Abstract
To evaluate the levels of heavy metals (Cd, Pb, Cu y Zn) in edible tissue, as well as some molecular biomarkers of oxidative stress, in the digestive gland of the triagonal clam Tivela mactroides from Caicara beach (Venezuela) during different pluviometric seasons, we proceeded to collect between 90 and 100 organisms during August and December 2007 (moderate rain and rain-drought transition, respectively), and April and July 2008 (drought and intense rain, respectively). Heavy metal levels were measured by inductively coupled optical emission spectrometry, while the concentrations of metallothioneins (MTs), total thiols (-SHT), free thiols (-SHF), total proteins (PT), and thiobarbituric acid reactive substances (TBARS) were determined by colorimetric methods. Cd, Pb and Cu concentrations increased in rainfall periods and Zn in the rain-drought transition. Cd and Pb concentrations in T. mactroides were elevated in comparison with clams collected from other Venezuelan coastal areas, exceeding the values suggested by international organizations, especially during the maximal rainfall period. MT, -SHF and TBARS concentrations did not show significant variations between collection periods; however, -SHT decreased in the period of maximum precipitation. The results of oxidative stress biomarkers did not indicate molecular alterations by contamination; however, accumulated levels of Cd and Pb are a signal of alarm of bioavailability and entrance of xenobiotics of anthropogenic origin.
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