced by Pb contamination, where aquatic animals may acquire the metal through adsorption to exoskeletons or gills from the surrounding water. Cationic Pb is accumulated preferentially in the nonedible fraction of shrimp, followed by exoskeleton, and to a minor extent in muscle. Lead contents in different tissues were lower than metal levels in exoskeleton. However, the presence of Pb in sediment due to purging may exert adverse consequences on shrimp as bottom feeders.

Urinary arsenic levels influenced by abandoned mine tailings in the Southernmost Baja California Peninsula, Mexico.

Gold has been mined at San Antonio-El Triunfo, (Baja California Sur, Mexico) since the 18th century. This area has approximately 5,700 inhabitants living in the San Juan de Los Planes and El Carrizal hydrographic basins, close to more than 100 abandoned mining sites containing tailings contaminated with potentially toxic elements such as arsenic. To evaluate the arsenic exposure of humans living in the surrounding areas, urinary arsenic species, such as inorganic arsenic (iAs) and the metabolites mono-methylated (MMA) and di-methylated arsenic acids (DMA), were evaluated in 275 residents (18-84 years of age). Arsenic species in urine were analyzed by hydride generation-cryotrapping-atomic absorption spectrometry, which excludes the non-toxic forms of arsenic such as those found in seafood. Urinary samples contained a total arsenic concentration (sum of arsenical species) which ranged from 1.3 to 398.7 ng mL(-1), indicating 33% of the inhabitants exceeded the biological exposition index (BEI = 35 ng mL(-1)), the permissible limit for occupational exposure. The mean relative urinary arsenic species were 9, 11 and 80% for iAs, MMA and DMA, respectively, in the Los Planes basin, and 17, 10 and 73%, respectively, in the El Carrizal basin. These data indicated that environmental intervention is required to address potential health issues in this area.

Thorium accumulation in the sedimentary environment of the Vigo Ria (NW Iberian Peninsula).

Thorium levels and their association with Fe, Sc, Ca, and Particulate Organic Carbon (POC) were researched in sediments of the Vigo Ria in order to assess the influence of radioactive gneisses from the neighbouring continental Galiñeiro Complex. Sediment of 50 surface samples and 1 core was analysed by ICP-MS and the results were validated with certificate reference material from marine sediment. It was found that Th accumulates in the middle Ria zone (9-15 mg kg(-1)) as a result of the terrestrial source. The thorium concentration in the Ria (average: 9.4+/-5.1 mg kg(-1)) is not anthropogenically impacted in accordance with its own regional background level (11.4+/-3.5 mg kg(-1)), which is two times higher than the content in earth's crust. Throughout the relationship Th/Fe, Th may be associated with the iron cycle in the Ria, probably through iron oxy-hydroxide scavenging.