Heavy metals in clams from Guaymas Bay, Mexico

Trace Metals in Two Geoduck Clams (Panopea generosa and P. Globosa) Exploited for the Regional Market from Two Areas of Northwest Mexico

Biological and fishery features of Panopea sp. clams have been studied in northwest Mexico because of their importance for human consumption. However, the content of pollutants in their tissues, along with their implications have not been addressed yet. The concentrations of cadmium (Cd), copper (Cu), mercury (Hg), and zinc (Zn) in soft tissues of Panopea generosa and P. globosa clams were examined in this region by atomic absorption spectroscopy. The metal concentrations (µg/g wet weight) ranged from 6.5 to 14.2, 0.97-8.09, 0.60-1.18, and 0.01-0.07, for Zn, Cu, Cd, and Hg, respectively. This study proposes that metal presence is related to weathering, upwelling, and drainage from adjacent agricultural lands to the coast. According to the Official Mexican Standard (NOM-242-SSA1-2009) and the World Health Organization (WHO, 2022), the metal content in siphon tissue indicates safe levels for human consumption.

Cadmium exposure in living organisms: A short review

Cadmium (Cd) is a toxic heavy metal that accumulates in living systems. Exposure can occur occupationally or environmentally. Workers within the electroplating, battery production, and pigment industries are at the highest risk for exposure and have been reported to have increased levels of Cd in their blood and urine. Environmental exposure can be the result of anthropogenic activities or smoking. Cd has a long half-life and bio accumulates in plants, invertebrates, and vertebrates. The toxic effects following exposure include growth retardation and organ system toxicity, with kidney and liver toxicity most reported with in higher organisms. At the molecular level, Cd leads to the production of reactive oxygen species, DNA damage, and inhibition of DNA repair. This article gives a brief overview of the correlations between exposure to cadmium occupationally and environmentally and levels measured in blood and urine. It also examines the bioaccumulation of cadmium in aquatic invertebrates and vertebrates indicating that accumulation varies not only by location but also within and between various species.

Comparative bioaccumulation of trace metals using six filter feeder organisms in a coastal lagoon ecosystem (of the central-east Gulf of California)

The Tobari Lagoon, located in the central-east coast of the Gulf of California, receives effluents from the Yaqui Valley, one of the most extensive agricultural areas of México. The Tobari Lagoon also receives effluents from nearby shrimp farms and untreated municipal sewage. Surface sediment samples and six different species of filter feeders (Crassostrea corteziensis, Crassostrea gigas, Chione gnidia, Anadara tuberculosa, Chione fluctifraga, and Fistulobalanus dentivarians) were collected during the dry and the rainy seasons and analyzed to determine concentrations of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn). Seasonal variations in metal concentrations in sediment were evident, especially for Cd, Cu, Hg, and Zn. The total and bioavailable concentrations of the five metals are not elevated in comparison to other areas around the world. The percentages of bioavailable respect to total concentrations of the metals varied from 0.6 % in Hg to 50.2 % for Cu. In the organisms, Hg showed the lowest concentrations (ranged from 0.22 to 0.65 μg/g) while Zn showed the highest (ranged from 36.6 to 1,702 μg/g). Linear correlations between the levels of Cu, Pb, and Zn in the soft tissues of C. fluctifraga and C. gnidia, and A. tuberculosa and C. gnidia were found. Seasonal and interspecies variations in the metal levels in filter feeders were found; F. dentivarians, C. corteziensis, and C. gigas exhibited the highest levels, could be used as biomonitors of metals contamination in this area.

Heavy metal levels in marine mollusks from areas with, or without, mining activities along the Gulf of California, Mexico

To assess the safety for human consumption of commercially important bivalves harvested from areas with or without mining activities, we compared the levels of heavy metals in mollusks collected from different coastal environments along the Gulf of California. We sampled the mussel Mytilus edulis and the clams Laevicardium elatum and Megapitaria squalida (June 2004) and the clam Chione californiensis (November 2006). Concentrations of cadmium, lead, nickel, zinc, iron, copper, and manganese in the soft tissue of the mollusks were measured by atomic absorption spectrophotometry. Based on dry weight, the highest average concentrations of iron, copper, and cadmium were found in clams from Loreto (572, 181, and 4.66 mg/kg, respectively); that of nickel, in mussels from San Luquitas (12.2 mg/kg); that of zinc, both in mussels from San Luquitas and in clams from Golfo de Santa Clara (94.3 and 91.8 mg/kg, respectively); and those of lead and manganese in clams from the Golfo de Santa Clara (9.2 and 3.68 mg/kg, respectively). Although mollusks were taken from coastal areas of the Gulf of California, which are considered to be contaminated by mining activities, the heavy metals in the sediments apparently were in a chemical form that had low bioavailability for the bivalves feeding in those areas. The interplay of oceanographic conditions and the chemical composition of anthropogenic inputs into the environment is not well understood. Thus, these factors or their interaction could potentially result in increased concentration and bioavailability of such metals in areas without effluent generated by mining activities.

Antioxidant enzymes and heavy metal levels in tissues of the black chocolate clam Megapitaria squalida in Bahía de La Paz, Mexico

The black chocolate clam Megapitaria squalida is a commercially important bivalve along the Pacific coast of Mexico and is used as a bioindicator in environmental health studies. Previous studies of Bahía de La Paz indicated significant differences in heavy metal content among localities in this clam. To identify areas affected by heavy metal pollution, lipid peroxidation (TBARS) levels and activity of superoxide dismutase (SOD) and glutathione S-transferase (GST) were measured in muscle, gonad, and digestive gland tissue and correlated with heavy metal levels of clams from six localities along the shore of the bay. Significant differences in TBARS levels and antioxidant enzyme activity were found among these tissues at all localities. Such differences are ascribed to the physiology of each organ. Higher levels of TBARS were found in areas with higher cadmium content. SOD activity in muscle correlated positively with cadmium, lead, and iron in areas with a higher content of those elements. This study suggests that TBARS levels and SOD and GST activity are affected by biotic and abiotic factors and have potential as indicators of heavy metal contamination.

Mercury in surface sediments and benthic organisms from Guaymas Bay, east coast of the Gulf of California

In order to know the concentration of mercury in surface sediments, macroalgae and clams from Guaymas Bay, Mexico, 20 surface sediment samples and several individuals of Codium amplivesciculatum (3), Enteromorpha clathrata (4), Gracilaria subsecundata (2), Ulva lactuca (2), Chione subrugosa (80) and Crassostrea gigas (40) were collected and their Hg concentration was measured by a cold vapor Hg analyzer, after acid digestion. In addition, granulometric analysis and quantification of total organic carbon, aluminum, iron and manganese contents in sediments were performed. A Pearsons correlation matrix was determined and, the enrichment factor, the geoaccumulation index and the biota-sediment accumulation factor were calculated. Mercury concentrations in sediments ranged from 0.3 to 2.3 microg g(-1), with the central and northern portions showing the highest values. Macroalgae had a content of Hg that oscillated from 0.058 to 0.134 microg g(-1), while the average concentrations of this metal for clams and oysters were 0.063 and 0.230 microg g(-1), respectively. A clear effect of Guaymas City and the anthropogenic activities carried out around the Guaymas Bay has been observed and the enrichment factor and the geochemical index suggest that sediments from this coastal ecosystem are moderately to strongly contaminated with Hg. However, according to the figure of the maximum human consumption of Hg per week recommended by the World Health Organization, people can ingest clams without risk to their health.