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.

Vanadium and Cadmium in Water from the Perdido Area, Northwest of the Gulf of Mexico: 2 years' Monitoring and Current Status.

Surface water samples from the Perdido study area presented Cd and V concentrations similar to those reported internationally for waters with: (1) fossil fuel extraction, processing and burning, and (2) sites polluted by anthropogenic wastewater. Results showed an order of magnitude increase in time for Cd, therefore, no general average value was established. For V, however, results of this study suggest a general average value of 1.4 µg L-1 for the area. The observed spatial variation of concentrations could be the result of: (1) temporal variation of external inputs to the area, and coincide with previously reported hydrodynamic patterns of dispersion related to significant river contributions and accumulation areas indicative of eddy circulation or fronts. The Perdido area showed Cd and V concentrations in surface water reflective of anthropogenic impacts, while its spatial and temporal variation could depend significantly on the hydrodynamics of the area.

Spatial and Temporal Variations of Vanadium and Cadmium in Surface Water from the Yucatan Shelf.

Surface water samples from the Yucatan shelf presented Cd concentrations similar to those reported internationally for non-polluted coastal and marine waters. V concentrations, on the other hand, fall within the range of anthropogenically polluted waters (25% of the sampling sites). In the study area, the probable sources of V could be: (1) carbonate sediments leaching V into the water column and co-transported with fine sediments resuspending as a result of the complex hydrodynamics in the area or, (2) accidental spills from cargo ships transporting oil between the Atlantic and the Gulf of Mexico. Significant spatial and temporal differences were found for both metals; therefore, a regional interval concentration is suggested for V from 1.28 to 1.84 µg L-1 and Cd from 0.003 to 0.09 µg L-1. These differences could primarily be the result of the observed hydrology and hydrodynamics created by the Yucatan current, submarine groundwater discharges and upwelling.

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.

Groundwater Quality in the Yucatan Peninsula: Insights from Stable Isotope and Metals Analysis.

High surface water-groundwater connectivity characterizes watersheds underlain by karsts, increasing contaminant transport risks. However, karsts are highly complex, making research necessary to understand the transport of contaminants from the surface, through the aquifer, to discharge areas. In Yucatan, the lack of waste water treatment raises the risk of groundwater contamination. We monitored stable isotopes (δ18 O-NO3 and δ15 N-NO3 ), cadmium, and lead to document waste water contamination and transport during the rainy and dry seasons, using water samples collected along the Ring of Cenotes during each season. Specific conductance and pH showed no consistent seasonality, with conductance ranging from 0.5 to 55 mS/cm and pH ranging from 6.6 to 8.6 for most samples. Nitrate concentrations in the cenotes averaged 205 ± 260 µM and no seasonal pattern was observed. Cd and Pb concentrations were 0.1 to 37.9 µg/L and 0.2 to 243.2 µg/L, respectively. Nitrate stable isotope values were 2.6 to 27.2‰ for δ18 O and 1.2 to 20.7‰ for δ15 N. The statistical relationship between δ15 N and δ18 O, in dry season samples, indicated that denitrification was occurring. A scale measure for waste water recognition showed: (1) high variability among sites probably related with dry/rainy seasons and/or diverse anthropogenic activities; and (2) specific water quality variables that contribute to contamination at each site during each season. Importantly, our analyses indicate that in the area surrounding the Ring of Cenotes, waste water exhibits spatial and temporal patterns related to complex transport and dilution processes, as is the case in karsts in general.

Organochlorine Pesticides and Potentially Toxic Elements in Groundwater from a Protected Reserve in the Maya Region of Hopelchen, Mexico.

Water quality degradation by organochlorine pesticides and potentially toxic elements is of worldwide concern. This research explores groundwater conditions, regarding organochlorine pesticides and potentially toxic elements, in Hopelchen, Campeche, which is located in the buffer zone of the Calakmul Biosphere Reserve. Unfortunately, agriculture is allowed and agrochemical use is not monitored and sanctioned. Results show that Heptachlor, Endosulfan, and Dieldrin, all recognized carcinogens, had concentrations above the Mexican normative recommended values. Conversely, Cd and Ni concentrations were below recommended values. These results demonstrate that government intervention involving immediate control over agrochemical use is mandatory. Also, the results underscore the contamination of groundwater in several of the Calakmul Biosphere Reserve's buffer zones by organochlorine pesticides concentrations, posing a probable threat for local inhabitants who consume this water and use it for recreation.